Is spray foam a good idea for my new build?

lithnightsJune 12, 2013

I posted this in the HVAC area but wanted to post it here too since I didn't know where was most appropriate. Sorry if that is bad forum etiquette.

I'd like to do spray foam on my 3250 sq ft new construction. I had assumed around $6K based on what the builder had guessed a couple times. We're almost ready to insulate, and he just now got me an official quote for $8500. I have 2 days to decide.

This would be closed cell for 2", just for exterior walls. The quote says it would give it an R value of 14. With unfaced R11 over it, I would have R25. Without the upgrade, I'd have R19, so we're looking at about 33% increase in R value.

I added up the walls and it comes to about 2900 sq ft of wall (based on 9 ft ceilings).

I know spray foam isn't cheap but isn't this a bit pricey?

Also a concern is that I don't even know who the sub is that is doing it, nor references etc. I've been asking for this info for months from the builder. I could be his first job for all I know.

I'm in SE PA, and I plan to use a high output fireplace to heat most of my house, with a heat pump (propane backup) as needed. Heat pump for A/C. Electric around $.16 khw. 2x6 framing, upgraded to Andersen 200 windows. R50 blown in attic.

If I knew how much I'd save in utility bills, I could do a breakeven/ROI analysis, but I have no idea if my energy savings would be 10%, 20%, 50% etc.

Is there anything else I need to think of before making this decision?


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Since your question is about price, you are the best judge of that based on competitive bids from local installers.

However, I wouldn't even consider going with any spray foam unless I knew who the installer was and their affiliations, training and experience. SPF is unlike any other type of insulation. It's mixed on site and one mis-step by an inexperienced installer in the mix or application can leave you with a virtually irremediable mess that, at best, may poorly insulate and, at worst, trigger health problems.

You might get some ideas for what to check by the link below to the Canadian Urethane Foam Contractor's Association.

Here is a link that might be useful: Canadian Urethane Foam Contractor's Association

This post was edited by worthy on Wed, Jun 12, 13 at 16:50

    Bookmark   June 12, 2013 at 4:44PM
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I'd put the spray foam in the roofline and create
an unvented, semi conditioned attic rather
than put the foam in the walls.

we build walls pretty air/water tight. then
with air tight drywall approach provide a
secondary air barrier. this allows insulation
(conventional types) to perform to spec'd

with sheetrock ceilings as the air barrier
between where we live & the extreme
attic temps, we don't do nearly as well
in creating an air/thermal barrier.

temps more extreme in attic than ambient.
and then we cut holes...recessed lights,
a/c supply & returns, stove venting...bath
so the ceiling as an air barrier is a fail.

moving the air barrier & thermal barrier
from the ceiling/attic floor to the roofline
changes the dynamics of the house.

lots of threads here on foam, lots of info
online. energy vanguard's blog has good
info for you to read also.
take some time and educate yourself...
then make the decision.

I'm not a fan of the whole you got two days
to decide option.

best of luck.

    Bookmark   June 12, 2013 at 5:09PM
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We looked at this a lot and concluded that wrapping the exterior with 2" of rigid foam and stuffing the cavities with cellulose provided the best bang for the buck. Up to 20% of wall surface is framing, with a minimal R value, to the exterior wrap provides an important thermal break

    Bookmark   June 12, 2013 at 9:18PM
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Rwiegand makes a good point. A 2X6 wall is called 'R-19', but actually performs at about R-13 because of heat transfer through all of the studs and plates. Any exterior foam, even an inch, will go a long way toward breaking that thermal transfer. The other really big factor is sealing your construction. They've found that air leaks play as big a role as insulation in temperature control. I don't know about your area, but some areas now require blower door testing to test and correct for air leaks.

    Bookmark   June 13, 2013 at 6:53AM
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So what about just asking builder to use rigid foam instead? And then just foam the small crevice between stud and foam board? Not as effective as spray foam, but more affordable and would limit that air movement that batts don't stop, right?

Do I assume they are using some kind of Tyvek wrap? Specs don't mention a wrap but isn't that pretty standard? The material itself doesn't look expensive. Does tyvek do a decent job of reducing air movement?

    Bookmark   June 13, 2013 at 10:13AM
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I don't know about spray foam insulation inside. I just set PU foam on fire by accident while welding and that burning foam produced the most sickening fumes ever. If you are unlucky to be in a burning house with spray foam insulation you probably die of poisonous fumes within a few minutes/seconds.

    Bookmark   June 13, 2013 at 12:14PM
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jridh...this is why spray foam has sheetrock between it
and the living space. and yes, burning foam produces
a gas as it burns. thus the need for fire rated sheetrock.

OP putting the foam sheating on the exterior is the
best investment for foam for walls.
proper nailing pattern, seams taped and any
holes sealed prior to cladding install.

the foam sheating can go on top of housewrap,
and if you chose foil/foam board and have brick get a radiant barrier for exterior of walls
with 3/4' air space between brick & foil.

air sealing doesn't just happen. even with sheetrock
& plywood sheating,,,air will find its way in through any
small gap & hole. to air seal you have to caulk areas
like sole plates to slabs & subfloors, seal wire & plumbing penetrations and any holes into the house
from both attic and ambinet.

however...if builder has limited time for foam in
walls or is doubtful that he will
be on board with adding foam sheathing to extrior
walls. when you add to depth of walls...window and
door framing/finishing changes.
this is why I didn't recommend this, for your situation.
itrw...the builder isn't going to spend time to make
this happen properly. the last thing you need is improperly flashed windows & doors due to last
minute add on of foam sheathing.

usually people who use sheathing on exterior
of walls go into framing with this in mind..not
an add on later.
although ithis is the best use of $$
for added insulation & air sealing qualities.
of walls. it iis in the planning stages that
foam sheathing is discussed...not once
walls are ready for insulation. as your doors
& windows are in place & flashed...I don't think
it will reasonably happen now.

what people need to think about is...the sun hits
one wall at a time. but it hits the roof all day...every
day. this is a better place to put the foam.
if you have hvac equipment..ductwork, in attic
and holes in the sheetrock ceiling..recessed lights
oversized cuts for supply vents & bath is difficult
to get these areas sealed properly.
great stuff in a can is oten used..but it doesn't seal
as well as people think..nor does it last.

other things like kneewalls in the attic..changes
of ceiling heights are also problematic.
while they are usually insulated..they are not air
sealed and allow attic temps to enter the house.

over the years we have used the same foil/foam
sheating to air seal knee walls & upstairs walls
shared with attics to stop the air movement & temp
it is a tough install, thus another reason that the
foamed roofline is so popular.
this install will cover all of the builder/trades errors,
allowing easier & affordable utility costs & smaller
sized hvac systems.

this late in the game...stick with air sealing walls
insulate conventionally & insist upon air tight drywall aproach through out the house. and easy way to
get it done is for sheetrock installers to install as if
no moldings were being used. this will make sure
that sheetrock is taped & floated behind ceiling
moldings. closing leakage from attic into the house
that is otherwise hidden behind crown moldings.

google air tight drywall approach (ada) to better
understand why this is an important part of the
performance of your walls.

best of luck.

    Bookmark   June 13, 2013 at 3:08PM
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We used foam in our 2009 build. I dont recall what the upcharge was but we are very happy with it. Both from an efficiency standpoint and from a comfort standpoint.

Something else I did was I bought a case or two of spray foam and every Saturday I would let myself into the house and go to town filling all the holes, gaps and voids created by the workers the previous week. I had the builders permission (mostly) to do this. In order to plug those leaks, you really need somebody who is anal and not in a hurry -that doesnt describe most contractors.

If I had it to do over again, I would have added more blown in insulation to the ceiling and I would have specified foam board on the exterior as well.

There's nothing better that sitting next to the window in a t-shirt and bare feet on a cold and blustery night and being perfectly comfortable. Good luck

    Bookmark   June 13, 2013 at 3:55PM
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Do I assume they are using some kind of Tyvek wrap?

No. A house wrap is not required nor necessary as long as there is some other secondary drainage plane. And if they are using housewrap, they're not all the same. The cheap micro-perforated ones beloved by builders on a budget are useless.

BTW, the main function (PDF) of housewraps is rain control, not air stoppage.

If foam is going on the exterior of the sheathing or is serving as sheathing it has to be planned before the floor plates are on.

At this point, as pointed out above, air sealing and a tightly fitting insulation between the joists, such as blown cellulose, will yield good results. You might also consider flash and batt--one-two inches of SPF followed by batts. This type of installation has its own critics. And you still must check out the credentials of the SPF applicator.

    Bookmark   June 13, 2013 at 4:19PM
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Yesterday I told the $8500 spray foam was out of my budget and I'd pass. Later in the day, he came back and suggested doing a rockwool type product. He also mentioned they could spray a wet cellulose (open not closed) product about 2-4 inches thick, then they'd add some kind of insulation to that. It would likely be about half the cost of the spray foam, and still do a decent job. It should get me about R21 and provide better air flow reduction than just R19 fiberglass. He was still gathering ideas from the insulation guy, so it was a bit unclear.

So I looked up rock wool (mineral wool), which looks pretty cool compared to fiberglass. Rigid (not flimsy), fits tight into bays, cuts easily without crushing it etc. But it doesn't look like it gets blown in (or can it?), so I have to check with builder to see exactly what he is proposing.

I like the concept of doing 2,3,4 inches of wet cellulose since it seems it will close up (I know not as good as spray foam would) any of those little gaps that I was hoping spray foam would get.

Both cellulose and rock wool seem to have slightly higher R values than fiberglass from what I've researched.

Thoughts on this new approach of cellulose and/or rockwool, since I simply can't afford the spray foam?

    Bookmark   June 14, 2013 at 11:42AM
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Have to back up the previous comments on air sealing. A difference of even 1 ACH50 will have a much bigger impact than whatever type of insulation you end up choosing for your wall cavity insulation. Air sealing is cheap, easy and has extremely measurable impacts. Walls leak very little compared to transitions.

Not very familiar with mineral wool as cavity insulation although I know its growing in popularity. Never heard of blown mineral wool. In general, I think mineral wool is not better at stopping air movement than FG batts. If you use FG batts, you almost have to flash to be competitive with spray foam or dense pack cellulose or fiberglass. Dense pack cellulose or FG would be the next best option after Spray foam but in my area they cost about the same.

As for housewrap, I agree with Worthy and for those doing foam sheathing (best use of foam for walls) I feel the housewrap is worthless behind the foam. Put it outside of the foam to get the advantages of overlapping flashings and foam joints.

    Bookmark   June 15, 2013 at 12:44AM
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Never heard of blown mineral wool

Might take some hunting, as the major North American mineral wool manufacturer, Roxul, markets only "loose fill" bags, plus a variety of batts. Mineral wool is unaffected by water and has an R Value of approximately 3.125 per inch.

Its big drawback has been cost, compared to fiberglass.

The simplest use of rockwool would be batts in the walls and batts and/or loose fill (or blown) in the attic.

The pros and cons of cellulose.

Fiberglass in the attic should be followed by a denser insulation or top cover to prevent R Value loss in the winter.

SPF on the rim joists seals better than anything else.

As mentioned several times, air sealing is essential. We've generally come a ways from the advice I used to always hear that "a house has to breathe, so don't obsess about loosely fitted insulation and the like."

This post was edited by worthy on Sat, Jun 15, 13 at 1:36

    Bookmark   June 15, 2013 at 1:31AM
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"wet cellulose (open not closed) product "

never heard of open or closed cellulose
spray foams...but not ground borate treated
I think someone misunderstood or mis spoke.

    Bookmark   June 15, 2013 at 10:17PM
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energy rater la,
When I say open or closed cellulose, I'm not referring to spray foam. I'm talking about a cellulose product that is mixed with glue and water and sprayed on similar to how spray foam is applied.

After more research, I believe cellulose is open celled which is less dense than the closed cell spray foam.

I'm meeting with an insulation company (does cellulose and spray foam) next week.. something I should have done months ago. : (

    Bookmark   June 22, 2013 at 4:31PM
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I ended up calling in 3 different insulation guys for ideas and pricing. I basically had them price out various options.. fill bay with open cell cellulose, fill 2" of closed cell sprayfoam then R15, fill bay with open cell sprayfoam etc.
One price was near the builder's proposal, but the other 2 were thousands less.. literally. I ended up agreeing to have one guy (highly rated, straight A on Angies list, good references, in business for decades) spray 2" of closed cell spray foam for about $5300. With R15 batts over that, I should be pretty tight. He also said he would foam the basement rim joists for a couple hundred more which I think would be worth it.

So, we'll see how it turns out, but I'm glad I shopped around and the builder was cool with that.

Thanks for everyone's advice.

    Bookmark   June 30, 2013 at 5:56PM
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