Cold Air Return Duct in Garage Ceiling (for bedroom above)

jbrocious

I've been searching online with no luck... here goes.

Bedroom above garage is COLD. Just ripped down the ceiling in the garage and found that it had little to no insulation. There is a cold air return cavity that extends the entire length of the garage. This return is for the master bedroom above the garage and is on the far exterior wall.

Is there anything I can do to insulate the cold air cavity between the floor joists? I thought about a 1" rigid foam attached to the floor above and a 1" rigidfoam on the lower side.

jbrocious

Any thoughts or additional information needed?

I found unfaced R-30 batts that are 9.5" deep that I could use in the remainder of the garage (not sure if I need vapor barrier here though). Should I be concerned with a single cavity being open for the return?

jbrocious

Does anyone have any input? I'm surprised there are no responses. Would pictures help?

drtbk4ever

I too am surprised you haven't gotten a response.

Can you give us an idea where your location is?

I'm just a small project DIYer so don't have any expertise. But yes, insulation should help a quite a bit. I don't know if you need a vapour barrier nor which side of the insulation is should go on (may depend on location and local codes).

Can you feel the cool air within the cold air return? Insulating it will help shield it from the cold but some returns are just empty joist bays so are not protected at all from the cold.

Is it possible to move the return air vent to a different wall in the Master Bedroom so the return air duct is shorter, and perhaps not exposed to the cool garage?

__________________
Bill

A DIY Noob that knows just enough to be dangerous.

jbrocious

Im in western pennsylvania so i believe vapor barrier should go on the warm side (under bedroom floor). Ive heard about vapor barrier paint. So I thought about using that with the unfaced batts.

I probably could move the return to the interior wall although that would require wall modification. If there would be a big benefit to doing that I would certainly consider it.

I'm also reinsulating the exterior garage wall and using drywall with frp panels.

jbrocious

I forgot to address the cool air question. It's hard to tell. The whole floor is cold above. I figured the open joist bay was simply making it worse. It is just an empty bay with drywall that was encasing it. Now that the ceiling is down I can do something to make it better. Id hate to insulate everything else just to have a cold spot where the empty bay is.

drtbk4ever

I'm thinking you are going to see a huge improvement by just insulating the majority of that floor.

I don't know if wood subfloor is a sufficient barrier or if that vapour barrier paint is required. But I would want to be doubly sure you have a really good seal. We need one of the experts to weigh in on that because this is above your garage.

It would be ideal if you could move the return air vent then you can button the entire floor up tightly. But you are correct, it is a lot more involved with the wall repair etc.

I don't know if the rules regarding the exposure of the rigid form insulation apply to the inside of a joist space that is also a return air duct. You may need to put drywall over the rigid foam to slow the burning/off gasing in case of fire.

Bring on the experts.

__________________
Bill

A DIY Noob that knows just enough to be dangerous.

Technow

It won't be cold....its return air....its air that is the same temp as the return its pulling from.

pics would help to see what you are talking about

rooms over garages are notorious leakers of air....you can stick a butterknife under the trim and see it in the garage.

techpappy

relocate return air to interior end of room and make sure supply air to middle of room. I have the same. Room over garage was originally only 8 feet and we had it built to 16 feet long...just had it insulated with R40 ( 2 layers of fibregkas batts) .also provided 2 supplies.a little cool at times but not bad..only a degree or 2 less than rest of house..perfect for sleeping OR whatever!!