Source: AAMA
Expanding aerosol polyurethane foam can greatly enhance the installation quality of prime and replacement fenestration products by sealing the gap between the rough opening and the window frame against air leakage. The installer’s usual approach is to finish installing a window from the outside of a building, then go inside and run a bead of the foam in the gap between the rough opening’s studs and the window frame. The foam then expands to assume the shape of the gap, and cures and hardens to provide an effective air barrier.
Determining Expansion Pressure Effects
The pressure exerted by the foam as it cures and expands, if excessive, can induce frame deflection that can hamper operation of the sash or cause gaps that actually degrade air leakage performance. Care must be taken to select a foam with an appropriately low “pressure build,” so that its expansion as it cures will not deform the window frame.
Foams can be characterized as having high, medium or low pressure build exerted by the fully-cured product; actual values can be obtained from the foam supplier or determined by test.
Once the maximum pressure has been established, it can be translated into the resulting window frame deflection for a given fenestration product by calculation or by physical test. Maximum theoretical deflection of a framing member can be calculated knowing the pressure build of the foam as the applied load, the modulus of elasticity of the framing material and the moment of inertia. This allows a window manufacturer to more specifically determine which foams are suitable for the installation of its products.
Dimensional Stability
Dimensional stability, defined as the resistance of the cured foam to shrinkage or expansion under a variety of temperature and humidity conditions, is a good indicator of foam performance over the long term. Apart from curing pressure, excessive post curing expansion or shrinkage can compromise the foam’s ability to provide an effective air seal. A foam sealant is generally considered suitable for window or door installation applications if its dimensions vary no more than ±10 percent.
The Role of AAMA 812
Working through AAMA’s Wall Interface Council, foam manufacturers developed standards for the safe use of their products in the installation of windows and doors. AAMA 812-04, Voluntary Practice for Assessment of Single Component Aerosol Expanding Polyurethane Foams for Sealing Rough Openings of Fenestration Installations is based on the properties of pressure build, induced deflection and dimensional stability, and offers test protocols for determining the extent of these key parameters.
In laying the foundation for the standard, extensive testing quantified the degree to which expandable foam sealant exerts pressure on window framing members as it cures. This led to the development of expansion pressure ratings for various foam sealant products, which a window manufacturer can use to accurately predict the effect on a given window design. Using these ratings, manufacturers can confidently recommend the use of low-pressure foams designed specifically for window installation.
The way AAMA 812 works in the marketplace is that, first, the foam manufacturer should have tested the product in accordance with the standard and either provides documentation upon request or appropriately labels the product. The conformance information must include the pressure-build result expressed in pounds per square inch (psi). For example, an acceptable conformance statement would read,“Conforms to AAMA 812-04 at XXX pressure-build.” A window manufacturer can verify whether the actual pressure-build as stated is acceptable for its window product.
AAMA 812 Update
In the nearly 10 years since the standard was written, the industry has evolved, encompassing an increasing variety of window framing materials, including newer composites. And, a widening variety of rough-opening materials (masonry, wood, wraps, panning, flashing, exterior insulation finishing system [EIFS], etc.) is in use to which the sealant must adhere.
In addition to the performance factors of pressure build, deflection and dimensional stability as covered in the current edition of AAMA 812-04, a number of other considerations could be addressed, such as air tightness, water vapor permeance, compressive strength, yield, water absorption, thermal resistance, flame spread classification, overall density, structural integrity and ‘green’ credentials.
The pressure exerted by the foam as it cures and expands, if excessive, can induce frame deflection that can hamper operation of the sash or cause gaps that actually degrade air leakage performance. Care must be taken to select a foam with an appropriately low “pressure build,” so that its expansion as it cures will not deform the window frame.
Foams can be characterized as having high, medium or low pressure build exerted by the fully-cured product; actual values can be obtained from the foam supplier or determined by test.
Once the maximum pressure has been established, it can be translated into the resulting window frame deflection for a given fenestration product by calculation or by physical test. Maximum theoretical deflection of a framing member can be calculated knowing the pressure build of the foam as the applied load, the modulus of elasticity of the framing material and the moment of inertia. This allows a window manufacturer to more specifically determine which foams are suitable for the installation of its products.
Dimensional Stability
Dimensional stability, defined as the resistance of the cured foam to shrinkage or expansion under a variety of temperature and humidity conditions, is a good indicator of foam performance over the long term. Apart from curing pressure, excessive post curing expansion or shrinkage can compromise the foam’s ability to provide an effective air seal. A foam sealant is generally considered suitable for window or door installation applications if its dimensions vary no more than ±10 percent.
The Role of AAMA 812
Working through AAMA’s Wall Interface Council, foam manufacturers developed standards for the safe use of their products in the installation of windows and doors. AAMA 812-04, Voluntary Practice for Assessment of Single Component Aerosol Expanding Polyurethane Foams for Sealing Rough Openings of Fenestration Installations is based on the properties of pressure build, induced deflection and dimensional stability, and offers test protocols for determining the extent of these key parameters.
In laying the foundation for the standard, extensive testing quantified the degree to which expandable foam sealant exerts pressure on window framing members as it cures. This led to the development of expansion pressure ratings for various foam sealant products, which a window manufacturer can use to accurately predict the effect on a given window design. Using these ratings, manufacturers can confidently recommend the use of low-pressure foams designed specifically for window installation.
The way AAMA 812 works in the marketplace is that, first, the foam manufacturer should have tested the product in accordance with the standard and either provides documentation upon request or appropriately labels the product. The conformance information must include the pressure-build result expressed in pounds per square inch (psi). For example, an acceptable conformance statement would read,“Conforms to AAMA 812-04 at XXX pressure-build.” A window manufacturer can verify whether the actual pressure-build as stated is acceptable for its window product.
AAMA 812 Update
In the nearly 10 years since the standard was written, the industry has evolved, encompassing an increasing variety of window framing materials, including newer composites. And, a widening variety of rough-opening materials (masonry, wood, wraps, panning, flashing, exterior insulation finishing system [EIFS], etc.) is in use to which the sealant must adhere.
In addition to the performance factors of pressure build, deflection and dimensional stability as covered in the current edition of AAMA 812-04, a number of other considerations could be addressed, such as air tightness, water vapor permeance, compressive strength, yield, water absorption, thermal resistance, flame spread classification, overall density, structural integrity and ‘green’ credentials.