If moss is happy in your environment, I would focus my efforts there. It can grow on vertical surfaces without much grip, if there is enough moisture and not too much sun...
But... how to keep sliding snow from ripping it off the roof? Retaining snow seems kind of counter to the purpose of a steep roof, but perhaps necessary to retain moss..
This isn't going to do much for thermal mass in the roof. Frankly I think this is better addressed inside the building unless you reconsider the pitch...
Catherine Windrose wrote:Found this recently:
Graham Chiu wrote:Why not just add another storey to get the extra space?
Dillon Nichols wrote:If moss is happy in your environment, I would focus my efforts there.