This second Barndominium article focuses on substrate preparation requirements for both open and closed cell SPF.
In a previous article published (W&C February 2024, entitled “Barndominiums and Metal Building Insulation with Spray Foam,”), we discussed the importance of carefully determining the required thickness (R-value) of open- or closed-cell spray foam insulation, as well as the potential need for an additional vapor control layer in metal clad buildings.
In conversations with insulation contractors across the country, several key considerations consistently emerge when installing SPF, whether open or closed cell.
1. Substrate Stability
There are seven primary metal building panel types, along with multiple variants, including R-panel, PBR panels, standing seam panels, corrugated metal panels, box rib panels, flat metal panels and insulated metal panels.
Metal thickness (gauge) and yield strength, fastener spacing, fastener type, framing type, and framing material all play a role in determining the structural integrity and stability of individual cladding panels and the overall cladding assembly. SPF contractors are advised to confirm that fastener spacing and fastener types meet the recommendations of the panel or building manufacturer. In retrofit applications, this may require installing additional fasteners prior to applying spray foam insulation.
Metal thickness and yield strength are the two characteristics most closely related to cladding durability. When closed-cell SPF (ccSPF) is applied to the interior surface of metal panels, it adds a high degree of stiffness to both the panel and the overall wall or roof assembly, increasing wind resistance and load-carrying capacity. Open-cell SPF (ocSPF), by contrast, provides no additional structural strength.
Contractors should always confirm cladding thickness and fastener spacing before installing SPF. Waves and oil-canning in 28- or 29-gauge metal can often be avoided by limiting the first foam pass to approximately one inch, allowing the foam to fully cure and cool, and then installing the remaining thickness per the manufacturer’s instructions. This approach reduces the maximum heat exposure to the metal during installation. Excessive heat—potentially 150 degrees Fahrenheit or higher—can cause metal expansion, delamination from the foam, oil-canning, and distortion.
2. Substrate Preparation
In all cases (especially when applying SPF to metal), proper substrate preparation is essential. Spray foam insulation is designed to fully adhere to the substrate. Machine oils, dirt, dust, rust, and mill scale left from the metal fabrication process can significantly reduce adhesion. The Spray Polyurethane Foam Alliance has published several documents outlining required preparation methods for various substrates, including metal.
Any areas of delamination must be removed and replaced with fresh foam. In cold-weather applications, it is recommended to apply an initial one-inch pass before installing full-thickness passes. This helps stabilize the metal substrate and reduces stress caused by applying thicker foam layers to cold surfaces.
In retrofit applications, substrate preparation often includes mechanical abrasion and the application of a primer to enhance bond strength between the foam and the metal.
In some new construction and retrofit situations, a bond break, such as Tyvek or another membrane, is installed or requested between the metal cladding and spray foam insulation. However, according to SPFA Technical Document 134, “Spray Polyurethane Foam for Metal Buildings,” unstable substrates such as membranes must be removed, and SPF must be applied directly to the metal cladding. In roof applications, vinyl liner insulation systems must also be removed prior to SPF installation. Any material that reduces adhesion between the foam and metal substrate is unsuitable for SPF applications.
Contractors and applicators are advised to perform pull-adhesion tests whenever foam adhesion is in question. The Air Barrier Association of America (T0002) and the Canadian installation standard CAN/ULC S705.2 provide specific methods and equipment requirements for verifying acceptable adhesion.
3. Framing and Transitions
Metal buildings can be framed in many ways—gable, clear-span, or multi-span—using purlins, eave struts, wall girts, wind straps, tension wires, and a wide range of girt and base plate layouts. Additional variables may include insulated or uninsulated slabs, radiant heating systems, and radon barriers. The range of options is extensive.
Spray foam contractors must ensure that the insulation system addresses air leakage, thermal performance, and code requirements for thermal or ignition barriers between the SPF and the occupied space.
Air leakage leads to increased energy costs, higher condensation risk, cold spots, and poor indoor air quality. Metal buildings are inherently leaky, and SPF is particularly effective at sealing gaps in structural components, fastener penetrations, and poorly fitted joints.
Contractors must also be aware of the cladding system, structural framing, and roof design in both retrofit and new construction projects. Certain roof systems, such as standing seam roofs, are designed to allow metal panels to move in response to temperature changes. Applying closed-cell spray foam may restrict this movement and could affect building or roof warranties. It is strongly recommended that contractors consult with the building manufacturer, builder, or owner regarding warranty provisions before installing ccSPF. The Metal Construction Association has published research outlining considerations related to the use of spray foam insulation in metal buildings.
Metal buildings may appear simple (posts, metal cladding, concrete floors, and a metal roof) but achieving proper building science performance can be more complex than it first appears. Spray foam insulation offers significant advantages over more conventional materials, but like all systems, it must be installed correctly to perform as intended. Education, understanding, and communication remain the cornerstones of a successful project.
References
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SPFA Technical Document 134 – sprayfoam.org
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Building Enclosure magazine, February 2024 Article
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Metal Construction Association, September 2023: “Spray Polyurethane Foam Insulation on Interior Surfaces of Metal Panels” – metalconstruction.org
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Polyurethane Continuing Education Campus – polyurethane-education.thinkific.com
