Best Vapor Barrier For Metal Roof

Will kraft faced 4 fiberglass insulation installed from the inside between the 5 1 2 wide trusses 12 on center be sufficient to inhibit condensation on the back of the metal roofing.

Best vapor barrier for metal roof.

The batts are located side to side on the rafter of the roof. Felt underlayment provides little resistance to air and moisture vapor migration and does not serve as an effective air barrier. The problem with using. Both materials make a great physical barrier between the interior building and the metal roof.

Architectural metal roofs with felt underlayment are best suited for buildings with proper slope and low moisture loads in dry or arid climates. However if a class i vapor retarder is used there is concern that any moisture e g construction moisture due to installation methods bulk water from weather etc that enters a roof system won t be able to dry out. A roof vapor barrier needs to have different properties to a barrier in a wall or one used to prevent radon permeating through a floor. Fiberglass batts or glass mineral wool metal roof insulation the most common material used for an insulating metal roof is fiberglass batts or glass mineral wool.

Most roofing membranes as well as a single layer self adhered bituminous sheets are class i vapor retarders. If a vapor barrier is installed correctly over the purlins no holes or seams can be present which covers all possibilities of climbing the roof via the purlin footholds. We ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point.

In this example although roofs and walls both need similar water vapor barrier properties the roof barrier often needs to be either inflexible or air permeable to prevent being blown away in an updraft caused in a storm. To prevent too much condensation from forming under your metal roof it s best. But a preinstalled membrane may be even more effective at removing condensation. Underlayment will help prevent this.