What size fascia board do you need?
Short answer. A fascia board needs to be tall enough to cover the plumb cut on the rafter tails plus a little extra to hide the soffit edge, which usually means one nominal size bigger than the rafters: 1x6 for 2x4 rafters or trusses, 1x8 for 2x6 rafters and 1x10 for 2x8 rafters. Steep roofs have taller plumb cuts and may need the next size up.
Why rafter size is not the whole answer
A rafter cut vertically at a pitch shows a taller face than its nominal depth. A 2x6 is 5 1/2 inches deep, but its plumb cut at 6/12 is about 6 1/8 inches, and at 12/12 about 7 3/4 inches. The fascia must cover that face, sit near the top of the roof sheathing so the drip edge can lap it, and drop a bit below the tail to hide the soffit.
Typical pairings
- 2x4 rafters or truss tails: 1x6 fascia (5 1/2 inches actual).
- 2x6 rafters: 1x8 (7 1/4 inches), moving to 1x10 on steep roofs.
- 2x8 rafters: 1x10 (9 1/4 inches).
- 2x10 rafters: 1x12 (11 1/4 inches).
How to measure your own
- Measure the existing fascia height and thickness if you are replacing it. Matching keeps gutters and soffit aligned.
- If the fascia is off, measure the plumb face of a rafter tail top to bottom.
- Add the soffit drop: how far below the tail the soffit sits, plus about 1/2 to 3/4 inch for a lip.
- Pick the board whose actual width covers that total.
Other details
- Some builders trim a level cut on the bottom of the tails, which shortens the face and allows a smaller board.
- Gutter hangers need solid backing, so a 2x sub-fascia behind a 1x finish board is common.
- Rake fascia on gable ends often matches the eave fascia for looks.