The illustration to the right shows the proper insulation of this style of roof.
Mansard roof insulation.
One strategy would be to incorporate the attic into the conditioned space and then use a sandwich of barriers and insulation under a furred vented.
This barrier may not be fitted to an older home and you should consider getting a contractor.
If the attic space remains uninhabited the air in the under roof space serves as a good thermal insulation along with the insulation of the floor.
In the case of the attic this is not at all the case.
Originally i was toying with the idea of closed cell spray foam for the whole mansard floor but i do not want to tear down historic plaster.
But what materials should be used to save energy on this type of house.
I recently purchased a home with a mansard roof i had some roofers come to give quotes to replace the top it is finished and they all recommend adding ventilation known issue with mansard s.
To insulate the roof you will need to use a combination of insulation to fully protect the roof.
Mansard and gambrel style roofs have always been hard to insulate.
After having dense pack installed in the building walls the mansard is the next target.
Here the insulation is very close to the roofing material and the task is not.
Step 1 add a vapor barrier.
A mansard or mansard roof also called a french roof or curb roof is a four sided gambrel style hip roof characterized by two slopes on each of its sides with the lower slope punctured by dormer windows at a steeper angle than the upper.
I have a house with mansard roof in boston.