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Green Basics

Remodel Project: Deep Energy Retrofit

Insulation, Air Sealing, & HVAC Offer Chances to Slash Energy Bills

Reductions of 50% to 90% are attainable

Superinsulating a home can radically improve the energy performance of an old house. These so-called deep energy retrofits achieve household energy up to 90% by addressing all (or nearly all) energy loads — space conditioning, hot water, lighting, appliances, and plug loads — and sometimes even transportation. Energy reductions of this magnitude require an intensive and extensive systems approach: The inherent relationships among energy, indoor air quality, durability, and thermal comfort must be honored throughout design and construction. Passive solar design and renewable energy systems are common in these projects.

Careful planning is required for this extensive and invasive green remodel
A deep energy retrofit can significantly reduce household energy consumption, but only as long as nothing is overlooked. Space heating and cooling, hot water, lighting, appliances and electric loads in general should be considered as part of the retrofit.

Current energy use is the key to improvements
You can learn how your house handles energy in a number of ways. Studying utility bills covering at least one year, and preferably more, is a good start. Blower-door testing, infrared imaging and duct-blaster testing offer valuable information about current energy consumption. An energy feedback device, such as the Energy Detective, measures electricity usage and can be useful. An assessment of existing conditions also should include a look at how the building envelope gets wet and dries out, and how energy improvements may affect where this moisture goes.

Energy improvements can affect moisture performance
A deep energy retrofit probably will include changes to the entire building envelope as well as heating and cooling equipment. Moisture must also be carefully managed; this may mean adding perimeter drains in the basement. Exhaust fans in the kitchen and bathroom, or a whole-house ventilation system, where those features are lacking play critical roles too. Plants and roots that are too close to the house may have to be cut back to encourage drying outside and open up the house to get more sun. In some cases, both the site and the structure should be examined with an eye toward adding rooftop- or ground-mounted solar-energy installations, solar hot water collectors, or a wind turbine. With a sharp reduction in heating and cooling loads it might be possible to downsize or even eliminate some heating and cooling equipment.

Don’t throw away the old stuff
What about building materials that might be replaced during the project? Cabinets, trim and flooring might be used elsewhere—in a basement or workshop, for example. Wood, gypsum drywall and other processed materials could become soil amendments or a base for a driveway or sidewalk with some planning.

Smart project planning can cut remodeling trauma
The stages of a project can make it easier to live through. Most of the living spaces will probably be involved, so if you’re planning to remain in the house while it’s being retrofitted, it’s important to figure out what you will need to use and what you can put up with. Disruption is significantly less when the project is tackled starting from the outside of the house. Approaching projects from the outside also makes it easier to keep the insulation and air barrier continuous. A Deep Energy Retrofit Case Study:


The goals of a deep energy retrofit are similar to those of a new green house, but as with all remodels, the difference is that you have to work around an existing structure. What follows is a list of house systems with areas of concentration you should consider

Building envelope

Insulate the slab and foundation walls.

Provide air sealing and moisture management.

Super-insulate existing walls, floors and ceiling or roof with formaldehyde-free insulation.

Install a durable roof.

Replace doors and windows with energy-efficient models, and specify glazing based on the house’s exposure to the sun.


Provide appropriate controls.

Specify high-efficiency mechanical equipment and heat pumps, where possible

Consider alternatives to conventional air conditioning.

Make sure than combustion appliances are vented properly.


Reconfigure plumbing to distribute hot water efficiently.

Insulate hot water pipes.

Choose a high-efficiency water heater.


Increase natural daylighting wneh possible.

Install energy-efficient lighting.


Provide an easy way to turn off equipment to eliminate phantom electrical loads.

Replace old appliances with energy efficient models.

Energy sources

Consider installing photovoltaic modules, solar hot water collectors, or a wind turbine.


In renovating old homes into super-efficient ones, there is a definite path to success. Betsy Pettit, of Building Science Corporation recommends starting where you can get the most bang, and working your way down the list. After you get past item 5, the house will be efficient enough to downsize the mechanical equipment, which you replaced in step 1. If you’re planning to go at least through step 5, keep that in mind before buying a new boiler or HVAC unit.

1. Upgrade the mechanical systems

An old furnace or boiler is often the worst energy user in an old house. Many houses built prior to 1920 still have old coal-fired boilers that were converted to gas or oil. These units are workhorses, but use a lot of energy. A new furnace or boiler can save energy dollars right away. Replacing window air conditioners, which we did in all these houses, with a central system also can save energy right away, as long as the ductwork has been placed in the conditioned space. Solar water heating is a good option to add here if you can afford it, but at the very least, upgrade the efficiency of hot water production by coupling the tank to the boiler.

2. Bring the basement and crawlspace inside the house

Warm, dry basements and crawlspaces can extend living and storage space. Wet basements are the source of high humidity levels and discomfort in the summertime in old houses. They also can be the source of mold growth that gets distributed around the house. Spray foam is a fast, effective way to bring these areas into the conditioned space while sealing the leaks between foundation and floor framing.

3. Super-insulate and air-seal the roof

If air leaks in at the bottom of the house, it leaks out at the top, which makes a house cold and drafty in winter. A poorly insulated roof also can make a house hot in summer. Air-sealing is a by-product of good insulating, so it’s really a one-step process. Using spray foam under a roof also can eliminate the need for roof venting, which is tricky in complicated roofs.

4. Replace the windows

With the bottom and top of the house sealed and insulated, the next opportunity is the walls. And old windows are like big holes in the walls. Old windows often leak both air and water into the house while functioning poorly. They might not open and close properly, and can be obscured with storm windows and screens that diminish the amount of light that can enter. Properly installed, Energy Star (or better) windows seal the holes in the walls to keep out water and weather extremes.

5. Insulate the walls

Filling empty wall cavities with cellulose is a cheap, easy, effective way to warm up an old house. Blowing cellulose into existing wall cavities is an art, to be sure, but there are many contractors who have been doing it for years. In fact, there are now inexpensive ways to check with infrared cameras to make sure that all voids have been filled without disturbing the existing plaster or sheathing on outside walls. Because siding or shingles on old houses might also have worn out, we take the opportunity to install foam sheathing on the outside of the house before re-siding.*

6. Buy Energy Star (or better)

fixtures, appliances, and lighting once you have reduced your space conditioning and water-heating loads, the lighting, appliance, and plug load will be your next big energy item. A new Energy Star refrigerator will use 15% less energy than a standard model. Replacing old light fixtures with pin-based compact fluorescent fixtures ensures your electric bill will stay lower (up to 30%).

7. Add a renewable-energy source

Once your energy consumption has been reduced significantly, it becomes reasonable to produce your own energy with systems such as photovoltaics, wind power, or hydro, if you happen to have a stream nearby. Until you slash the energy usage, though, it’s not worth the investment in renewable power sources. Conservation is still the cheapest game in town.

*Note to item 5: Go back to Step 1 and reduce the size of the mechanicals. An airtight house with insulation on all six sides of the cube and good windows provides predictable performance, so the mechanical contractor won’t have to guess at the quality of the enclosure. Downsized mechanical equipment can defray the cost of steps 2-5.


Case Study

COMPLEX UPGRADES TO A SIMPLE HOME Any house built thirty years ago, like this 1970s ranch in Boulder, Colorado, needs improvements. A new addition and extensive, soup-to-nuts upgrading of all the house’s systems improved the comfort and health of the inhabitants while completely reducing it energy use.
Image Credits: Eric Doub, Ecofutures, Inc./REGREEN

From zero insulation to net zero

In deciding to remodel, the owners of this 1,000-square-foot 1970s ranch in Boulder were seeking to both add space and make dramatic energy improvements. Like other houses in the neighborhood, this one had single-pane windows and no insulation in the walls, making it drafty in the winter and “an oven” in the summer. The family had made some improvements five years earlier, replacing windows, adding insulation, and installing radiant floor heat, but they didn’t have the experience to take it as far as they would have liked. This time, wanting more comprehensive improvements, the family hired a contractor with experience in high-performance building. Eric Doub’s team retrofitted the existing space for energy efficiency and remodeled it to include a home office in the aboveground space and a play area in the basement. Adding 700 square feet gave the owners a new dining area, expanded the kitchen and great room, and improved solar access and lighting.

Design Approach

A project manager knows about best building practices

Super-insulating and air sealing throughout the home improve comfort and passive survivability, allowing the home to stay warm without heating for a few days in 0°F, cloudy weather. A project manager knowledgeable in building science best practice was always on site to ensure that proper detailing, critical to a successful energy retrofit, was accomplished. The increased square footage improves the daylighting as well as the livability of the space. An all-electric design allowed the homeowners to cap their natural gas line, which was of particular importance to them because of local environmental degradation caused by natural gas drilling and distribution. Their efforts to be as green as possible extended from the structure to energy supply and to finishes.


MULTIPLE PANELS PROVIDE HEAT, HOT WATER, AND ELECTRICITY. This net zero house in Colorado uses panels on the roof to provide domestic hot water as well as space heating, using in slab radiant tubes. And photo-voltaic panels provide 6.15 kW of electricity.
Image Credits: Eric Doub, Ecofutures, Inc./REGREEN

Key systems


*90% of construction waste diverted through on-site reuse, salvage, and recycling

*Recycled-plastic decking

Building Envelope


*Walls improved to thermally broken R-28: cellulose blown in to existing frame and walls wrapped with new external insulated 2’x4′ framed wall

*Roof improved to R-70 by 8″ spray-in-place open-cell ½’- lb. foam (SPF)

*Below grade improved to R-17: ½” rigid foam and cotton batts in 2’x4′ framed wall added to interior

*Prior installation of 1 ½” gypsum concrete floor with radiant tubes over existing slab

*All-in-one vapor barrier, bubble wrap and ¼” flexible closed-cell foam added between gypsum and basement slab


*R-27 walls: 2’x6′ frame, faced with 1½” resilient channel on interior, creating a 7″ wall cavity filled with Icynene spray-foam

*R-42 SIP roof with 3.5″ SPF in dropped ceiling for R-50 total

*U-0.15 overall window rating

*FSC-certified and engineered lumber

*6″ core ICF crawl space with dropped joists to break thermal boundary; 12″ SPF between joists


*Operable windows and motorized skylight for ventilation

and cooling

*Energy recovery ventilator for continuous ventilation during winter and hot summer days


*Dual-flush toilet

*Direct-from-solar-tank hot water dispenser to reduce energy demand in cooking


*Natural daylighting enhanced with four solar tubes, two skylights, and 30% more glazing

*Compact fluorescent lighting


*Existing Energy Star washer and dryer, plus clothesline

*New refrigerator and electric oven to eliminate use of natural gas

*Separate switch to eliminate phantom electronic loads

Interior Finishes

*Low- and zero-VOC paints and stains

*Water-based floor finish

*Clay plaster

*Linoleum tile with low-VOC adhesives

*Formaldehyde-free cabinets

*Concrete and sorghum-based countertops

*Oriented-strand board subfloor

*Natural wool carpet

Energy Sources

*Evacuated tube solar hot water system provides 90%–100% of domestic hot water as well as space heating using in-slab radiant tubes; the system has cloudy cold-snap backup from on-demand 9-kW modulating electric boiler

*Grid connected solar PV (6.15kW installed on new porch and existing roof)

*EPA-approved wood-burning fireplace


A VARIETY OF INSULATION TYPES were used on the addition and the retrofit original house. Types included blown-in celluose, rigid foam, and cotton batts.
Image Credits: Eric Doub, Ecofutures, Inc./REGREEN

Project wish list can differ from real-world realities*

In a comprehensive retrofit of this sort, it can be easy to miss some of the ways in which the systems interact; even manufacturers may overlook details of advanced energy systems. For instance, the team learned that the evacuated tubes for solar hot water could overheat and break if the power went out on a sunny day. To prevent this, they installed a single solar panel that provides backup power so that the pump can continue to circulate water through the tubes. Despite of their deep-green objectives, the homeowners also had to make some trade-offs. The cost premium for certified wood led them to forgo using FSC-certified wood exclusively in favor of investing more in renewable energy systems.

Team & FInances

Team and processes

With highly committed homeowners, the team was able to push far beyond typical energy retrofits, and explore new approaches to comprehensive efficiency. At the project outset, the contractor and energy designers worked with the homeowners to calculate electrical loads, and used computer modeling to understand heat and energy flows. This critical step in the design process informed all stages of project development. During construction, the homeowners, designers, engineers, and contractor continued to work closely together to ensure project success. For example, when the homeowners asked about thermally retrofitting the exterior of the building to minimize disturbance, the contractor verified with modern building science resources that this approach would work well to create continuous air and thermal barriers.

Location: Boulder, Colorado

Homeowners: John and Vicky Graham

Architect: Andy Johnson, DA J Design

General Contractor: Eric Doub, Ecofutures Building Inc.

Area affected: Remodeled existing 1,000 ft2; added 700 ft2


With the intention of building their “dream home,” the homeowners selected high-quality finishes throughout, pushed energy measures as far as possible, and took full advantage of Colorado’s new incentives for renewable energy systems. According to the homeowners, construction costs were comparable to those of other high-end remodels, and with recent reports that local electricity prices may increase by 11% in the next year, the projected return on investment keeps getting better.


Remodeling Details


In Arlington, Mass., Alex Cheimets oversaw a deep-energy retrofit project at his 80-year-old duplex.


LEED for Homes For deep energy gut rehabs, energy retrofit strategies can influence up to 27 points in EA1-9 (Energy & Atmosphere).

NGBS-Remodel Refer to the ANSI standard and follow the appropriate path based on conditioned floor area involved in the remodeling or addition project and the year in which the original home was built. NGBS


  1. Jeff Wilson | | #1

    Deep Energy Retrofit in Ohio . . .
    I've been working on a DER of my home in Ohio . . . we've shot video of the process all the way along and you can see it at We're in the final stages, doing an interior curtain wall in the basement with spray-foam insulation and adding solar-air heaters. We've gone from a leaky, 70-year-old home to a super-tight, well insulated home. Even with the harsher winter last year, we cut our heating bills by 2/3 and now are nearly net-zero on our electricity with a 4kW solar array.

  2. V3M7LbuKUY | | #2

    window film as glazing retrofit
    While many old windows leak air and water and truly need to be replaced, there are many homes with tight windows that have clear single-pane, clear IG, or even tinted or low-e coated IG that can save a lot of air conditioning load dollars with good SHGC window film. Many of these films are now performance rated by the NFRC, ( recommended as an authority within this forum) and recently film with Emissivity as low as 0.07 has entered the marketplace. SHGCs as low as .50 (film alone on clear single pane) are available with a VLT as high as .70 --about the same as a car windshield and barely noticeable from outside or inside.

  3. napulitane | | #3

    You mention "indoor air quality" and "moisture management" but don't give any suggestions for how to deal with it. Superinsulating and tightening the envelope restrict the introduction of fresh air, that needs to be compensated for. The best way, following PassivHaus principles, is to replace the traditional "recirculating" type heat/air conditioner with a heat exchange unit that conditions fresh air instead or recycling stale, moist, mold-inducing air. That's how to create good indoor air quality in a superinsulated structure.

    1. Expert Member
      MALCOLM TAYLOR | | #4


      You may find this link useful:

      1. napulitane | | #6

        Malcolm, thanks for the link!

    2. GBA Editor
      Martin Holladay | | #5

      Malcolm Taylor provided one link to a useful article. (Thanks, Malcolm.) GBA has many more.

      For a list of many more similar in-depth articles on ventilation, visit GBA's "Category" page on ventilation. Here is a link: GBA Category page with links to articles on ventilation.

      You may also want to read this article: "All About Indoor Air Quality."

  4. Dave933 | | #7

    I've been restoring properties since I retired in 2014. Can someone please point me to article indicating how to deep retrofit a brick ranch home? 1980 style 3000 sq/ft ranch with brick on 80% of exterior.
    Original plan was to remove drywall and insulation on all brick exterior walls then spray 3.5" closed cell, add 1" foam board on inside of of studs, tape and seal everything before reinstalling new 1/2" drywall.
    *All attic penetrations foamed
    *New Anderson casement windows and all new oversized doors.
    *Complete rewire airtight shallow can lights - foam/sealed/8.5w LED
    *R60 ceilings.
    *2" closed cell basement walls and header plate.
    *Dual Carrier multi stage modulating NG furnace and multistage A/C
    *Doors and windows are in garage, so can't change.
    *Age-in-Place design
    Doing most work myself so 2 year project. Hope by 70th birthday.
    Would love to see how a Building Science guy would suggest.

    1. GBA Editor
      Martin Holladay | | #8

      Your plan will certainly lower the home's energy bills. But none of us can make many useful recommendations over the internet. We don't know much about your existing windows, your existing insulation, or your existing air leakage rate. Nor do we know your climate zone.

      It's certainly true that it's usually a good idea to do air sealing work. If you focus on air sealing -- and it sounds as if that's your plan -- then you need to come up with a plan to install a whole-house ventilation system.

      If your house is in a cold climate, some experts might suggest triple-glazed windows, but it sounds as if it's too late for that.

      Some GBA readers don't like spray foam, and might advise you to develop a plan that uses less spray foam.

      Some GBA readers might point out that the cost of the work probably can't be justified based on future energy savings -- but you probably already know that.

  5. Dave933 | | #9

    Thanks for your reply Martin,
    I deliberately did not provide detail about my specific remodel because i did not want to write a book. I really was looking for suggestions on articles to help me better understand insulating a wood structure with a 80% brick facade.
    Thank you for mentioning air quality. My HVAC guy is working on loads and some version of a ERV to provide fresh air. I also plan to include a whole house dehumidifier for winter months. During summer the multi speed furnace & A/C units should take care of internal moisture.
    The other thing that I could use some help understanding is moisture movement with 3.5 inches of closed cell and additional 1" foam thermal brake under drywall. In fact there should be no moisture or little heat movement externally. Is this going to give me issues with my brick facade? Managing moisture is the biggest thing that concerns me in this renovation.
    You mentioned payback. Money is not the issue in this project. I read an excellent articular on this site that talked about financial payback is not always the driver. This home will likely be our forever home and we have already budgeted 200k for materials and another 20k on miscellaneous labor that I'm unable to complete myself.
    I wanted to insulate outside walls given that I will be enlarging every door, windows are flush finished with drywall and most internal walls have moved for ADA. So we already anticipated most walls will already be torn up. The renovation plan includes replacement of 90% of drywall on all walls. If it wasn't for the 18" of insulation already in the ceiling, I'd probably replace ceilings as well.

  6. pakrat1 | | #10


    I am in the same boat as you, 3400 sq/ft Ranch. same basic game plan as you, 75 years old, aging in place forever home. I am in Houston TX but guessing you are farther north.

    My biggest issue is my brick walls. I am adding a 2x3 inner wall, total 6" and filling it
    up with either dense pack cellulose which can handle significant moisture as long as it is
    allowed to dry or dense pack rock wool.

    The real issue is my sheathing is exterior Gypsum board which is not a WRB, a 1" gap which is not vented and brick which has been painted.

    Will I be getting in trouble with moisture in the Gypsum sheathing, with only 2" of rock wool insulation there was never a mold problem after 70 years, but that was before my super air sealing project


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