Insulating a bonus room

dencrimi

I am building a bonus room over a three car garage and live in a very cold part of the country. The floor is 2x8s. I am also planning to have a wood plank cathedral celing (2x10 rafters). How should I insulate the floor -- any vapor barrier to keep out fumes? How about the ceiling? Do I need to sheetrock?

concretemasonry

Use fiberglass or cellulose between the gargae and bonus room. That barrier is not like the difference between inside and outside (much less temperature differential). Definitely use a vapor barrier on the warm side of the insulation. Your 5/8" sheet rock should be taped completely for fire protection purposes.

Catherdral ceilings are always a challenge in a colder climates. How cold do you thinks is cold -30F? - Your choices are a rigid extruded styrofoam applied to the exterior or filling the 2x10 cavity with the possible addition of rigid on the inside.

AtlanticWBConst.

Absolutely....as was mentioned: 5/8" S/R with a minimum coat of 'fire-taping' on it.

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NHBuilder

You REALLY should be getting a building permit, fire protection is a HUGE deal with local authorities and frankly you want to protect your family. The building permit may also bring up a situation about your 2x8 floor joist, they may or may not be large enough.

As much as people hate getting permits, most inspectors actually can be quite useful and help you solve these problems.

Good luck!