Insulating the garage

Most any area is going to have local codes calling for insulation there. It is likely close to the max that will fit in there now. I don't suggest adding more below the finish ceiling. If you do use the foam, remember that you will need to cover it will fire resistant drywall.

I do have a suggestion however. Are the outside walls of the garage insulated? If not I suggest insulating them. That will keep the garage warmer and your floor warmer. BTW my bedroom is over a garage and I added that wall insulation before the first winter.

As other poster mentioned... it'd be a good idea to cover with flame retardant barrier, such as more drywall... foams can release some nasty stuff when on fire. (don't know about those

perhaps... perhaps not... you might want to drill a test hole to look for yourself.

If there isn't anything in there, you might want to consider retrofit blow in of insulation. Either foam or cellulose. (Fomofoam has a lowE retrofit DIY foam spray i think.)

Leaving polystyrene foam insulation uncovered or unprotected by some sort of fire shield is both dangerous and mostly illegal.

Garage + uncovered foam on ceiling + living space above will set off alarm bells for every knowledgeable person who wanders by.

I would cut a hole in the drywll and look to see if it's insulated. If not, blow-in cellulosic is one option.

Regards Old Al

Call Owens Corning for free advice (1-800-get-pink). They will tell you insulating the garage walls is also a bad idea because it keeps the garage cold when you want it warm, and warm when you want it colder.

-B

Thank you all for your replies..

The garage walls are as far as I know insulated.. except the garage doors aren't..

If I do add the foam and add another fire retardant drywall on top of the existing finished garage ceiling.. do I need to put any type of vapor barrier (assuming the insulation inside the finish ceiling has a vapor barrier already)? Or just the rigid foam board and drywall?

Does anyone know what the R value of a drywall is adding to the foam board??

another question.. I went to the hardware store and found these insulation that's made with bubble sheet lined with foil on both sides..

Has anyone used these before? If so how good/effective are they.. if I use this instead of the foam, do I still have to cover with fire retardant barrier?

Thanks again for all your time and replies..

That is generally a problem with detached garages, but it is a different matter with attached garages, especially when there is a room overhead.

No additional vapor barrier needed.

Not very effective for what you want. I don't believe I would want it used unprotected in a garage, but I don't know what code may say about it.

Actually it is true in a detached garage only if you don't use it. The car stays much warmer in a garage (and I want it warm) in the winter if the garage is insulated. It would take a very flexible mind to figure out how insulation would make the interior colder in the morning as the temperature dips from 30 F at 6 pm to -5 F at 6am when I go to work. The insulated garage will obviously retain more heat from the car engine, than an uninsulated garage. It works well in the summer also, just open the garage for a while when it cools, and the car will be cool when you go get in it at 3 pm.

There are mixed blessings. In the snow - salt part of the world, a car will be better protected from rust and the action of salt, if it stays cold.

It would take a lot of insulation to make a meaningful difference in a detached garage after 12 hours. There will be little heat left from the engine.

However, that said, I really don't think it is going to make much difference good or bad.

That wasn't the question. So I didn't comment on it.

It would seem that way, but it would also require very little heat to keep the car warmer than the outside. I do know that a car parked inside an unheated garage (even with broken windows) will be warmer and easier to start than a car parked outside. The difference is greater with a large diurnal change in temperataure.

Unless you want to heat the garage with a 100 W bulb.