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by • July 28, 2011 • UncategorizedComments (5)1071

Passivhaus in Austin’s Climate?

I’ve been learning and hearing more about Passivhaus standards alot these days.  The quick definition of Passivhaus is a building that uses little or no energy to heat/cool itself.  This is generally achieved through maximum insulation and tight air sealing.  This movement started in Germany, but it’s gaining traction in the US.  However, most of the buildings built to this standard are built in heating dominated climates.  I can’t stress enough how building a house in hot/humid Austin, TX differs from building in a Northern climate.  I ran across this article on Greenbuildingadvisor.com and thought I’d share the link.   I’m not convinced that this method works well in our climate but once you read the article I’d love to hear your thoughts.  -Matt Risinger

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  • Okla. State Univ. school of Architecture in there publications does not recommend insulation below grade as to get get the earth cooling effect. Passivhaus wants a r20 thus eliminating heat loss that way. In my new home under construction. we put in r5 foam slab insulation. That is just for thase days like we had in Feb. when we still had several sub zero days. This summer we have had high humidity and and 25 days in a row with temps over 100. So our designs are better off losing heat to the earth.

  • Matt,

    I’m not quite sure why you aren’t convinced… In our design for the NoLa Passivhaus (referenced in the GBA posting), we looked for pretty much the lowest cost path to achieving Passivhaus:
    -double pane windows w/ decent u-value, low SHGC.
    -a few inches of polyiso around walls/roof to prevent solar vapor drive (sim to the BSC ‘perfect wall’).
    -a construction method that wouldn’t need double walls or interior secondary wall for MEP runs

    Passivhaus works in cooling-dominated environments – even hot/humid ones. When I migrate the NoLa model to Austin, the biggest issue is that the insulation needs to be higher due to increased cooling loads (as Austin gets more sun/solar gain in summer). According to the model, the only way to get there is slightly more insulation than the NoLa model.

    Despite OK-lawman’s comment, my PHPP model shows that the cooling load is actually higher (7.36kBTU/ft2a)in the house with no sub-slab insulation than with 2″ (5.90 kBTU/ft2a).

  • Thanks for your comments. It’s been my understanding that a slab on grade house in our climate would greatly benefit from slab perimeter insulation. That exposed slab to the outside transmits heat into the house on hot days and loses heat to the outside on cold days. But, with termites being a major threat in our area this is a TRICKY detail. I expect to be doing this in the next 1-2 years on my houses. Let us know how your build turns out. Thanks, Matt Risinger

  • Great comments guys. I’m coming around to the Passivhaus ideal, just attended a two day Building Science Expert’s session with Building Science Corp and they shed some new light on getting super-insulated for our Hot/Humid climate. Stay tuned for more on this in the future, you’ll be seeing lots of rigid foam on future Risinger Homes builds. Matt

  • I saw Joe Listiburek speak last week and he made these comments about PassivHaus in Austin’s climate.

    You can’t conserve your way to cold/dry.
    You can design to no-AC it’s called Uncomfortable.

    At the end of the day in hot/humid climates you need to expend energy to make them cold/dry.

    I thought those were interesting comments regarding this cold climate approach to building where the approach/goal doesn’t always work in our hot/humid climate.
    Matt