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Designing a passive solar / net zero house in NC Mountains

moseleyb | Posted in General Questions on

My wife and I are designing a new mountain home in Banner Elk, NC. We are in the initial design stages with our architect and are confused by the numerous options to consider. Our house will be built in the Eagles Nest community which has a pacific northwest lodge feel. Our home site is at a 5,000 foot elevation on the mountain ridge with a northern view.

We are designing the house utilizing a passive solar design while still trying to maintain the integrity of the community we are living in. Some of the design elements we are hoping for include a super tight house, radiant heating, concrete floor on both floors, fiberglass windows and solar panels.

Because of the location in the mountains, the winters are fairly brutal and the house is subject to some strong winds.

My architect is very creative but not an expert in green building. I would like to know where the best place is to get advice on construction including insulation, HVAC options, HRV systems, exterior material choices……

We have just built a house and I am familiar with construction and the construction process. Any thoughts or advice would be greatly appreciated!

Bill Moseley


  1. user-2890856 | | #1

    Construction including insulation and exterior materials : Right here or Building Science Corporation's Website .
    HVAC options : Heating . Main Wall
    You'll probably want an ERV more than an HRV . Again , right here .

  2. charlie_sullivan | | #2

    I would say you'd want to someone experienced in this stuff on your team--either an energy consultant or a builder with expertise and experience in passive houses, net-zero buildings, or the like. Ideally both a builder and an energy consultant. One way to look for qualified professionals is to look for passive house certification--even if you don't want to build to that standard, that certification means they have a lot of the expertise you want.

    But do ask here as well!

  3. jackofalltrades777 | | #3

    If you are in the mountains and experience high winds, especially Exposure C types of home sites where high winds hit the home unobstructed, I would recommend an ICF home. It's quite feasible to build a strong and airtight home out of wood but it's much more difficult to make it strong and air tight when you are exposing the home to high winds and heavy amounts of racking. If fire danger is also a problem in wooded areas, ICF is the better solution also.

    It can be done out of wood but will take some good engineering, more $$, and a well skilled contractor. Wood homes rack in high winds, that is a fact. While it may seem anecdotal, I've been in an ICF home when it was getting hit with 60mph winds but inside the home it was as solid and tight as a bank vault. The wood frame home across the street was popping, creaking, racking, and even whistling (air leaks) during the same wind event.

  4. GBA Editor
    Martin Holladay | | #4

    It's your house, and you should build it exactly the way you want, but here is some feedback.

    1. Concrete floors will be expensive, and the thermal mass / passive solar plan that you envision is based on 1970s thinking that has been superseded by a better understanding of superinsulation principles. For example, see these two articles:

    Study Shows That Expensive Windows Yield Meager Energy Returns

    All About Thermal Mass

    2. Even if you have your heart set on a classic 1976 passive solar design, you probably don't want in-floor radiant heat, since in-floor radiant heat is incompatible with traditional passive solar principles. For more information on this issue, see All About Radiant Floors.

    3. Unlike Peter L., I firmly believe that it's possible to build a wood-framed house that can meet your design wind loads -- and that a wood-framed house will cost less than an ICF house.

    4. To answer your question: "Where is the best place is to get advice on construction including insulation, HVAC options, HRV systems, and exterior material choices?," I would say, "Right here on the Green Building Advisor web site."

  5. user-2890856 | | #5

    You could install radiant floors and capture the energy in the floors when Solar overloads same and use it to make DHW or store it to use at night for space heating . Not that complicated and damn passive .
    Since this is a passive house what many don't understand is that the Design supply water temps will be very low , below the temp that the slab will reach during solar heat gain . Unlike many envision that fluid will actually help to keep the room from overheating unless in one of these houses cold goes to hot instead of the energy from the hotter slab being transferred to the cooler fluid in the floor .

  6. STEPHEN SHEEHY | | #6

    I'd get a new architect. An architect in 2014 should be highly familiar with green building design. If he or she isn't, I'd hesitate to be the guinea pig.

  7. user-659915 | | #7

    What Stephen said. Creativity is a fine thing in an architect, competence is even better. Not being thoroughly versed in green building at this point in time does not speak well of an architect's skills. Not only that: if he or she is not in tune with the values and aspirations you personally wish to embody in the home you will never be happy with the result. Those values need to be embedded in the design from the very beginning by someone who is both knowledgable and fully committed to their fulfillment.

  8. jackofalltrades777 | | #8


    It's quite apparent that you are not a fan of the Passive House movement. There are many scientists that would disagree with you about it being a "1970's thinking" because it is a modern scientific building methodology. There are many PhD's out there that would debate you and disagree with you about your comments.

    Why the resentment against the PH design? European countries like Germany are making it a standard in their building codes. How could so many scientists be wrong?

  9. GBA Editor
    Martin Holladay | | #9

    Peter L.,
    I think that you are confusing two different types of buildings: passive solar buildings and Passivhaus buildings.

    The confusion is understandable.

    Bill Moseley wrote that he wants to build a passive solar building. He didn't say that he wanted to build a Passivhaus or a passive house.

    The term "passive solar" has been in common use since the 1960s or 1970s. The German Passivhaus movement began in the 1990s. The Passivhaus Institut was founded in Darmstadt, Germany in 1996.

    Most of the homes I built in the 1970s and 1980s, including the one I am now living in, were built according to passive solar principles. I am familiar with these houses. However, I have increasingly come to realize that if you include so much south-facing glazing that the glazing needs to be balanced by the thermal mass in concrete floors, the house probably has too much south-facing glazing. We've learned a lot since 1975.

    You are right that I have criticized the Passivhaus standard, especially when used to build homes in cold climates. (In cold climates, the Passivhaus energy budget of 15 kWh/m2*year results in insulation levels that aren't cost-effective.) But I admire the concepts that launched the Passivhaus movement: an emphasis on superinsulation, airtight techniques, and simple HVAC systems.

  10. Expert Member
    Dana Dorsett | | #10

    Radiant heating is a cost-adder, and in a Net-Zero house with low heat loads the floor is barely warmer than the room air most days. The additional comfort factor may not be "worth it", especially if you're burning propane or something expensive to run it. (Air source & ground source hydronic heat pumps would cost less to run, but would have very high upfront costs compared to high-efficiency air source heat pumps.) Suffice to day, deciding on the HVAC system before you even know the likely loads is a bit silly.

    Banner Elk's climate is basically a warm-edge of US zone 5 climate. With simple floor layouts (very few bump-outs & corners to the outer shell of the house) it's pretty easy to hit Net Zero with ~R35-40ish walls and R60-70 ish attics and U0.25 double panes if you don't go nuts on over-glazing the place, and you'd be able heat & cool the place with ductless (or mini-duct) modulating air source heat pump techology, which is comparatively cheap, and can at least be sized correctly for low-load houses.

    Carter Scott successfully builds Net Zero houses on the cold edge of zone 5 into zone 6, in a locations that get less sun than Banner Elk, with only marginally higher R / lower-U specifications than that:

    Many of his designs are heated & cooled with one ductless mini-split wall coil per floor. Some suffer a bit from a "shoe box with a gable" look from an architectural point of view, but by having just four corners to the footprint the exterior surface area to floor area ratio is minimized, along with the thermal bridging & air leakage factors that come with every corner. If you can, try to limit the number of exterior corners to six, eight at the absolute most (an L or T topology footprint), and avoid unnecessary bump-outs or dormers you can do pretty well.

    Here's one of his "keep-it-simple-stupid" rectangular footprint designs that worked. It is something of a "New England Traditional" look rather than the Pacific Northwest Lodge effect you're looking for, but you can do a lot with roof angles & eave overhangs, wraparound porches etc, using similar principles, but with a Cascades Rustic look to the roof lines & exterior finishes.

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