Insulating garage roof

[Steve Bakken]

I have a 28 x 32 2+ stall garage. I was given a 100,000 btu heater that I have hanging in the rear corner facing out at an angle. Works great for those evening projects, but I need to get the garage insulated. The problem is that I use and need the area above the rafters for storage so I would probably be insulating the underside of the roof itself instead of putting in a ceiling and insulating on top. Now the way I understand it is that in a traditional setup the insulation is spread on top of the ceiling and the soffit vents allow air circulation above the insulation to prevent ice buildup under or on the shingles. Soooo, if I put the insulation directly on the underside of the roof, is there a product or a method to ventilate and prevent the moisture buildup?

[walleyeseeker]

You can install the chutes made for air flow all the way to the peak and then insulate under these. Air from the soffit will still be able to flow up and cool the underside of the roof. Good luck.

[sparcebag]

Ya its a long involved process,but on each rafter/truss you would nail on a 1x2 butted up to roof sheathing on each side of each rafter/truss,then install rigid insulation between each rafter/truss butted up to 1x2s creating a 1&1/2 inch space between roof sheathing and top of rigid insulation,making air flow space,then apply some rolls of backed insulation and staple in place with flange provided on backed insulation,lay it in so it goes all the way down to top plate of wall to stop draft betewwn rigid insulation and top plate.

You could use any spacer in place of 1x2,say a strip of rigid or what ever comes to mind just to hold rigid in place till backed insulation is in place.That 1&1/2 is minimum and important for air flow to keep roof sheathing at outside temp.to prevent freeze thaw and ice dam.

[BoxMN]

What I did on mine (28x36) is use R13 23" kraft faced and staple to the trusses, like you said you are not going to do. (My trusses are 2x4, not 2x6, so I have to get 3.5" thick stuff for the flooring to fit over it.) However, I use mine for (light) storage as well, so I just put a attic staircase and left a 5' area where I "could" slide wider things up there. On top of the ceiling, or truss floor, I put 1/2" OSB before I put the insulation up.

That keeps me from heating the entire space, and I can still get dozens and dozens of decoys, and even 25' extra siding panels, right up the attic staircase. In fact, I don't even think I will ever need to use my 5' opening space, as I can get anything I need up the stairs.

Anyway, depending upon what you plan to store up there, you still can use it for storage and heat less, and not worry about proper attic ventialtion, and it is pretty easy to do.

Good luck with whatever you end up doing!

[Shack]

With a 5/8" sheet rock ceiling, I put in two layers of r19 bats. I criss crossed the entire attic twice. I also made shelves up off the insulation to put outside holiday stuff, snowmobile parts and other junk. I also put alight up in attic.

[TRITC]

Shackbash and others,

If you insulate the truss floor (with criss-crossing layers) what do you do about walking around up there. I also use my attic space for storage but it's a fairly large area so I need to be able to walk around up there. I have been thinking that I may need to build up from the trusses to get the floor over the insulation.

Thoughts???

[walleyeseeker]

There is no need to use 1X2's, just use the premaid chutes. You staple them to the back of the roof sheeting. Be sure to block the heel area of the truss to stop the insualtion from filling the soffit.

[Shack]

Cat walks.

When I finished ceiling off in my garage about two years ago, I referred to this area as He11. I have to go up and bring some Halloween and deer hunting stuff up there this weekend. When I am up there, I will take some picture to give you an idea of what I did. First and foremost, insulation and R value are the main factors, before anything else (I.E. shelves or flooring. I figured energy saving was first and then work on flooring later.

[sparcebag]

Steve one thing I forgot? To create air flow you'll need roof venting besides soffit,the roof can be continous vent or if you create a ceiling at the peak (collar ties short joists) then just normal roof vents.

[Surface Tension]

You can use the chutes for the whole run or 1x2s. 1x2 ripped from standard pine will cost less. You could even cut strips of 1" foam.

My personal preference wouldn't be to go that that route. Your heating a bigger area and your not getting much R value. Your also making for a very small space for air flow. Because of the thermal break being so close to the roof deck, any warm air leaking through will immediately hit the underside of the cold roof deck and frost up. If you go that route do a good job on fitting the foam and caulk all edges and joints to reduce the warm air leaking out.

You can go the conventional route and still use the attic space by laying plywood down the center and use an attic door or make an access. You can add more space above the floor using the web for racks. You'll have 3 1/2 " of insulation under the center where the plywood is you can add more every where else. Now you'll be able to use a vapor barrier and rock the ceiling.

[fishinpapa]

Here is another thought...while your insulating your attic, rough in some outlets in your soffits for plugging in christmas lights. Very handy!!

[Tom7227]

Is the insultaion really necessary? If you rock the ceiling you are going to create a barrier to the heat moving up into the attic. Then if you put in a set of stairs you can use them to access the storage area. Put some 1/2 inch plywood down as flooring and you're done. I suppose the insulation would make sense if you were going to heat the garage all the time to 70 degrees, but my guess is that few actually do that. The cost of all that insulation and all the effort involved seems to make this a project with a real long pay-back.

A number of years ago I created a heck of a mess. I put too much stuff into the garage attic and ended up having trusses start to fail. Keep that in mind when you're loading that garage attic up with those extra bundles of shingles and car parts.

[fishinpapa]

I was able to blow in 6-8" of insulation for a 30x28 garage for about 120$ (blower usually free). Well worth it from a extra layer of protection along with the sound deadening quality. My garage faces NW so it gets blasted all winter.

P.S. I have one small opening to the attic for skiis or sleds, I never want to be able to access it too easy. Nor do I want to accumulate that much "stuff".