How to Insulate a Slab Foundation
In Texas where I build the most common foundation type is Slab on Grade. In effect, we pour a big rock of concrete on top of the ground (also mainly rock) then build a house on top.
|My Project Manager Ryan on top of this newly poured Slab Foundation.|
I just completed my first house with Perimeter Slab Edge Insulation and I thought I’d walk you through the process. First, let’s talk about why to insulate the slab. As we build tighter and better insulated houses the uninsulated slab becomes more of a heat loss in the winter time for these High Performance Homes. Check out this Manual J energy loss chart from a house we remodeled recently.
|Check out the BTU loss through the un-insulated concrete slab on this house.|
The chart above is from a house with R-19 walls, and an R-40 roof. As we build better that slab becomes a larger % of the loss of heat!
|This is for a house with an R-11 Insulated Slab.|
Now look at this chart with a house with similar specs for walls/roof but it has an R-11 Perimeter insulated slab. Big difference! As a percentage of heat loss the floor went way down compared to the un-insulated slab house.
So, let’s look at the mechanics of actually insulated the slab. One of our first concerns for this process is Termites! Adding foam to the outside of a slab is a big no-no in Termite country. First, we used Borate impregnated foam from Nisus Corporation. I’ve been using their Bora-Care on my framing lumber for about 10 years now, but I only recently realized they make a termite resistant foam aptly called Bora-Foam. Our local Termimesh dealer sourced it for me and did the install.
I want to thank Joel Roeling from Termimesh for his help in this project. Also want to extend a big thanks to my Energy Rater/Tester Kristof Irwin of Positive Energy here in Austin, TX. His modeling really helps us decide what approaches will yield benefits long term for the houses I build. Last, but certainly not least was the amazing Architect/Client on this house Scott Ginder of Dick Clark & Associates. Scott and his wife Andrea are wonderful clients and it was such a pleasure to build this beautiful high performance home with them! Here’s some detail photos but be sure to watch the video too.
|Here’s the tall slab before insulation.|
|The Termimesh guys installing Bora-Foam.|
|After the foam is installed we installed Termimesh to the slab/foam joint.|
|It really didn’t take too much foam to do the entire slab.|
|We basically turned the foam on the foundation into a standard STO EIFS install.|
|Here’s the completed house.|
|Architect & Client Scott Ginder had a very nice “Wrap” party for us!|
|Matt Risinger, Dick Clark AIA, Scott Ginder AIA|
Matt Risinger – Risinger Homes in Austin, TX
Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.
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