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Green Homes

1970s Home Goes Net Zero

Photovoltaic and evacuated-tube solar panels on the roof provide all of the electricity and much of the heat this house uses. Extra electricity is "stored" in the local power grid and heat is stored in two insulated 168-gallon water tanks.
Image Credit: Eric Doub
View Gallery 6 images
NATURALLY BRIGHT. During the day, tall windows spread sunlight across the entire kitchen, providing plenty of natural task lighting. More remote parts of the home are lit by solar tubes (tubular skylights).
Image Credit: Eric Doub
KEEP THE HEAT IN. Horizontal metal channels prevent the drywall from directly contacting the 2x6 studs. After filling it with polyurethane spray foam, the new wall has an estimated R-value of 27.
Image Credit: Eric Doub
MAKE THE BEST OF THE SITUATION. A 2x4 wall framed around the old portion of the house was constructed where a layer of brick veneer used to sit. This new framing created space to add polyurethane spray foam insulation. Metal brackets hold the new framing off of the existing wall to create a thermal break.
Image Credit: Eric Doub
ON A LOW-PITCH ROOF, solar collectors, like these evacuated tubes, can be mounted on a rack so they can be tilted to the ideal angle.
Image Credit: Eric Doub
A WELL MANAGED SYSTEM. This energy-efficient house relies on a number of components to manage the solar heat and hot water systems. A Web Energy Logger (WEL) collects data to evaluate how well everything is working and where improvements can be made.
Image Credit: Eric Doub
THERMAL BREAKS MAKE A DIFFERENCE. Plenty of insulation is a good thing, but a conventionally framed wall will still transfer a lot of heat from the drywall to the exterior sheathing. Ecofutures was careful to create gaps in the building envelope - often with small brackets or perpendicular channels - to stop thermal bridging across the studs. The new floor framing is attached to the side of the insulated foundation creating a more effective buffer than if placed on top, as is more typical.
Image Credit: Toshi Woudenberg

A remodel with an insulation and energy system update that’s hard to beat

Intensive renovation has made this modest ranch house in the suburbs of Boulder, Colorado, an example of what all green builders strive for — a net zero energy home. Changes include an extreme insulation retrofit, a 6kW photovoltaic array installed on the roof, and an evacuated-tube solar hot water system.

The build team now expects this house to produce 130 percent of its own energy needs. A grid-tied system allows the excess electricity to be “stored” until occasional winter cold snaps require the 9kW modulating electric boiler to fill in.

A team effort with high-tech tools
Motivated owners, a dedicated group of designers, consultants, and builders, and state renewable energy incentives allowed the project to shoot for lofty goals. Carefully balancing the value of individual improvements by looking at them as parts of a bigger system was crucial.

Energy-use monitoring and computer modeling helped maximize overall efficiency of the home. A Web Energy Logger (WEL) was permanently installed to monitor performance and plan for future energy upgrades.

Upgrade on the outside
Starting from the ground up makes it relatively easy to insulate structures like the 700 sq. ft. addition included in this project. Retrofitting existing buildings is not always as straightforward. Together, Eric Doub of Ecofutures Building and owners John and Vicky Graham decided that wrapping the home with additional 2×4 framing and sprayed polyurethane foam would be the least intrusive method.

Although some of the work involved replacing upgrades that were only five years old, and the cost was on par with those for a typical high-end renovation, continually rising energy costs made John and Vicky’s choice to create their energy efficient dream home a great long-term investment.

Lessons Learned

Aside from the obvious utility cost savings, this remodel aims for the goal of passive survivability — the ability of a building to remain habitable when utility disruption occurs during extreme outside temperatures. The actual performance of the home falls slightly short of projections — something that builder Eric Doub believes could be tempered by the use of movable window insulation. "My recommendation is to have at least some cellular shades, if just to reduce convective heat transfer." That's getting pretty deep into the details of energy efficiency. Good job, Eric!

General Specs and Team

Location: Boulder, CO
Bedrooms: 4
Bathrooms: 3
Living Space: 2700
Cost: 250
Additional Notes:

Basement remodel cost: $81/sq. ft. (1,000 sq. ft.)
Main floor remodel: $250/sq. ft. (1,000 sq. ft.)
Addition: $250/sq. ft. (700 sq. ft.), including renewable energy systems

See More About This Project: Deep-Energy Retrofit

Builder: Eric Doub, Ecofutures Building, Inc. Architect/designer: Andy Johnson, DAJ Design


Foundation (existing:) concrete walls covered with 1-in. XPS on interior (R-5)
Walls (existing) : 2x4 framing filled with blown cellulose; 2x4 framing added to exterior, filled with Icynene spray foam (R-28 total)
Windows (existing): foam-filled fiberglass window frames with two layers of Heat Mirror, krypton/argon filled (Duxton, R-7.1)
Roof (existing): 8 in. open-cell foam and 12 in. blown cellulose (R-70)
Garage: attached; thermal and air separation

Foundation: (addition): 6 in. ICF crawl space (R-30)
Walls (addition): 2x6 frame faced with 1.5 in. resilient channel on interior, filled with 7 in. Icynene spray foam (R-27)
Windows: (addition) foam-filled fiberglass frames with two layers of Heat Mirror, krypton/argon filled (Duxton, R-7.1)
Roof (addition:) SIPs (R-42) with 3.5 in. SPF in dropped ceiling (R-50 total)


  • Natural daylighting
  • CFLs throughout home
  • Direct-from-solar-tank hot water dispenser to reduce energy demand in cooking
  • Insulation far above recommended standards
  • Energy Star ceiling fan, washer, and dryer
  • Separate switch to eliminate phantom loads from electronics

Energy Specs


  • Operable windows and motorized skylight for ventilation and cooling
  • Solar hot water - 180 evacuated tubes, two 168-gal. insulated storage tanks (R-80); cost, $34,000
  • Backup from on-demand 9kW modulating electric boiler
  • EPA-approved wood-burning fireplace

Water heating: Same as space heating (solar with electric backup)

Water Efficiency

  • Dual-flush toilet
  • Xeriscaping
  • Drip irrigation

Indoor Air Quality

  • ERV
  • Linoleum tile with low-VOC adhesives
  • Formaldehyde-free cabinetry
  • Low- and no-VOC paints and stains
  • Natural wool carpet
  • Natural clay plaster walls

Green Materials and Resource Efficiency

  • Most construction waste recycled or repurposed
  • FSC-certified lumber for framing
  • Recycled-plastic decking
  • Water-based floor finish
  • Clay plaster
  • Concrete and sorghum-based countertops
  • OSB subfloor

Alternate Energy Utilization

Photovoltaic: Grid-connected, 6 kW (cost, $25,000)


  1. homedesign | | #1

    This image is what gives pv a
    This image is what gives pv a bad name...
    If you are going to use least integrate into the Architecture. Would you buy and maintain a house that looks like that?
    I would be outraged if my neighbor did this.

  2. homedesign | | #2

    There are a lot of good ideas
    There are a lot of good ideas in this house..It is just hard to get over the not so attractive arrays on the front of the house. Aesthetics is important to sustainability..If we love it will will maintain it.

  3. dajdesign | | #3

    The Rest of the Story
    This project has an extremely difficult site due to the original placement of the building in 1970 and the neighboring vegetation. The existing structure was heavily evaluated for its solar access, and due to its orientation the panel arrangement ended up being a compromise of production and aesthetics (with the homeowner wanting to maximize production). The front of the house faces just slightly north of due east. The panels arrangement without a tilt end up facing NE due to the compound angles. The other side of the roof faces west, which is the least desirable direction in our locality due to afternoon clouds and showers. The current panel configuration is the result of 4 different tries to meet production, and keep a lower profile on the roof.

    I agree whole heartedly about the need to integrate alternative energy measures into an elegant architectural design. I also believe that architectural styles and aesthetics (while absolutely important) are just ideas, and now we have this really important driving force determining what the architecture of this century needs to be about - sustainability is that driving force. As an architect faced with the need to create resilience for my clients in a post-carbon world, sometimes it means compromising certain elements. Honestly, one may not feel so bad when viewing the interior spaces and the courtyard oasis created out back of the house.

  4. homedesign | | #4

    I slammed this house

    I slammed this house before I "looked under the hood"
    In home marketing it is all about curb apeal and "you have to get them past the front door"
    I am ashamed to say I am as shallow as some of the consumers.
    You have done some VERY good things with this house.
    Your house is an extermely high performance house even without the PV.

  5. PhilipScheffer | | #5

    Re: This image is what gives pv a bad name
    Hey John, I agree that it would be great to integrate the photovoltaics better, but not everyone is going to have the opportunity to.

    Financial constraints would probably be the number one reason why someone would shy away from integrating the pv into their design more. Also, from what I have seen, most of the well integrated photovoltaics follow a certain design pattern that many people may not be particularly fond of.

    That said, it would be nice to see more integrated design like this: - where the photovoltaic array slides out for shade in the summer (looks nice imho and is functional... and is in Sweden, naturally.)


    How about solar fences?
    I was at the Solar Decathlon in Washington DC a couple of years ago and the German entry had a sort of venetian blind looking slat wall of 3' x 6" PV slats mounted horizontally but rotated to the proper solar orientation for that latitude. I have over 900 feet of fencing at my house for my horse and goat, about 1/3 of it runs east to west. It would be very cool if I could mount these type of PV collectors on my fencing and control my animals while collecting electricity and keep the PV off the roof.

    Anything like this out there yet?

  7. furniturefarmer | | #7

    more insulation
    It's nice to see such an amazing project, but it does make me wonder if more insulation (which is relatively cheap and lasts forever) could have decreased the need for such a huge and expensive renewable energy system.

  8. GBA Editor
    Martin Holladay | | #8

    Insulation levels seem pretty good
    Dave Brach,
    I'm not sure I agree with you that this house needs more insulation.
    Wall insulation varies from R-27 to R-28; roof insulation varies from R-50 to R-70. The new addition has an R-30 ICF foundation. The weak link seems to be the R-5 basement walls on the existing house. Clearly, that's the first place to beef up the insulation. But the house as described is well above most U.S. houses. If we could get most U.S. homes to the level described here, it would be cause for rejoicing.

  9. furniturefarmer | | #9

    Of course, it’s


    Of course, it’s impossible for an outsider like me to say the house “needs” more insulation. Renovations are extremely challenging, and it looks like the siting of the existing home was probably not ideal for solar gains.

    But getting to net-zero cost effectively requires AGGRESSIVLEY pushing down demand with passive measures so that the active systems don’t need to cost an arm and a leg. And if the drawings provided here are correct, there is no insulation at the bottom of the conditioned crawlspace. There is also no insulation between the top of the foundation wall and the joist/rim joist in the existing house (which is a large perimeter thermal bridge). In the existing basement, there is no insulation between the new gypcrete and the existing slab. I could be mistaken, but even a ½” of XPS here would have a dramatic effect, especially given the fact that the floor is heated, and heat loss is directly proportional to temperature differential.

    Again, this house is truly an amazing achievement, I just get attentive when I see big and expensive renewable systems without (what seems like) equally rigorous building shells.

  10. GBA Editor
    Martin Holladay | | #10

    You've got a good eye
    You obviously spent longer looking at the details than I did. That's good. You've spotted some areas that indeed appear to be weak links in the chain. Thanks for your comments.

  11. happy saini | | #11

    Roof Repairs
    really it is very difficult to construct and maintain the house at that kind of place but if you want to construct then it will take more time,strive and make an effort to reach a goal.A lot of risk is there for making house.But it is looking very nice if we make house there.But this house is really a great achievement
    because making house at that height is impossible and a lot of money also spend for making house at that type of conditions.

  12. Dave Tool | | #12

    Don't mind the roof at all....
    Maybe I'm not the finicky neighbor type, but I'd be proud (and a little bit jealous) to have a PV installation like that in my neighborhood. In this day and age how could you find it conceivable to complain about anything regarding a house that generates 130% of it's own energy requirements. The NIMBY attitude has cost us plenty already when it comes to renewable resources (I'm thinking most recently of the Long Island and Cape Cod protesters who blanched at barely visible, off shore windmills spoiling their summertime views.) Think of all the eco-damage caused annually by the senseless attachment to the idea of a lustrous green lawn on every home in America.

    I think it's long past the time when we need to put our vainglorious ideals of 'keeping up with the joneses' behind the more pressing needs of, hmm, I don't know, fresh air and clean water perhaps?

  13. Dick | | #13

    Adding a Wall to a Wall
    Just how was a new 2X4 wall added to the outside of the existing 2X4 wall? Is it just *hanging* off the existing wall in shear, or was some foundation-extension added to hold the weight of a new wall?

  14. GBA Editor
    Rob Wotzak | | #14

    Using the existing foundation
    I'm not 100% sure on this, but if I remember correctly, the new outer wall replaced an old brick facade. The existing edge of the foundation that once supported the brick now holds up the 2x4 wall. That said, It's not uncommon to screw or bolt exterior insulation systems that add considerable weight (such as Larsen trusses or thick layers of rigid foam) to the outside of existing framing, with no direct support from the foundation.

  15. Ryann Anderson | | #15

    In depth article about this retrofit
    These comments are all very interesting--thanks for all your thoughts! Perhaps a few of your comments and questions can be addressed by reading the in-depth, 4-page article we wrote for the Jan/Feb 2010 issue of Solar Today. It can be found here (just be sure to use the zoom controls so you can actually read it): Thanks!

  16. Ryann Anderson | | #16

    I'm an employee of the GC that did this deep energy retrofit.

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