I live in a very cold environment (VT). I recently had an energy efficiancy company come and insullate the exterior walls of my house by blowing in dense packed cellulose. They also airsealed my attic and recommended that I add more insulation in my attic.
I just bought this house 6 months ago. The attic has no soffits, has floor boards on top of the joists creating a floor, and about 3-4" of insullation under the floorboards leaving a few inches of empty space. The old owners added about 6" of loosly blown celluse on top of the floorboards. The attic has two gable vents on either side. They are pretty big and the attic seems to get addequite air flow.
The insullation company recommended that I blow insullation under the floorboards and then blow more insullation on top. They wanted a considerable amount to do this. A surprising amount considering the amount they charged to do the exterior walls (about the same price).
I want to increase the r-value of the attic to about 40 or 50. My question is this: Do I really need to blow and fill in the empty space under the joists? They already airsealed and there are no soffits. Can't I just add insullation on top of the floorboards? Yes there will be a small empty space but how is that any different than the empty space that is the second floor of the house. I will still be adding heat trapping insullation. It just seems like a lot more work for a very little amount of added efficiency.