Installing Vapor Barrier Under Metal Roof

It doesn t matter if the air space is a half inch or six inches because the condensation factor will remain the same.

Installing vapor barrier under metal roof.

Traditionally metal roofs have used standard 30 pound felt paper underlayment. This is by far the most common way to install a metal roof. 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.

We recommend a polypropylene scrim reinforced underlayment made up of multiple layers. 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. What type of vapor barrier should i use unser the roof above the sleepers. Metal roofs must be laid flat on a vapor barrier because steel will condensate if there s any air space underneath it.

Most metal roof companies recommend installing felt paper on roof sheathing before you install the metal roofing. Once again this is used on cold roof construction. In a low slope roof assembly the vapor retarder is normally installed under the primary roof insulation. The asphalt in the felt paper is waterproof and does a great job of protecting the.

Underlayment must also act as a secondary weather barrier in case the roof fails. 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. I am planning to install a 29 ga metal roof on my new 2 story garage office. Put the steel down directly on a vapor barrier.

The cavity under the sleepers is 9 1 4 and it will be insulated and finished with wallboard. 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. Make sure the product is designed to be used under metal. As long as the plywood under the shingle roof is in good condition this way can provide many benefits.

This type of underlayment is critical to a quality roof installation.