Can I use spray foam insulation directly on the underside of metal roofing with open decking?

Yes. Spray foam insulation can be applied to metal panels on open decking systems after the metal panels are installed, provided the following care is taken:

• Thermal spacers must be used on all metal purlins/framing to prevent rust or uneven color.
• All panels are properly installed and fastened securely
• No overspray of foam insulation gets onto the top side of the panels
• Spray is uniformly applied: non-uniform applications can cause thermal shock and loosening of fasteners, or potentially create uneven color.
• Insulation should be pH neutral (non-acidic and non-alkali) to avoid corrosion of metal panels.
• All structures and conditions comply with prevailing building codes.
• All proper surface preparation and application procedures are followed per manufacturer guidelines and per SPFA-134 linked here.
• If possible, apply foam in an inconspicuous area to check adhesion before applying to the entire job.

The Spray Polyurethane Foam Alliance, an association representing leaders in the SPF industry, has created a guideline for insulating metal buildings with spray polyurethane foam. It can be reviewed by clicking here. More information is available on their website at www.sprayfoam.org.