Garden room exteriors: cladding, fascia, soffit and guttering Once the frame is up and the walls and roof are insulated, the outside is what keeps the weather out and what everyone sees. Get it wrong and you get damp behind the boards, a gutter that drips down the door, or a fascia that sits 50mm short of the roof deck. This guide covers the outside of a typical timber-framed garden room with a flat or pent roof: what goes behind the cladding, which cladding to choose, how to