Building Sciences - Foundation Insulation

Wall section showing insulation at different conditions of the wall

Insulating your home is an extremely important part of home renovations, home improvements and new home construction projects. Last week we covered a broad introduction to the different areas of your house which should be insulated. Today we’ll dig a little deeper into one specific area: Foundations.

Click here to go to Part 1: Introduction to Insulation

Part 2 - Foundation Insulation

 Although your foundation walls are often buried in the ground, they should still be insulated, especially on new construction projects where the work of insulating will not disrupt an existing foundation. Heat from your house will look to escape to any adjacent cold area, whether that’s air outside of your upper level walls, or the dirt outside of your foundation walls. According to the Department of Energy, foundation insulation can also help prevent problems due to moisture, insect infestation and radon.

 One great way to insulate your foundation is with Insulated Concrete Forms, like those pictured below. In a traditional slab-on-grade foundation, your contractor will dig a trench, then build a wood forms in which to pour the concrete. When the concrete cures the wood is removed and dirt is backfilled against the concrete. Sometimes insulation is installed outside of the concrete before the dirt is filled in.

Insulated Concrete Form in a trench prior to the foundation being poured.

Insulated concrete forms simplify this process by combining the insulation with the formwork. After digging the trench, a contractor creates the forms with pre-fabricated foam pieces. When the concrete cures the foam remains in place to act as insulation for the foundation wall.

 There are a number of ways the slab can then be poured and connected to the foundation walls. One method would be to simply pour the foundation on compacted fill within the extent of the formwork. The detail below shows our plan for an upcoming project. After the forms are built, the contractors will remove the top four inches of the foam on what will be the inside of the house. The foundation will then be poured up to that lower height. When the foundation hardens, the slab will be poured on compacted fill and over the stem walls. The four inches of foam that was NOT removed on the outside will insulate the edge of the slab. This will then give the framers one continuous slab on which to attach their base plates and begin framing the house.

Check back soon for the next installment of our series on insulating your house.