Post in 'The Green Room' started by Billy123, Mar 9, 2013.
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Very interesting. Thank you for posting it.
It would have been better if they had other comparisons in it, rather than just going "look how better much spray foam is than fibreglass". Still, given who was paying for it that shouldn't be a surprise.
I became a bit confused on why they varied the appliances inside it and such. If you were testing insulation wouldn't you keep everything the same except for the insulation? I would only want one variable.
It seems like a lab could do a better job with shed sized boxes insulated and sealed different ways with sensors and heat lamps. That said, it was a reasonable attempt at using the same floorplan on the same street, etc.
Matt, you're right. I thought they did a good job evaluating different contribution to the bottom line. But, if you really want to break down the performance of the insulation, you should keep everything else fixed. You might want to look at the special projects at BSC:
They have been putting wall assemblies into thermal chambers under small pressure differences and seeing what happens in a 'lab' setting.
r30 attic and r13 walls.... What kind of building code is that? 2x4 walls... For a house?!
For a southern home, things might be different? Having the attic as conditioned space worked the best.
I always get confused on what works best vs cost breakdown. You can spend more, but the payback might make sense to?
The EPA suggested levels versus climate zone should have good ROI and NPV:
IMO, they are conservative, but assume that low-cost insulation is used.
99% of the houses here have 2x4 walls and maybe R30 in the attic. Most don't have any insulation in the walls. Wood is pretty strong in compression. It's the sheer force that causes the issues.
I'd be interested in how a house with spray foam walls but blown in cellulose for the ceiling would perform. Would the extra air sealing capabilities of the spray foam sealing the walls do better than sealing the attic? In this study they made the attic into conditioned space so that they could run the ductwork in conditioned space. In Texas where this study was done they typically do not have basements to run the ductwork so that makes sense. What about in an area that typically has basements where the ductwork is run, would it still make sense to have an unvented attic in that condition?
I personally think it would. I feel that the whole soffit/ridge vent makes really good air sealing difficult if not impossible... at least in an existing house. A cold roof done with foam would allow this to happen very easily.
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