Rainwater
Fascia and soffit board lengths and soffit area
- where
- fascia length including waste (m)
- total fascia run (m)
- waste and cutting allowance (%)
- board lengths needed
- stock length of board (m)
- soffit area (m²)
- soffit depth (mm)
- spare length after cutting (m)
Explain this equation
Counts the fascia and soffit boards to order for a run of eaves and gives the soffit area. Use it for uPVC or timber fascia and soffit replacements.
The fascia run is increased by a cutting allowance and divided by the board stock length, rounding up to whole boards. The soffit follows the same run, so the same number of lengths is usually needed. The soffit area is the run times its depth (converted from mm). X shows how much board is left over, ignoring the waste allowance.
Whole boards from a total length, plus a simple strip area.
Sense check: 24 m of fascia with 5% waste on 5 m boards needs 6 boards, leaving 6 m spare. A 300 mm deep soffit over that run is 7.2 m².
Watch out: joints should land on rafter feet and corners need mitres or trims, so short runs can waste more than the percentage suggests.
Counts stock lengths of fascia and soffit board for an eaves or verge run, and gives the soffit area for ventilation and finish.
Enter your values to see the result.
Good to know
Measure each run including returns and the overhang at gable ends. uPVC boards are commonly sold in 5 m lengths: enter your supplier’s length. Allow for joint trims and corners at each change of direction, and keep joints off the gutter brackets. If gutters are being replaced, the fascia run is also the gutter run for Approved Document H sizing.
Common mistake
Counting lengths from the total run alone when there are many short runs. Each short run needs its own board, so count per run if the runs are under one stock length.
Limits
Simple count on total run. Trims, corners and fixings are not counted. Soffit area assumes a constant depth.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the roof covering manufacturer’s fixing specification, BS 5534, BS 8000-6, BS 6229, the Lead Sheet Training Academy guidance and Building Regulations. Wind uplift and structural design need a competent designer.