Slab Edge Insulation
ASHRAE 90.1 based energy code standards for building envelope design as well as the IBC (International Building Code) and IRC (International Residential Code) require the placement of insulation at the foundation and slab edge using one of two methods:
1. exterior application extending from the top of the slab to 24” below top of slab, or
2. on the interior of the foundation extending through the slab to the finished floor elevation, in essence, forming a “floating slab” situation.
Foundation and slab edge insulation is required by the 2009 IRC building code in climate zones 4 and above. Almost all energy codes and building science research facilities promote the use and importance of slab edge insulation as an integral part of the buildings thermal envelope.
Because of the complexities existing at this critical transition of materials and environmental conditions, detailing of a functional slab edge insulation solution has been difficult. With no consistent answer, design, construction and code enforcement professionals have often defaulted to acceptance of sub-standard details yielding minimal performance. David Hales, Building Science Professor at the University of Washington, called slab edge insulation “one of the most abused details in construction”. The default detail commonly accepted by the industry is to place foundation insulation on the inside of the foundation and return the insulation for some horizontal distance from this edge. The common practice of placing belowgrade insulation behind the foundation and under the slab does little to isolate the concrete from the exterior. Simply put slab edge insulation is underutilized.
places insulation at the slabs edge where code recommends its placement. This allows the slab edge insulation to align with the wall insulation. The slab edge alone represents approximately 60% of the total heat lost from the foundation face. Below grade foundation insulation is placed on the outside edge. EnergyEdge provides the transition from the wall system above to below grade insulation at the foundation, completing the envelope and saving energy through the use of the slab edge insulation.
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