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.

Do i need vapor barrier in garage ceiling.

Between the two air leakage moves far more moisture than vapor diffusion. There s one other important qualification. You can see a couple pictures of the garage and rafters here. Where the poly meets the spray foam at a.

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

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. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. And the ceiling acts as a enough of a vapor retarder.

This will help to exhaust the water vapor that will collect. Understand that this is a climate specific recommendation. So you don t need a vapor barrier in the garage ceiling. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

Installing the vapour barrier in this type of insulated garage is a little different then normal. Without making sure of these components you could end up with a mold and mildew mess. 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. The space that will become the attic is vented via wall vents under the peak of the roof on both sides of the garage.

If you are going the extra mile to insulate your garage ceiling try to stay away from faced insulation. A vented attic in a moderately cold climate or mixed climate. 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. And again do i need a vapor barrier.