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Metal buildings present a different insulation challenge than a conventional wood-framed home. Large metal roof and wall panels can transfer heat quickly, have very little thermal resistance on their own, and can become extremely hot or cold depending on Outdoor conditions. Spray foam provides a continuous insulation and air-sealing layer directly against the building assembly, helping control heat flow and unwanted air movement.

Why Spray Foam Works So Well in Metal Buildings

Metal buildings often have large surfaces, seams, fasteners. penetrations, and irregular areas that make it difficult to create a continuous insulation and air barrier with traditional insulation. Spray foam adheres directly to the surface and expands around irregularities, helping create a continuous layer rather than leaving gaps around the building's many details.

• Creates a continuous insulation layer across large metal surfaces.
• Seals many of the gaps and irregular areas where uncontrolled air movement can occur.
• Reduces heat transfer through the roof and walls.
• Helps reduce the extreme temperature swings experienced by the interior side of metal panels.
• Can improve comfort in conditioned metal buildings.
• Can help reduce the heating and cooling load placed on the building.
• Can be installed in new construction as well as many existing metal structures.

Why ISO Recommends Closed-Cell Foam

For our metal-building applications, ISO recommends closed-cell spray foam rather than open-cell spray foam. The reason is not simply R-value. The moisture behavior of the complete metal assembly is a major consideration.

Closed-cell spray foam has substantially lower vapor permeability than open-cell foam. DOE Building America guidance identifies closed-cell foam as a vapor retarder, while open-cell foam is not a vapor retarder. That difference matters when foam is installed directly against metal roof or wall panels.

Metal can change temperature rapidly. When warm, moisture-laden air reaches a sufficiently cold metal surface, moisture can condense. Because open-cell foam is more vapor permeable, it allows more water vapor to move through the insulation toward the metal surface.

That is why ISO does not recommend spraying open-cell foam directly against metal roof panels in our

metal-building applications. The issue is the behavior of the entire roof assembly, not whether open-cell foam can physically adhere to metal.

Closed-cell foam provides a much more vapor-resistant layer directly at the metal assembly. Building Science guidance also recognizes closed-cell spray foam as an effective way to control airflow and reduce the potential for moist air to reach a roof surface where condensation could occur.

Heat Transfer Through Metal

A bare metal roof can become extremely hot under direct sunlight and can transfer that heat toward the interior of the building. In winter, the same assembly can rapidly lose heat to the outdoors. Without an effective thermal barrier, the interior temperature can closely follow the conditions of the metal shell.

Closed-cell spray foam creates a continuous high-R-value insulation layer that slows this heat transfer. In a conditioned metal building, that can make the interior environment significantly more stable and reduce the amount of work required from the HVAC system.

Air Sealing Matters

Insulation alone does not stop air movement. Metal buildings contain seams, penetrations, fasteners, transitions, and other potential pathways for uncontrolled air leakage. Spray foam can seal around many of these areas while simultaneously providing insulation.

A properly installed spray foam system helps bring the insulation layer and air barrier together. That is important because uncontrolled air movement can carry heat and moisture into the building assembly, reducing the effectiveness of the insulation and increasing the potential for moisture problems.

Roof and Wall Applications

Spray foam can be used on both roof and wall assemblies of metal buildings. The appropriate installation depends on the building design, the location of the thermal boundary, interior conditions, and the intended use of the space.

• Metal warehouse buildings
• Shops and workshops
• Agricultural and utility buildings
• Commercial metal buildings
• Conditioned storage facilities
• Existing metal structures being converted to conditioned space
• New metal-building construction

Existing Metal Buildings

Existing metal buildings can be difficult to retrofit because the original construction may have little or no insulation and may have been designed as an unconditioned space. Spray foam can create a new continuous insulation and air-sealing layer without requiring the entire metal shell to be rebuilt.

Before installation, ISO evaluates the existing assembly, roof condition, interior environment, and intended use of the building. Existing moisture or roof problems should be addressed before the insulation system is installed.

New Metal-Building Construction

New construction provides the opportunity to design the insulation and air barrier as part of the building envelope from the beginning. Spray foam can be incorporated into the roof and wall assembly so the insulation is continuous and the building envelope is properly detailed.

Moisture control is one of the most important reasons ISO takes a different approach with metal buildings. The temperature of a metal panel can change quickly, and interior humidity can create a vapor drive toward colder surfaces.

The goal is to control heat flow and air movement while also limiting the movement of moisture into locations where it can condense. Closed-cell foam's lower vapor permeability makes it better suited to this role than open-cell foam in our metal-building applications.

The Finished Building

A properly designed metal-building spray foam system can transform an otherwise difficult-to-condition structure into a much more comfortable and controllable environment. The insulation helps slow heat transfer, the foam helps control air movement, and the closed-cell structure provides additional vapor control.

The correct foam thickness and installation approach depend on the building's construction, climate, use, HVAC system, interior humidity, roof configuration, and finished assembly. ISO evaluates these factors before determining the appropriate spray foam system.

For metal buildings, our goal is not simply to put foam on the walls or roof. The goal is to build an insulation and air-sealing system that manages heat, air, and moisture as part of the entire building envelope. 

Contact Insulation Systems of Oklahoma for an evaluation of your metal building and a spray foam system designed for the application.

DOE Building America guidance identifies closed-cell spray foam as a vapor retarder and open-cell foam as vapor-permeable. Building Science guidance discusses closed-cell spray foam as a method for controlling airflow and moisture movement in roof assemblies.