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How To Insulate An Attached Garage

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Insulating an attached garage has some special considerations that you must address differently then a unattached garage. The most important issue is that attached garages must have a system in place, to keep carbon monoxide (CO2) from a running vehicle inside the garage ,from filtering through the walls and ceiling into the house. This is a building code violation and a huge safety risk to you and your family! The second consideration is that you want the rooms in your home that are above or around the garage that are sharing common walls or floor/ceilings to be warm.

My first choice to insulate an attached garage is to use a closed cell spray foam. Now I know most of you reading this are D.I.Y.ers and as such want to do these projects yourself but sometimes calling in the pros is the way to go. I realize that getting someone in to spray foam can be costly up front but the payoff comes in the fact that the spray foam takes care of CO2 and cold rooms very very well. To help reduce the overall cost you may consider having only the wall and ceiling areas that are shared by the garage and house spray foamed and then insulating the rest of the garage with traditional bat style insulation and blown-in insulation.

So let's say that this is what you have decided to do. As far as the spray foam goes have the professionals come in and do their thing. I would also have them spray any heating or air conditioning ducts that are exposed in the same areas that they are doing. Now once they are gone you can insulate the remaining wall and ceiling areas on your own. See INSULATING WALLS article and INSULATING CEILINGS article.

Installing the vapour barrier in this type of insulated garage is a little different then normal. 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. See INSTALLING VAPOUR BARRIER

Tip: Because the closed cell spray foam acts as a vapour barrier if you cover it again with the poly vapour barrier you will have condensation troubles between the two materials. This is because no matter how warm you keep you garage when that overhead door opens you fill the garage with cold moist air and this will build up as condensation between the poly and the spray foam.

So poly the walls and ceiling and seal everything up well. Where the poly meets the spray foam at a framing member seal the poly to the framing member as close to the spray foam as possible with acoustical caulking.

Now that the poly and insulating is complete, you must drywall the inside of the garage, well at least you must cover the spray foamed areas. Unless you used a fireproof spray foam, you must protect it by code from fire because when it burns it gives off deadly gases. Most government codes allow you to use 1/2" drywall.

Tip: Always check with you local officials on the building codes for your area before starting your projects.

So I would use 1/2" mold / moisture resistant drywall because usually your garage is pretty humid in the winter especially now that it will be insulated and polyed. You also will have to at least "fire tape" (apply one coat of mud and tape) all the joints.

You can also use fiberglass batt insulation in place of the spray foam but in the case of attached garages with a "bonus " room above them I would always use spray foam. Most all of the people that have a newer home with the bonus room above the garage and complain of those rooms being to cold is because they are not done with spray foam!

So hopefully this article gives you some insight and hints on properly insulating your attached garage. Good luck.