Perimeter Foundation Insulation

How to mitigate heat energy loss in this often overlooked area of the building envelope

The best way to improve this detail is to install rigid insulation over the drain tile gravel before backfilling the foundation walls. From a heat loss standpoint, it doesn't matter whether the insulation gets installed on the inside, below the concrete floor or on the outside of the footings above the drain tile gravel. Installation on the outside does carry a couple of advantages that make it a superior location.

One of the things we never want to do is to have frost penetrate into the soil below the footing area, placing it at risk for structural frost heave. Exterior perimeter insulation allows heat transfer from the basement to the soil below the footing and impedes the travel of frost down through the exterior soil deeper towards the footing area while still insulating against thermal loss.

The most practical insulation thickness is between 1" to 2 ½" depending on your homes installation conditions. A HOT2000 computer analysis can help you make the correct decision in this area on your R-2000 Home.

The cost to install this insulation consists mostly of material costs, as the foundation contractor typically just places the rigid board insulation at the same time the drain tile and gravel is installed before the foundation is backfilled.

As this layer of rigid insulation is installed with all joints only loosely butted to one another, ground surface water drains easily through the insulation layer down to the drain tile to be removed from the area as normal.