How to Set Out Hip and Valley Rafters
1. Lock In Your Key Measurements Before touching a saw, confirm: - Span (outside to outside of plates) - Run (half the span) - Pitch (roof angle) - Plan layout (hip or valley location, building shape) These control the entire hip/valley system. 2. Use the Hip/Valley Multiplier Hip and valley rafters are longer than common rafters because they run diagonally. Each pitch has a hip/valley multiplier: Pitch Hip/Valley Multiplier15°1.03520°1.06422°1.07825°1.10330°1.155 Hip/Valley Length = Run × Hip/Valley Multiplier Example (22° roof, 3 m run): 3 × 1.078 = 3.234 m This gives you the length from the ridge to the birds mouth. 3. Mark the Plumb Cut Hip and valley rafters use a different plumb cut angle than common rafters. Why? Because they sit at 45° to the building, so the angle changes. Use your speed square: - Set the square to the hip/valley plumb angle (found on the hip/valley scale) - Mark a clean plumb line - Cut accurately — this determines how the hip meets the ridge Tip: Most speed squares have a dedicated “HIP/VAL” scale for this. 4. Mark the Birds mouth The birds mouth on a hip/valley rafter is the same concept as a common rafter, but: - The seat cut is longer because the hip sits diagonally across the plate - The heel cut is steeper due to the hip angle Steps: - Measure down from the plumb cut the calculated length - Mark the heel cut (plumb line) - Mark the seat cut (horizontal line) - Keep the depth within one‑third of the rafter 5. Allow for Overhang Hip and valley rafters also need overhang, but the length is different. Use the hip/valley multiplier again: True Overhang = Horizontal Overhang × Hip/Valley Multiplier Example (450 mm overhang, 22° roof): 0.45 × 1.078 = 485 mm Mark the tail cut using the seat‑cut angle (90° – pitch). 6. Cut One Perfect Pattern Hip/Valley Rafter Just like commons and jacks: - Cut one hip/valley rafter perfectly - Test it at the ridge - Test the birds mouth on the plate - Check fascia height and overhang alignment