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.
Insulating a hip roof attic.
Insulating a finished attic there are two basic ways to insulate a finished attic.
I would recommend that you install them the full length from the lowest part of the attic to where there is an adequate air space existing.
In this way you prevent the heat from the rooms below escaping to the attic rooms above.
Insulating your roof and attic space will help retain energy in your home often leading to cost savings and comfort improvement.
These challenges go away if the entire roof is insulated typically by applying spray foam insulation to the underside of the roof deck.
Additionally insulation serves as a way to enhance sound proofing on the uppermost envelop of your house.
Furring down the slopes can often be avoided by using high density closed cell foam.
In this case the area behind the knee wall will be uncomfortably hot or cold.
At the same time the areas below the roof benefit from increased comfort both during the winter and the summer.
This is a styrofoam shoot that you staple to the underside of the roof deck stopping the insulation from compressing against the underside of the roof and creating a 1 1 2 airspace for 4 to 8 long.
Insulating in and around your roof attic space also prevents long term damage from moisture build up or ice damming which results from the warm air trying to escape through the apex of the roof but instead heating up the snow.
When hvac equipment is in the attic insulation and an air barrier at the roof line brings that equipment within the conditioned enclosure envelope thereby allowing it to operate in more favorable temperature and humidity conditions without air leakage and heat loss gain directly to the exterior.
This brings the entire attic into conditioned space and thus the knee walls do not have to be air sealed or insulated.
But the best solution is actually to insulate both the attic floor and the underside of the roof.