A flat dormer roof is a roof that protrudes from the end of the pitched roof, and is in a sloping shape. The dormer is an extension and is not connected to the attic of the pitched roof, so many times it is considered a dormer flat roof. Since the attic is not connected, insulating a dormer flat roof can prove to be a challenge.
Inspect to make sure that you cannot access your dormer via the attic. Occasionally they are connected, and you do not have a flat dormer roof.
Break the drywall of the ceiling of the dormer. Hammer the middle of the drywall to make a hole and try to pull it down. The corners will most likely need to be hammered to remove.
Measure and cut the fibreglass insulation. Use the tape measure to measure the distance from the end of each roof beam. Put on your gloves when handling the insulation, and cut the insulation with your utility knife to the proper size.
Push the insulation in between the roof beams with your hands and staple it. Start from one end, push it up with one hand and with the other hand staple the paper side of the insulation to the roof beam. Work your way to the end until it's all stapled in place.
Cover and finish the ceiling. Cover the ceiling with drywall or whatever material you like to use.
It is easier to have someone hold the insulation for you while you staple it. They can hold it using a stick or another long instrument.