Search Document Types   →   Enclosures That Work   →   High R-Value Foundation Assemblies   →   High-R Foundation 10: 6" 0.5 PCF Spray Foam with 2x4 Framing Offset 2.5" from Concrete
ETW

Enclosures That Work

High-R Foundation 10: 6" 0.5 PCF Spray Foam with 2x4 Framing Offset 2.5" from Concrete

By Building Science Corporation    Created: 2011/01/15

  • Concrete foundation wall
  • 21/2" gap
  • 6" open-cell spray foam
  • Gypsum board with vapor retarder paint
  • Dampproofing
  • 2" XPS rigid insulation under slab

 


Thermal Control

Open-cell spray foam provides very good continuous thermal control. Spray foam is an air barrier, so convective looping and air leakage thermal losses do not occur. This wall system has an R-value of R-21 and a predicted annual heating energy loss of 16.3 MBtus.

 

Moisture Control

Open-cell spray foam is an air barrier, but is vapor permeable. The relative humidity was predicted in the center of the open-cell spray foam insulation and was found to be at safe levels (Figure 2).

Low permeance interior wall finishes should be avoided with this construction strategy.

 

 

Figure 2: Predicted RH at the interior surface of open-cell spray foam

 

Constructability and Cost

This solution is more practical than High-R Foundation 7 if the plan is to finish the interior of the basement.

 

Other Considerations

Spray foams have been improved considerably for human health and the environment. Ozone depleting substances in the process have been removed, but some spray foams use greenhouse gases that are much worse than carbon dioxide. There are options available of more environmentally friendly spray foams that release green house gases, such as water blown foams, on the market and should be considered. 

 


Reference

Mitalas, G.P., Calculation of Basement Heat Loss, National Research Council Canada.