Development of a Leave-in-Place Slab Edge Insulating Form System

Concrete slabs represent the primary foundation type in residential buildings in the fast-growing markets throughout the southern and southwestern United States. Nearly 75% of the 2005 U.S. population growth occurred in these southern tier states. Virtually all of these homes have uninsulated slab perimeters that transfer a small, but steady, flow of heat from conditioned space to outdoors during the heating season. It is estimated that new home foundations constructed each year add 0.016 quads annually to U.S. national energy consumption; we project that roughly one quarter of this amount can be attributed to heat loss through the slab edge and the remaining three quarters to deep ground transfers, depending upon climate. With rising concern over national energy use and the impact of greenhouse gas emissions, it is becoming increasingly imperative that all cost-effective efforts to improve building energy efficiency be implemented. Unlike other building envelope components that have experienced efficiency improvements over the years, slab edge heat loss has largely been overlooked. From our vantage point, a marketable slab edge insulation system would offer significant benefits to homeowners, builders, and the society as a whole. Conventional slab forming involves the process of digging foundation trenches and setting forms prior to the concrete pour. Conventional wood form boards (usually 2 x 10's) are supported by vertical stakes on the outer form board surface, and by supporting 'kickers' driven diagonally from the top of the form board into soil outside the trench. Typically, 2 x 10's can be used only twice before they become waste material, contributing to an additional 400 pounds of construction waste per house. Removal of the form boards and stakes also requires a follow-up trip to the jobsite by the concrete subcontractor and handling (storage/disposal) of the used boards. In the rare cases where the slab is insulated (typically custom homes with radiant floor heating), the most practical insulation strategy is to secure rigid foam insulation, such as Dow Styrofoam{trademark}, to the inside of the wooden slab edge forms. An alternative is to clad insulation to the perimeter of the slab after the slab has been poured and cured. In either case, the foam must have a 'termite strip' that prevents termites from creating hidden tunnels through or behind the foam on their way to the wall framing above. Frequently this termite strip is a piece of sheet metal that must be fabricated for each project. The above-grade portion of the insulation also needs to be coated for appearance and to prevent damage from construction and UV degradation. All these steps add time, complexity, and expense to the insulating process.

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