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Bigbartguy

Insulating a garage? insulation experts?

11 posts in this topic

hi folks

I've got an uninsulated garage that I'd like to insulate. It was already drywalled and taped (argh). I've blown insulation in the attic but need to insulate the walls.

I know some folks that have had insulation blown in between the studs (drilling holes in drywall) but am concerned about no vapor barrier? is this ok? Will my garage rot from the moisture accumulation?

my other option is to yank all the drywall off and install vapor barrier/proper insulation, which is probably the 'right' way to go but would prefer not to

thanks!

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Was there a vapor barrier in the ceiling or did you add one there? Will the garage be heated all year around? If you are only heating it occasionaly you may be ok.

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There is a spray foam insulation that you can out in finished walls that will get you a vapor barrier as well as a quality insulation. I do not know much more about it, but my Dad was looking to do it to his house since it is older and needs insulation. The way I understand it, they drop the hose down the stud cavity, and slowly pull it out as they fill the cavity.

I have no idea about costs, but it beats tearing out finished walls.

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Have you thought about how often you're going to heat it, what it would cost to just heat it the way it is on the rare occasion you need to use it in the winter, or are you going to use it enough to make the possible 2Gs it will cost to heat and insulate worthwhile? Just a few questions I've been struggling with. Bored in January and wishing the garage could be made comfortable to work in but then realized that making blue bird houses really wasn't worth the cost of the furnace and the spray foam. My quote on the spray foam was about $2.10 a sq foot for R14 but that was on totally unfinished surface.

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re: vapor barrier in attic. No, that would require me actually thinking, which is kinda rare. :-) I'm considering dropping the drywall and letting the insulation 'fly' and reblowing it in after proper vapor barrier installed.

Spray foam at $2.10 sq ft? I'd yank the drywall before I paid that. My drywall is just taped w/ 1 coat of mud.

I heat it up maybe 1-2x per week in the winter. Usually when the neighbor guys and I want to hang out and drink beer for an evening.....garage logic.

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For a couple weeks a year I would leave it just the way it is and spend a little more on fuel. You have the ceiling insulated which is where most heat loss is. Your dead air space will slow heat loss a quite a bit. Give it a try I think you would be suprised how easy it would heat. If you wan't to heat it all the time then tear down and do it right. My garage is well insulated with floor heat, I keep it 50-60 degrees all winter and it doesn't cost much to heat and I love that.

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i think you will be ok for a long time but the fiberglass will rot away the celling and wall in time,the celling you can brush the inus.to one side and put poly between the truss the move to other side and do same thing this will save you one re donig the celling

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Drill the holes (2)to blow the walls. One for material and one for air to escape during filling. (rectangular, easier to patch)

Blow the stud cavitys full.

Use a speedpatch on the drywall holes.

Finish the drywall to desired level of finish.

Paint the walls with vapor resistant paint.

("Vapor barrier" paints are also an effective option for colder climates. If the perm rating of the paint is not indicated on the label, find the paint formula. The paint formula usually indicates the percent of pigment. To be a good vapor diffusion retarder, it should consist of a relatively high percent of solids and thickness in application. Glossy paints are generally more effective vapor diffusion retarders than flat paints, and acrylic paints are generally better than latex paints. When in doubt, apply more coats of paint. It's best to use paint labeled as a vapor diffusion retarder and follow the directions for applying it.)

Dont worry too much about vapor transfer, as one electrical outlet in the wall will carry more moisture into the stud cavity that the rest of the whole surface of that wall.

You would be way better off if you used airtight electrcal boxes in the wall, rather than worrying about the diffusion rating of the whole wall.

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If you control the air flow you will limit the moisture in the wall. Seal up around all potential air leak sources. Seal with silicone caulk, expanding foam, duct mastic around outlets, switches or wherever the drywall has an opening. An overlooked area is along the bottom of the drywall. Paint is actually a good vapor barrier. Do not leave unpainted drywall.

Use a dense pack cellulose insulation. To keep cost down you can rent a machine and do it yourself. Dense pack will do a better job of controling airflow than fiberglass.

How does water vapor become a problem in a wall system? It requires an air flow to transport to the vapor. Then when the vapor reaches a surface at the right temp you get condensation thus water. How much air does it take to carry enough vapor to be a problem, quite a bit, a steady air leak. It you air seal and then use an insultaion that controls air flow you will not have the vapor source for condensation. How else can water get into the wall - water not vapor from the outside. If you have water problems because of a bad drainage plane then you have bigger problems.

Same thing will apply to the cieling. Seal all potential air leaks. That means around all ceiling light fixtures, outlets, etc.

Fiberglass does not control air flow. If it is not in a 6 sided (4 sides top and bottom)enclosure then there is no way to control the air flow. If you already have fiberglass in the cieling then I would air seal and blow cellulose over fiberglass as cellulose does a much better job of trapping air.

One last thing to think about and consider are what are the moisture sources. In a garage there will be few sources of water from people, showers, cooking, humidifiers etc. The indoor humidity level will be close to the outdoor level which in winter is low. So unless your are doing something the spews a lot of moisture then the garage will have a lower potential for moisture problems then the house.

I should say dont use an unvented combustion heat sources as that will introduce a very heavy vapor load.

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Just Fishing - thanks for the very informative post! I already have cellulose in the ceiling, so sealing up my 2 ceiling outlets and painting the ceiling would be the best way to prevent roof moisture?

I may pull the wall drywall to add more wiring anyway, so I may put proper barrier in the walls

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