[Greenbuilding] Crawlspace foam insulation -- how much?

[Alan Abrams]

well, there is some logic to that, but that's a huge amount of surface area
to cover, compared to a flat surface under the joists. We could get into a
further dialog about the global warming nastiness associated with closed
cell foam, too...which suggests that if you're gonna use foam, use as
little as possible.

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 3:41 PM, Leslie Moyer <unschooler at lrec.org> wrote:

>  And why would this be preferable to just spraying the joists, too?
>
> On 6/12/15 2:17 PM, Alan Abrams wrote:
>
> 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, AIBD certified 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
>>
>> Sustainable Tahlequah
>> Web: SustainableTahlequah.org <http://www.SustainableTahlequah.org/>
>> Discussion List: groups.yahoo.com/group/SustainableTahlequah
>>
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>
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