Insulation above car port ceiling

[yong321]

This 1990 house has 4 bedrooms, all upstairs. Only the one above the carport is noticeably hotter than the others. I think the most important reason is that the underside is outdoor instead of indoor (living room, kitchen etc). I asked other people whose houses have a bedroom above the garage. They all say that bedroom is quite hot in summer. Now I'm thinking of having a contractor remove the sheetrock above the car port (i.e. below the floor of this bedroom). Unless there's already insulation (I would be very surprised!), I'll have them add good insulation materials to it. Hopefully they're good enough to put the sheetrock back as if nothing has happened. Any comments? Thanks.

I may also have the carpet in the room changed to wood floor. So doing it from above (in the bedroom) can be considered too, but I think that's more work than doing it from under.

[pushkins]

Add a minimum of R19 faced insulation to the area over the carport, make sure the paper side is faced towards the bedroom floor.

[Janeofalltrades]

You are on the right track in my opinion. Have you considered a blow in insulation like cellulose? This type of insulation has a great R rating, is environmentally responsible, and is also treated so as to be fire retardant. I agree that placing hard wood flooring would be a nice addition to the space. It might take you a bit of extra money and time to put hard wood in but it will be cleaner than carpet, require replacement less often then carpet, and feeling cooler on the feet.

[yong321]

Thanks both. I haven't decided on which insulation material is the best in this case. Cellulose doesn't seem to have a high R value according to en.wikipedia.org/wiki/Building_insulation_materials
But it may lighter. Weight probably matters because the sheetrock bears the weight. Right?

I talked to a contractor that previously did roofing for me. He thinks adding a few more roof vents and changing the few soffit vents to a continuous one will help much more than insulate the car port ceiling. To be honest, I never heard of anybody insulating the ceiling of car port (or garage) to cool down the bedroom above it. But I believe my logic is correct.

[pushkins]

Under code any finished room (habitable) must be insulated on all exterior sides including finished bonus rooms or those over garages. Under current code rules if you remove the drywall from under that bedroom (in the carport) you must replace it with 5/8" drywall to meet current building and fire codes.
As for your concern with weight issues, you have nothing to worry about, the insulation weight in either option is negligible, for the most the faced insulation will support itself as it's kind of loosely wedged between two floor joists.
Blown in insulation will be problematic to install and achieve a good result in a horizontal application without removing the sub floor from the bedroom (then you might as well lay faced insulation) in many jurisdictions it's an unacceptable process if the work is being inspected by city/county inspectors. This is mainly due to you cannot guarantee complete coverage when drilling holes and trying to force insulation into a cavity, anything that is in the way (electrical wire etc) will stop the flow of blown cellulose almost immediately, add onto that you will need to cut at least two 4" holes in every joist cavity.
Also in adding insulation you really should ensure that you add a vapor barrier, this is almost impossible (actually it is impossible) with blown in cellulose in your particular application. If you use batts/fiberglass the "paper" (faced) is your vapor barrier. If your joist height is 8" you can add R30 faced insulation.

[Janeofalltrades]

I agree that is it very important to stick to the local and federal building codes so that the structure is safe as well as easily sold. I did some additional digging on information about insulation types and their respective R values. This is what I found:

Insulation Type R-value per Inch of Thickness:
Fiberglass blanket or batt: 3.2
High performance fiberglasss batt: 3.8
Loose-fill fiberglass: 2.5
Loose-fill rock wool: 2.8
Loose-fill cellulose: 3.5
Dense-pack cellulose: 4.0*
Expanded polystyrene board: 3.8
Extruded polystyrene board: 4.8
Polyisocyanurate board, unfaced: 5.8
Polyisocyanurate board, foil-faced: 7.0
Spray polyurethane foam: 5.9

Perhaps this will help you decide on a type and the amount of R value you require. I also think it is a good idea to add vents as your contractor recommended.

[knowitall]

I would not get rid of insulation all together. If you get a contractor to remove insulation that is already there, I would look into replacement insulation that my allow for better heat and cooling transfer. You could even check around with something like angie's list reviewsto find someone to remove the insulation safely for you. Contractors can give you a better judge of what you really need to do with your specific rooms.