by • August 21, 2013 • Foundations, Insulation & Air SealingComments (5)7045

Insulated Concrete Slab

  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 builder 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 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.
Be sure to check out my video blog on YouTube.

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  • Jim Van Overschelde

    Hi Matt. What did you cover the insulation boards with (before the stucco), if anything, and how did you avoid additional termite problems – termites coming up between the outside of the board and the protective cover?

    • Jim, We used Termimesh on top of the foam so the termites coming up would have to take a detour outside and you’d see them. See picture above.

      • Jim Van Overschelde

        Thanks Matt but I wasn’t clear with part of my question. I meant, what did you put on the exterior of the foam to protect it – before the stucco, if anything? It sounds like in your video that you had something on the outside to protect the foam. If the termimesh went over the top, it also had to go over the protection board, right?

        • Jim, We used a STO finish on the foam not a traditional 3 coat stucco. The protection is a mesh with a latex base coat as part of the STO EIFS system.

          • Jim Van Overschelde

            Great. Thanks Matt. Just what I was looking to know.