Insulate the room addition after the framing and the rough wiring have been inspected. (You may have already insulated under the sub-floor) Your plans will specify required R values and type, usually fiberglass batts or blankets.
Install insulation according to manufacturer’s recommendations. Wear a dust mask, goggles, and gloves for protection against irritating fibers. Cut blanket insulation with a utility knife, changing the blade often. Compress thick insulation with a board to make cutting easier.
Make sure insulation fills the entire stud or joist cavity, even tiny nooks and crannies. Cut it to fit around electrical boxes, blocking, and other obstructions. Split blankets to fit on both sides of wires rather than com pressing it to fit behind them.
Staple the flanges to edges or faces of studs, depending on the manufacturer’s recommendation. Most insulation includes a vapor barrier, which must face the heated space. If a separate vapor barrier is specified in your plans, stretch 4-mil plastic sheeting over the completed insulation. Staple it to studs and joists. Cut out around all electrical fixtures and doors, but wait until plasterwork is complete or wallboard is installed before cutting out windows.