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Seeking Advice on Insulation & Partial Conditioning of Crawlspace

13 years ago

We're completing our build in NY State: house sits on 2000sf crawlspace of which approx 2/3 nom 6' height, 1/3 4' height. We have taken good care to prevent moisture infiltration, but the area is still damp/clammy, esp in the shoulder months (house about to be insulated and hvac not yet operating). The crawlspace is only accessible from the outside via bulkhead door (no connection or stairs from inside the house).

We have decided to insulate and partially condition this space (meaning to maintain ±55-60º year-round). The house hvac is installed, and has no air supplies or returns to the crawlspace (we maxed out the cfms of the unit with the house).

This raises some questions:

1) We're planning to use 2" closed cell spray foam on rim joist and all the way down the walls. The slab floor was not insulated, but it has an excellent vapor barrier.

I have read that the rim should not be completely covered by foam--to leave a small area for visual termite inspection *and* for any vapor drive issues that might come from outside. But I cannot find specific details abt where that gap shd be, and how to achieve it?

2) Since this is crawlspace (never planned for living), and only accessible from the outside, will firestop (intumescent paint) be necessary over the foam to meet code? Our AHJ does not have much experience with this type of insulation and we have a good relationship--so he requests I give him details as published and will accept that as the standard.

3) To partially condition the space, we want to install an energy efficient unit to keep temp at ±55º and humidity at 4) Lastly, we are concerned abt cold floors on the first floor of the house. Wd it make sense to do some insulating under that floor? We can spec open cell, closed cell, or blown-in mineral wool in every joist bay that's not occupied by hvac supplies and returns. I am thinking that 1" of closed cell wd slow transfer of heat and provide some sound deadening at nominal upchg, b/c it can't be used everywhere. But I don't know how that will affect wood floors above, for example. The mineral wool and open cell will allow some perming--is that good or bad in this application?

In all the houses I've built over the years, never have I given so much consideration to the non-living, partially conditioned spaces. But it seems as everything else gets tightened up, the requirements in this area increase, too.

Thanks so much all for your feedback. Worthy, I hope you're on line for this one!

Best, Mark

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