How much cladding do I need per square metre?

The number of cladding boards per m² depends on the board width and overlap. For timber shiplap with 150mm boards and 25mm overlap, the effective cover is 125mm, so you need 8 boards per metre height. For featheredge with 50mm overlap, effective cover is 100mm, so you need 10 boards per metre height. Board length determines how many pieces are needed across the wall width.

What battens do I need behind cladding?

External cladding requires a supporting framework of battens (typically 25x50mm or 38x50mm treated softwood) fixed vertically at 600mm centres. Counter-battens may also be needed horizontally to create a ventilated cavity behind the cladding. This ventilation gap is essential to prevent moisture build-up and is required by BS 8104 and Approved Document C.

Do I need a breather membrane behind cladding?

Yes. A breather membrane (such as Tyvek or similar) should always be installed behind external cladding to protect the structure from wind-driven rain while allowing moisture vapour to escape. This is a requirement of Approved Document C (Site preparation and resistance to contaminants and moisture). Allow approximately 15% extra membrane for overlaps.

What is the difference between shiplap and featheredge cladding?

Shiplap boards have a rebated (stepped) profile that gives a tight, overlapping joint with a consistent shadow line. Featheredge (weatherboard) boards are wedge-shaped — thick at the bottom and thin at the top — and overlap by 50mm or more. Shiplap is more weather-tight and easier to install; featheredge is more traditional and often cheaper but requires more overlap, so you need more boards.

How much wastage should I allow for cladding?

Allow at least 10% wastage for cladding boards. This covers cutting around windows, doors, and corners. If the wall has many openings or complex features (bay windows, stepped walls), increase wastage to 15%. Composite and fibre cement boards are more expensive, so accurate measurement is even more important to minimise waste.

Cladding Calculator — How Much Cladding Do I Need?

Calculate cladding boards, battens, counter-battens, breather membrane and fixings for external wall cladding. UK standard profiles.

Input Method

Wall Length

Total length of wall to be clad

Wall Height

Height of area to be clad

Cladding Type

150mm boards with 25mm overlap = 125mm effective cover

Board Width

Nominal board face width

Board Length

Standard lengths: 2.4m, 3.0m, 3.6m, 4.8m

Overlap

Board-to-board overlap

Include wastage allowance

Adds 10% extra for cutting and waste

Wastage Percentage

10% standard; 15% for walls with many openings

Price Per Board (optional)

Enter price per board for a cost estimate

How We Calculate This

This calculator determines the number of cladding boards by dividing the wall area by the coverage area of each board (effective cover width x board length), then adds battens, counter-battens, breather membrane and fixings.

The formula

Boards = Wall area / (Effective cover x Board length) x Wastage factor

Effective cover = Board width - Overlap

Default profiles

Timber shiplap: 150mm boards, 25mm overlap = 125mm effective cover
Featheredge: 150mm boards, 50mm overlap = 100mm effective cover
Composite: ~170mm boards with clip system, no overlap
Fibre cement: 190mm boards, 30mm overlap = 160mm effective cover

Supporting materials

Battens: Vertical at 600mm centres (treated softwood)
Counter-battens: Horizontal at 600mm centres for ventilation cavity
Breather membrane: Wall area + 15% for overlaps

Standards

Cladding installation should comply with BS 8104 (Code of practice for assessing exposure of walls to wind-driven rain) and Approved Document C (moisture resistance). Timber cladding per BS 8417 (preservation of wood).

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.