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Passive House 2: Reader Questions and Responses

Thanks for your participation!

Exterior of the West Asheville Passive House showing the 'band' and furring strips.
Image Credit: Chris Otohal, Homeowner

Check out floor plans, site plan, a model and details plans of this project.

Today, I am meeting with Aaron & Calder Wilson (The Architects) for conversation and drinks. I will relay our conversation to you, at least the relevant parts, which could come fewer and farther between as the drinks continue to flow. Who knows, if it sounds good it could end up as a podcast.

Check out pictures of the project at my Flickr page.

I am totally charged about the number of responses I’ve gotten from the first Passive House blog. In this entry, I will list them (paraphrased). I think it’s best to dive into these issues one by one and pick them apart since they are getting into the real understanding of these green building practices. Here’s a list of questions from your input:

  • Dan S: How did the project team refine and decide on the products and equipment used for the home?
  • Dan S: Why did they choose the guidelines and resources used to guide the project?
  • Dean D: Could you share information about energy recovery ventilators?
  • Bruce C: How did the project team decide on the windows used in the project?
  • Boone G (A Green Builder buddy of mine): Should up-front money be invested in the thermal efficiency of the envelope, or would it be better spent on other systems? At what point does the return on invest become impractical?
  • John B: Could we share home plans, project team comments, (including the HERS rater) and data from the project?
  • Pat M: Since closed-cell foam manufacturers say that the perm ratings of their foams is about the same as oriented strand board, does the high permeability of open-cell foam make a whole hill of beans’ difference?
  • Brian K (Another Green Builder Buddy of mine): Does Manual J or other modeling software underestimate the effects of passive solar, or does the Passive House software kick us rear end?
  • Donald L: What’s the best way to hit R-60 in the roof that I am about to build? I’m considering 16-in. parallel chord trusses to get an open ceiling, with 1/4-in. ply to get a vented roof, 2 in. XPS foam with the seams taped below the trusses and the space filled with 15″ of blown-in fiberglass insulation. Would foam on the bottom of the sheathing be better for air sealing?

Here’s a list of comments:

Chris Otohal’s (owner, engineer, and builder) comments:

  • Cellulose is appealing due to its extremely low embodied energy. Chris and his installer are considering installing drywall first and then cellulose to achieve the appropriate density. He likes the idea of a thin layer of foam first, followed by cellulose.
  • Chris decided on Vaproshield when he decided to use Corten siding. He is using Vaproshield’s Wrapshield product, lapping and taping the seams, which the company states will provide an effective air barrier. The project team is not solely relying on that, however.
  • The heating and cooling loads were determined by energy modeling performed by the US Passive House Institute using the Passive House Planning Package (PHPP). Chris is working on getting the data for us to share with you. The data are dependent on compliance with the air infiltration criteria of 0.6 ACH at 50 Pascals.
  • This home will not receive Passive House certification, which requires an annual heat requirement of 15 kwh/m2 due to the solar heat gain coefficient (SHGC) of the windows. Chris opted for less expensive Inline Fiberglass windows from Toronto. Thermotech windows were recommended, which had a higher SHGC but were $9,000 more expensive. Chris’ home will be closer to 20 kwh/m2/yr. The extra $9,000 would have resulted in an ROI of 180 years. Chris will be following the PH guidelines, but the home will fall short of certification.

I have tons of comments and opinions on all of these topics, but I am going to hold on to them so that I can approach these topics methodically. What issues that are most appealing to you or stand out the most? Comment, and that’s what we will hit first. Do a little research, and we will discuss.

18 Comments

  1. Mary Zappa | | #1

    Passive Homes
    My brother John Dowse is a a certified passive home engineer in Illinois.
    He also is a liscenced engineer in Illinois as well as many other states in residential housing.

    How could he contact someone who desires to build a passive home or apartment building and is in need of his expertise?

  2. John Brooks | | #2

    Passive House Consultant
    Rob,
    Is the team working with a passive house consultant?
    I understand how to measure airtightness...but how do they know that the entire envelope is "Thermal Bridge Free"

  3. Jamie Wolf | | #4

    Not a Passive House
    I wish to respectfully request that you not use the term Passive House to describe a building that does not meet the criteria. The standard is explicit. This is an ambitious low load building inspired by the principles of PH design. This is not a Passive House.

    The choice to use lower performing glazing introduces a set of cascading results that, most significantly, introduce unacceptable thermal bridging at the window frame, lower surface temperatures at the glazing that effect comfort and convection, and compromise the ability of the system to benefit from internal gains that exceed losses which in turn allow HRV/ERV options to satisfy the bulk of the heat demand.

    PHPP is a rigorous and uncompromising modeling tool that is meticulous and miserly. It allows the designer to accomplish a very delicate "energy balance" for the building. And it treats the whole system. It does not attempt to make decisions in isolation about 180year paybacks as a criteria to use exceptional glazing or not.

    Sorry to be cranky about this but PH is a system that requires careful study and is uncompromising in its application for reasons that require those who choose to use the term and pursue the principles to understand them thoroughly.

    These case studies are invaluable and I appreciate what is being shared, but please be clear about what is being described. We all have so much to learn.

    PS: According to the PH website, John Dowse is not a certified PH consultant.

  4. Rob Moody | | #5

    Thanks for the clarification.
    Thanks for the clarification James. I am a stickler for certification lingo with LEED, so it's good to know what Ps and Qs to keep in mind for PH. I did clarify above that Chris will not achieve certification, but I will refrain from referring to his home as a Passive House.

    Also, to clarify, Chris' windows do have an insulated frame, but the discrepancy with PH is the SHGC.

    I have a podcast coming up with Clarke Snell of Think Green Building who just completed the PH consultant training course in Urbana, Illinois.

    In this series, I am pointing out some of the differences between this home, not PH certified, and another home that Clarke is building that is going for PH certification.

    Thanks again and stay tuned.

  5. Nora | | #6

    Looking for recommendations
    Hi Guys

    I have been reading your comments but they are more to do with DIY, I am looking for a company who will build me a turnkey passive house http://www.germanpassivehouses.com has been recommended to me, what they have to offer looks really good, but i do not know enough about the whole Insulation, Zero Carbon, etc. I was wondering if any of ye could maybe recommend a builder to me?

    All information greatly accepted

    Nora

  6. GBA Editor
    Martin Holladay | | #7

    Where do you live?
    Nora,
    To get advice on a builder, you need to tell us where you live.

  7. Nora | | #8

    Hi Martin
    I am in the North

    Hi Martin

    I am in the North of Ireland,

  8. Paul Smith | | #9

    http://www.passive.ie

    Hi Nora

    I have been searching the market for some time now on Passive Houses, I have been in contact with a few company's Eco Home, Hanse Haus, Huf Haus, but German passive Houses have a super specification and quality, I saw their polar walls, triple glazing with alloy finish, looks impressive!! I'll let you know when my house is built.

  9. John Brooks | | #10

    Ok...It is Not a Passive House
    Rob, I realize that this project is not a registered "Passive House" .. but it is an interesting "low energy" home and I would like to see more progress photos and comments.

  10. Observer | | #11

    Hmmmmmm
    Nora and Paul Smith both work for germanpasssivehouses.com - Nora mainly does office work but is handy at other stuff like collections etc, and Paul works in the stores but doesnt work fridays. Of course the above is just made up by me, Ive no idea what they do but I suspect they are the same person (like Mrs Doubtfire) and probably work in marketing. Good advertising though guys, ye seem to be able to get to all the eco-forums to ask if germanpassivehoouses.com are as good as ye have been told...

  11. Sascha | | #12

    @ Nora
    Just beware of those comments. They're just commercial spam. That's the way they work over there: they sell Swedish houses as German ones and abuse blogs for commercial purposes. I think this kind of deception speaks volumes...

  12. Chris Otahal | | #14

    James:
    The house was modeled

    James:

    The house was modeled by PHIUS using the Passive House Planning Package. The windows I'm using are triple glazed with insulated fiberglass frames and thermal edge spacers. The windows I chose give me an annual heat requirement of around 20 kwh/m^2/year. I could have achieved the 15 kwh/m^2/year using different windows, but the extra cost (and it was significant) was not feasible.

    So, I now say that my house was 'inspired by the passive house concept', and I'm fine with that.

  13. Seamus | | #15

    Chris Otahal
    Chris

    Well done on your achievements with your house, do you mind if I was to ask the sqftage? and costs of you home?

    I am looking into self build at the moment and keeping all my options open.

  14. John Bingham | | #16

    Update Link to Plans
    Hey Rob,

    It looks like a great project and I was interested in the floor and site plans, but the link is no longer working. Could you please update that link.

  15. Rob Moody | | #17

    You Bet
    My apologies. I updated the website. Here it is: http://www.organicthink.com/organicthink/GBA.html.

  16. HARRY AULMAN | | #18

    Energy efficiency
    We live in south central Alaska. Winters are long (six months +), dark (five hrs. of sunlight midwinter), and cold (we have seen minus 50 degrees f.) We are finishing up building a new home but the finishing work is mostly cosmetic. Our builder is quite experienced in this arctic climate and built this 1,600 sq. ft. home to a 96.8% rating for a five star plus energy rebate program. The energy rater has never seen a tighter building. If you research CCHRC (Cold Climate Housing Research Center) and find the REMOTE insulation method you will solve any thermal bridging problems. Triple paned windows, though expensive, were an absolute must. Ours clocked out at an R-value of 6+. Sixteen inches of blown in cellulose in the attic and a seriously vented COLD roof make our masonry heater possibly too much thermal mass for comfort. The main insulation is two layers of 2" thick rigid insulation and R-11 fiberglass in the 4" walls. The building sits on a 4' ICF foundation that has 8" of reinforced concrete in the ICFs. (
    seismic requirements). The tightness of the structure dictated an HRV system for safe air exchange.

    Being very careful with sealing around all openings to the exterior and managing thermal bridging with the REMOTE building method has proven to be the most effective method of construction so far discovered, at least for an arctic zone. Check out CCHRC which is affiliated with the Univ. of AK., Fairbanks.

    Harry

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