How to Insulate Metal Roofs

Posted on: 27 March 2017

If you have a metal roof, or you plan to install one, it should be insulated properly. Metal is becoming a popular choice for commercial and residential roofs because of its durability and low maintenance.

The only con of metal roofs is they insulate poorly, which translates into higher cooling and heating. Insulation also helps muffle typical roof noises. Here are tips to insulate a metal roof.

Gather Supplies

For this project, you need:

  • work gloves
  • safety glasses
  • duct tape
  • utility knife
  • paint roller
  • wood screws or staples
  • industrial grade building paper
  • plywood sheathings
  • drill
  • rigid foam insulation
  • spray foam insulation
  • fiberglass batting
  • elastomeric roof coating

When you look for insulation, it helps to understand R-value. The R-value measures how well the insulation reflects heat or cold. A higher R-rating means the better it insulates.

Lay the Sheathing and Paper

Staple or screw in the plywood sheathing at right angles, so it is perpendicular with the roof joints. Nails damage the roofing. Staples and screws are much easier to remove for repairs.

For an existing roof, examine it for plywood sheathing and little framing crosswise pieces called purlins. If there is already sheathing, skip this step.

Staple the paper down over the board. Many homeowners skip this step, but it is essential to prevent leaks. Overlap each piece by six inches.

Install the Insulation

Pack the foam batting in between sheathing gaps and panels. For an existing roof, stuff the batting into gaps you notice between the sheathing and joists. Don't stuff the batting too tightly, or it won't be as effective.

Cover wider panels with rigid foam board insulation. Staple or screw them down; trimming them to fit with a utility knife.

Don't overlap the foam boards. Seal seams with duct tape to stop leaks. 

Apply Spray Foam

Spray foam insulation can be bought from home improvement centers or hardware stores. Drill a small opening in the roof in the ceiling to access the framing. 

Do not use spray foam insulation without the sheathing on the roof. Install the sheathing. Spray the insulation in the hole. The foam should expand to fit the shape of the roof structure. Patch the hole you cut.

It is wise to apply a layer of roof coating with a paint roller for extra sealing. If you don't trust your skills, or the roof is seriously damaged, consider hiring a contractor. Check out sites like to see contractors in your area.