Foundation Insulation

We had some warm December weather and Dave thought he could do another outdoor project so he started digging the trench to repair and replace the foundation insulation.

Digging the trench

Digging the trench

Although we thought the white insulation was EPS with its lower insulating value, it turned out the insulation is blue XPS, just faded to white where it was exposed. That means instead of an exterior foundation R value of about 12 it is closer to an R-20. Combined with the R-15 interior XPS the total foundation protection is R-35 or about the same as the walls.
After the trench was dug to the level of undamaged insulation, or about 10 inches deep, I cut out the broken and chewed away insulation and replaced it with new XPS. I also extended the insulation to the top of the foundation for the full 4″ of XPS at that level.

Applying pink XPS insulation

Applying pink XPS insulation

After fixing the insulation against the foundation with liquid nails, it was covered with the fiberglass packing corners from Repurposed Materials. I had to cut away the edge of the wooden sill under the block wall to fit the corners and to cut away any rotted wood. Then I treated the remaining wood with preservative.

Applying fiberglass corners

Applying fiberglass corners


I was able to use power cement nails to fasten the fiberglass to the concrete sill in some places but in others the concrete crumbled so I used pieces of rebar as I did under the french door sills to hold the fiberglass against the foundation. Then the cracks between fiberglass pieces were filled with dark brown caulk.
Fiberglass covered insulation

Fiberglass covered insulation


We were able to get the job done just in time for much colder weather. We just have to fill in the trench when we return from our grandson’s second birthday party!

This entry was posted in -Chronological Recent Posts, Air Intrusion/Thermal Envelope. Bookmark the permalink.