Exterior concrete wall with plumbing electrical – spray foam and rigid combo insulation
Hi,
As per the great advice I have received here I am going to ask contractor to do rigid insulation( foil backed with foil facing the concrete) and then spray foam around pipes and gaps etc on my above grade concrete wall that is already framed with plumbing and electrical … my question is that some sections of the pipes and studs are currently touching the concrete, will sliding a 1/2 inch piece of rigid foam behind them then spraying around that be sufficient ? Or should we just leave it touching the concrete then spray foam all around them and add the rigid between the studs and spray foam the perimeter? Also does the rigid always need to be glued or just sealed at the edges?
And if we do batt insulation on top of the rigid and spray foam after as he is suggesting should I add a smart vapour retarder such as membrane after behind the drywall?
Sorry if any of this is redundant , the information is a little overwhelming ..
Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
It's best to get some amount of insulation between the pipes and wires and the wall if possible. You can also spray foam over that stuff.
You only need to seal the rigid foam at the edges unless you're using the adhesive to support the panel, in which case you need it in some kind of pattern on the panel too (lines or blobs periodically so that it will stay stuck to the wall without bowing out in the middle).
Bill
Thank you! Am I to add a smart vapour retarder behind the drywall as well? Like membrain?
Hi Bill,
I am getting my cathedral roof spray foamed and the spray foam guy is going to charge me almost same or less to spray foam the area downstairs as my contractor will to cut and cobble it all , in my scenario would you just spray foam everything downstairs and be done? I know you mentioned you prefer rigid on concrete and below grade walls and I would prefer that too but is it worth all the extra labour /cost ect?
I am really struggling to make a decision on this as it is seems like a very important one and I have been caught up in fear of making wrong choice.. especially given its not exactly straightforward in my situation with the plumbing and wiring already framed in ..
In small sections is not an issue as long as there is some foam. For any of the above grade walls you want enough rigid behind most studs for condensation control in your climate. This is at least R5 in zone 5 and R7.5 in zone 6 assuming 2x4 studs.
1/2" rigid for small areas is fine, but won't work for the whole wall. You need a bit more rigid.
P.S. I'm assuming the above grade is not structural brick but brick veneer attached to the concrete with brick ties with a WRB over the concrete.
Hi Akos,
If you had a choice in my scenario would you just spray foam the whole thing or do the cut and cobble method?.. I am getting the roof spray foamed as it is a cathedral so they can do the downstairs as well for less than if I was doing it alone and for about the same or possibly less even than what my contractor is going to charge me to do the cut and cobble ( his original quote only consisted of fibreglass and poly ) and with the cut and cobble some of the plumbing and studs are currently right against the concrete and he cant really move them out so its ALOT of cut and cobble on those walls in particular..
I have been very stressed about this decision and worried to go the wrong route.. especially as there is plumbing /electrical and this will be my kitchen area..
Also wondering if poly should 'wrap' anything or go behind anything that is touching the concrete before spray foam is applied in either method...
And yes I believe the walls are cinderblock actually and 'parged ' inside..
and yes 2x 4 studs..
You definitely don't want cut and cobble. A bit around the plumbing sure, but the rest need to get insulation behind the studs. Doesn't matter if spray foam or rigid, you want the studs off the concrete with the gap filled with rigid/SPF. Your contractor will have to do this work no matter what.
If you have the spray foamers on site, the cost of 1.5" flash coat is pretty small increase and simpler install. I would still go for a flash+batt approach. This would limit the amount of spray foam to minimum and keep most of the plumbing end electrical free. Trying to dig through 4" of SPF is not fun.
P.S. I would also do flash and batt for your roof for the same reason. Roofs need more spray foam for condensation control than walls. In zone 6 you want about the same R value spray foam as fluffy (ie R17 SPF +R14 batt for an R31 roof).
In Ontario, which is mostly equivalent to US DOE climate zone 6, if you have at least 1/3 of your total wall R-value in the foam layer(s), you only need painted drywall on the interior. If you're in the northern part of the province, CZ7, you need 45% of the total R-value to be in the foam layer(s). The exact thicknesses and R-values depend on how far the framed wall is getting moved inward and how much spray foam you want to use in conjunction with the rigid foam.
What will be its effect in summer? Any idea about this?
In warm weather, the foundation walls will likely be cooler than the indoor air. The foam layer will prevent humid air from condensing on the cool surface of the concrete.