If you do not want any extra living space in your attic then you can install a low height roof but you will also have a small space to install the insulation and the ventilation system.
Insulating a gambrel roof room.
One of the best ways to protect your mansard roof from the problems of ventilation is to use a vapor barrier on the inside.
To insulate the roof you will need to use a combination of insulation to fully protect the roof.
Step 1 add a vapor barrier.
Because the gambrel roof doesn t go very high above the brickwork you can discover that you do not have enough living space in your attic.
If you have an existing house with this style then dense pack cellulose or pour in place open cell foam are your only options.
This should be a must see video for venting a gambrel r.
How to vent a gambrel roof using reflectix.