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Howdy, great article. Got me wondering why are they slab on grade with large amounts of foam slab insulation verses a crawlspace with super insulated joist bays?
Re: May 2012 JLC article Inexpensive passive house
And a lot less digging. There's a blog on GBA that Chris has weighed in on, and another Maine builder, Alan Gibson, wrote a piece for JLC a couple of years ago on shallow foundations.
Re: May 2012 JLC article Inexpensive passive house
Thanks guys. The shallow foundations resist frost heave so is it the mass insulation to resist the slab potential to heave? Here in southern OR homes built with 18" crawl spaces. They are a head banger to work in but not much in concrete for the foundation. I'm confused about the green aspect of slab on grade concrete production makes lots of CO2 Foam has real issues too. Would think a deep engineered I joist plenty of insulation an acoustic caulked vapor retarder seems to me to be better. Good old Frank L wright brought back, to USA, from a trip to Europe the shallow foundations way back in the day...
Re: May 2012 JLC article Inexpensive passive house
Albion, when you insulate under a shallow foundation you run the foam out, down or both far enough so that no frost gets under the foundation. The earth is warm, it only freezes due to cold air, so you are balancing the heat of the earth against cold air. Here's more information: http://www.huduser.org/portal/public.../frostprt.html.
With a FPSF you have less material overall, fewer surfaces that need to be insulated, and fewer joints between different materials. For "regular" building that's not a big deal, but if you're going for super high performance at a low cost you need to cut out anything you can.
I do question whether a slab-on-grade home is green in the sense that it's not as easy to remodel, and to me, being able to remodel is an important factor in the longevity of a home. But I've been inside the house in the JLC article and it's a comfortable, well-designed space.
Re: May 2012 JLC article Inexpensive passive house
Howdy Mr Mike Maines. Thank you for the additional information. In the homes zone, what is the frost dept for a conventional foundation? Wish the information you referenced was download able but i cannot an error message instead. Might you know of another location to access the information?
Re: May 2012 JLC article Inexpensive passive house
Albion, if you google "frost protected shallow foundation" you will get a lot of hits. I'll PM you a copy of an NAHB booklet about it.
I'm not sure what you mean by "the homes zone." Here in Maine we have to be 48" to the bottom of the footer. With a FPSF (frost protected shallow foundation) we need to go out roughly 48", or down 24" and out 24".
Howdy, great article. Got me wondering why are they slab on grade with large amounts of foam slab insulation verses a crawlspace with super insulated joist bays?
Great question. The truckload of foam under a PH has always confused me.
Re: May 2012 JLC article Inexpensive passive house
Howdy again MR Mike. cold hardy plant zone- been landscaping too much lately.
I was under the impression that a shallow foundation on top of 2 foot of compacted gravel was enough with a frost zone of 48".
Re: May 2012 JLC article Inexpensive passive house
As usual, Martin Holladay already has some great info about this topic in a GBA blog post.
The whole post, and comments, are worth reading. Martin quotes John Straube using a Marc Rosenbaum metaphor to explain:
" Passivhaus designers have only a few dials to turn when adjusting a home’s specifications...Once the designers have specified the best available windows, for example, the window dial can’t be turned down any further. These houses are just about as airtight as buildings can be built, so the airtightness dial has basically been bottomed out. Once the easy dials have been turned, the only remaining variable under the designer’s control is insulation thickness — so, to make the house work, that’s what gets adjusted"
Re: May 2012 JLC article Inexpensive passive house
I think the number one most overlooked "dial" is size, because they way I see it, most codes and programs peanilize small houses. In fact, I am at the point I can estimate a HERS Rating witin 1-2 points without software, and every time a large house comes in, I know it's in the bag just by following the base code, it's the small ones that the the effort.
Let's talk about good, efficient design, not insulation and air barriers.
Did I spell "peanilize" wrong or have I embarrassed myself?
When you've got them by the balls, their hearts and minds will follow.
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