Installing Vapor Barrier Under Metal Roof

As long as the plywood under the shingle roof is in good condition this way can provide many benefits.

Installing vapor barrier under metal roof.

Underlayment must also act as a secondary weather barrier in case the roof fails. I am planning to install a 29 ga metal roof on my new 2 story garage office. The best underlayment for metal roofs. 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.

We recommend a polypropylene scrim reinforced underlayment made up of multiple layers. Metal roofs must be laid flat on a vapor barrier because steel will condensate if there s any air space underneath it. It doesn t matter if the air space is a half inch or six inches because the condensation factor will remain the same. I am installing it on 2 x4 sleepers at 16 o c.

Once again this is used on cold roof construction. Therefore one will often see it installed directly on a roof deck such as a concrete or wood deck or on a continuous substrate such as gypsum board or wood panels that is installed directly over a metal deck. The first goal of roofing underlayment is to keep the roof deck dry before installation of the metal roofing material. Most metal roof companies recommend installing felt paper on roof sheathing before you install the metal roofing.

Make sure the product is designed to be used under metal. The cavity under the sleepers is 9 1 4 and it will be insulated and finished with wallboard. It serves as a moisture barrier as well as a slip sheet. 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.

The asphalt in the felt paper is waterproof and does a great job of protecting the. In a low slope roof assembly the vapor retarder is normally installed under the primary roof insulation. This type of underlayment is critical to a quality roof installation. What type of vapor barrier should i use unser the roof above the sleepers.

Put the steel down directly on a vapor barrier.