Insulating a Basement Walkout Entry
Foam Board Insulation Installation
We’re at the bottom of the stairs in this basement walkway entry we’re building. Something crucial for the footings is the foam board insulation. This two-inch thick R10 insulation allows a footing not to be 30 inches deep or below the frost depth. Essentially, it creates a barrier — a thermal break — to keep the steps from going 30 inches below the grade. As it sits, it will only be four inches below the grade, which is essentially just the thickness of the concrete.
Why is this Important?
The moisture underneath the footing in the soil can freeze and then create a frost heat, where that water expands and lifts the footing. This insulation is an integral part of the project to guarantee that this footing area is safe, even though it’s not 30 inches deep or below the frost steps. The insulation continues up for three steps to protect the footing on the home and the new foundation walls.
What Goes Under The Insulation?
Underneath the insulation, we have our drain and then the structural rebar. Because this rigid foam board is pretty soft, we have to put rebar in here, 12 inches on the center horizontally and vertically.
Moving on up the walkout basement stairs, we have these rebar dowels put in. We used half-inch #4 rebars in every stair going up the stairs. That will ensure that if this soil underneath the stairs ever settles, even a fraction of an inch, these basement stairs outside will be entirely supported by the rebar dowels on every single step on both sides.
Connecting the Stairs to the Basement Insulation
The other thing I want to discuss today is how the slab (the original footing) on top of the basement walkout stairs will meet the existing slab inside the basement.
How Can That Happen?
We have our mark on the foundation wall to indicate where the top of the concrete floor will be. That corresponds with that inside one and slopes down this way slightly. So we will be pouring concrete underneath the door and filling it in so that it’s nice, tight, and solid. That will also tie in with the rebar, so it won’t crack and will rest on this original footing. And that’ll give it a nice seamless transition from the addition into the existing old space.