A valley rafter extends diagonally at a 45º angle from the inside corner of intersecting wall plates to the ridge. Easy Rafters can calculate valleys rafters for roofs that intersect at 90º and have equal spans and slopes. Use the Unequal Span Valley option to calculate valleys for intersecting roofs with equal slopes, but different spans or use the Blind Valley option to calculate valleys for intersecting roofs with different spans and/or slopes.