NAHB BUILDING WALL TEST

SPRAY FOAM INSULATION ADDS UP TO 300% SHEAR STRENGTH TO THE STRUCTURE

Introduction
The NAHB Building Wall Test was initiated by the Polyurethane Foam Structural Quality Assessment Committee of The Society of the Plastics Industry, Inc. in March 1992. The objective was to establish the structural value of spray in place polyurethane foam used in wood frame wall constructions. The original plan called for three phases. The first was a paper review of all available data, the second was laboratory evaluation and the third was full model testing.

Objectives
The original plan intended to quantify the structural value quality of the sprayed polyurethane foam (SPF). The tests were to show that the sprayed polyurethane foam could replace building components such as studs, sheathing and corner bracing. The National Assn. Of Home Builder's Research Center was selected to carry out the plan. It was determined that tests would be performed for racking (shear) resistance and also for compressive (axial) resistance. A total of 45 panels would be built using different configurations.

Racking (Shear)
This test evaluates the resistance of the wall construction to wind forces on the wall. Conventional construction of walls requires bracing using panels or diagonal bracing straps. Thirty racking panels were constructed. Eighteen of these were filled with sprayed polyurethane foam (SPF). For comparison, twelve control panels were constructed without SPF. These panels were built using 2x 4" and were 8 ft. high by 8 ft. wide. Half inch, 4 ft. x 8 ft. sheet rock was installed horizontally on the panel with the seam taped and finished. The conventional panels used half inch fiberboard sheathing or half-inch plywood on the exterior walls. As compared to the panels without foam or sheathing: the foam filled panels were 300% higher in pounds of resistance for the wood siding (T1-11) and 200% higher for the vinyl panels. This clearly proves that sprayed polyurethane foam adds racking strength to wall panels.

Compressive (Axial)
The second test that was performed is designed to determine if the PF would add any strength to the compressive capabilities of the wall construction. The axial test measures the resistance of panels to a compressive load as would be imposed by the dead or live loads of overhead floors or roofs carried by the walls. The wall strength in this test comes from the stud spacing and the sheathing materials. Adhesion of all the construction elements is important to the overall strength of these test panels. Again both wood and vinyl siding were used without sheathing for the sprayed polyurethane foam. The test was for 16" on center and also 24" on center studs. Each stud spacing variation was done with the vinyl and wood siding.