Fastening sheathing to timber frame

[wvwoodworker]

I'm building a timber frame house with a living roof (soil and plants on top, with an EPDM liner over the sheathing). The architect that spec'd the roof stressed that it's crucial the fasteners don't pop up as they can punch holes in the EPDM. (This is a problem with stick framed roofs so I expect it would be even worse when framing with green timbers.) As a solution to this, she recommended either putting down 1/8" felt over the entire roof (expensive) or to cover every single nail head with a 4" glue-down EPDM disc (time consuming). My first thought was to use screws, but since I'll be screwing the sheathing into green timbers, I'm worried that the timbers will shrink and the screw heads will end up proud of the sheathing, puncturing the lining anyway. I'm using 2x sheathing so screws are 3.5" inches long, going into white oak rafters. I'm thinking as long as I sink the screws a bit below the surface of the sheathing I should be OK, but this is my first timber frame so I'm not sure about that assessment. I'd appreciate any advice other members might have.

[Don P]

@Furby