Maybe on balance the dollar cost is the same but roofing is a messy business and that s a lot of foam to go into a landfill.
Roof foam peeling.
You ll just have higher energy bills than a house with code minimum insulation.
Then get a light airy fabric from a craft store and cut it to fit the ceiling shape leaving an extra inch or.
Direct attachment peel stick to the plywood then use 2 foam process to attach the concrete roof tiles.
Lstiburek takes blame for bad language.
A metal roof may need to be replaced when it grows rusty and begins leaking.
Either way use a wire brush to remove what foam is left if it s falling apart.
On a hip roof there isn t much point in spend extra for ventilation channels above the rigid foam since soffit to ridge venting is impossible on a hip roof.
It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.
Cleaning and inspecting the roof regularly can help prevent major damage from occurring.
Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.
Install 30 roofing paper mechanically attached to the plywood then peel and stick then 2 foam process to attach the concrete roofing tile.
But if you have an spf roof and don t re coat it in a few decades it will probably have degraded to such a point that it will have to be torn off and completely redone.
If you end up with r 20 foam or r 24 foam instead of r 49 foam your roof won t rot.