I have no idea what a lag is(this is not a term us welsh boys are familiar with) please describe.
I was going to use a tusk tenon joint as illustrated on page 60 of Tedd Bensons "Building the timber framed house" but as the purlin does not hit the valley beam/rafter at 90 degrees the joinery will be slightly different. How much will a joint like this weaken the valley beam/rafter, the purlin meets the rafter about half ways up its length/span. If this joint requires a peg would you peg down through the entire 11" of the valle beam?
