Having recently built a small home, we decided to spend some extra money and install foam insulation instead of batt. Though batt insulation has been the standard in our area for many years, is inexpensive and easy to install, it has limitations; mainly insulating value, but equally important doesn’t have the ability to block air flow like foam. Air flow is not usually regarded as a factor when talking about insulation but with air also comes moisture and possibly mold. Also moisture reduces the insulation “R” value of batt insulation.
So now on to Foam insulation; and I’ll admit I don’t know everything, but this is my experience and so far what I know. 1st there’s open or closed cell. Being just that, one has closed cells not letting any air through and the other open cells which allow a small amount of air through (negligible amount in my opinion). Closed cell is more expensive and weighs more per s.f. but blocks air flow completely. Closed cell is also hard when cured which creates a structural advantage by locking the framing in which it’s installed together. It’s also a bit harder to work with and the contractors we talked to said they almost never fill the entire wall cavity full with closed cell; partly due to cost and partly due to R-Value. They say install an inch or two and fill the remainder with batt. They say by doing that you get the air barrier and also the R-Value you need. Speaking of R-Value, you can get the specifications of each on line, I won’t spend the time here to go into that, basically closed cell is a bit better but both do degrade some over time.
We chose open cell foam because we didn’t want any airspace in our walls and it’s less expensive and in my opinion a little more environmentally friendly, not off-gassing as much as closed cell. My understanding is many companies are creating more environmentally friendly foams now, but you’ll have to do the research when you’re ready to purchase. One other factor for us was the fact that open cell foam is still soft when cured and easy to patch, dig into and re-fill if say you need to modify some electrical wiring in the wall or something. You just buy an applicator gun and some small cans of the foam from local suppliers and do it yourself. I think the cans of foam were $10-$15, not at all expensive. Not the same stuff as the foam you buy at the home centers though, At least not yet.
One other factor for us was that our small home has a hand framed 2x10 roof with 2x6 Shed dormer and the bottom side of the roof rafters is our ceiling. It’s not possible to get enough batt insulation into a 2x10 ceiling let alone a 2x6 so we filled the entire roof frame with open cell foam right down to the bottom of the rafters, leaving no room for air.
So how do we like it? WE LOVE IT and it far exceeds what we expected. Why? 1st our small house is just that, small at about 500 total s.f. and we can heat it with a 1500W electric heater (decorative fireplace) no problem even in the middle of winter. 2nd It’s SO quiet inside it’s amazing. When we shut the windows it’s almost like we're in a sound-proof room.
So that’s it, our take on foam insulation. Look for the cost to keep coming down but even now still worth the investment in my opinion.
Look for my comments soon on what's important to spend a few extra dollars on when building a home, which will include how to do foam insulation in a home with roof trusses.