best way to insulate detached garage?

bandit86

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would like to do som work in it this winter, it's a bare shell right now, nothing but some siding, chipboard and 2x4s. what's the best way to insulate it? styrofoam? do I worry about a vapourbarrier if it's not heated?
 

dolluper

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Re: best way to insulate detached garage?

First what are your center's 16" or 24"...foam is more expensive but takes less room with a higher R rating,,,,with the pink much cheaper all you will get is R12 sized for 16" or 24" center's 2x4 wall's,read the labels and yes use vapor barrier with it you don't want be breath in fiberglass when working,the foam you don't need vapor barrier
 

Mark42

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Re: best way to insulate detached garage?

I agree with dolluper. If you want more than R12, pick up a few bundles of 2x2" x 8'. They are cheap, and just tack them to the 2x4's. Then you can install R19 glass. You might want to put down a bead of constuction adhesive (liquid nails) between the 2x4 and 2x2 in case you later want to add heavy duty shelving to the walls. Again, liquid nails is cheap and works very well for that purpose.

Be sure the craft paper face on the insulation is facing the living space side of the room (or garage). I would not add any additional plastic sheeting/vapor barriers. Justs leads to condensation and water problems.
 

Bigprairie1

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Re: best way to insulate detached garage?

Being a former 'Ontarian'...I'd say your equal challenge will be to get a good heating source for the winter months.
If you just insulate you will not really be any warmer in there...you'll just keep the ambient temperature (...cold!!) stable.
Do you have plans for heat? (electric, wood burning? or?)
BP
 

Mark42

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Re: best way to insulate detached garage?

Another issue is not just insulating the walls and ceiling, but sealing the garage door. If its a common wood door its easy to add the rigid foam insulation pannels to the inside. Good for R7 or so. Double up if you can. Just use the foam adhesive sold for that purpose. If the door is aluminum or steel, the foam adhesive will take weeks to dry. Try using Gorilla Glue instead. Just brace the pannels for an hour with some 2x4 or the like.

Also buy the door seal for bottom and door casing with rubber lip to seal against the door sides and top. Insulation isn't worth much if the air just leaks in and out, and the door seals are inexpensive.


Let us know what direction you take.
 

bandit86

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Re: best way to insulate detached garage?

it is real 2x4 (not 1.5x3.5) and the rafters are all open to the outside. I was kinda thinking maybe get some sprayfoom, more $$ but I know it's solid. what should i puty on the walls, drywall or plywood?

I wanted as much room vertically as possible for the underside of the roof, since I know I need ventilation up there to keep the shingles happy, should I put up a layer of plywood, then some more 2x4 to hide the insulation or get some channels put up and just sprayfoam over? or would I be better up to build a false ceiling since I already have some beams going across to put insulation on?

here is a quick shot of the garage roof from underneath
garage.jpg
 

arboldt

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Re: best way to insulate detached garage?

Being a freestanding garage, you probably have a few more options. If it were attached, I think you'd need to use drywall properly taped an mudded to meet fire resistance guidelines. You'd also need to have the same type of drywall for the ceiling.

Plywood for the walls and ceiling would be rather expensive, I'd think, unless you were planning on hanging a lot of tools and paraphernalia all over. Unless you painted it, plywood etc would also absorb a lot of light.

The other major factor is the question of a heat source. In a moderate climate, simple insultation may help you extend the season a bit, but by mid-January it's gonna be cold no matter what. What are you planning on doing for heat? Each type of heater has its own setback requirements as well as specifying what the nearby wall surface is composed of.

A previous owner put a normal residential gas furnace in our garage. I'm not a real gear-head, so I only use it 2 - 3 times a year. But when I need to work on the car mid-winter, it sure is nice to not freeze while I'm doin' it.

Especially if you heat the garage, you'll need insulation and ventilation for the "attic" (do you plan on storing anything on the rafters?) Simple gable vents are probably the easiest if the garage rood is gable-end. Make 'em nice and big for lots of ventilation. Be sure they're well-screened against bugs and weather. Hip roofs will require cutting some holes and fitting other things like soffit vents under the eaves and turbine vents on the roof.

All this said, if you're not going to heat the garage, why not just leave the wall studs? You can fit a lot of storage between the studs, and you don't have to worry about repairing a finished surface.
 

arboldt

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Re: best way to insulate detached garage?

One more thought...

If you do decide to cover the walls, be sure to put in wiring. Put in at least twice the number of 20 amp outlets as you think you'll need. It would be good to run it from it's own breaker box in the garage. Much easier to put it in now than later.
 

bandit86

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Re: best way to insulate detached garage?

have a wood stove sittin around for heat. would be nice to work on my jeep one in a while when it's below freesing. driwall would be chaeaper butI was worried about weather i need a vapour barrier or not
 

itstippy

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Re: best way to insulate detached garage?

I want to run a small woodburner in my 24' X'24' detached garage to extend the season. I'd just heat it when I'm using it on weekends and some nights after work. I don't plan on insulating the walls, but am considering 4" kraft faced pink for the roof. That's where the heat disappears so I'd make a big difference in a hurry. The garage has a roof vent the entire length to dispell heat in the summer. What will happen if I cover it up with insulation? Will the insulation elliminate the need for the roof vent? I know that in Summer when I go up in the rafters to get at my wood and metal stock it's hot (hot!) up there. Will it be horrible with the roof vent covered with insulation? Will it destroy the structure? Or will the insulation help keep the heat out of there?
 

Xcusme

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Re: best way to insulate detached garage?

You think it's hot now, with the roof vent open, try blocking it and see how hot it gets! The roof and the soffit vents work together to provide an airflow that allows the heated air to rise out through the roof vents. Cooler air is drawn in through the soffit. The second function of any vented roof system is to purge moisture from the attic space too. Now , you can insulate the roof itself and have the ridge vent open to draw fresh air up between the back side of the insulation and the roof deck. This really only works for roofs that have a continuous ridge vent, like Cobra Coil etc. This arrangement basically puts the attic within the insulated envelope.Keeping the roof deck cooler will extend the life of the shingles too. The only time you have to worry about a vapor barrier is when you have moisture on the heated side of the insulation. Since water holds 5 times the latent heat of air, you want to keep that moisture , and the heat it contains, on the living or heated side of the insulation. Water vapor migrating through the drywall will carry the moisture into the insulation. When that moisture reaches the colder side of the insulation, it can condense and freeze, and that's bad. You won't stop the heat loss, just slow it down. The rate of heat loss is determined by the type of insulation and the temperature differential between the inside and outside surfaces. The greater the temperature difference, the faster the migration or loss. Another tidbit of info, heat doesn't rise....heated air rises. Heat travels in all directions, from the more heated area to the less heated area.
 

itstippy

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Re: best way to insulate detached garage?

The garage was built in 1961 and originally had no ventilation at all. I reroofed it four years ago and intalled a full length roof vent on the peak. There's a 1 1/2" gap at the peak, only partially blocked by a 1"X6" board, so I thought I'd take advantage of it to get some ventilation up there. Since then I've increased my shop time considerably and now I want to use the shop during times when it's cold but not when there's snow on the roof. I'll leave the walls alone (except for paint), and use styrofoam panels to insulate the aluminum door. But I want to insulate the roof if possible to keep the heat in. Kind of a big ice shanty to work in. I took some pics:
100_0939.jpg

Exterior of garage. Part of it is a hot tub room. The rest is garage/shop.
100_0941.jpg

The eves. No Sofit, no ventilation.
100_0942.jpg

Interior walls are Celotex tar board and tons of "stuff"
100_0943.jpg

The roof interior peak. Joists(?) are 24" on center, when they're lined up. Crude but pretty strong.
100_0944.jpg

Inside shot of the eves. No airflow at all that I can tell???
100_0946.jpg

Behind the hot tub room is 8' more shop space. That's where I'll put the little wood stove in the Winter, maybe use a fan to circulate air into the bay area when working in there. I'll take the woodstove & pipe off in the Summer. Maybe use the stovepipe through the roof to mount a bathroom-type vent fan?

So, is it worth getting 24" wide kraft faced pink and doing the roof between the joists(?)? I could even hang an old ceiling fan up there to blow warm air back down. If I don't block the ridge vent won't I just set up a convection current where all my heat goes out the peak and I'm left in the cold? I've got a lot of stuff stored in the rafters so I really really don't want to seal off that "attic" area with a ceiling.
 

arboldt

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Re: best way to insulate detached garage?

The pic of the outside of the garage with all the windows really told us something. The outside eaves are all boxed in -- I didn't see any ventilation. You'e got a ridge vent (great!) but no real way to get air moving up the underside of the roof decking.

I encountered a similar situation at the family cottage. The siding had extended up between the rafters to seal the roof, which my late FIL boxed in, leaving no ventilation to the roof. I removed the wood boxing in the eaves and put in continuous-venting vinyl (aluminum is available, too, but not quite as easy to work with). I also had to cut an inch or two from the top of the siding (being careful to stay above the top plate so I wouldn't cut into it) in order to provide an air channel from the eaves to the roof. There were other issues why I had to do this, but it gives an idea.

If I were you, I'd measure and buy eave vents. Cut openings for 'em and install as many as I could fit. They're on the underside and screened, so there's no weather or critter concerns. You also need to make sure there are airway openings from the boxed eaves to under the roof decking. The idea is to get lots of natural-convection air flow from the eaves up under the roof and out the ridge vent.

Then you can think about putting in an insulated ceiling to retain heat. Just remember you want lots of eaves-to-ridge ventilation in all seasons year-round.

HTH

Al
 

mthieme

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Re: best way to insulate detached garage?

Been there done that.
Let me tell you what I did to my garage.
First it is 12'x40' block with a gable roof.
The very first thing I did was to caulk all the holes and there were plenty. Once the cold air stopped rushing in, half the battle was over. I had some insulation leftover, so I put that up in the rafters. I stopped there, the only other thing I could do is to rock the ceiling which if I run across a very cheap supply I might consider. White is a good thing in a shop too.
Okay, no holes and insulation, heat source next. Well, I ran into a fellow woodworker who was moving and he gave me a small pot-belly stove. The price was right. Perfect, now I have somewhere to get rid of the the constant supply of wood scraps. The only problem with this is that it takes a while to heat up and doesn't really spread the heat well. Next I had a buddy "permanently loan" me a baby torpedo heater (LPG) - gotta be the smallest one made. This will heat up the shop in a hurry. So I fire this up, then do the stove. 10 minutes later the shop is comfy and I turn off the torpedo. I also have a vintage Alladin Blue Flame heater which merely sips fuel (1/2 gallon used last year) and can be placed at the other end of the shop to make up for the wood stove's shortcomings. Three different heat sources. Oh, I started out with electric heaters, but they are long gone as they were a bad choice.
Also, no flammables are stored in my garage.
 
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