Insulating ceiling between garage and bedroom above

[jwb]

I am in the middle of remodeling a 150sqft garage. Directly above the garage is a bedroom. The garage is not heated, and the ceiling is not insulated, so as you can imagine the floor of the bedroom is very cold in the winter.

I tore out the ceiling which was button board and plaster with a concrete finish. The floor is 2x10 joists 16" o.c. I plan to install R-25 fiberglass between the joists, supported by wire rods, and replace the ceiling with 5/8" type X drywall.

I am wondering if I there is anything I can do about air infiltration between the garage and the bedroom. I've read every manner of conflicting opinion on the web regarding vapor barriers. This house was built in 1948 and has no vapor barriers anywhere, so I'm reluctant to add it in a single place for fear of creating a pocket of moisture that can't escape. On the other hand, if it is safe and would make the bedroom more comfortable, I'd like to do it. Any thoughts?

An additional concern I have is whether I should put in extruded foam board against the rim joists and caulk it. Will that cause moisture problems?

I also have several places where water pipes and armored cables run through holes cut in the rim joist of the interior wall. Should I spray-foam these holes?

The last option I am considering is adding a hot water radiant heating system, since I already have access to the entire joist space. Maybe if I hit the lottery

 

[harvero]

Holmes on Homes deals with this problem many times. The best solution is solution is spray foam. If you want to have a warm floor spray foam is really the only option.

 

[northern skink]

Holmes on Homes deals with this problem many times. The best solution is solution is spray foam. If you want to have a warm floor spray foam is really the only option.

And you could look into using closed cell foam, which would provide a vapor barrier, and kill the air infiltration problem - neither of which would be addressed by fiberglass batts.

 

[rsanter]

I vote spray foam as well
you get insulation and sealing at the same time

just for good measure I would fill the remaining space with fiberglass because its cheap and it will also offer a little more noise reduction on top of the added insulation factor

bob

 

[walrus]

I'll give you another option, can you put sheets of 2" foam over the joists.? I'd put the fiberglass in and then cover the whole thing with 2" foam, caulk or can foam any cracks, put your 5/8 fire x over that

 

[burleymike]

If you decide to put 4x8 sheets of foam on the bottoms of the floor joists be sure to use foil faced foam as it will not allow moisture to move. Spray foam will be your best bet though.

 

[Rosco]

if the insulation is not in direct contact with the bottom of the floor you will still be fighting a cold floor. Best solution is closed cell spray foam. Next best is caulk every seam and put fiberglass bats tight up against the bottom of the floor.

 

[jwb]

Thanks for all the options. I understand why the floor is cold etc. I am just worried that I will ruin something with the vapor barrier and in three years find out I have rotted framing. By the way I live in a year-round heating climate; we don't have air conditioning and the temperature rarely exceeds 75F.

 

[jklingel]

I'd be very leery of a true vapor barrier, instead opting for the airtight drywall approach. You have a potential rot problem w/ the VB, as you noted. Air sealing is what is critical, and having a vapor open cavity. What is on top? Carpet? Vinyl flooring? If vinyl, then your floor has no where to dry but to the bottom, thus a VB would kill you, I suspect. Leave the FG insulation at the store and either use closed cell spray foam or cotton, cellulose, or rock wool batts. Make sure the cotton or cellulose are treated w/ borates.

 

[KMR Construction]

I did a job where it was the same sistuation. During a very cold spell they turned the heat down in the bedroom above the garage. Pipes froze and broke in the bedroom filling the ceilling with water and dropping the drywall on top of there cars. Both cars had alot of damage and took $20k to clean up the mess. Do yourself a favor and spray foam the ceilling.

 

[mobetta]

if you decide on foam, for such a small area, you will likely be paying more in setup than product. so maybe you have a few other areas that need attention- the rim joist throughout the basement? an out building? etc....

 

[HomeBrewA4]

where do you live that the climate doesn't exceed 75 much? I would personally go r30 in a 2x10.

If you go spray foam, closed cell is what i'd def use. We use BASF and yield a R6.2 per inch of foam.

Our going cost is $1.00 per sq ft, your area could be more or less, but gives you an idea of where costs might stand.

 

[6768rogues]

If you want 1-hour of fire protection for a fire starting in the garage and trying to migrate to the bedroom, use two layers of 5/8 type X drywall. It is Gypsum Association assembly RC2601, for our architect friends.

 

[Burl]

I just fixed the same sitiuation in my garage with the bedroom above. The garage had 3 1/2" insulation between the 2 X 8 joists (which was very old and deteriorated), and I added another 6" of paper-backed and followed it up with the 1" white foam insulation board from Lowes, it made a HUGE difference in my floors.