Vapor Barrier On Roof Deck

But a preinstalled membrane may be even more effective at removing condensation.

Vapor barrier on roof deck.

The roof membrane on the top is clearly a vapor barrier. Another option for the roofing system is to recognize a hardboard or sheathing layer can be a vapor open air barrier. The bottom membrane s primary function is that of an air barrier but it s material. In a low slope roof assembly the vapor retarder is normally installed under the primary roof insulation.

The midwest roofing contractors association mrca is advising a vapor retarder of less than 0 01 perm is necessary over new concrete roof decks. In fact it is almost a perfect vapor barrier. This can be a problem where brick is installed over building paper and vapor permeable sheathing. Concrete contains a significant amount of moisture and there is no test to.

We ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. It is therefore suitable for most roofs. Roofs over concrete decks should always have a vapor barrier installed. The caveat is that the vapor retarder needs to be sealed at all perimeters and penetrations and tied to the wall air barrier so air does not bypass the vapor retarder layer.

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. A gypsum fiber board has a perm rating of approximately 24 to 30 perms depending on thickness and if this board is fastened to a steel deck and the joints and transitions are taped it could be an effective air barrier that allows some drying. That means that when we use a vapor retarder in a roof system it s also acting as an air barrier. A vapor retarder is commonly installed on the warm interior side of a roof or wall.

This can be a problem in any air conditioned enclosure. The solid substrate for fluted metal decks is typically a gypsum underlayment and the concrete is the solid substrate for concrete decks. Resistant to foot traffic the engineered composition of v gard provides high resistance to static loading and dynamic impact. Like fully adhered insulation fully adhered vapor barriers need a solid substrate below.

Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. Most fully adhered vapor barriers are also air barriers and can serve as a temporary roof during construction. Classic compact flat roof the most famous double vapor barrier of them all. This can be a problem in any below grade space.

Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful. And the membrane on the bottom is also a vapor barrier. V gard provides an excellent vapor barrier with a vapor resistance value expressed by an sd equivalent air layer thickness of 1 500 m. Everyone knows that water in roof systems is never a positive.

This method is shown in the image above.