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Cite this document
As the desire for building envelope energy efficiency increases, the sensitivity of the building envelope to small changes in the air, water, and vapor transmission can mean the difference between a functional system and a problematic building. Continuity of the building’s air and vapor barrier assembly is critical to insure that the air and vapor transmission remain consistent with the design assumptions and within permissible limits. As a result of the demand for simple, continuous air barriers systems, Spray Polyurethane Foam (SPF) has become a popular choice among design professionals and contractors alike. It is a versatile material that can be applied to either interior or exterior wall systems, providing a useful combination of water, air, and water vapor penetration resistance. However, because the product is essentially fabricated on site by the installer, differences in mixture proportions, thicknesses, ambient and substrate temperatures, moisture or humidity conditions, and other factors can result in dramatic variations in the physical properties of the material, as well as the behavior and performance of the system. One of the most significant problems experienced recently in the use of SPF for air barriers is short and long term shrinkage variations in the foam system, particularly when applied to the exterior of the building. Such shrinkage can result in damage to flashings, closures, and terminations in exterior veneer systems. This document explores the potential causes of excessive shrinkage in SPF systems, the physical changes that can cause the problem, and best practice measures to minimize the potential for significant problems during installation.
spray polyurethane foam, air barrier, shrinkage, leakage, failure, building envelope, insulation, flashing, dimensional stability, temperature
Wagner, Andrew W.
Senior Engineer, Whitlock Dalrymple Poston & Associates, Inc., Charlottesville, VA
Peterson, J. Eric
Principal, Whitlock Dalrymple Poston & Associates, Inc., Manassas, VA