Insulating/finishing garage

audio1der · 07-15-04, 10:56

I'm ok for daoing the walls- have all the elec. outlets, speaker locations and cable oultet planned.
But I may use at least some portion of the rafter area for storage of large lighter items like my factory exhaust system, etc.
Is it okay to insulate & poly the underside of the roof, rather than the normal rafters, deleting that pocket of air?
It is an attached, unheated garage for now. I would like to heat it in the future- but that may be a very distant dream. I could easily insulate & poly the rafters when I do decide to heat it- right?
All thoughts appreciated.
Audio

Scott P · 07-15-04, 12:44

If you are installing a ceiling, you can insulate between ceiling joists and still offer space on top of the joists for storage. Insulating teh underside of the roof (rafters) is easy enough. As long as you use spacers to keep the insulation off the direct underside of roof sheathing. The R-Value would be based on how deep those rafters were.

If you insulate above the joists, you can add more insulation. more heat escapes upwards than outwards.

audio1der · 07-15-04, 03:11

Thanks!
So that "air pocket" normally found between the ceiling (rafter joists) and ceiling joists isn't important, as part of the insulation process?
(this was my main concern)

txz28 · 07-15-04, 03:48

The air pocket is important. I do not remember why. Scott P said that you need to use the spacers in this area. These are formed polystyrene foam channels that keep the insulation away and provide an air space between the roof and insulation.

fiberrich · 07-15-04, 04:20

If your garage has gable and/or roof vents, I'm not sure how much putting insulation on the underside of the roof is going to help in retaining heat in winter (it will just go out the gable vents) or keep the garage cool in the summer (you may get heat escaping through the gable vents, but not the roof vents if your blocking them).

I think if your goal for insulating is to keep heat in your garage during cold weather. It would be better to install the insulation in the ceiling joists.

Lost Pup · 07-15-04, 04:32

The air space is critical. The sheathing of the roof must be permitted to breathe.

joeychgo · 08-03-04, 12:24

Quote:

Originally posted by txz28
The air pocket is important. I do not remember why. Scott P said that you need to use the spacers in this area. These are formed polystyrene foam channels that keep the insulation away and provide an air space between the roof and insulation.

Moisture is the reason. COndensation can forum is there is no air flow and that moisture can rot the insulation.

They make a styrofoam channel that is secured to the roof sheathing, and then your fiberglas insulation goes over that, then a vapor barrier, and whatever your finishing with (drywall, etc)

blackcaraddict · 08-03-04, 12:44

Ridge vents--all roofs SHOULD have them.

joeychgo · 08-03-04, 12:46

Exactly. The channels I spoke about connect the soffit to the ridge vent allowing air to flow along the inside of the sheathing.

Redcar GUY · 08-04-04, 06:02

all good posts in this thread! I insulated between the rafters and I do have the little vents that let the air from the sofit go up to the peak. Mine are called duravents..