Installing Vapor Barrier Under Metal Roof

Once again this is used on cold roof construction.

Installing vapor barrier under metal roof.

In a low slope roof assembly the vapor retarder is normally installed under the primary roof insulation. I am planning to install a 29 ga metal roof on my new 2 story garage office. Metal roofs must be laid flat on a vapor barrier because steel will condensate if there s any air space underneath it. I am installing it on 2 x4 sleepers at 16 o c.

The first goal of roofing underlayment is to keep the roof deck dry before installation of the metal roofing material. It serves as a moisture barrier as well as a slip sheet. Traditionally metal roofs have used standard 30 pound felt paper underlayment. The cavity under the sleepers is 9 1 4 and it will be insulated and finished with wallboard.

As long as the plywood under the shingle roof is in good condition this way can provide many benefits. What type of vapor barrier should i use unser the roof above the sleepers. This type of underlayment is critical to a quality roof installation. Underlayment must also act as a secondary weather barrier in case the roof fails.

Put the steel down directly on a vapor barrier. Most metal roof companies recommend installing felt paper on roof sheathing before you install the metal roofing. We recommend a polypropylene scrim reinforced underlayment made up of multiple layers. Make sure the product is designed to be used under metal.

Several considerations must be addressed in the roofing system design including ensuring that the four barriers needed in any building enclosure i e water barrier thermal insulation barrier vapor retarder and air barrier are provided and are in the correct location for a given climate. 3 install 1x4 purlins down over the shingles before installing the metal roof the third way to install a metal roof over shingles is by applying 1x4 purlins over the shingle roof. Build your structure where possible in an elevated position with good natural drainage place a vapor retarder under floor gravel or concrete ventilate enclosed building when concrete is being poured and continue to ventilate until it is cured use heaters that are vented to the. It doesn t matter if the air space is a half inch or six inches because the condensation factor will remain the same.

This is by far the most common way to install a metal roof.