Save on Pinterest


Are you trying to decide if your next foundation is going to be block, poured or SIP’s? Don’t make that decision until you read about the ultimate concrete sandwich. 

1 / 4
Theromass concrete foundations viewed from the side | Construction Pro Tips
Construction Pro Tips

Concrete sandwich? 

Thermomass is an Iowa company that has been building cast-in-place (CIP) concrete sandwich walls since 1980. What is a cast-in-place concrete sandwich wallTraditionally, concrete foundation walls were insulated on the exterior, interior or both sides. Thermomass decided that insulating the center of the wall was a better solution.  

2 / 4
Thermomass spool assembly | Construction Pro Tips

How it works

The Thermomass CIP system, sometimes referred to as T-mass, is all about the fiber resin connecting rods that hold each side of the concrete in place. These super strong rods have minimal thermal conductivityFactory installed spool assemblies (grommets of sorts), hold the rods in place. The rods are installed into the spool assemblies on site, and once the metal foundation forms have been set, the foam boards are dropped down into the forms from the opening at the top or slid in from the side. The rods keep the foam boards centered in the form. They also have V-grooves in them which creates a channel for the rebar to sit in.  

3 / 4
Setting up the frames for thermomass foundations | Construction Pro Tips
Construction Pro Tips

Order to fit

The T-mass foam foundation system can be ordered with foam from 2 inches up to 4 inches thick, and these walls obtain R-values ranging from R-16 to R-31Of course, the thicker the foam the thicker the wall. If a standard wall is 8 inches thick and you want 2 inches of foam, your wall would go from 8 inches to 10 inches thick. The foam boards can be ordered in various dimensions to accommodate most wall heights. and they can be trimmed down for exact fits.   

4 / 4
Walls built with Thermomass technology | Construction Pro Tips
Construction Pro Tips

T-mass pros & cons


  • Provides a vapor barrier where it belongs 
  • Resists hydrostatic pressure / keeps basements dry 
  • Dry basement means no mold or mildew  
  • Electrical conduit can be run inside walls before pouring 
  • Electrical boxes can be installed before pouring 
  • No need to build and insulate interior walls 
  • Interior walls can be skim-coated and left as is 
  • No exterior foam to get damaged during backfilling  
  • Structural load capabilities are just as strong as traditionally poured walls 


  • Takes more time to install 
  • Cost is about 18-20 percent more 

Spending approximately 20 percent more on your basement foundation will reduce energy bills, and thwart mold and mildew. But most importantly, a T-mass CIP foundation system will almost guarantee you’ll end up with a comfortable living space in your basement. We are big fans.