Many thanks for your perspective on this. I can certainly use some good advice.
I own a 72 year old home located in Quebec Canada which has the original mansard style roof with which it was built. The roof top is made with steel and the tiles on the side are slate. The house was insulated originally with horse hair and other than a few minor modifications has effectively no insulation. There is no insulation at all in the roof which brings me to this e-mail.
In an attempt to be more “green”, get some control on our heating bills and eliminate ice damming (typically have to climb up and scrape off a few times a year), I would like to insulate it. I have inquired with professionals and the advice given was to use blown cellulose. My understanding is that if it gets wet, the cellulose needs to be removed. As the roof used to leak like a sieve (lots of tar sealer, polyacrylamide paint on the steel and sealing the chimney brick seems to have virtually eliminated the problem for now…) and I can’t assume that it will be waterproof.
My other issue is the ventilation (or lack thereof) in the roof. When the roof was originally built there was no ventilation. Subsequent owners have installed a couple of vents on top but no soffit equivalent due to the mansard style. I am finding it challenging to find a good venting solution. In addition, to get some vents in at the base of the roof I will need to cut through the slate. I have only been able to locate one organization that can work with slate in my area, they are not roofing experts and were not interested in the project.
So, my best guess as to the right thing to do is Roxalt insulation attached between the joists on the roof with a plastic vapor barrier installed on top of it and fiberglass insulation on the floor. No good idea what to do about ventilation. Maybe install vents in the steel near the roof edge and a powered fan in the center high point?
Any advice, recommended good books or suggestions re the best way to do this would be very much appreciated.