What size fascia board do I need?

The most common UK fascia board sizes are 150mm (6"), 175mm (7"), 200mm (8") and 225mm (9") wide. The correct width depends on the depth of your rafter feet at the eaves. For most modern UK houses, 175-200mm is standard. uPVC fascia boards are typically 18mm thick and come in 2.5m, 3m or 5m lengths.

What is the standard soffit depth in the UK?

Standard soffit depth (the horizontal projection from the wall to the fascia) is typically 200-300mm on most UK houses. Bungalows and older properties may have deeper soffits of 300-400mm. uPVC soffit boards are usually 300mm wide (to cover the most common sizes in one piece) and 9mm thick.

Should I choose uPVC or timber for soffits and fascia?

uPVC is by far the most popular choice for UK homes. It requires no painting, does not rot, and lasts 20+ years with minimal maintenance. Timber fascia and soffits need regular painting (every 3-5 years) and are prone to rot, but some conservation areas or listed buildings may require timber. uPVC is typically more cost-effective over its lifetime.

Do I need ventilated soffit boards?

If you do not have a breathable roofing membrane, you will need ventilated soffit boards to provide airflow into the roof space and prevent condensation. The Building Regulations (Approved Document F and C) require a continuous 25mm gap or equivalent ventilated area. Vented soffit boards have small perforations along their length to allow air circulation. Use our Felt and Batten Calculator to check if breathable membrane is included in your roofing spec.

How many joining trims do I need?

You need one H-section joining trim at every joint between boards (where two board ends meet). You also need external and internal corner trims at each corner of the house. For a standard detached house, this is typically 4 corners. Do not forget J-trim or F-trim where soffit meets the wall.

Soffit and Fascia Calculator — How Many Boards and Trims Do I Need?

Soffit and Fascia Calculator — Boards, Trims & Lengths

Calculate soffit boards, fascia boards and joining trims for your eaves. Covers uPVC and timber with UK standard sizes.

Total Eaves Length

Total perimeter of eaves (all sides)

Soffit Depth

Typical UK range: 200-300mm

Material

Board Length

Include wastage allowance

Adds 10% extra for cuts and joints

Wastage Percentage

10% is standard for soffit and fascia work

Price Per Fascia Board (optional)

Price Per Soffit Board (optional)

How We Calculate This

Our soffit and fascia calculator works out how many boards and trims you need based on your total eaves length, soffit depth and chosen board size. It covers both uPVC and timber options.

The formula

Fascia boards = Total eaves length ÷ Board length
Soffit boards = (Total eaves length ÷ Board length) × Rows needed

Soffit rows depend on your soffit depth vs. the standard 300mm board width. If your soffit is 250mm deep, one row of boards suffices. If it is 500mm, you will need two rows.

Standard UK sizes

Fascia boards: 150-225mm wide, 18mm thick, lengths 2.5m/3m/5m
Soffit boards: 300mm wide, 9mm thick, lengths 2.5m/3m/5m
Joining trims: H-section connectors at every board joint
Corner trims: Internal and external corner pieces

The calculator assumes 4 corner trims as standard. Adjust based on your roof shape — a semi-detached house may need fewer, while an L-shaped roof needs more. Always add 10% wastage for cuts and fitting adjustments.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Soffit and Fascia Calculator — Boards, Trims & Lengths

How We Calculate This

The formula

Standard UK sizes

Frequently Asked Questions

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