The main factors that impact the cost are.
Insulating attic walls roof.
To meet all three goals insulating your finished attic ventilating the roof and maximizing headroom use a combination of dense batt insulation rigid foam sheeting and air chutes.
Most codes require a specified minimum amount of headroom and it s tough to meet this requirement when insulating a finished attic especially since most codes require insulation equal to r 38 or more.
Type and material of your insulation.
There are two basic ways to insulate a finished attic.
Choose the fiberglass blanket or batting product that will provide the r value your house.
Contractor or insulation installer s fee.
Measure the depth of the wall framing which is the width of boards that form the attic roof structure.
Proper attic insulation is the best way to prevent heat loss in the winter and retain cool air in the summer.
If only the living space will be insulated wrap the insulation around the room s walls and ceiling and then continue along the floor of the non living space.
In this case the area behind the knee wall will be uncomfortably hot or cold.
So it s time to pay close attention to what s happening up there.