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July 12, 2023
When it comes to insulating a building envelope, there are various methods that can be used depending on the building’s purpose and the required level of insulation. However, combining metal roof and wall panels with spray polyurethane foam insulation (SPF) is widely considered one of the most effective ways to achieve secure, strong, and long-lasting insulation. Utilizing this method of insulation offers numerous benefits including the sealing of panel joints, creating a vapor barrier, providing thermal insulation, and producing air barriers. This guide will discuss in detail what SPF insulation is, the advantages of utilizing this method, and outline the proper use and applications of SPF on metal panels.
One of the most notable advantages of utilizing SPF insulation is that it can be used to fill spaces in the panel assemblies and function as a key component of an air barrier system, effectively reducing air leakage. However, there are a few design parameters to be mindful of when considering the use of SPF insulation for metal roof or wall panels. The Spray Polyurethane Foam Alliance (SPFA) has conducted research on the installation of SPF on steel panels and has suggested the following best practices for applying SPF to the interior surface of metal panels:
What is SPF Foam Insulation?
SPF insulation is made up of two chemical components that are combined using a spray gun. When mixed, a reaction is created which leads to polymerization through an exothermic reaction.
During curing, the foam may reach core temperatures as high as 325°F for short periods of time. Research suggests that during the curing process of closed cell SPF, the temperature of a metal panel in contact with the foam can increase in temperature as much as 80°F. Control of these temperature increases and the potential deformation or oil canning of metal wall panels can be avoided utilizing SPFA installation guidelines.
Open-Cell and Closed-Cell Foam
There are two classes of SPF products: open cell and closed cell.
Open-cell SPF provides both insulation and air sealing for the building assembly. The aged R value of open-cell SPF is approximately 3.5 Hr·ft2 °F/btu per inch (2), however, the open cellular structure will permit water to migrate within the insulation and does little to restrict the movement of moisture vapor making it vapor permeable. With these limitations, open-cell foam is not recommended for applications where the foam is likely to encounter water and an additional vapor retarder to control condensation.
Closed-cell SPF insulation uses chemistry like open-cell SPF; however, a different blowing agent is used to create the foam. The cellular structure is a series of adjoined closed cells that hold the blowing agent gas, providing better insulation than air. The closed-cell structure prevents the entry of water and reduces the movement of moisture vapor, making separate vapor retarders or water-resistant barriers unnecessary. Closed-cell SPF typically has a permeability that is less than 1 perm when applied at 2” thickness and an aged R value of 6 or 7 Hr·ft2 °F/btu per inch (2). Closed-cell spray foam insulation is the most common SPF type on metal panels.
It is important that a certified foam spray technician applies SPF to the required insulation thickness to achieve the optimum insulation density, adhesion, and thickness. The recommended application method when applying the foam is to use the controlled thickness spray technique, commonly known as the “picture frame” technique. SPFA describes this technique as if someone were following through the motion of picture framing, in which the applicator surrounds the interior perimeter of the wall framing stud and allows the foam to rise along the stud. This technique can also help to prevent SPF from getting between girts and architectural metal wall panels which could cause metal deformation.
The thickness of the initial pass fillet during picture framing should be at least 0.5 inch and should not exceed the maximum pass thickness recommended by the foam manufacturer. The minimum thickness of the initial pass is specified to provide enough material to activate the blowing agent and initiate the cure. After picture framing the perimeter of the area, the applicator fills in the center of the cavity using the maximum thickness recommended by the foam manufacturer. Maximum pass thickness varies by foam formulation and is listed in the technical data for each SPF product. Excessive pass thickness can result in inferior quality due to the increase in foam temperature during curing. For most closed-cell SPF, the maximum pass thickness is 1.5 to 2 inches. It is important for applicators of closed-cell SPF to follow manufacturers’ installation instructions on pass thickness limits and proper cooling times between subsequent passes made if they wish to develop the desired total thickness of the insulation.
Installers are trained to check the substrate surface for moisture, dirt, oils, rust, or other conditions that can interfere with proper foam adhesion. It is also important to clean the surface of these contaminants prior to spraying the insulation. If there is uncertainty surrounding the amount of adhesion needed for a metal surface, this can be determined onsite using a pull-tester in accordance with ASTM (American Society for Testing and Materials) D 4541 (Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers).
When the time comes to change an outdated or damaged panel, many SPF contractors use a release material such as building wrap or fabric to allow for a seamless and pain-free swap out. However, it is important to keep in mind that the use of a release material poses the potential of creating air gaps between the back of the SPF foam and the metal panel. These gaps could allow condensation to accumulate between the SPF and the panel and framing members.
Building owners should regularly inspect metal roof assemblies to detect any potential leaks. Undetected leaks can potentially cause accelerated panel corrosion. Visual detection of roof leaks may be more difficult with SPF, so be sure to contact an SPF contractor if you need assistance.
Closed-cell Spray Polyurethane Foam is a viable insulation material for the interior surfaces of steel and aluminum metal wall panels. This foam application can be highly nuanced, and there is a possibility of deformation, distortion, or oil canning if the application of the SPF is done poorly. To avoid this, a metal panel manufacturer should be consulted when considering using SPF because the installation conditions, installation application methods, product selection, are all key factors to consider when installing this type of insulation.
Most importantly, a metal panel manufacturer should be consulted to ensure that there is no restriction of the intended thermal movement of the roof panels. If applied correctly, SPF is one of the most effective ways to achieve secure and highly supportive panels for your building.
Contact an SPFA-PCP accredited contractor or certified installer to become familiar with SPFA guidelines and gain access to SPFA resources. For more information, contact your sales representative.
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