I have noticed a possible issue with the valley in our new extension. There is an existing roof - 49 degree pitch with attic trusses and a new roof with a 45 degree cut and pitch roof with ridge beam. The two sections of roof intersect with a pair of valleys. One on side, the valley rafter has been cut into the trusses. The tops of these cut trusses meet flush with the valley rafter, looks good. However on the other side of the valley rafter, the new roof rafters dont meet flush with the top of the valley rafter. As you move along the valley from bottom to top, the tops of the new rafters are increasingly proud. The peaks of the existing and new roofs are the same. The rafters in the new roof are 150 x 50, the existing are 170 x 50, but I would have thought the valley rafter would have been set at angles such that the old and new rafters met flush with the top of the valley rafter, the difference in rafter depth being felt to the underside where it could be cut flush and dealt with by internal finishing. the valley rafter is a pair of 200 x 50 bolted back to back.

I'd appreciate comments from anyone who understands roof framing, it looks wrong to me. Only spotted it on friday so have not had a chance to discuss with carpenters yet. I've attached a pic, the new rafters are to the left, the existing trusses to the right.

GRP valley.

but bottom line is the valley rafter angles are off, no?

natural slates

I see what you mean about the centre line and would agree if it were not the case that the step decreases, the rafters pictured highlight the step but lower down the valley the step tapers away and the lowest rafters are flush with the valley while the trusses meet flush all the way along.

I havent had a good look at the the valley/ridge detail yet to see how it all sits up there.