‘Beauty is in the details’ is a phrase thrown around in the field of architecture a lot. While we believe it does rain true, we also know from experience that ‘performance is in the details!’ Take in point this edge of slab detail, where the exterior wall meets the slab and foundation wall. The exterior wall is well insulated for the climate zone the project is located in, as is the slab (R-44 and R-25 respectively). However, the typical detail to meet IECC 2021 requirements results in a huge thermal bridge where the two assemblies come together.

As you can see in the image above, if the concrete slab and concrete foundation wall touch each other, heat pours through the concrete because, well…there is no insulation there to stop it!To fix this, all we have to do is add a mere 2 inch thick strip of insulation between the concrete slab and foundation wall. This stops heat from traveling through the heat conductive concrete by creating a small, but very effective thermal break.

As you can see in the image above, with this simple and cheap modification, the detail performs about 10 times better!There are a number of things we could do to eliminate the thermal bridge all together, but for this project, we elected to bring a 1 inch thick piece of polyiso insulation over the exposed portion of the foundation wall.

This last image shows that this small addition brought our thermal bridging down to -0.006 BTU/hr.ft.F. You can see the final detail to be constructed in image 4.To summarize the importance of this detail: With the addition of only 3 inches of insulation, we have completely eliminated a significant thermal bridge along the entire perimeter of the building. If this went unaddressed, it would be like having a window cracked open in every single room all year long!

This is why details matter.