Insulating Garage help

[bigbearcountry]

I have an attached garage with a bonus room above it. Part of the garage is insulated and part it not. I'm trying to figure out what is the best way to insulate.

The front half of the garage is not insulated and is 10 feet to the ceiling joists. The ceiling joist are built with 2x4's and has 1/2' OSB board above it for storage. The roof rafters are made of 2x4 and has one vent on it near the top roof. I'm thinking of installing baffles under the roof running up from the soffits and putting r13 roxul between the roof rafters and leaving the top open with no vapor barrier for air circulation. Next, I was thinking of installing r13 in the ceiling joists and then adding a vapor barrier to it. After, I would drywall the ceiling.

Would this be an acceptable way to insulate? I want to make warm (I will be heating) and have storage (can be cold) without any moisture or other long term issues.

Thanks for your help!

 

[DC73]

I think your plan could work but you have to get the details right. Not sure about having a vapor barrier where you suggested. I would triple check that detail so you don't have any moisture issues.

Some people are building their own baffles out of rigid foam board. They nail 1" spacers to the sides of the rafters, then put rigid foam on the spacers and finish by caulking the edges around the rigid foam. If you use a rigid foam with a foil side, put the foil toward the roof deck and it will act as a radiant barrier which helps with heat gain in the summer.

With this approach, it would be best to install a continuous ridge vent and not have anything open from inside the attic. Continuous ridge vents are pretty easy to install depending on your roofing material. Remove the existing ridge cap shingles, set your circular saw to just cut through the roof deck exposing a couple of inches over the entire length of the roof on either side of the roof peak (actual size determined by ridge vent manufacturer), then just nail down the ridge vent and recap with shingles.

You'll also need plenty of soffit vents but they are cheap and easy to install.

Here are a couple of article from the Green Building Advisor site that are worth reading:

http://www.greenbuildingadvisor.com/blogs/dept/musings/creating-conditioned-attic

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

DC

 

[bigbearcountry]

Thanks for the reply. The way my garage is attached, I'm not able to do a ridge vent as the peak of the roof goes into the upstairs wall of the house. I have lots of soffits so that isn't a problem. I've read a lot of articles and I am now thinking that I will double the 2x4 joists to make it 2x8 so I can get more insulation in there and see how it keeps it heat. Hopefully that does the trick!