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Old 12-08-2012, 01:15 PM   #1
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Insulating Detached Garage Workshop

Greetings all. First time posting and relatively new woodworker.

We have recently moved into a home with a 25x30 detached garage in back. As a woodworker, I am in hog heaven except for one thing I can only manage to work in there a few hours a day if at all - even in our moderate climate (upstate SC). It has 9 ft. walls and a fairly high roof 5/12 pitch I think) and is totally uninsulated. It has ridge vents and soffett vents, and I can literally feel the air blowing through when it gets windy outside. It is a bit underengineered with only 2x4 rafters and wall studs, but feels sturdy. The previous owner had laid down plywood over the middle of the ceiling joists, but otherwise the ceiling is open. I would like to keep it that way, because it makes for great storgage which I really need.

I only have a budget of about $1,000 to insulate it. I don't want to live in it, just extend the hours I can work in it with only portable heat sources and a window A/C in the summer. I was thinking along the lines of foil faced foam board nailed to the bottom of the roof rafters (foil facing up) and glued to the inside of the garage doors (facing in), reflective tape to seal the joints in the foamboard, faced fiberglass in the walls, and caulk and Great Stuff to plug other air leaks.

Please let me know if this would be a viable option that would make sense, not cost much, but actually keep the workshop warmer in the winter and cooler in the summer.

Along those lines, I have read about double foil faced polyiso foamboards like Thermax, but haven't found any place that sells them locally and don't know how much they cost. Any suggestions??



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Old 12-08-2012, 01:49 PM   #2
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If the ceiling rafters are only 2 X 4's then you should not be storing anything up there. Anything above that ceiling is just wasted heat and cooling.
By just adding sheetrock to the ceiling even before the insulation went in you would feel a huge differance.


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Old 12-08-2012, 03:35 PM   #3
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Yeah, I've considered that but i really like the extra storage. I'm not storing anything heavy - mostly boxes and bins of household stuff, some PVC, closet doors. etc. In fact, I suspect the sheetrock would be heavier than what I have stored up there.

I guess I could take down all the plywood and make some shelves and dividers to separate my woodworking area from a paint room, office, and yard and garden equipment storage.

But assuming I take that route, what if I put up double foil foam board instead of sheetrock. It's a lot lighter and easier to work with and I think it would provide better insulation than sheetrock. Plus, the reflective foil would keep out a lot of radiant heat in the summer. I don't think single foil foamboard would be safe because no fire barrier on the underside. Again, any idea how to get Thermax or equivalent and how much it costs?
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Old 12-11-2012, 01:11 PM   #4
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I did something similar to my old house in the garage. I took some old 1 1/2" Extruded Polystyrene from a reroof we did and screwed it up to the rafters. I left a area about 3' wide running the width of the garage so I could access the storage up there. Basically just laid in the sheets on top in that area. I didn't bother sealing any of the other air gaps up top or anything, and If I needed ventilation I would remove one of the pieces of insulation that was lose. I bought some screws and plates from work to install it and used about 6 per 4x8. You might think about talking to the local commercial roofers in the area to see if they have any used Extruded they will sell cheap. Also if you have a used building materials recycling center that sells used building materials try there.
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foamboard , insulation , polyiso , workshop

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