Rafter length and pitch
Common rafter length, ridge rise, angle and overhang from the span and roof pitch.
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- Your own numbers, worked out as often as you like
- The full roof cut list you can print or save to My work
- 5 cited sources, linked, with the checks to make
- Every other tool for the same role, in the same plan
- A plain-words read of your result (a fuller AI read with the Bifrost AI add-on)
Included in these role plans
Example result · fictional numbers
What you get: roof cut list
Worked out by this tool from its default inputs. Its role plan lets you run your own numbers, print the sheet and save it.
66 2x8 rafters at 17 ft 7/8 in (18 ft stock), 2x10 ridge, 48 sheets of sheathing
- Run (after ridge deduction)
- 13 ft 11 1/4 in
- Rafter length, plumb cut to seat
- 15 ft 7 in
- Tail length
- 1 ft 5 7/8 in
- Total rafter length
- 17 ft 7/8 in → order 18 ft stock
- Ridge rise above wall plate
- 6 ft 11 5/8 in
- Roof angle
- 26.6°
Rafter cut list
- Common rafters
- 62 (31 a side at 16 in on center), plus 4 for the rake overhangs
- Each rafter
- 17 ft 7/8 in long from 18 ft 2x8: 15 ft 7 in plumb cut to seat, 1 ft 5 7/8 in tail
- Plumb cut (ridge and tail)
- 26.6° off square; 6 and 12 on the framing square
- Seat cut
- Level, square to the plumb line, 3 1/2 in long for the 2x4 plate
- Birdsmouth depth
- 1 9/16 in, square to the rafter edge
Also on the sheet
- Code checks · 4 lines, starting with “Birdsmouth”
- Sheathing and trim · 4 lines, starting with “Roof area, both slopes”
- Fall protection · 1 line, starting with “Eave at 10 ft”
The plain-words read of this example
A 40 ft building at 16 in on center needs 66 2x8 rafters, each 17 ft 7/8 in cut from 18 ft stock at 26.6°. The birdsmouth on the 2x4 plate is 1 9/16 in deep, within the 1/4-depth limit. The ridge must be at least a 2x10 to cover the 8 1/8 in cut end. Both slopes take about 48 sheets of sheathing. It is a steep roof with the eave at 10 ft, so fall protection is required.
5 cited sources
- IRC 2021, Chapter 8 Roof-Ceiling Construction (R802) (International Code Council)
- Birdsmouth cut: what the code allows (Building Code Trainer)
- 29 CFR 1926.501, Duty to have fall protection (OSHA)
- 29 CFR 1926.500, Scope and definitions (fall protection) (OSHA)
- APA resource library (Engineered Wood Construction Guide, roof sheathing) (APA, The Engineered Wood Association)
Plus 5 step-by-step checks, a print layout and a link that reopens it with your numbers.