A lot has been written about insulated concrete forms (ICFs) the past few years but mostly by manufacturers. We have two winters and one summer under our belts now and it’s time to weigh in from a home owners point of view. Our temperature extremes run from 105F in the summer to -9F in the winter so we have a pretty good idea of how well this insulated building system has performed.
ICFs are usually 2’ long x 1’ high x 2 1/4” wide Expanded Polystyrene panels that are stackable and fit together like Legos. Plastic inserts hold the inside and outside panels together creating a space to be filled with concrete. The end result is a concrete wall with 2 ¼” insulation on both the inside and outside.
I’m not going to get into a lot of the selling points for ICFs in this blog. I’ll let the marketing departments and you or your contractor figure out what is and isn’t true about the so called advantages for using this system to build the walls of your home. I will say there are some advantages for sure but not all of their marketing claims are accurate. I would rather speak to my own experiences as a home owner and general contractor about the results we got in our home.
There is no question this is a good building system over all but as with any system there are items in both the Plus and the Minus columns. Those are what I would like to focus on for this article.
My biggest gripe: This is the kicker for me – In all exterior building walls there is a hot/cold line, the place where the inside and outside temperatures meet and even out. That usually occurs at or near the insulation. In this wall system it occurs somewhere in the middle of the concrete wall.
That doesn’t work well in colder climates. We should be heating the concrete mass from the inside and the concrete will help hold that heat and reflect it back into the house, but with this system we have 2” of foam between your heating source and the concrete. What you end up with is an extremely even inside temperature that rarely fluctuates which would be fine in a more moderate climate but not so good in a cold climate. You end up using more heat than you should have to in order to push the cold line back to the outside. I would rather see the hot/cold line at the outside insulation layer.
In the hot summer months our house stays in the lower 70s no matter what which is good, but in the winter months you really have to pour the heat on if you want to raise the temperatures and keep them there.
I believe it would be better to have poured the concrete walls and put 4” of insulation on the outside or purchased the ICFs that are 2” of insulation on the inside and 4” on the outside. If I had it to do over, that’s what I would have done.
What we have works and is acceptable but one of the two options above would have been better.