Do I Need Vapor Barrier In Garage Ceiling

Whether or not you need a vapor retarder hinges on three main factors.

Do i need vapor barrier in garage ceiling. The traditional way to insulate the walls and ceiling of a typical garage is to install fibreglass batt insulation in the walls and attic space followed by a six mil poly air vapour barrier and drywall. You can see a couple pictures of the garage and rafters here. Unless you have converted your garage into a kitchen a bathroom a laundry room or a space that generates a lot of moisture even for that a dehumidifier can absorb all the moisture in the garage to keep the air dry. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

This will help to exhaust the water vapor that will collect. This is normally done because it s the most cost effective method to achieve the desired level of comfort and ease of installation. Hence the need to reduce moisture flow into the attic and the need for a vapor barrier. Because you do not want to add a vapour barrier over the spray foamed area all you need to do is install one in the area that you did yourself.

Between the two air leakage moves far more moisture than vapor diffusion. First of all a garage is not a signicant source of vapor as it is not occupied that much and you don t cook or bath in in it. A vented attic in a moderately cold climate or mixed climate. The space that will become the attic is vented via wall vents under the peak of the roof on both sides of the garage.

And again do i need a vapor barrier. There should be a continuous ridge and soffit ventilation. So poly the walls and ceiling and seal everything up well. Vapor moves in two ways by diffusion through materials and by air leakage through gaps and holes in building assemblies.

Understand that this is a climate specific recommendation. So you don t need a vapor barrier in the garage ceiling. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. Not every wall does.

Having said that i do not have a problem with relieving some of the moisture load in the house via diffusion hence a vapor retarder in a ceiling rather than a vapor barrier through a roof assembly that can handle it i e. There s one other important qualification. If you are going the extra mile to insulate your garage ceiling try to stay away from faced insulation. Where the poly meets the spray foam at a.