Putting Up A Moisture Barrier Metal Roof

The problem with using insulation alone.

Putting up a moisture barrier metal roof. It will help you to eliminate problems that may come when the house becomes extremely cold in the winter and terribly hot in the summer. Make sure the product is designed to be used under metal. We ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. I plan on putting down 1 x 4 strapping on top of the shingles screwed to the joists and then screw the metal panels to the strapping.

When you install a metal roof over a finished living space in just about any place other than the atacama desert where it s not rained for decades water vapor can and will float up through. But a preinstalled membrane may be even more effective at removing condensation. It serves as a moisture barrier as well as a slip sheet. That reduction of air and moisture infiltration can then help improve roof longevity.

This is often accomplished using vinyl backed fiberglass insulation to prevent humid air from coming into contact with the cooler metal roof which may be at or below the dew point. In order to add moisture barrier under metal roof you can spray the undersides of the roof by using a thick layer of polyurethane spray foam. Once again this is used on cold roof construction. I have a 16 x 20 unheated with no insulation garage that has shingles on it.

Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. A roof design that includes an adhered roof membrane with multiple layers of insulation with board joints offset and staggered over a vapor retarder air barrier helps lower the risk that air and the moisture it carries will infiltrate the roof system. The problem with this is that as the metal heats up and expands or cools down and contracts it moves a little on the roof. Traditionally condensation is managed by insulating the metal roof so that the panel temperature never reaches the dew point.