Closed cell foam and its benefits under slabs.

We use foam in one way or another on better than 90% of our projects. Its air sealing properties, leave no void, and incredible insulative properties make it a big win. Sure you have to let go of a little more green on purchase, but the cost savings quickly add up.

I usually install a few feet of 2″ rigid foam board around the perimeter of a slab, which is code, but this time I decided to use closed cell foam beneath the entire slab. This slab will be the ground floor for a writing/recording studio. Providing insulation under the entire slab on this project made a lot of sense.

Here is a short clip of that foam being sprayed on!

The cost of the foam is very comparable to rigid foam board. Sure you can buy the material for a little less, but after you calculate in labor, the price difference becomes a wash. On this type of application, you can estimate between $2.00-$2.50 a foot.

Here is what the closed cell foam gives you!

1. Conforms infinitely to gravel and foundation as a substrate. Won’t break when stepped on unlike rigid foam board.
2. Forms a continuous vapor barrier especially sealing around electrical and plumbing penetrations in slab.
3. Forms a great surface to pull concrete across.
4. Another benefit I hope we will see is keeping external noise at bay by decoupling the slab from the substrate. Ever feel that big truck rumble by?
5. Excellent R values. At about 7.5 an inch, the slab should be closer to room temperature than ground temperature.

Now remember, only closed cell foam can be used in this capacity! Open cell foam would be crushed beneath the concrete, and would not perform as a vapor barrier.

So the next time your loading your truck with that pink board, think of calling in a foam installer instead. I think you will be happy.



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