How Many Fascia and Soffit Boards Do I Need? UPVC (UK)
Fascia is the board along the lower edge of the roof, and soffit closes the underside of the overhang. 15 m of eaves with a 300 mm soffit takes 4 fascia boards, 4 soffit boards and 4 lengths of trim in 5 m lengths, with 5% for cuts. The fascia and soffit calculator counts the boards for your roof.
Boards by eaves length
With 5 m boards, a 300 mm soffit with 300 mm boards and 5% extra:
| Eaves | Fascia | Soffit | Trim | Soffit area |
|---|---|---|---|---|
| 8 m | 2 | 2 | 2 | 2.4 m² |
| 12 m | 3 | 3 | 3 | 3.6 m² |
| 15 m | 4 | 4 | 4 | 4.5 m² |
| 20 m | 5 | 5 | 5 | 6.0 m² |
| 30 m | 7 | 7 | 7 | 9.0 m² |
Board length
Boards come in different lengths. For 15 m of eaves:
| Board length | Fascia | Soffit | Trim |
|---|---|---|---|
| 2.5 m | 7 | 7 | 7 |
| 4 m | 4 | 4 | 4 |
| 5 m | 4 | 4 | 4 |
| 5.5 m | 3 | 3 | 3 |
Deeper soffits
A soffit deeper than the board is wide needs more than one row. A 600 mm soffit with 300 mm boards is two rows, so 7 boards for 15 m, against 4 for one row. Measure the overhang at several places, since it can vary.
Before you order
- Check the rafter ends and the timber behind the old boards: a new board over rot will not last.
- Decide on vented soffit boards or vents, because the roof space needs air at the eaves.
- Count corner pieces, joints and any gable ends separately: this counts the straight runs only.
- Plan to replace the guttering at the same time, since the fascia carries the brackets.
Fitting
- Make joints over a rafter or support, and stagger them between the fascia and the soffit.
- Leave a small gap at the ends for the plastic to expand, and cover it with a trim.
- Keep insulation from blocking the airflow at the eaves.
- Fix the fascia first so that the soffit can slide into its channel.
See the guttering calculator and the roof tile calculator. Lengths and widths vary by make: use those on the pack.
Frequently asked questions
How many fascia boards do I need?
Divide the length of the eaves by the board length and add 5%. 15 m takes 4 boards of 5 m.
How many soffit boards do I need?
4 boards of 5 m for 15 m of eaves with a 300 mm soffit and 300 mm boards. A 600 mm soffit takes 7.
How long are UPVC boards?
Most are sold in 5 m lengths, with shorter lengths for small jobs.
Do I need trim?
Yes, a J-trim or soffit trim finishes the soffit at the wall: 4 lengths here.
Should I do fascia, soffit and gutters together?
Yes. The scaffold is up, and the new fascia carries the new gutter brackets.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.
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