[Greenbuilding] Crawlspace foam insulation -- how much?

[Alan Abrams]

Hi Leslie

somehow I don't like the idea. I assume the insulation contractor is
proposing to apply foam to the underside of the floor sheathing. If that is
the case, there is the possibility of the exposed portion of the joists
getting below dew point, and becoming saturated with condensed water vapor.
IIRC, Joe Lstiburek has some really ugly photos of this condition.

my preference (at a minimum) would be to seal and insulate the perimeter of
the floor cavity with caulk and batts, and apply a smart membrane (like
MemBrain) to the underside of the joists, carefully lapped and taped, and
then some rigid mineral fiber insulation under that. Fire resistant, mold
resistant, thermal bridge resistant, and semi permeable. The crawlspace can
then behave or misbehave as it pleases, without impact on IAQ

-aa

Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
cell     202-437-8583
alan at abramsdesignbuild.com
HELICON WORKS *Achitecture and Education*
<http://www.heliconworks.com/index2.html>

On Fri, Jun 12, 2015 at 2:55 PM, Leslie Moyer <unschooler at lrec.org> wrote:

>  Yeah, well, I considered that option first and was ridiculed for that on
> this list several months ago. My crawl space is tight (for humans), but
> well-ventilated, so I'm going to go with this option as I think it is the
> most practical.
>
> --Leslie
>
> On 6/12/15 1:18 PM, Frank Tettemer wrote:
>
> Hi Leslie,
>
> You may want to re-consider the idea of foaming the floor in a crawl
> space. My concerns would be that the foam would act too well as a vapour
> barrier, and you may have moisture/mildew problems down the road in the
> crawl space. I AM in Canada, so your geographic climate might create
> different problems than here.
>
> I always design any neccessary crawl spaces as a definite part of the
> conditioned space of the home. That means insulating the walls and the
> floor of the crawl space, and leaving the floor as a vapour-open plane, as
> well as including the crawl space in the heating design. This avoids
> condensation trouble, by keeping the air warm and dry.
>
> Frank
>
> Frank Tettemer
> Living Sol ~ Building and Design
> www.livingsol.com
> 613 756 3884
>
>
> On 12/06/2015 2:02 PM, Leslie Moyer wrote:
>
> I am in NE Oklahoma.  I'm in the process of getting estimates for
> crawlspace insulation in the floor joists--closed cell foam.  My crawl
> space is dry now that we've fixed some plumbing problems, but I'm having
> some cupping issues with some wood flooring and part of the fiberglass
> batts that were originally in the house when we bought it were taken out
> over time for this and that. Anyway--closed cell foam seems to be the best
> solution.
>
> The first guy who came this morning wants to quote me 1.5" foam, though
> said he would quote 2" if that's what I really want, saying that would be
> enough for "Canada".  I understand about the benefits of air sealing, but I
> was still thinking I would need more inches of foam according to what I've
> read on R-value & this area.  Thoughts?
>
> --
> *Leslie Moyer*
>
>
>
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> --
> *Leslie Moyer*
> Email: unschooler at lrec.org
> Phone: (918) 772-6150
> Cell: (918) 633-8820
>
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