# closed cell SPF vs JM spider spray fiberglass insulation on cantilever extension



## munkyboi (May 19, 2015)

hi all

my house has an extension that does not have any masonry foundation underneath, instead, the whole section sits on steel beams and columns (i suppose that's called a pier foundation?).  hence, the underneath of the whole section is exposed to the exterior elements.  the square footage is about 554 sq ft.

currently, there are multiple cement board panels that are attached to the underneath frame of the house through screws.  i suspect that once the panels are removed, i will see the original insulation (probably mineral wool or fiberglass batts) up in the cavities.

i want to remove the old insulation and install new insulation.  based on what i read, spray closed cell foam seems to be the most efficient option (R value wise as well as moisture barrier wise).  however, i am concerned about the potential health risk of out-gassing due to its petroleum based nature.  so, i'd like to explore other alternatives even if i have to make some compromise to the efficiency as long as it would still reasonably insulate that part of the house and keep moisture from getting into the house.

i got a quote from a contractor to spray R-38 2 lb heatlok 200 closed cell foam with 5.5" thickness for about $3000

is JM spider spray fiberglass a viable option?  do you have any other recommendations that would suit my need?  we are basically talking about insulating the underfloor area.  i am in zone 4.

thanks,
m


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## EatenByLimestone (May 19, 2015)

munkyboi said:


> hi all
> 
> my house has an extension that does not have any masonry foundation underneath, instead, the whole section sits on steel beams and columns (i suppose that's called a pier foundation?).  hence, the underneath of the whole section is exposed to the exterior elements.  the square footage is about 535 sq ft.
> 
> ...




When you pull the insulation, spray the underside of the floor and joists with a borate solution.  I'd also cover the bottom of the foam with 1/4" hardware cloth.  Carpenter ants and mice love foam.


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## munkyboi (May 19, 2015)

i thought carpenter ants only love moist rotten wood, can you please elaborate on why they love foam?

thanks.




EatenByLimestone said:


> When you pull the insulation, spray the underside of the floor and joists with a borate solution.  I'd also cover the bottom of the foam with 1/4" hardware cloth.  Carpenter ants and mice love foam.


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## EatenByLimestone (May 19, 2015)

It's easier to bore into than actual wood.  

They do like wet wood.  95% of the time carpenter ants will go for the wet wood.  But not always.

Professionally, I've treated plenty of carpenter ant infestations in foam.  I wouldn't discount foam due to the ants, but a simple treatment before the foam is applied will remove the chance of them getting into the structure themselves.


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## munkyboi (May 19, 2015)

thanks for the explanation.

i am actually having second thought about foam due to the potential outgassing.  i am looking further into spray fiberglass now.

have you professionally treated carpenter ants and/or other insect/pest problem in spray fiberglass insulation?





EatenByLimestone said:


> It's easier to bore into than actual wood.
> 
> They do like wet wood.  95% of the time carpenter ants will go for the wet wood.  But not always.
> 
> Professionally, I've treated plenty of carpenter ant infestations in foam.  I wouldn't discount foam due to the ants, but a simple treatment before the foam is applied will remove the chance of them getting into the structure themselves.


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## EatenByLimestone (May 19, 2015)

I have no experience with spray fiberglass.  

I've blown fiberglass in, but it was dry.  It's much cleaner than cellulose.  Hardly any cleanup... 

Since it will be open I think I'd still do the borate treatment.   And the bottom will still be open to critters.  I'd still put the hardware cloth over it.  It's much easier to deal with now vs when rodents get in.   You may even be able to apply through the hardware cloth.

 I have to open the walls of my family cabin this summer.  I'll be treating the open bays with Boracare.


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## semipro (May 20, 2015)

I had a similar situation with a cantilever section on our house.  I installed 2" foam board against the floor, sealed it in place with canned spray foam, and then filled the cavity with packed cellulose insulation.  A webbed fabric, like landscaping fabric, was used to contain the cellulose until the outer protective soffit boards were re installed.


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## sportbikerider78 (May 20, 2015)

semipro said:


> I had a similar situation with a cantilever section on our house.  I installed 2" foam board against the floor, sealed it in place with canned spray foam, and then filled the cavity with packed cellulose insulation.  A webbed fabric, like landscaping fabric, was used to contain the cellulose until the outer protective soffit boards were re installed.




I was going to suggest 2" XPS or EPS.  Makes much more sense to me then $3k in spray foam.


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## munkyboi (May 20, 2015)

by the way, i forgot to mention that the whole piered section is the master bedroom wing which prompted me to consider the potential out-gassing issue with the spray foam.  afterall, i will be spending 8 hours a day every day breathing in the air right above the insulation.

what's the best efficient way/procedure to seal the cavities if i choose to go with the XPS or EPS route?  i am thinking about the challenge of attaching the boards due to gravity.

thanks.




sportbikerider78 said:


> I was going to suggest 2" XPS or EPS.  Makes much more sense to me then $3k in spray foam.


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## sportbikerider78 (May 20, 2015)

munkyboi said:


> by the way, i forgot to mention that the whole piered section is the master bedroom wing which prompted me to consider the potential out-gassing issue with the spray foam.  afterall, i will be spending 8 hours a day every day breathing in the air right above the insulation.
> 
> what's the best efficient way/procedure to seal the cavities if i choose to go with the XPS or EPS route?  i am thinking about the challenge of attaching the boards due to gravity.
> 
> thanks.



There are products like liquid nails that work well.  If it was me, I'd stick it into location with a screw or two, then great stuff the perimeter to get a decent seal.


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## semipro (May 20, 2015)

There is a specific glue for XPS.  http://www.loctiteproducts.com/p/pl_ca_300_voc/overview/Loctite-PL-300-VOC-Foamboard-Adhesive.htm
However, if you cut the boards carefully and with a bevel you can friction fit them in place and then use canned spray foam to seal around the edges in the space created by the bevel.

I strongly suggest investing in a professional foam gun. https://www.hearth.com/talk/threads/multi-use-foam-applicator-gun-follow-up.107613/


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