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Red Squirrel 04-18-2010 07:37 PM

Insulating garage / adding attic
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Right now my garage ceiling is just open with the rafters/trusses and is not insulated. If I add an attic, it will be only like 4 foot high at the top-most part. Can I just totally pack that with insulation and not have an attic, and not worry about ventilation? Or would I still need to leave space for ventilation and add a venmar vent on top?

I'm also debating on just leaving it open, but adding insulation against the roof itself like one would do with a catedral ceiling. The pro here is I can still use the rafters to store 2x4's and stuff, the con is that it would take longer to heat the garage. I would only heat it when I actually want to go in it.

I don't think I'll even do this project this year, but just thinking about what the best plan is. I eventually want to fully insulate it, and run a sub panel and add some source of heat and basically turn it to a shop where I can even go work in during the winter and still feel comfortable. I might have to do something about that leaky garage door though, it lets snow in. :P

The garage is attached to the house and separated by a block wall. The house attic is not accessible from the garage as the brick wall goes right to the top.


beerdog 04-18-2010 11:23 PM

If you close it up you have to ventilate or you could have major problems in the future with mold and roof damage. Easiest way would be to add blow-in insulation, a ridge vent, and proper intake vents.

Red Squirrel 04-19-2010 04:58 PM

Hmm figured, so even if I pack it to the top with insulation right? If I go with the open concept ceiling, how does ventilation work in that case? Would I basically just build another slopped ceiling, then insulate that so there's a pocket of air between that, and outside?

Upon further research think I see how I'd have to do it:

Given the joists don't all meet at the center, I can't just cover them all with foam or something as some of the sections would not be ventilated, so I'll have to work around that, but I have a few ideas in mind. I'm thinking I could add small "blocks" of 2x2 pieces on the existing joists, but they would be spaced. I could then nail foam on them to create a 2nd ceiling space that meets with the wall. I would add a venmar vent at the peak of the roof. This would allow air to go through the overhang venting, between the rafters and foam insulation, and to the venmar vent.

I would then build another ceiling over the foam, and add fiberglass insulation, or I suppose I could just make it a flat ceiling and pack it with insulation then. Does this sound ok?

beerdog 04-19-2010 05:07 PM

You never pack insulation to the top. I also notice that the roof is only sloped on one side. I forget the roof term for it. You never want the insulation against the roof sheats. The plywwod has to be allowed to breath. It would be kind of difficult to insulate it without putting in a cieling. You could possibly run baffles all the way up to the top, then add batting, and then a cieling. but that would be a lott of work and would give you very little insulating R-value. i think your best bet is the following

Close it up
- Add a cieling
-add intake ventilation
-ridge vent or power vent
-add roof ventilating baffles
-blow-in to the insulating value recomended for you area which would be maxed out at like 50

Leave it open
-intake vent
-power vent or ridge vent

It will be interesting to see what any of the pros on hear suggest.

Red Squirrel 04-19-2010 07:33 PM

Good to know about the insulation. I figured it would be ok to do, but that's why I check, before I assume. ;)

What I will most likely do then is just treat it like an attic and make a normal flat ceiling. Probably the easiest way.

Also anything wrong with doubling the walls? What I mean by that is I would insulate the existing wall stud spaces, but add another wall right over, then add more insulation, then vapor barrier, then drywall. I'd do all the electrical in the 2nd wall. It would most likely be "bonded" to the existing wall. The ceiling would rest on this wall too, so it would become a load bearing wall. I'd lose a bit of space but think it would be worth it for the extra R value. This garage has a crawlspace under it, by using the floor as the support for these new walls should not really be a significant load increase right? Considering it can hold a car. I'd also make a single wall on the side where the blocks are. Don't really need to insulate given it's the house side, but the wall would be needed to hold the ceiling as those few joists going into the brick arn't really enough to take all the load. I'd also add an attic hatch near the chimney (not in use) in case I need to access the small attic space.

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