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A 107-Year-Old Net Positive Victorian Retrofit

Even in chilly Minneapolis, a ‘standard’ house can be renovated for net-zero performance

Net energy producer: With a thick layer of rigid foam on the exterior and a 17 kW photovoltaic array, this refurbished Victorian in Minneapolis makes more energy than it uses.
Image Credit: TK
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Net energy producer: With a thick layer of rigid foam on the exterior and a 17 kW photovoltaic array, this refurbished Victorian in Minneapolis makes more energy than it uses.
Image Credit: TK
Exterior walls are insulated with 7 1/2 inches of expanded polystyrene insulation. Rafter bays are insulated with closed-cell polyurethane foam, sprayed in from the top. The new roof assembly includes a layer of sheathing below the I-joist rafters. CertainTeed says its AirRenew drywall will absorb formaldehyde in the air and convert it into an inert compound. A structural ridge supported at each end by a steel post holds up the new roof. Above the OSB sheathing are I-joists rafters insulated with closed-cell spray foam. Rafter bays below the sheathing are insulated with fiberglass batts. One challenge was finding craftspeople skilled enough to tackle the Victorian details inside the house.

In 2014, I learned about net-zero energy at the Minneapolis Home & Garden Show. Shortly thereafter, my wife and I purchased our retirement home and interviewed five sets of architects to compose the core of the design team. We settled on Marc Sloot of SALA Architects and Sean Morrissey of Morrissey Builders in St. Paul, both with considerable experience in sustainable design and construction. The result is our net-zero Victorian, showing that a standard city house on a standard city lot in chilly Minneapolis can be renovated to be net-zero in energy with no sacrifice in attractiveness, space, or comfort.

The design and permitting took more than a year, beginning in August 2014 through the end of 2015. We sought a variance in local zoning since the exterior walls on one side of the house were already over the side-yard setback from the property line, and then added 1 foot of exterior insulation, which moved the exterior wall surface even closer to the property line.

This kind of variance was unusual for the Minneapolis community economic planning and development board. We also requested approval for a 500-square-foot addition — just within the legal limits for the lot. After four months (late 2015-early 2016), approval was granted for both.

Construction process

Construction took 15 months (twice as long as we anticipated), from September 2015 through December 2016, although we were able to move in by late October 2016. Delays were due to adjustments in what needed to be done, scheduling problems, difficulties of constructing the envelope in the middle of winter, the level of detail required, particularly for interior Victorian style woodwork, and an insufficient number of skilled craftsmen.

The exterior walls required multiple layers — OSB, EPS blocks, window frame boxes, plywood sheathing, furring strips and lap siding — all of which generated a more extended period of construction noise than is usual.

Four legs of the net-zero stool

Efficient insulation, effective air and moisture barriers, reduced energy consumption, and sources of renewable energy for both heating/cooling and electricity were the biggest drivers for the design and energy outcome of the home.

Typically, old houses are insulated by tearing out the interior plaster and putting in fiberglass batts, or punching holes in the walls and filling the cavities with cellulose. This house was insulated on the outside by attaching a 7 1/4-inch-thick layer of rigid insulation board (see Image #2 below). When added to the fiberglass insulation already in the stud cavities, we ended up with R-40 walls. The rigid foam used was expanded polystyrene (EPS), with 1,000 times less environmental impact than extruded polystyrene (XPS).

We also sprayed closed-cell spray foam between the rafters of a new roof (see Image #3 below). In tandem with fiberglass batt insulation below, the R-60 worth of foam gives the roof assembly a total R-value of 80. A new foam chemistry has a much lower global warming potential than earlier spray foam formulations.

A tight house also needs to keep heat in the basement from leaking out. Typically, the foundation wall is insulated on the inside — not very effective — or by digging a deep, wide trench on the outside, which makes a huge mess. Our renovation was one of the first in Minneapolis to use a relatively non-invasive method of insulating the foundation wall from the outside. Kinzler Construction Services removed a 4-inch-wide slice of dirt all the way down to the footings, then inserted a 1-inch foam sheet and 3 inches of sprayed closed-cell foam. The net insulating effect for the basement was R-30 while removing very little dirt.

The house has triple-glazed Andersen A-series windows throughout, further reducing heat loss.

Air and moisture tightness

Much heat and moisture is lost through leaky walls. We wrapped the house in a sticky membrane made by 3M (3015 air moisture barrier). This product is a vapor barrier. Twenty-five percent of the insulation is inside the 3M barrier, so moisture will evaporate back into the living space where humidity averages a comfortable 40-50%.

Seventy-five percent of the insulation is outside the 3M barrier but inside a Tyvek barrier. Air (and moisture) are allowed to circulate freely under the siding without entering the house. It’s not quite the recommended 60%-40% split, but we’ve had virtually no moisture on window interiors through two pretty harsh winters

Our house is almost five times tighter than the building code, measuring 0.63 ach50. It is ventilated by an ERV (energy-recovery ventilator), drawing exhaust air from the kitchen and bathrooms. When the range hood operates, makeup air is drawn from outside past the refrigerator coils for more efficiency.

Formaldehyde is poisonous gas given off by some types of particleboard and some forms of insulation. Formaldehyde is a threat to health, and our house is so tight that inadvertent leakage would do nothing to reduce the threat. To combat this, we installed CertainTeed’s AirRenew wallboard, which absorbs formaldehyde and renders it inert for a promised 10 years (see Image #4 below).

Reduced energy consumption

The house uses three heat pumps: a 3-ton geothermal (ground-source) heat pump, with a COP of 5.0; a heat-pump water heater; and a heat-pump ventless clothes dryer. We disconnected our natural gas line and made the house all-electric. For heating and cooling, four linked geothermal wells were drilled in the 30-by-40-foot backyard. The wells are 250 feet deep, in a diamond pattern 10 feet on a side.

One lament of owners of old homes is that they must run the faucet a long time to get truly hot water from their centrally located water heaters. Our hot water typically arrives within five seconds, saving water and energy. To accomplish this, our plumbers installed a recirculation loop of thickly insulated (R-4) piping inside the building envelope. A pump quickly moves hot water from the tank to the sinks. To save energy, the pump is activated by motion detectors — people entering the kitchen or bathrooms.

All lighting is LED, whether in traditional fixtures, cans, or in other locations.

Recycling heat is another way that we reduce energy consumption. In this house, heat is recycled in three ways. 1) The heat exhausted from bathrooms and the kitchen is used to warm incoming outside air through the ERV. 2) Excess heat from the geothermal heat exchanger pre-heats water in a pre-heat tank for the domestic water heater. 3) Our water heater is driven by a heat pump which sucks heat from basement air. It’s three times more efficient than an electric-resistance water heater.

Energy is also saved through a new dryer design. Conventional dryers waste energy by heating with an electric coil and then venting warm exhaust outside at the rate of 135 cubic feet per minute. Our Whirlpool dryer (WED99HEDW) generates warm air with a heat pump. Instead of exhausting the warm air to the outside, it condenses the moisture from wet laundry into liquid. The warm liquid water then flows down a drain. No heat is lost to the outside air.

Renewable energy source

The house has 54 photovoltaic modules (42 on the house and 12 on the garage, at 315 watts each) for a 17 kW capacity. This system was sized through modeling, which initially projected an annual consumption of 19,000 kWh. The actual 2016-2017 output was 17,000 kWh, more than enough to cover 12,000 kWh consumption in the first year.

The 42 PV modules on the house weigh 1,500 pounds. To support them, a new roof was built over the old crooked and weak roof. The new roof consists of I-joists and the space between them is filled with 10 inches of closed-cell spray foam. Including the 6-inch batts installed between the rafters of the old roof just below, the roof assembly achieves R-80. This spray foam employs a recently introduced blowing agent with a far lower greenhouse gas potential (GWP is 1) than other products.

Supporting all this new construction is a massive laminated beam running the length of the attic, which workers installed by hand (in six 300-pound pieces) rather than by crane. The beam rests upon steel posts which run down invisibly through the walls to thick footings in the basement (see Image #5 below).

Building operation

The home’s operation requires little involvement on a day-to-day basis. The ERV refreshes the interior air 20 minutes per hour. No thermostat setback is needed at night, and humidity remains at comfortable levels (40%-50%).

An eGauge system was installed to allow the internet-based monitoring of 24 individual electrical circuits throughout the house, while the performance of the solar system is also monitored over the internet through SolarEdge software.


Our aim was to create a low-maintenance natural Minnesota environment. The yard is bordered by hardscape frame — Versalok blocks capped with New York bluestone (which also is used for the front walk and terracing). Minnesota perennials, mostly drought-tolerant, cover 2,500 square feet of the yard. A three-zone drip irrigation system is installed to carry these 800 plants through a dry summer.

One-fifth of the yard is planted in Kentucky bluegrass, with no installed irrigation. Managing precipitation is another priority. The house keeps runoff — even from the heaviest of rains — from reaching the street and storm drains. The water is channeled into FloWells, perforated plastic barrels buried underground. These hold the water until it percolates back into the ground.


We have the satisfaction of knowing that we have rescued, renewed, restored, and repurposed a perfectly viable Victorian treasure in a way that preserves its character and demonstrates that a neighborhood can be revitalized without being reduced to a brownfield.

The house has achieved — and surpassed — net zero. The energy-conserving measures described here have kept the electricity consumption to 12,000 kWh for the first year — far less than the 17,000 kWh we generated from solar panels during the same time frame. Our house is therefore “net positive,” producing more energy than it uses.

This extra energy is sold to our local utility, Xcel Energy, at an effective rate of approximately 20 cents per kW hour. In our first year, the system produced about $3,000 worth of electricity, yielding a return of about 7% on the initial investment of $40,000 (after the federal tax credit).

This post originally appeared at the Zero Energy Project and is republished here with the permission of the author. Stewart Herman also is the author of Decarbonizing Your Retirement as You ‘Age in Place’


  1. calum_wilde | | #1

    "One lament of owners of old
    "One lament of owners of old homes is that they must run the faucet a long time to get truly hot water from their centrally located water heaters. Our hot water typically arrives within five seconds, saving water and energy. To accomplish this, our plumbers installed a recirculation loop of thickly insulated (R-4) piping inside the building envelope. A pump quickly moves hot water from the tank to the sinks. To save energy, the pump is activated by motion detectors — people entering the kitchen or bathrooms."

    I keep seeing recric hot water systems come up as an efficiency upgrade and I just can't wrap my head around it. I can certainly see how it would make life easier, but how does it save electricity?

  2. GBA Editor
    Martin Holladay | | #2

    Response to Calum Wilde
    Circulation loops are an imperfect solution to a design problem. (The design problem is locating the water heater far from the rooms where the hot water is used, coupled with the use of hot water tubing with an excessive diameter.)

    If the alternative is letting the water run down the drain while you wait for hot water to arrive, a demand-controlled circulation loop saves water.

    A circulation loop controlled by a motion detector is imperfect, since it is activated when someone enters the bathroom to get some aspirin or to find the nail clippers. A demand-controlled pump (controlled by a switch) is better.

    More information here: "Hot water circulation loops."

  3. Expert Member
    Peter Engle | | #3

    Recirculating hot water
    As I understand them (and I do have the Metlund D'Mand system in my own home), They significantly improve water efficiency because of the water that is not thrown down the drain. They also save time waiting for the hot water. They do not save energy over non-recirculating systems because the same volume of hot water is eventually used and the same volume of hot water eventually cools in the pipes during standby. In fact, there is a small energy use increase because of the pumping energy required.

    OTOH, it is becoming common for larger homes in our area to have full-time hot water recirculation (GRRRR). These waste energy both for pumping and the heat loss from the full-time hot water storage in the normally uninsulated (another GRRRR) pipes. So, on-demand recirculation saves loads of energy compared to the really bad conventional local practices.

  4. user-2511396 | | #4

    Theseus's paradox
    I'd like to see a picture of the original house. As a historic preservationist I'll tend to stand on the side of Theseus's paradox that that is not the same house.

    It's a very nice house. It looks like a superbly energy efficient house, but it's not a rescued or restored house. Most every component of the house appears replaced or covered with something of a different size or material. It's a piece-by-piece replacement house with a few rooms of salvaged interior millwork.

    Still, a very very nice house. I wished all modern green building looked as nice. But it's no longer a Victorian house.

  5. GBA Editor
    Martin Holladay | | #5

    I still have my grandfather's ax
    "I still have my grandfather's ax. Of course, I've replaced the handle twice and the head once."

  6. Stewart Herman | | #6

    My answer to Theseus' paradox
    Let me chime in, as owner. The house was doubled from its original before we bought it, and the (2005) addition was crappy. Still, the frame is original--beefed up in places. All the original woodwork (well over 1000 feet, plus 12 doors) was retained, but was only sufficient to cover 1/3 of the house--all relocated to the second floor. Then we added millwork identical, even down to the wood species, to the original . The birch floors are original--in the older part of the house. So we moved the second-floor birch to the first floor and redid the second floor in maple salvaged from other old houses to cover the second floor. Now, of course the house has entirely new plumbing, electrical and heating systems, and new siding, bumped out on all sides by a foot to accommodate insulation. But we preserved everything worth preserving, and pieced in millwork, flooring, etc, that is 100% true to the design of the original. I would call it a brand new 1907 house, true to the Victorian spirit of design. So let me make a suggestion. Since we saved everything physically possible to save, and faithfully followed the design decisions of the original otherwise (down to the japanned door hardware), how about a new dual category--"restored where possible, recreated where not"?

  7. Expert Member
    Dana Dorsett | | #7

    Sure it's the same house- Theseus does not apply @ Brendan Meyer
    Covering isn't the same as replacing. The original framing & sheathing are still there, as well as the pre-existing (though not origianal) blown fiberglass insulation in the wall cavities. Putting a foam coat and additional non-structural hull over the ship isn't the same doesn't remove & replace the ship any more than painting the hull would be akin to replacing the hull and the structural ribs.

    This is definitely NOT a "... a piece-by-piece replacement house...", not even close! The only structural elements replaced were (apparently) the roof assemblies. The original siding is gone, as well as exterior trim, as well a the original windows, but that's pretty much it. The majority of the structure, including most of the interior non structural materials are what was installed 107 years ago.

    Regarding recirculation systems, they do NOT save energy, but they do save water. Even with the return lines insulated there is MORE energy abandoned in the plumbing with a recirculation system than hot water distribution without recirc. Home- runs from every hot water tap of 3/8" plumbing to a manifold will usually reduce hot water energy use, but may not reduce the wait times by enough to matter, and not quite as much water savings as with recirculation. The energy cost of supplying that water to the house in MN is probably a LOT less than it is in drier locations where water to cities is sometimes transported 100s of miles, often with large elevation hurdles, such as in CA or AZ.

    Seeing that it's net energy positive, perhaps it's time to think seriously about plug-in-vehicles(?).

  8. Stewart Herman | | #8

    picture of original house
    In response to your request, here are pictures of the original front and rear. As you can see, there was not a whole lot to preserve, regarding the exteriors. The siding was not original, and the 2005 addition was about as ugly (in the rear) as could be. So we took a 1907 house which had been degraded through subsequent work and restored (actually, probably improved) its original exterior look with admittedly new materials. I don't see much point in branding it as "no longer Victorian" when in architectural spirit it is now more Victorian than at any point since it was built.

  9. Stewart Herman | | #9

    on plug-in vehicles
    Well, thanks for the suggestion. We do have a plug-in vehicle--a Ford CMax energi. Its energy consumption is included in our annual total of about 12,000 kWhrs (vs 19,000 kWhrs generated). We calculate that we are fairly close to the 2000 watt society standard, without any diminution of quality of life.

  10. Expert Member
    Dana Dorsett | | #10

    Adding on isn't replacement either @ Stewart Herman
    The 2005 addition probably didn't remove any (or very much of) Theseus' ship either (?).

  11. Stewart Herman | | #11

    further conversation
    I really appreciate the comments, which have made me think (and consult my architect!). I'll have to table conversation for a few hours--have to run off on errands. Thanks, everyone!

  12. AntonioO | | #12

    PV models way off
    I'd say the biggest lament was the electricity consumption modeling. Overestimating consumption by almost 60% seems unacceptable to this reader.

  13. GBA Editor
    Martin Holladay | | #13

    Response to Antonio Oliver
    I have to agree. I've reported on dozens of net-zero homes, and most have had PV systems in the range of 4 kW to 8 kW.

    A 10-kW PV system is huge. This house has a 17-kW PV system. How did that happen?

    Of course, until the local utility changes its mind, the homeowners are in the enviable position of being paid 20 cents per kWh for excess electricity generated by their oversized PV system. For the time being, the oversized system looks like a good investment.

  14. calum_wilde | | #14

    I'm hoping I can get


    I'm hoping I can get permission for a 15 kW system when it comes time, so it can power two electric cars as well as the house. (I'm estimating the cars will use about 3000 kWh/year each but will hopefully be able to refine that estimate more in time.) I hope that line of thinking becomes more common as electric cars become more common.

  15. Stewart Herman | | #15

    solar size
    Antonio wonders why our consumption was so overestimated. Our architect used standard modelling tools, without any basis in the house to go on. I doubt the modelling included some subsequent decisions, such as having three heat pumps in the house (hot-water heating, dryer, and the latest geothermal heat pump--with a COP of 5) Certainly the model did not account for my miserly habits; I spend half my life turning out the lights, and we keep the thermostat at 69 in winter and 77 or so in the summer. Also, we are not putting nearly as many miles on our plug-in hybrid as the model anticipated. I can't fault the architect for our lifestyle preferences.
    Martin wonders why we super-sized the PV system at 17kW. Recall where we live--the most winter- challenged major city in the US. We are lucky to get 300kWh per month in the dark months, and we have many, many cloudy days. Of course, in summer, we get 100kWh on a good day while using 25kWh.
    Yes, the decision to supersize was made easier by the fact that the utility pays us 19 cents/kWhr for surplus production. At the current rate, the system will cover the investment cost in about 13 years. As Martin notes, it is a good investment. But don't discount the larger picture--the psychological value of paying my way, as it were, in terms of carbon. We offset 12 tons a year. That is something I was and remain willing to pay for. We cut the gas line and eliminated a fireplace from the house design, and in general are minimizing our use of fossil fuels. Not to be holier than anyone, but just for the personal comfort of knowing that we are trying to minimize our contribution to the world's carbon problem.
    I'd encourage Calum to size his system as large as he can. The payoff is continuous and almost maintenance free....
    Thanks for your critical comments; I appreciate the learning value in being challenged.

  16. GBA Editor
    Martin Holladay | | #16

    The 2,000 watt society
    In comment #9, you mentioned the 2,000 watt society. To achieve the 2,000 watt target, U.S. citizens would need to pare not just residential energy use, but energy use from all sectors -- including transportation energy use (not just personal vehicles, but freight trains and jets, too), industrial energy use (General Motors, Ford, U.S. Steel, Google), government offices, and -- no small consumer -- the U.S. military.

    While your residential use may be at 1,369 watts continuous, Americans would need to cut our residential consumption a lot more than you have to reach the 2,000 watt target.

    For more information on the 2,000 watt society, see:

    What Does ‘Sustainable’ Mean?

    Understanding Energy Units


  17. msloot | | #17

    Hot Water Re-Circulaton System
    Wow, lots of good conversation here. I will try to add to it and hopefully clarify a few things.

    For the record, on this project, for many reasons it made sense to keep the mechanical room in its existing location, which was roughly in the center of the basement.

    The entire hot water circulation system does not reduce overall energy use, but I do not believe it increases energy usage very much either, since a re-circ pump sips very little energy and the pipes are very well insulated to minimize thermal loss.

    Myself and many Green Building Certification programs believe that it does have a net benefit to the environment as a whole, if configured for on-demand, not to mention it is really nice to have immediate hot water when turning on the faucet.

    GreenStar used to actually have a negative 1 point for energy and positive 3 points in water conservation when these were installed.

    Now I see they have changed that to zero points in energy and 1 point in water conservation. I do not know why they changed it, but maybe their rationale is that the net energy used is negligible when the energy saved at the utility vs. the energy used at the house are considered holistically.

    While I agree with Martin, that no system is perfect, I still think the motion detectors are the best way to go, all things considered:
    --> They turn the system on and off automatically on demand, and I believe that a very high percentage of the time when someone goes into the bathroom they will be using the hot water. Thus I believe the number of times they turn the system on unnecessarily is not that often.
    --> Flexibility. . . They are simple, inexpensive and can be operated as a standard on/off switch if the homeowner really wants to operate them in that way when it is just them in the house. The owner can also perhaps just set them to auto mode when they are planning to have guests who would not be aware that they need to turn on the pump when they enter the bathroom and equally important that the need to turn it off again when they leave the bathroom. Of course that is one more thing to remember, but perhaps would save a few BTUs of energy.

  18. msloot | | #18

    Energy Modeling
    As Stewart mentions, from an energy perspective, a major goal they had in this entire project was to reduce their carbon foot print as much as possible. The goal was not to see how close we could get to hitting net zero. As has been mentioned by others, it is a good financial investment right now. Environmentally, it helps put a greater percentage of renewable energy in the grid which is a good thing too. Thus our approach was to:
    1. Reduce energy consumption as much as possible first.
    --> Excellent building envelope, insulation, air sealing and elimination of thermal bridging, while being reasonably sensitive to the law of diminishing returns. We essentially used the PERSIST method.
    --> Install mechanical equipment that uses a minimal amount of energy. Thus we selected equipment that had heat pump technology where possible.
    --> Unfortunately our ability to incorporate passive solar design features was severely limited due to the close proximity of neighboring homes and mature trees, but it also is notable that those conditions are typical for most urban houses in neighborhoods in existence that were built in the late 1800's and throughout the 1900's.
    2. Produce as much power as possible.
    --> Thus we maximize the amount of PV panels we could tastefully fit on the roofs without having them hanging off of the edges, etc.

    We did do energy modeling, since the owners wanted to at least achieve the threshold of net zero energy at a minimum, since they had recently learned about that as a notable threshold starting to be promoted in housing. Like most homeowners they wanted a prediction of whether it was possible with their challenging site to achieve this threshold.

    We used the well-known REM/Design software for our modeling. As Stewart mentioned, we did not adjust the model to every nuance of their lifestyle, thinking that being somewhat conservative would not hurt. Keep in mind that the modeling is based on a 4 bedroom house, and I believe assumes more occupants, whereas in reality it is typically just the two owners there. Based on the modeling we did expect the performance would cover the consumption of 1 all-electric car driven a typical number of miles in the year. I think overall the software may be a bit more conservative than it needs to be, but if everything was normalized for lifestyle I thought the energy modeling software did a reasonably good job. If I recall, their first year of occupation was also a somewhat mild winter. Since Minnesota is the Land of 10,000 Weather Extremes, it will be interesting to see how the averages play out over 5 - 10 years, and beyond.

  19. msloot | | #19

    2000 Watt Society Calculations
    I did the rough calculations to try to address all of the items that Martin mentions, and thought that the Herman's were "close", as Stewart mentioned. I do not have those handy with me right now, but can dig them up another day and share them also if people are interested in them.

  20. msloot | | #20

    Regarding Remodeling vs. Tear Down
    A good amount of embodied energy was preserved by remodeling this house.
    Some people lament that remodeling does not necessarily save any money, since there is often more labor involved. Thus a shift from money spent on materials to money spent on people. I agree that shift is a reality on most remodel projects compared to new-build, but I actually think a shift like that is a good thing.
    --> More jobs, which is of course great for local communities, economies, etc. on all levels.
    --> Less impact on the environment for harvesting raw materials.
    --> Keeping people employed helps keep the pool of skilled workers strong.

    Sometimes a teardown is the only reasonable way to proceed, but too often I believe the holistic benefits of remodeling are overlooked when people make a decision to tear down.

  21. GBA Editor
    Martin Holladay | | #21

    More on the 2,000 watt society
    Using the bar graph in my article ("What Does ‘Sustainable’ Mean?") as a starting point, we know that U.S. per capita energy use averages out at 12,000 watts continuous.

    Using the Lawrence Livermore National Laboratory graphic that I reproduced in Comment #16 as a guide, we learn that 13.3% of this energy use is residential (1,601 watts continuous), 10.9% is commercial (1,313 watts continuous), 41.8% is industrial (5,023 watts continuous), and 33.8% is transportation (4,062 watts continuous). Clearly, some portion of the transportation energy use consists of private vehicles.

    From this information, it's clear that an individual American citizen can't achieve the 2,000 watt target by simply adjusting residential energy use. Even if residential energy use is zero, the other uses put per capita use over the 2,000 watt target.

    If each American is committed to reducing energy use to 1/6 of the current level -- the type of change needed in all sectors to hit the 2,000 watt goal -- then per capita residential energy use would have to adjust down from its current level of 1,601 watts per capita to 266.8 watts per capita. So we have a long way to go.

    If Stewart Herman is part of a two-person household committed to the principles of the 2,000 watt society, the household should aim for 534 watts. He can throw in a few more watts for personal transportation without violating the principles advocated by the 2,000 watt society.

  22. GBA Editor
    Martin Holladay | | #22

    Another response to Marc Sloot
    I am aware that we are all piling on here, and that your admirable project -- which created a house that is beautiful as well as energy-efficient -- is getting an undue amount of critical scrutiny. That seems fundamentally unfair, in light of the goals and achievements of this project.

    That said, I'll continue the discussion, since this project has been presented in great detail for GBA readers to consider.

    In comment #18, you wrote, "As Stewart mentions, from an energy perspective, a major goal they had in this entire project was to reduce their carbon footprint as much as possible."

    The problem with this type of project -- heavy on capital investment -- is the front-loading problem. All of the carbon emissions associated with this project are released into the atmosphere now, at a time when the planet is particularly vulnerable. The front-loading problem is a huge challenge to green builders -- enough of a problem that it may change how thoughtful architects and builders address future green projects.

    For more on the front-loading problem, see Carbon Emissions By the Construction Industry.

  23. GBA Editor
    Martin Holladay | | #23

    Response to Stewart Herman (Comment #15)
    You wrote, "I'd encourage Calum to size his [PV] system as large as he can. The payoff is continuous and almost maintenance free."

    Before Calum takes your advice, Calum should read the fine print on the net metering contract offered by the local utility. Some utilities don't offer net-metering contracts.

    Even if the utility offers a net-metering contract, remember that most utilities re-set the meter to zero once a year, even if your PV system produces more electricity than you use. These utilities don't pay homeowners for excess production. The excess production is simply a donation to the utility. Because of these facts, most homeowners who have access to net metering choose to size their PV system to match, but not exceed, their annual electricity use.

    The fact that your local utility pays you for your excess production puts you in a tiny subset of homeowners. Your utility offers what amounts to a feed-in tariff -- a type of PV reimbursement which is fast disappearing from the planet.

    Finally, GBA readers should recognize a political reality: with each passing year, utilities are under increasing political and economic pressure to alter their net metering contracts in a way that disadvantages owners of PV systems.

  24. eyetrply | | #24

    Stewart, While one can argue the authenticity of the finished product (is there such a thing as a Victorian House Concours d'Elegance?), your upgrade IMHO is indeed beautiful.

    Can you comment on the windows (efficiency), vendor, and the (glazing) trim used (as seen in the front elevation)?

    Thanks for posting this project - and congratulations!

  25. JC72 | | #25

    Awsome house !
    I really dig the front elevation and the interior millwork. A++

    I hope you'll be able to recoup your investment.

  26. Stewart Herman | | #26

    general comment
    Good morning, everyone, and let me say off the bat I am stunned by the quality of the exchange going on here--particularly Martin Hollady's persistently skeptical take on everything (!). Note the detailed replies by architect Marc Sloot. He is a gifted and conscientious professional and gets the credit for the 'recreated' Victorian look and all the esthetic embellishments (thank you Dana and John for your appreciative comments), as well as the sustainable technology he hunted down for us. My fondest wish at this point is that someone asks him to design a set of retirement townhouses that blend net zero with aging-in-place accommodations--I think that would be a fabulous combination for seniors wanting both physical comfort and the psychological comfort of leaving the world not much worse than they found it. I don't know if he shares this dream, but I do think it is a template for responsible retirement by the 70 million boomers in the US....
    More to comments to follow; I am happy to keep this thread going as long as there is interest.

  27. AlanB4 | | #27

    Very interesting project
    I am very impressed that you were able to pull this off (the timeline while longer then you expected is not terrible). That said i have some questions
    Are you comfortable sharing with us the cost for the project and projected payback (if calculated) with solar separated?
    The basement insulation method is one i have never heard of, i assume it was more cost effective then the standard methods?

  28. Expert Member
    Dana Dorsett | | #28

    I too find Marc Sloot's approach & comments credible.
    ( Even if the name "Sloot" means "ditch" in Flemish / Dutch / Afrikaans, I thoroughly respect this guy! :-) )

    This was obviously a well considered and conscientious project on many levels.

    Overshooting the PV spec by a 1.6x factor isn't a crime.

    I recall in some blog reading that Wolfgang Feist (PassivHaus founder) pooh-poohs Net Zero with statements to the effect that to be TRULY net zero the PV on the house has to produce about twice it's actual annual use, to make up for the lower wintertime production. Putting that to the test, has there been any month so far with this house that was NOT net zero for this house? If yes, how much net power was drawn from the grid in the worst performing month?

    Compared to the cost (and lifecycle carbon) of taking it fully to PassivHaus levels it's probably still better to have 1.6x oversized PV, even if it isn't quite Net Zero on some given week or month.

  29. Stewart Herman | | #29

    net zero solar production
    In Germany, being so far to the north, perhaps one has to overproduce. But Feist's claim makes no sense. To achieve net zero, all one has to do is produce as much energy as one uses on an annual basis. That said, let me offer up some numbers. In December and January, we produce about 250 kWhrs per month, while using 50 kWhrs per DAY, or some 1500 per month. But in the summer, we typically produce 100 kWhrs on a clear day, while consuming about 25 kWhrs. So our summer production more than makes up for the slim winter solar pickings--in our first year, we produced about 25% more than we used, making us solidly net positive. This year (our second year), we are in the same ballpark so far.
    The months when we fall short of net zero run from mid-October to the beginning of February--at least in our first year. I never expect to achieve net zero in twelve out of twelve months--that would take a monstrously large array.

  30. Stewart Herman | | #30

    cost and payback
    Alan, sorry, I am not comfortable sharing the overall cost. Let's just say it was considerable. But I will share a few numbers. The four legs of net zero (insulation, air/moisture barriers, solar and geothermal) added a premium of about 15%--relative to what would have been the cost of 'normal' insulation, heating system, etc. The solar will pay for itself in about 13 years, thanks to the 30% federal rebate and our utility's mandated policies of buying not only our unused solar output, but the solar attribute of all our output. I haven't figured out how to calculate the payback of our geothermal system--please let me know how and I will give it a try. Marc may come up with a number there. Ditto for the insulation.
    Our exterior basement insulation is a relatively new concept, I believe. We were the first in Minneapolis, and it was not cheap--something in the neighborhood of $10,000, I believe. I have no idea how to calculate payback on that. Our (almost full) basement also has 2" of foam under half the slab, and stays at a constant 63-64F with just two or three ceiling ducts and no interior insulation.

  31. GBA Editor
    Martin Holladay | | #31

    Response to Alan B
    Like you, I look forward to hearing from Stewart Herman on the topic of "the cost for the project and projected payback with solar separated."

    In the meantime, here's some napkin math.

    The average Minnesota household in the northern half of the state pays $1,947 per year for all residential energy expenditures (source: 2009 RECS data).

    Another source estimates the average residential energy expenditure for northern Minnesota households at $1,941. We'll go with $1,947.

    If we exclude the PV system, Stewart Herman now uses 12,000 kWh per year. At the published Minneapolis residential electricity rate of 11.47 cents per kwh (here is the source), that much electricity would cost Stewart Herman $1,376 if he didn't have a PV system.

    So his envelope improvements and other retrofit measures are saving his family about $571 per year (not counting PV).

    If his deep energy retrofit cost him $100,000, the simple payback period is 175 years.

    If his deep energy retrofit cost him $200,000, the simple payback period is 350 years.

    If his deep energy retrofit cost him $300,000, the simple payback period is 525 years.

    Stewart Herman could have saved himself a considerable amount of trouble if he had simply installed the 17-kW PV system, without performing any envelope improvements. The return on investment for the PV system beats the return on investment for the envelope improvements, hands down.

    Later edit: I see now that Stewart Herman was posting a response as I was typing and doing my calculations.

  32. Stewart Herman | | #32

    Recouping investment
    John expresses a wish that we might recoup our investment. Well, there is a perhaps weird angle here. We have put more investment into this house than the neighborhood currently will bear, in terms of real-estate prices. But since this is our retirement home--with luck the last house we will live in--and since we have equipped it so that we might 'age in place' as long as possible, I am not so worried about recouping our investment. The real estate market may catch up, or it may not. Our children are financially self-reliant at this point.
    The bottom line is that after twenty years of working constantly to improve the resale value of our previous house, it is a liberating feeling not to be strategizing about market value and ROI. I realize this may sound weird, given the usual necessity of working affordability into decisions about sustainability.

  33. STEPHEN SHEEHY | | #33

    The estimate of the average MN home energy cost of $1941 is based on a house meeting 2012 IEEC. I guess at some point we need to consider whether meeting current code is pretty close to pretty good house territory.
    Like Stewart, when we built our pretty good house, we really didn't worry about return on investment. Houses are usually lousy investments. We'd never be able to sell it for what it cost, but so what? We love the house and plan to live In it until we're dead.

  34. GBA Editor
    Martin Holladay | | #34

    Response to Stephen Sheehy
    You're right that the $1,941 figure is based on a house meeting the 2012 IECC. However, the $1,947 figure I used (from the 2009 RECS data, the most recent RECS data available for Minnesota) is based on the average cost for all residential energy expenses (including all fuels) for residents of Minnesota.

    Of course, Stewart Herman might tell us that the actual pre-retrofit energy costs for his house were above average. But I don't know if that's true, so my napkin math used the Minnesota average.

    The fact is that the post-retrofit house that Stewart Herman lives in has annual energy costs that are $571 less than the state average (if we don't consider the PV system).

  35. Jon_R | | #35

    I suggest that people should use programs like BEopt and, if they are interested in green building, at least attempt to avoid optimizing for energy metrics (eg net zero energy).

    XPS, tankless electric water heaters and solar panels that would be much more cost effective located elsewhere are examples of outcomes that one might get if they don't do the latter.

  36. Stewart Herman | | #36

    Utility costs
    I think Martin's estimate of $1947 might be on target for the average house, although I haven't been able to get figures from our utility (Xcel). We generate solar electricity worth $3000 per year. I estimate our usage for HVAC about 5000 kWhrs per year--unfortunately have not been able to get a breakout from eGauge, so this is a rough estimate. Without our superinsulation, I guess our all-electric house would use at least double that, maybe more. Marc might want to chime in--he has worked through these numbers more than I. Overall, then, we are not going to see a payback in my lifetime for the HVAC system plus insulation costs although the numbers may not be as bad as Martin calculates.

    Let's not forget other benefits of the investment in superinsulation, however. Our house has no drafts,no cold spots. There is no moisture condensing on the windows in the winter. The humidity stays at a comfortable constant without active management. This is one major reason why I think net zero and aging in place are so compatible. Our aging bones are exceedingly comfortable in this house! How might such value be quantified? I am not sure, but comfort is not on my worry list as we get older, and that means quite a bit to me. And our energy costs are not only minimal (only in winter) but stable. Surely that is worth something as well.

  37. AlanB4 | | #37

    @ Martin I love napkin math. That is not bad for energy costs though, the payback sucks of course. I live near Toronto Ontario so climate zone 6, just my heating bill when i moved here was well over $1947/year so i suspect the payback would be quicker here.

    That said payback is of course not the only motivation for an upgrade but it is nice to have numbers. Of course the payback period on granite countertops is often infinite, especially if the colour goes out of style or the next buyer hates it...

    I don't get the gripe about going beyond net zero, much of our electricity footprint is not residential, there is commercial and industrial as well, so if everybody went net zero then we would still need to generate lots of power to energize non residential so i think going beyond net zero is great. Also your payback is quicker is it not, the extra sold to the utility plus your offset consumption, which i suspect would make your payback closer to 8-9 years.

  38. GBA Editor
    Martin Holladay | | #38

    Response to Alan B
    Since it looks like the simple payback period for Stewart's energy retrofit is somewhere between 175 and 525 years, I don't think it's worth imagining how much better the situation would be if the house were located in Toronto. The fact of the matter is that deep energy retrofits cost so much money that they almost never make any sense from an energy payback perspective.

    Here at GBA, we've discussed the discouraging math of deep-energy retrofits in many articles; see, for example, Deep Energy Retrofits Are Often Misguided.

    That said, if someone lives in a location where the local utility offers a favorable net-metering contract, the payback for an investment in a PV array is swift. Stewart calculated his simple payback period for the PV system at 13 years.

    Since Stewart's oversized PV system is now producing an annual surplus, there's a good chance that he could have ended up with a net-zero house had he simply installed the 17-kW PV system, without making any other changes to his house.

    As several people have pointed out, energy payback isn't everything. Comfort and beauty matter, too. If a homeowner wants to spend $200,000 to make their house more comfortable or more beautiful, that's great. But it's hard to justify the work based on energy savings.

  39. Stewart Herman | | #39

    payback from deep energy retrofit
    Alan and Martin, let me respond to the skepticism about deep-energy retrofits. My architect Marc will have more numbers, but these will suffice for starters.

    The RECs projection for our unimproved house is 44,660 kWhrs--so high because the house was so leaky (3890 cfm50). Marc's own model estimated even more consumption--59,631 for all house uses of electricity (this involves a conversion from Therms to kWhrs, since the house had a gas furnace.)
    Renovation reduced the infiltration to 350--a greater than ten times reduction. And the heating/cooling consumption to 5-6000 kWhrs. No doubt much of this reduction is due to our heatpump, with its COP of 5. Let's just say that we are using 7 times less energy to heat/cool the house than before it was renovated.
    So what is the value of this improvement? Without it, we would have had to had a solar array more than twice as large (39 kw, according to Marc's calculations--clearly impossible on our house and lot.) We could not have solarized ourselves to net zero without insulating and sealing the house, no matter how cost effective that might have been. And we still would have had to bolster the frame/roof of the house to support the solar array--part of the envelope expense.
    So we effectively had to invest in the envelope despite the payback running a hundred years or more. But does this make deep-energy retrofitting irrational? I think the question is considerably more complex than a dollar-cost calculation. Consider:
    1. comfort, as I listed earlier (no cold spots, no drafts, no condensation)
    2. energy security. The envelope enables the house to maintain its temperature. It dropped only 6 degrees over 12 hours of zero weather this past winter when the geothermal system conked out due to a software glitch. Imagine being elderly in a leaky house when the heat goes out...
    3. health benefits from controlled infiltration
    4. reduced carbon footprint. We are offsetting 12 tons of carbon per year, much of that due to reduced consumption made possible by envelope improvements
    5. stabilization of energy costs at lower level (12,000 vs 44 to 59,000 kWhrs per year)
    6. An investment (in the envelope) that is utterly passive--will continue to protect the materials in the house for decades to come with little or no maintenance or further investment.
    The upfront cost is to be sure an important factor, but energy payback is not the only relevant criterion for deciding how much investment to put into a house.
    Have I missed anything here? I welcome further thoughts.

  40. GBA Editor
    Martin Holladay | | #40

    Response to Stewart Herman
    In general, I use the term "weatherization" to refer to energy retrofit measures that are cost-effective. The federal Weatherization Assistance Program (WAP) has a good track record of implementing this type of work -- generally involving blower-door-directed air sealing, attic insulation improvements, and sometimes the installation of dense-packed cellulose in stud bays.

    The type of work undertaken at your house -- over 7 inches of exterior rigid foam on the walls, and a new "over-roof" with R-60 of spray foam -- puts the retrofit in a different category from weatherization. This was a deep-energy retrofit.

    When measures on this scale are undertaken, the price is generally in the $100,000 to $200,000 range, and cost-effectiveness is impossible.

    The fact remains that you could have bought an average Minnesota house and ended up with an average Minnesota energy bill of less than $2,000 per year, before retrofit work. If you chose your house carefully, you could have bought an old house with an unshaded south-facing roof, and added a PV system. I don't know whether your house would have been net-zero energy, but it would have been a more cost-effective approach than the approach you took.

    Finally, you could have performed the sort of weatherization work on your older house that WAP employees do routinely -- some blower-door-directed air sealing and insulation improvements. That work would have been cost-effective.

  41. msloot | | #41

    Payback & Net Zero Projections

    I agree that analyzing simple payback based on the cost of energy alone is not a strong argument to do a deep energy retrofit.

    You rightly mention that that there are additional important benefits and considerations. I would probably expand the list and add that while many are not easy to quantify monetarily, they are equally important.
    —> Health.
    —> Beauty.
    —> Comfort
    —> Durability.
    —> Environmental Impact. Current energy costs do not reflect true cost to the environment. For example, natural gas prices are currently staying low due to fracking, which has side effects too, and I am not sure we even fully understand what all of those are.
    --> While the existing roof of this house has a good orientation and size, it was not structurally capable to support the physical weight of adding solar panels without improvements.
    —> I really believe the more we do deep energy retrofits, the better we get at doing them and the cost will continue to come down. As retired educators, I loved that one of the goals that the Herman's had was to educate others and use their experience to help move the industry forward. We need passionate people like them and everyone on this blog to move the industry forward.

    Regarding Net Zero Energy Projections:
    Base on the energy modeling, I am not seeing that simply adding a 17KW array would have gotten anywhere close to net zero for the house. Nor would have they had enough room for solar on their site to reach net zero without making the other significant improvements that they made, much less go beyond net zero for the house and start to offset their transportation carbon footprint as well.

    I believe the 2009 RECS data that you reference says that for our upper Midwest region, homes averaged 46.6 kBtu / sq. ft. / year of total energy consumption.
    The size of the house before construction was 3270 sq. ft.
    Thus 3270 x 46.6 = 152,382 kBtu per year total projected energy consumption.
    Dividing that by 3.412 kBtu per kWh.
    Thus the projected annual consumption of the house before doing any improvements to it would have been 44,660 kWh per year based on RECS data.

    Based on a site analysis, the solar system designer / installer, projected that we had a potential annual production of 1.135 kWh per year per KW of array size installed. I believe some sites in Minnesota can produce around 1.2 kWh or a little more per year per KW of array size installed, but even that would not get them much closer.

    Thus to produce 44,660 kWh of electricity per year to reach net zero, they would have needed an array that was 39,348 KW, which is 2.3 times bigger than what they had room to install.

    The energy modeling software predicted 59,631 kWh per of annual consumption of the existing house before improvements were made, which is obviously higher, but did take into account an actual pre -remodel blower door test result of 3,890 cfm50, which should make its results more house specific than the RECS data. Post construction blower door test result was 350 cfm50, which I am sure we could not have achieved without applying the PERSIST system to this house.


  42. user-2642926 | | #42

    Beautiful project!
    Stewart, despite the payback criticism, that's a beautiful project. Thank you for sharing it.

    I also performed a rebuild / expansion of a house that has been in my family since 1976, and didn't even bother considering the payback details. I wasn't shooting for the performance levels you achieved, but in my Southern California location it wasn't necessary.

    What I have is a very, very comfortable house that uses almost trivial electricity and natural gas. Frankly the comfort factor and longevity were my primary goals. Given that the first (shoddily constructed) version of the house lasted nearly 56 years, I'm hoping this one is working well and comfortably standing in another hundred, and still in my family.

    You can't easily value the intangibles in a project like yours.

  43. Stewart Herman | | #43

    payback issue
    Isn't there a real difference between building/renovating for a space that one will live in--and hopefully pass down to the next generation--and building/renovating to meet economic targets? I appreciate your comment, just so I won't start thinking I was crazy for not keeping our renovation within some energy payback criterion. I expect that Martin might also put energy payback on the backburner if it was a house he planned to live in indefinitely.
    A wise old organization theorist (Chester Barnard) distinguished effectiveness from efficiency. Effectiveness involves achieving a purpose; efficiency involves doing so at least cost. Deep energy retrofits perhaps are measured better by effectiveness and efficiency, particularly when the purpose is to make a building that will last 100 or more years. Your house is approaching 50 years--actually probably older. Our house is already 110. We hope it will remain habitable and attractive for another 100.
    Thanks for your comment.

  44. GBA Editor
    Martin Holladay | | #44

    Why are we talking about payback?
    This discussion of payback started when Alan B. (in Comment #27) asked about payback. I simply used what I call "napkin math" to attempt to answer his question.

    I think we can all agree on the basics: This house is beautiful. It is comfortable. And it has low energy bills.

    Remodeling projects occur for many reasons. Some remodeling projects include cost-effective energy savings measures; others include retrofit measures that cost so much that the payback period is very long. As long as the homeowners feel their money was well spent, there's no reason to worry very much about payback.

  45. Stewart Herman | | #45

    payback issue
    A gracious conclusion to the discussion. Thanks, Martin

  46. AlanB4 | | #46

    Payback is just a number, not always a decision maker
    I didn't mean to cause any arguments. I am a numbers guy, not to say i would only bankroll something based on payback but i do like to know what it is so i know what i am working with. I might get granite countertops knowing the payback is infinite, but i like to know going in. An example was my fridge replacement, when i moved here i inherited an 12 year old one that was in an awkward location and could not be moved into the designated fridge spot (previous resident made some silly choices), the payback will not pay for the fridge replacement but having more space and better space utilization in a small not ergonomically designed older home made it worth it (for the record the payback period of 400Wh/day saved is about 25 years). And i did donate the old fridge to charity for resale so it was not junked since it was still working mostly fine.
    In general i calculate payback on everything, another example i replaced my router, its saving about 50Wh/day, its payback is about 15 years. Again not worth it except the new one is more reliable, more secure and faster.
    If this were my project i would have looked at cost effective upgrades, their costs, their paybacks and their kWh use per year saved and projected. Then i would have looked at my budget and decided how much further i wanted to go, for intangible purposes, for non money related ones and for complexity. I might have gone as far as the author, but i would know what i am getting for the difference. Sometimes its an add on cost, if i am getting siding done the extra cost for exterior foam may not be much more and its payback is reduced (the siding is not an energy upgrade but a structural one that was being done anyways)
    This is how i decide on things, a different process for everyone of course.

    Oh and my incandescent to LED bulb replacement saves about 5.5kWh/day, which almost pays for the rest of my electrical usage :D

    So again my apologies, i'm just a numbers junkie.

  47. Stewart Herman | | #47

    on replacing fridges
    Alan, your fridge comment reminds me that these decisions rarely involve simple A or B choices based on payback alone--at least for renovations. The house we were working with offered some pretty poor choices. The walls were 2x4--and had to be beefed up to support the collectors (1500lbs). So we could have kept the siding (which was frankly crappy) and removed all the plaster inside and gotten a pretty low R-value with only 3.5 inches to work with. The alternative was to remove the siding and insulate the exterior--really the obvious choice, but more expensive. Same with the roof. It was uneven and not nearly strong enough to support the collectors. We had to build a new roof, then the only question was--make it from 2x6s and settle for that amount of insulation, or put on OSB I-beams and gain a lot more room to insulate.
    In general, the shabby state of the structure made a deep-energy retrofit a pretty obvious choice; there was not an attractive middle ground between settling for the structure we had or making it radically more energy-conserving.

  48. user-1147460 | | #48

    Foam panels vs spray foam
    Can i ask what's probably a dumb question. You have clad the walls with panel insulation, but chosen to spray the roof. Why not spray the lot or panel the lot?
    I'm in New Zealand and i'm negotiating to buy the highest hotel in the country. As it stands it's spectacularly energy inefficient, but is absolutely ideally suited to being re-skinned with insulation. So if you could walk me through your decision making, please.

  49. Stewart Herman | | #49

    which kind of foam
    Hi, Sam -

    We used EPS (expanded foam--much better for climate change than XPS) for the walls in part because we were cladding the vertical exterior of house--that lent itself to stacking up the panels and screwing them on (4x8 feet, 7.25 inches thick).
    For the roof, a sloped surface where we needed to get insulation under and around various pieces (to minimize thermal bridging), it made more sense to squirt foam. Does this make sense?

  50. Expert Member
    Dana Dorsett | | #50

    Depth/flatness vs. conforming to uneven surfaces @ Sam Clarkson
    When applying insulation to the broad areas on the exterior it's useful to use materials manufactured to a uniform thickness with fairly tight tolerances, which delivers a fairly flat exterior surface without needing a lot of precision detailing.

    When applied to the interior between framing that like the webs & flanges of I-joists/rafters, that has to be air tight to prevent moisture accumulation in the roof deck from interior moisture drives using spray foam saves a lot of careful cutting detailing & sealing. They might have been able to use foam board on the exterior of the roof deck, but it might have been difficult to hit the performance they were after without affecting the Victorian roof thickness & trim, and complicates the mounting of the PV.

    On the foundation it sounds like they used 1" foam board as the exterior form/mold and filled in the space between the board stock and foundation with closed cell foam. That provides the exterior flatness of the board material, along with the air-sealing continuity of the sprayed foam.

  51. user-1147460 | | #51

    foam vs panels
    So If i get good at spraying foam and then trim to an accurate depth, spraying would potentially be the more airtight option? (not that I'd be relying on foam to be my airtight membrane as such, but snug is better right?) Does it come down to time spent detailing the tight fit of panels vs the time spent trimming foam to an even depth, which is the better use of my time? Which is the better outcome?
    If I get this Hotel i'll be approaching the NZ Passive House institute to use this as a training opportunity. It lends itself ideally for a study project. It needs EVERYTHING done to it.

  52. Stewart Herman | | #52

    adapting insulation to the situation
    Exactly, Dana. Thanks for the granular explanation.

  53. GBA Editor
    Martin Holladay | | #53

    Response to Sam Clarkson
    It's possible to use spray foam to insulate the exterior side of the wall of an older home, although the technique is rarely used because of the high cost of the spray foam. Here are links to two stories describing the process:

    Deep Energy Makeover: One Step At A Time

    Brand New Appearance and Performance for An Older Duplex

  54. Jud_Aley | | #54

    Hot Water Re-Circulaton System vs. point of use electric?
    For the hot water would it make sense to have a small on-demand electric water heater close to the point of use instead of the complexity of an electronic eye, circulating pump and related heat loss?

    I live in a long narrow house, the utility room/hot water tank is 50’ from the master bath and it’s a long wait for the hot water. I’ve thought about putting something like this in a closet close to the master bath thinking it would provide the initial need for hot water and once the hot water arrived from the utility room boiler it would shut down the on-demand electric?

  55. user-1147460 | | #55

    Martin reply
    Sorry to hijack the thread, but I'm looking to do an entire hotel, search Skotel New Zealand. At this scale i'm looking to buy an entire rig. But, I'm not the owner yet, and when i get there I'm going to start a thread for you experts to help me in that learning process! If you do search it up, you'll see there are entire wings and entire buildings to bury in foam (or whatever).

  56. Expert Member
    Dana Dorsett | | #56

    Electric on-demand is a grid-disaster @ Judson Aley
    At a 75F rise (35F in, 110F out at the sink tap) even 1 gallon per minute is about 11,000 Watts, and needs to be on a dedicated 50A/240V breaker. Even four of them adds up to 200A/240V of service to the house, and that's when not even using anything else!

    Multiple point of source on-demand water heaters (or even one single whole-house electric tankless) almost never makes sense:

    The grid infrastructure required to support large intermittent loads like that is a big cost adder to the distribution grid that we all have to pay for.

    With the hot water in this case being heated at very high efficiency with a ground source heat pump, which makes the losses of the recirculation system pretty tolerable. The total electricity use is far less than the unleveraged efficiency of resistance heated hot water. Even at 99%+ efficiency for the on-demand water heater it will never come close to the ~400%+ efficiency of the ground source heat pump at domestic hot water outpu temps, even after distribution and recirculation losses.

    In your case, a small point of use electric TANK can make sense. A 50' of 3/4" has about a gallon of water in it, so even a 3 gallon local tank kept at 140F would have enough dilution factor on the ~65-70F incoming water to deliver reasonable water temps until water from the main heater arrived.

  57. GBA Editor
    Martin Holladay | | #57

    Response to Sam Clarkson
    I did some Googling as you suggested, and discovered that you just bought a hotel that is appraised for tax purposes at $3.5 million New Zealand dollars.

    Considering the value of your investment, you obviously need to consult with architects, energy consultants, and general contractors familiar with New Zealand materials and methods.

    For inspiration, you might want to read this GBA article: Solving an Ice Dam Problem With Exterior Rigid Foam.

    That said, I don't think you should take any advice from an American web site. Get local help. Good luck.

  58. Stewart Herman | | #58

    deep energy retrofits
    Thanks, Martin, for passing along articles about two deep-energy retrofits--the in Somerville, the other in Brattleboro. Given the idiosyncrasies of older houses, every project is going to be remarkably different. Little standardization possible. And owners likely are going to have to be heavily invested--not only in money but in knowledge, patience, etc. So this is likely never to be more than a niche trend, sad to say.
    Still, I am curious--you seem to be tracking this. Any idea how many have been done, nationwide? I found a couple on the ILFI site, but those are only the ones that seek certification. I am particularly curious about the projects that aspire to net zero and are 100 years old more, but a wider net would yield an interesting nosecount as well.
    Or is there a good source to go to for such information? Thanks in advance for any breadcrumbs you can point to.

  59. Stewart Herman | | #59

    heating water at a distance
    Dana, you make a strong case against on-demand water heaters. Good to know.

    I wonder then how well a recirc system would do at 50 feet distance? Obviously insulating the lines is needed. We wrapped our lines in R4 insulation. Would you recommend more?

    By the way, our water heater uses an air-source heat pump (bolted onto the top of a conventional-looking water heater (although a separate pre-heat tank draws excess heat from the ground source heat pump that heats/cools the house). I am guessing the air-source is not as efficient as the ground-source, but perhaps not enough to be undercut your recommendation.

  60. Expert Member
    Dana Dorsett | | #60

    Insulating recirculation loops @ Stewart Herman
    If your water is being heated by burning $100 bills it's definitely going to be worth insulating a 50' recirculation loop to something greater than R4 (which is already greater than the code-min R3).

    If the water is being heated with a tank-top heat pump at a COP of ~2, half the heat is either coming from a ground source heat pump at COP of 4-5-ish during the heating season, or actively reducing the cooling load during the cooling season. So maybe it's really only averaging 150% efficiency annually, not 300%+, that's still a LOT more than the sub-100% achieved by a tankless. Are you really going to lose 30%+ of the total heat in the distribution plumbing? (I doubt it, with a 50' recirculation loop.) With electricity that is in real time either coming from on-site PV in or drawn a local & regional grid that is rapidly decarbonizing, the case for going higher than R4 is pretty thin on both financial & environmental grounds.

    All insulation has diminishing returns with increasing R, but with the geometry of cylinders working against it those returns diminish a lot faster with pipe insulation than with planes such as walls/roofs/floors. With pipe insulation on 3/4" or smaller pipe the total exterior surface area increases significantly with thickness, increasing the thermal coupling to the room, reducing the net effectiveness. Doubling the R value from R4 to R8 still cuts the rate of heat loss, but the reduction is far LESS than a reduction by half, the way it (nearly) would be for a wall, due to the substantially greater exterior surface area that comes with extra thickness at these small diameters.

  61. GBA Editor
    Martin Holladay | | #61

    Response to Stewart Herman (Comment #58)
    Green Building Advisor is one of the best available sources of information on deep energy retrofits. We have been reporting on this topic for many years, and there are lots of articles on GBA on the topic.

    To get you started, see these articles:

    Deep Energy Retrofits Are Often Misguided

    The High Cost of Deep-Energy Retrofits

    The History of the Chainsaw Retrofit

    An Old House Gets a Superinsulation Retrofit

    Remodel Project: Deep Energy Retrofit

    Alex Wilson: Deep-Energy Retrofits

    Brand New Appearance and Performance for An Older Duplex

    Exterior Insulation for an Ugly Brick Building

    A True Net-Zero Gut Rehab, New England-Style

    A Leaky Old House Becomes a Net-Zero Showcase

    Solving an Ice Dam Problem With Exterior Rigid Foam

    Deep Energy Makeover: One Step At A Time

    Video: Spray Foam Blankets a 100-Year-Old House

    More Job Site Visits in Maine

    A Deep-Energy Retrofit in Northwest Vermont

    Jefferson City Deep Energy Retrofit

    Wrapping an Older House with Rock Wool Insulation

    Window Installation Tips for a Deep Energy Retrofit

    A Deep Energy Retrofit Using Nailbase Insulation Panels

    Mission Zero House: A Net-Zero Retrofit

    A Practical Look at Deep Energy Retrofits

    A German Deep-Energy Retrofit

    Net-Zero Energy on a Mass Scale

    The First Passivhaus Retrofit Certification in the U.S.

    When Remodelers Carve Paths to Passive House

    One Man’s Quest for Energy Independence — Part 1

    Rebuilding a Mid-Century Dinosaur

    From ‘Tea House’ to Tight House

    A 100-Year-Old Energy Star Home

    Michigan's First LEED Platinum Gut-Rehab

    1970s Home Goes Net Zero

    Foam Shrinks, and Other Lessons

    Extending Window Openings for a Deep Energy Retrofit

    Video Series: Exterior Insulation Retrofit — How to Install Foam On a Roof

    Exterior-Insulation Retrofit — How to Choose Retrofit Details and Materials

    Video: Deep-Energy Retrofit, Portland, Oregon

    Part 1: What Is a Deep Energy Retrofit?

    Deep Energy Retrofits, Part 2: Focus on the Envelope

    Deep Energy Retrofits, Part 3: Apply the Energy Efficiency Pyramid

    The Big Rewards of a Deep Energy Retrofit

    Number Crunching on a Deep Energy Retrofit

    All About Larsen Trusses

    Study Shows That Expensive Windows Yield Meager Energy Returns

    Learn the Real (Hard) Work of Residential Design

    Making an Old Tract House Sunnier and More Efficient

    Providing Outdoor Combustion Air for a Wood Stove

    A Two-Home Demo for Deep-Energy Retrofits

    Marc Rosenbaum: Moving to a New House

    Blog Review: MinnePHit House

    U.K. Victorian Finds Its Way to Passivhaus Performance

  62. Stewart Herman | | #62

    deep energy retrofits
    Thanks, Martin, for forwarding such a compendious list of articles. What is to be learned, in aggregate?
    1. Of the 20+ retrofits here, most do not involve seeking certification as net zero.
    2. They are wildly different--in approach, in cost.
    3. They require extensive planning, manual labor, in-course corrections as challenges arise.
    4. Hands-on involvement by owner is the main way to keep down costs.
    5. While the original project you seem to admire (Saskatoon--almost ten years ago!) was achieved at low cost, most of the subsequent ones were expensive--hence your disillusionment?
    These are just some observations. On to a few generalizations:
    a. A variety of approaches are being tried, and presumably will continue to be experimented with, given the different conditions evident in projects. Experimentation is good.
    b. There likely will be no cookie-cutter approach to deep-energy retrofits which will permit cost-cutting through standardization and volume.
    c. In the absence of soaring energy costs, deep-energy retrofits are likely to be undertaken mainly by committed owners and builders, rather than foster the growth of a new industry.
    d. Since certification does not appear very popular (that too costs money!), we're not likely to get an accurate count of how many retrofits result in net-zero houses.
    I offer these thoughts informally and tentatively. From your observations over the years, would you amend or disagree with any of these points?
    Thanks again for providing all the links.

  63. GBA Editor
    Martin Holladay | | #63

    Response to Stewart Herman
    You wrote, "While the original project you seem to admire (Saskatoon--almost ten years ago!)..."

    In fact, the original chainsaw retrofit in Saskatoon occurred in 1982, which (if my math is correct) was 36 years ago, not 10 years ago. Here is a link to my article about that project: The History of the Chainsaw Retrofit.

    You wrote, "While the original project you seem to admire was achieved at low cost, most of the subsequent ones were expensive -- hence your disillusionment?"

    As I've written many times, I usually distinguish between weatherization work (usually defined as measures that are cost-effective) and deep energy retrofits, which are never cost-effective. I'm a big believer in weatherization. Deep energy retrofits -- not so much. My analysis and opinions are provided in this article: Deep Energy Retrofits Are Often Misguided.

  64. Stewart Herman | | #64

    With 'almost ten years ago" I was referring to your (2009) post, not the project itself. Sorry for the unclear reference.

    The Saskatoon project was a pretty radical 'weatherization' project, if you want to call it that. What intrigues me about it is that it was presented as a single recipe for retrofitting all of Canada's aging housing. And it is beguilingly simple idea, and the proponents claim it works. That makes me wonder what happened to the concept. Have you heard of anyone else trying the same approach (poly wrap, with foam boards for insulation?)

  65. GBA Editor
    Martin Holladay | | #65

    Response to Stewart Herman
    The chainsaw retrofit in Saskatoon was groundbreaking because it was the first time that an entirely new thermal envelope was installed on the exterior side of an existing house. The researchers who performed the work were unsure of whether the work would be cost-effective. In their report, they wrote that "costs for the total retrofit were high."

    All of us in the energy-efficiency community salute Rob Dumont and Harold Orr because they were pioneers. They were also careful researchers who documented their work.

    Almost every deep-energy retrofit since that first project in 1982 takes the same approach: Strip off the existing siding and roofing, and then install a new thermal envelope (including insulation and high-performance windows) on the exterior side of the existing sheathing. While the type of insulation and air barrier materials have changed over the years, the basic method has not. Rob Dumont and Harold Orr invented the technique.

    Dumont and Orr did not find the technique to be cost-effective; nor have subsequent followers of the method like Paul Endrenkamp.

  66. Expert Member
    MALCOLM TAYLOR | | #66

    DIY Savings
    Stewart commented that "Hands-on involvement by owner is the main way to keep down costs."

    Given that labour is a significant part of all construction budgets, this is true of new construction too. However, when evaluating the cost effectiveness of a retrofit, or publishing the cost of any project, including the savings from work done by owners distorts the analysis, as it really just hides labour costs the owner didn't charge for.

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