A home’s structural capacity is one of the most important elements in the longevity of a home. New materials are constantly being developed and tested to help develop the next generation of structural lumber, most of which is made of laminated lumber. For existing structures, adding rigidity and structure to a home can be as simple as insulating your home with closed cell spray foam.
Closed Cell Spray Foam Structural Qualities
Although there are several different densities of closed cell spray foam, the most commonly used density for insulation purposes is 1.7-2 lbs per cubic foot density spray foam. The R-value of this product is R-7 per inch, which is as high as spray foam will get in terms of R-value. The foam expands in the cavity when sprayed due to a chemical reaction when the two components mix, causing heat. The foam then cures into a solid surface. It is the solid state of the closed cell spray foam which is the most interesting, as it has formed a bond between itself and the material that it is sprayed against (typically wood or metal). This bonding ties the framing of the building together and creates the affect of tying all of the framing together. This same type of structural aspect is applied when the exterior sheathing is installed. Basically, adding closed cell spray foam to a building is like adding a thick layer of sheeting to the building.
Areas Of Structural Importance
Unsupported Two-Story Walls
Exterior walls in A frame homes typically have several windows on the wall to give the homeowners that most view and light possible in the home. One issue that arises constantly with these types of walls is their ability to withstand wind shear and their relative structural stability. On windy days in older A frame homes, it is not uncommon to see the wall flexing. Large beams are used as lateral support on these types of walls. In modern A frame wall construction, engineered lumber is used to withstand these forces. Adding closed cell spray foam insulation adds extra rigidity to the wall, tying the framing components together. This is especially true for walls with many windows.
Old Roofing Rafters
Homes with 2×4 roof rafters will typically see some sagging and can see movement from snow loads in the winter time. Filling the rafter cavities with closed cell spray foam creates a monolithic thermal blanket and adds significant structure to the roof, tying all of the framing together.
Stone Foundation Walls
If you have large gaps in your stone foundation or the mortar seems to be crumbling from between the stone, filling the voids with closed cell foam can help hold the stones together. The stone surface and all dust and dirt must be cleaned off of the stone before it is sprayed. Once the foam adheres to the surface of the stone, the rigidity of the foam will add some structure to the wall, much like the mortar that had decomposed had for decades.
One thing that should be made clear, is that closed cell spray foam is not a structural substitute for lumber and should not be treated as such. However, if you have a home that has an older style roof, tall walls, or crumbling foundation stones, closed cell spray foam is a great way to add the extra rigidity needed, along with extreme energy efficiency.