I’m struggling with a decision on whether or not to add 1/2″ of foam to my new house. Here’s the story. My insulation contractor gave me a bid on blown in cellulose with the option of 1/2″ of foam. The walls are 2×6 construction and when I asked my contractor about doing exclusively foam he said that if that was what I wanted to do I probably should have just gone with 2×4 because filling the 2×6 cavity would be very expensive and would never show a payback. He tells me that the 1/2″ foam option would do a couple of things, 1. would serve to glue everything together, adding strengh and 2. seal all outside air infiltration. The remaining cavity would be blown in cellulose. The foam option would add $1180 to the $3000 bid. While $1180 doesn’t sound like much as you know when you are building $1000 here and $1000 there doesn’t take long to add up. My contractor is a real straight shooter and I trust what he says. He tells me that the payback would be 10 years +. I asked him what he would do if it was his house and he said he would do it but his opinion was biased because he does it for a living. The house is around 2000 ft on a slab with ground source heat pump.
Opinions and experiences shared would be greatly appreciated.
Tom
Replies
There are all sorts of answers to this question. I'll offer my thoughts, as will others. It all comes down to what your overall objectives are, with respect to heat loss, comfort, and air quality.
Using a thin layer of foam for sealing against air infiltration is an alternative to very well detail WRB on the outside of the sheathing. Each approach to sealing has its shortcomings, meaning places that won't be sealed if not specifically addressed. In particular, there are places at the sill and between framing members of the outer wall that need something like acoustic sealant during assembly.
Look beyond 10+ years, and guess what fuel cost may be then. You have one chance to do this house right, and "$1000 here and $1000 there" may ultimately seem like chicken feed. Reducing air infiltration is just one aspect of really beefing up the outer shell of your house. There are other things that can be done to go far beyond just that.
Tell us, what is the "payout" of buying an upscale $30,000 SUV to haul one person around vs. a $12,000 basic transportation subcompact?
silas1804
Insulation is one of the most cheated on costs and it shouldn't be..
My home is twice as big as the old house and has three times as much windows yet using the exact same furnace my winter heat costs went from $500 a month to $200 a month (and the new house hasn't been carefully tightened up yet..) that's inspite of a 30% increase in costs.
My old house was well insulated my new house is super insulated..
Twice as large 3x as many windows same furnace
$300 a month cost savings..
If you haven't started building yet please stop and look into either SIP construction, ICF construction or super insulated.
I used both SIP & ICF and if I had it to do all over again I'd go with straight ICF.
IF you already have the studs in the air, it's too late. Do the best you can..
Well, here's a way to look at it:
$1180 on 6% paper will get you roughly an extra $7.20/month on your house payment. So, all you have to figure out is if the foam option will save you more than $7.20 per month on energy costs.
If you can find a way to work it into the budget, do it. There are a few things I wish we'd done on our build that got cut, but insulation wasn't one of them. It's a real PITA to fix, so do it right the first time.
Jason
I have a couple of thoughts on this, modified by the fact that you have not said what climate area you are ion, so that handicaps my answers.
I wonder what kind of foam his is talking about. If icynene, I would not bother. It is ipen celled and has nearly the same R-value as cellulose. You could get some benefit against infiltration with caulk here and there.
If closed cell polyurethene foam, that has double the r-value of the icy and a host of other advantages. When budget can handle it, we use it and all my customers who have it are glad of it.
But I can't imagine spraying only 1/2" of it. The way it goes on, it is hard to control thickness to that accuracy. You are more likely to get 1" in places and barely anything in others if he is trying to shoot only 1/2" That makes the idea less beneficial. I have heard of guys shooting 1" to 1-1/2" for the hybrid system you describe.
Another way to upgrade your insulation system would be to add either 1" or 1/2" foil faced foam panels on one side of the wall or the other. This would also prevent thermal bridging and add a VB as well. Cost with labor would be close to the same as spraying this 1/2", but if you are doing your own work, there is a savings in the labour cost. I would need to know the climate before saying to place this on the inside or outside of the wall.
An added benefit of foam is that it makes for a quieter house.
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