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detached garage - insulating the rafters?


aconti's Avatar
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09-30-09, 05:26 AM   #1  
detached garage - insulating the rafters?

What can I use to insulate the roof of my north eastern PA single car detached garage? There are no ceiling joists. I would like to insulate over or between the rafters if possible since I use the space below for hanging storage. Thanks.

 
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09-30-09, 07:59 AM   #2  
A garage can have a real moisture issue when used for cars, summer or winter, but winter is the worst. Loaded with snow, that water needs a way to runn off and evaporate. Without good ventillation, most of that water will be transferred from your floor to the walls and ceiling surface and into the cavities where air leaks exist.

Think of the space like a bathroom with a heavily used shower. The recommendation is to have an exhaust fan running until all of the moisture is gone.

Now, if you don't use it for cars with water or snow, then your options are insulate and sheetrock with enough space above the insulation to vent out the ridge. Assuming ridge and soffit vents. Or, if no venting is needed, just the insulation and covering. I prefer the venting approach.

Bud

 
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09-30-09, 11:47 AM   #3  
Thanks for the response.

I will be using the garage as a workshop (my truck doesn't fit anyway ). The walls are insulated and I installed an insulated gargage door now just have to do the roof. It has a ridge vent but no soffit vents. Do you know how much space is needed between the insulation and the roof to allow for enough ventilation to the ridge vent? Also do you know of anything out there that could be blown onto the rafters and onto the underside of the roof?

I was planning on heating the area with a small propane heater since the space is so small it wouldn't take much to warm up.

tks!

 
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09-30-09, 12:40 PM   #4  
They have DIY spray foam kits ($$$), but something should be used as a fire rated covering, check local codes. 1/2" sheetrock is the most common although I am reading up on some new spray coatings that are supposed to meet fire codes.

You can sheetrock the lower surface and blow in cellulose or fiberglass to fill the cavity.

Besides the normal caution about combustion gasses from the propane heater, one of the by products is a ton of water. I've had water dripping from the nails in the ceiling. Vented heaters are best.

You generally want at least one inch above the insulation if you go that route. One option would be to strap each side of the rafters up against the roof deck with the one inch spacer, apply 1/2" or 1" pink or blue rigid foam, then fill with fiberglass and cover with sheetrock. Pink or blue without any plastic or foil covering will breathe to dry out any moisture that gets in. Of course you would need soffit venting to match the ridge venting.

Bud

 
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10-02-09, 05:16 AM   #5  
I checked out the spary foam kits and your are correct about the ($$$). May be too much for my budget. I will most likely go with sheetrock, foam board and filler. Gotta get going soon since the temps dropping fast. Thanks.

 
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10-02-09, 06:55 AM   #6  
Remember, the can foam does not like the cold. If you will be using a lot of can foam, consider the pro gun. It's not that it will cost less, but the control is great, from a small bead to a generous fill. And when you set it aside, you can come back days later and it still works. Just leave a can on it at all times.

Bud

 
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