Type of Insulation for Garage Ceiling

[Cherrybark]

Thought I would go with a question rather than simply "Hi" for my first post. Seems appropriate since exploring so many helpful threads over the past few weeks is what led me to join.

Taking advantage of the Spring weather here in East Texas to air condition the 22 x 32 garage to have a year round work shop. A trusted, family owned business will install the mini-split while I take care of the manual labor jobs of insulating the walls and ceiling.

The ceiling is sheet rocked with 2 x 8 joists on 16" centers. A 1/2" OSB decking floors the attic space above the garage for light storage. I've ripped up the decking and will start putting down batts in a couple of days. The Owens Corning site says a slightly compressed insulation will give somewhere in the area of R25. Not idea but I'm trying to make a tolerably comfortable workshop, not a living space.

It would be tough to do a good job of attaching the vapor barrier of a faced insulation against the sheet rock that is already in place. Would an unfaced insulation be a better choice in this situation, relying on the sheet rock and OSB decking to serve as vapor barriers?

Honestly, I have a tough time understanding which side of a regular wall should get the vapor barrier since it freezes here in the winter and is in the 100s in the summer.

 

[DougWil]

Vapor barrier goes to the side that is warm in winter.
A good coating of latex paint will provide a great vapor barrier if you don't have cracks and unsealed penetrations in the drywall.
So you don't need kraft paper backed insulation it in the attic, the wall you do for something convenient to staple to.

More than you probably want to know about the subject.
http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barriers

 

[theoldwizard1]

Poured fiberglass OR cellulose will have about the same R value. Cellulose is cheaper.

I would also consider some type of radiant insulation tacked directly to the roof deck.

 

[csp]

Poured fiberglass??

 

[DougWil]

Poured fiberglass??

Think he meant blown.

 

[encantofred]

i did blown fiberglass in mine.

tom

 

[Cherrybark]

Thanks for the useful replies and I'm glad I asked the question. For some reason, I had decided blown cellulose did not have nearly the R rating of fiberglass batts and, seeing the thick layer of existing cellulose in the open attic, decided it would not work as well in the 7 1/4" depth between the garage ceiling joists. I'll call a local contractor rather than try and convince my wife how much fun it would be to rent a blower and DIY.

I'm enough of a nerd to read the linked article and to chase ideas of paint being a vapor barrier or retarder. One point made repeatedly is sealing air leaks around light fixtures, garage door electrical outlets and other holes is very important. After installing a couple of new light fixtures, I'll crawl around with a can or two of spray foam sealing leaks. Sealing and paint should do the job.

Another thread on this topic suggested insulating between the joists then attaching a layer of foam insulation boards with radiant barrier across the top of the joists before replacing the deck. I'll look more into that option.

To admittedly "drift" my own thread. A couple of finished sheet rocked walls need insulation. Do I remove the sheet rock, install batts and install new sheet rock? Or is this a waste of time and money when blown cellulose is just as good? My concern being blown cellulose will settle over the years.

 

[DougWil]

To admittedly "drift" my own thread. A couple of finished sheet rocked walls need insulation. Do I remove the sheet rock, install batts and install new sheet rock? Or is this a waste of time and money when blown cellulose is just as good? My concern being blown cellulose will settle over the years.

There is an art to blowing insulation in walls.
Too fluffy and it settles excessively, but easy to blow.
Too dense and it is hard to blow in, clogs in the line, can bulge the walls and lowers the insulation value.

Probably easier to just R&R the sheet rock.
EPS foam sheeting can be installed over the batts on the studs and really helps the R value, air infiltration (if fitted nicely) and thermal conductivity through the studs/framing.