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Chemistry 101: are all foams created equal?BASF Polyurethane Foam Enterprises LLCJuly 7, 2006Building Design and ConstructionYou probably don’t spend a lot of time thinking about chemistry when you consider adding insulation to improve energy efficiency. Yet one popular insulation material – spray-applied polyurethane foam (SPF) – relies entirely on chemical cleverness. Are all foams created equal? Quite simply, the answer is no. Spray-applied polyurethane foam is a two-component product that is manufactured on-site, but engineered in the molecular level to optimize performance for a specific application. By varying key components, the finished product can be modified to meet specific performance requirements for roofing applications, insulating air barrier systems, adhesive applications or wall insulation. Currently, three types of SPF are commonly used within the construction industry: ·medium-density (MD) 24 kg/m3 to 48 kg/m3 (1.5 pcf to 3 pcf) ·low-density (LD) 8 kg/m3 to 12 kg/m3 (0.5 to 0.7 pcf) ·sealant foams The most important distinction is whether the formulation produces an open-cell or closed-cell foam. MD foams are formulated to have a closed-cell content of greater than 90 percent, combined with an effective R-value of over 6.0 per inch. LD, open-cell foams have approximately 60 percent open-cell content and offer an R-value between 3.0 and 3.6 per inch.
But R-values are only the beginning when it comes to energy efficiency. It is the air permeability capabilities that are the true differentiator. Yes, you need insulation. But in order to make a building truly energy efficient, you need an effective, continuous air barrier system. Without it conditioned air escapes through the building envelope, and the HVAC system has to work harder to keep the indoor environment comfortable (see sidebar: Air Barriers Go Legit). Most open-cell foams have not been tested and, therefore, do not qualify as air barrier systems in ‘typical thickness’ of less than four inches. One open-cell foam manufacturer’s product requires an application of 5.5 inches (its maximum allowable thickness) to pass the minimum requirements of ASTM International E 2178, Standard Test Method for Air Permeance of Building Materials (air leakage rate of 0.005 L/s/m2 @ 75 Pa). Compare this with closed-cell foams, some of which provide air leakage rates of <0.001 L/s/m2 @ 75 Pa at 1.5-inch thickness. Because the systems are spray-applied, fully-adhered and seamless they also eliminate connective loops behind the insulation and therefore eliminate moisture. And since mold requires three things to grow – moisture, warm temperatures and a food source – and closed-cell foams do not provide any of these things, MD, closed-cell SPF can help to prevent dangerous mold infestations. Open-cell foams offer a slight cost advantage when compared on an equal-thickness basis, and in general they provide greater sound control. On the other hand, closed-cell formulations can actually improve building durability and structural strength. Testing conducted by the National Association of Home Builders (NAHB) Research Center shows closed-cell SPF insulation between wood- and steel-stud wall panels increased rack and shear two to three times over standard stick-built components and glass fiber insulation when sprayed onto gypsum wallboard and vinyl siding, and increased racking strength by 50 percent when sprayed onto oriented strandboard (OSB)[1]. Both closed-cell SPF systems and open-cell foams provide environmental responsibility, have no adverse effect on the ozone layer and do not emit volatile organic compounds[2]. [1] Canadian Construction Materials Centre (CCMC), Evaluation Report 12932-R, National Research Council (NRC) of Canada. [2] Air Barrier Association of America (www.airbarrier.org) © 2009, Reed Business Information, a division of Reed Elsevier Inc. All Rights Reserved.
UL ENVIRONMENT: Sustainability Claim Validation and Certification Johns Manville Insulation San Diego Gas & Electric Company |
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