I am building a screen house with a metal roof -- do I need roof felting, and if so, is there a non-asphalt nontoxic alternative?
The roof will not need to be insulated. it seems to me I can screw the metal directly onto a simple wooden framework. I have chemical sensitivity and would like to build without asphalt, rubber or plastic in the roof, all of which heat up in the warm weather and cause outgassing. I'd prefer no felting if possible.
Generally speaking, I would always recommend using a separation layer (including air-gap) between a metal roof and a wood/plywood substructure since a reaction between wood treatment and metal roofing might occur and cause future damage.
A great product to use as a separation between the metal and the substructure is the so-called Sharkskin. Please review the information of the manufacturer to determine if this product will work for your project.