Passivhaus on a Budget | GreenBuildingAdvisor.com
Regarding the URL and the post above.
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- Close to the ideal form. It is almost a cube, a sphere would be ideal for energy use, but those are expensive to build. As is it only has 2 extra corners, and is missing a story.
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Agree, cube is great. A sphere is not only expensive to build but people usually put furniture and appliances flat against walls too, if things had to be centered to allow for the curved wall, it would require a larger structure with wasted space. Something is nice about a flat floor too.
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About the only thing I'd do differently with that house is use advanced framing, and reducing the exterior insulation by an inch or two.
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I agree with advanced framing. I think that using 2x6 with 24" framing with a cellulose stud fill would be more ideal with 4" of XPS, although with *proper* installation of fiberglass and air sealing done well, I can't fault R21 fiberglass that much. I think R40ish is great for my climate.(winter design temp is -13f here) For a winter design that doesn't go under 20f, I suppose 2x4 walls with dense pack cellulose and 3" of XPS or 4" of EPS to get to roughly R30 would be decent too. I think appropriate windows for the climate get critical here, especially in the sunniest and coldest regions. I think they went with more foam on the outside versus the inside for thermal bridging purposes. I think things get better cost optimized when you have about 20 in and 20 out if the total goal is R40. Once you've got 15 or 20 on the outside, thermal bridging is in good shape. Seems that many new publications that I've been reading prefer to have at least as much foam on the outside as the amount of insulation on the inside. ..granted my mid-80s house has R5 polyiso on the outside and R13 on the inside, it seems to be surviving just fine but it seems to avoid potential condensation issues, the current recommendation is to have at least half of the insulation on the outside to keep the indoor side of the moisture impenetrable zone above the dew point.
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If you were DIYing the build further money could be saved by using recycled foam insulation instead of nailbase.
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Great idea, where do I find this?