Insulating Garage Ceiling

[stealthmagic27]

Need some help everyone. Long story short i scored a bunch of unfaced insulation. I would like to use this to insulate my garage ceiling.

The garage has cement block walls and the hollows at the tops of the walls are exposed/open. There is no attic, ceilings are cathedral. My plan is to install styrofoam raftR vents, then the unfaced insulation on top. I will eventually be finishing the ceiling with sheet rock. When i do this will i need to install some type of vapor barrier? Tyvek or something? Help is appreciated!

 

[Chris705]

If you live in an area that requires you mostly heat your garage vs. air condition it, then yes your plan is sound...baffles to allow air flow from your soffit up your rafter bays then out a ridge vent.....pack in your unfaced fiberglass batts in the rafter space and prior to putting up the GWB use a 4mil poly vapor barrier to totally create a vapor barrier. If you live in a predominate cooling requirement then you want to put the poly up before your fiberglass....its all about where you want the moisture to not condense. And you might want to see if you can use foam in your cells of your block walls....maybe a diy kit of closed cell foam....or at least cap the tops of the block with a foam cap. Good Luck!

 

[stealthmagic27]

Thanks for the reply Chris! However there are no rafter spaces. My plan was to use the styrofoam rafteRvents to balance air in the hollows of the cement blocks to the ceiling. Does that seem right or will i have to build some kind of venting ?

 

[Charles (in GA)]

I thought I understood what you wanted, now I don't. Possibly a pic or two of the inside of the roof would help.

Charles

 

[James-W]

I thought I understood what you wanted, now I don't. Possibly a pic or two of the inside of the roof would help.

Charles

Yeah, I am confused too, and I agree, a picture would be nice.

 

[stealthmagic27]

Best pic I have right now. There is no venting to outside. Do I just insulate the top opening of the block walls. and but the Styrofoam raftrvents to keep the insulation from being directly on the ceiling?

 

[Tireman]

I have something similar to this but my roof is four sided. Cinder block walls too. I,ll be keeping an eye on this one. Thanks for starting this thread.

 

[Chris705]

The only way I am aware of to insulate directly to the underside of the sheathing where you will NOT provide any air circulation (soffit vents to ridge vent) is to use closed cell foam. You have rafters so you have rafter cavities....but if you want to use the fiberglass that you scored then I'd add soffit vents and a ridge vent.....if you don't you'll likely "cook" your shingles and they will fail in short order. You use the baffles to allow an air channel to go from soffit to ridge cooling the inside of the roof sheathing. You can do a modified version where you add soffit vents and gable end wall vents. You'd have to add rafter ties 1/3 of the way up your rafters creating an attic space....vent this to the exterior thru gable end wall vents. Seems easier to add a ridge vent and cap it with shingles.

 

[DC73]

If you get the details on this wrong, you could create moisture (condensation) problems. Read this article on GreenBuildingAdvisor.com and then post any questions to their Q&A section:

How to Build an Insulated Cathedral Ceiling
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

Also, visit BuildingScience.com , go to the "Information" link, and read their technical papers on insulating ceilings.

DC

 

[stealthmagic27]

Thanks again guys, you are right I was thinking in the wrong direction. What Chris mentioned is the answer. Thanks for those links DC!

1. Add rafter ties.
2. Add Gables at the front and rear of the garage.
3. Add Styrofoam baffles.
4. Then insulate with the free stuff