garage shop insulation question

[Mike Gager]

i have a 24x28 garage i use for my workshop. it is currently uninsulated and has open studs and joists. the garage also has no venting in the gables, eaves, or on the roof itself and as you can probably imagine in the winter it gets to cold and summer too hot to work out there so i want to insulate so i can use heaters more effientantly and maybe get a window AC unit for summer

anyways my question is about the roof/ceiling insulation

should i put the insulation on the bottom of the roof along the rafters or should i build an "attic floor" and lay the insulation on it?

since the garage has no ceiling currently my thinking is if i go with the bottom of the roof installation i would save money by not having to buy ceiling/floor material and i would be able to keep my over head joist storage. i just didnt know if that was a good way to do it or not. any thoughts?

[Lee Koepke]

You can put insulation at the bottom of the rafters ( roof level ). Be aware of ventilation though, you need to have air flow, dont know what part of the country you were in, but if you dont ventilate, you could end up with condensation problems.

Personally, if you have adequate structural support for storage on the bottom chords, its hard to give that space up ...

[Dave Westover]

i have a 24x28 garage i use for my workshop. it is currently uninsulated and has open studs and joists. the garage also has no venting in the gables, eaves, or on the roof itself and as you can probably imagine in the winter it gets to cold and summer too hot to work out there so i want to insulate so i can use heaters more effientantly and maybe get a window AC unit for summer

anyways my question is about the roof/ceiling insulation

should i put the insulation on the bottom of the roof along the rafters or should i build an "attic floor" and lay the insulation on it?

since the garage has no ceiling currently my thinking is if i go with the bottom of the roof installation i would save money by not having to buy ceiling/floor material and i would be able to keep my over head joist storage. i just didnt know if that was a good way to do it or not. any thoughts?



I have/had the same situation. I came across some ceiling tiles to support the insulation. Works well and was inexpensive. Keep in mind that if you insulate the underside of the roof instead of installing a ceiling, you will increase the square footage of insulation needed depending on the pitch of the roof. But, you can avoid venting that way.

Venting will be needed however if you insulate the ceiling, thereby creating an attic space where the heat from the shop rises to meet the underside of your roof. I installed soffit vents only, but plan to add a gable vent once I upgrade the heating in the shop. No ice damming yet with 3 feet of snow, and accumulating.

I can still utilize the attic space for storage if I need to but havent yet. Not as handy as open rafters but I like the ceiling. Gives it a finished look with the T8 troffers I bought for lighting.

[Von Bickley]

Mike,

It would be nice to know where you are at. That will help in knowing how much insulation you need. Rule of thumb would probably be R15 in the walls and R30 overhead.
As mentioned earlier, you can get into trouble insulating the rafters if you don't have proper air flow. I would put R30 batts in the ceiling joist and put up some type of ceiling. It could be sheetrock, plywood, osb, etc.
I would also look at some type of gable vents, roof vents, or some type of venting system for the attic.

[Jeff Wright]

You could install closed-cell foam (available up to 2-inch thick) and put it between the joists. I'm told doing so would not require any ventilation. Or, you could have closed-cell foam sprayed into the cavities between the joists. Either way, it is not cheap.

[Mike Gager]

hey guys thanks for the responses. i am located in NE kansas

[Karl Brogger]

I'd put a ceiling up, and either blow in insulation, or spray foam it. That space should be vented somehow as well to keep the "attic" space cold in the winter.

[Ron Knapp]

I received a quote today for my garage which is 24 X 26 two story but I will only insulating one floor. Foam for the 1st floor ceiling and the walls is around 3K installed. Traditional around 1.4k installed

[Ben Franz]

Paper faced fiberglass is supposed to be covered by drywall to avoid having a flammable material exposed. Also, by itself, there is too much convection flow through FG batts which drastically reduces performance.

[Mike Gager]

ben, would radiant barrier foil be a better choice? it is supposed to stop convention loses

[Jim O'Dell]

I'm not sure I understand.. are you saying that you have no ventilation in the attic of your house? Or is this a detached garage? If it is detached, then I think you will want some form of ventilation no matter what you do. My detached shop did not have any type of ventilation either. I cut and put on a ridge vent system. Not too expensive and is low profile. Mine is the colored metal type, but there is the black plastic that you put shingles on top of so it really disappears into the roof. Then I cut in some continuous vents in the roof overhang. You can do individual as ones as well. Our house has the individual 4 X 8 IIRC in every other bay, with 4 turbines (2520 sq ft plus garage). You could probably cut in one turbine for the shop. But if you close it in with insulation, you will need the ventilation. And make sure there is an opening to the overhang to the attic space, or the air still won't get through. Don't pile blown in insulation up against this area. Or since you don't have a ceiling in place yet, get some of the formed chutes made just for this. That's what I did. Still need to insulate the ceiling, though. :rolleyes: Jim.

[Mike Gager]

yes its a detached garage, sorry if that wasnt clear

[Joe Chritz]

You won't find better (or more expensive) insulation then spray foam. However, for an attic I always use blow cellulose since it is an easy do it yourself project.

Hang some drywall or OSB and have at it.

Joe

[Maurice Ungaro]

The spray foam you want is called Icynene. It is the bomb.
I have it throughout my house and garage/shop.

http://www.icynene.com/

[Mike Gager]

the foam stuff looks great but its a bit out of my price range, im on a pretty tight budget :o

[Jason Hanko]

Hey Mike,
Im also in the same situation as you - I just got a furnace installed in my 24*24 detached workshop (err...garage. Yeah) But theres not a stitch of insulation in the whole thing and Im tired of melting all the snow off the roof. I plan on insulating as soon as I can afford it (ha!).
Id like to keep the storage I currently use on the ceiling joists, so I'll be going with a combo of 1'' thick sheets of rigid styroam board and unfaced batted insulation.
I have 2x6 rafters, so I plan on filling them in with the batted insulation rolls, and then nailing the syro-board insulation right to the bottom of the rafters. I'll be getting batting that's ~4'' thick, so that should leave a 2'' air gap between the top of the batting and the roof sheathing. The batting will rest on the top of the foamboard, which should help hold them up. (that stuff never stays up all by itself - dont let them fool you into buying the faced stuff and tacking only that between the rafters...it'll be at your feet eventually).
The 1'' foam board is about a R5 I think, and the batting should give me R14 or so. Not quite R30, but better than nothing! My cost for my 24x24 garage with a 6/12 roof will be about $400 ( I cant afford the nice closed cell sprayfoam either...sigh).