Putting Up A Moisture Barrier Metal Roof

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Putting up a moisture barrier metal roof.

Metal roof over shingles condensation. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. If you choose to omit the plywood from a residential construction install a vapor barrier between the purlins and the metal roof or plan to spray closed cell foam insulation between the rafters to eliminate the temperature differential between the air in the building and the metal. Some people think that they can just install the metal roofing right over the old shingles roof without any barrier in between but this is highly not recommended.

Metal roofs must be laid flat on a vapor barrier because steel will condensate if there s any air space underneath it. When exposed to moisture metal components can oxidize and weaken decreasing the life of your customer s building. Corrosion of metal components even on surface treated 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.

It s also a good idea to discuss the options with your roofing contractor because they will be able to check the type of shingles your roof has and advise on the suitability of leaving the shingles in place or removing them. Put the steel down directly on a vapor barrier. Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. 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.

Whether or not you need a vapor retarder hinges on three main factors your climate your home and the location of the wall you re insulating. But a preinstalled membrane may be even more effective at removing condensation. Single bubble vapor barrier is a bubble wrap type material that is faced with reflective foil on the upper side and white vinyl on the inside. It blocks condensation from dripping into a pole barn and runs it out of the eaves as well as adding a slight r value to the roof and also.

It doesn t matter if the air space is a half inch or six inches because the condensation factor will remain the same. Single bubble vapor barrier and 2. In metal buildings there are a few possible consequences of trapped moisture in wall and roof systems.