How do I calculate cladding boards with overlap?

The effective cover of each board equals the board width minus the overlap. For 150mm shiplap with 25mm overlap: effective cover = 125mm. Boards per m² = 1000 ÷ 125 = 8 boards per metre of height. Multiply by the wall area for total boards. Add 10% for wastage on cuts and ends.

What is the difference between shiplap and featheredge?

Shiplap has a uniform thickness with a rebated overlap of about 25mm — boards slot together for a flat appearance. Featheredge (weatherboard) tapers from thick at the bottom to thin at the top, with a 40mm overlap. Featheredge is more traditional and sheds water well, while shiplap gives a cleaner, more modern finish.

Do I need a breather membrane behind timber cladding?

Yes, a breather membrane is essential behind timber cladding. It allows water vapour to escape from the building while preventing wind-driven rain from penetrating. Fix the membrane to the wall, then install battens over it to create a ventilated cavity of at least 25mm behind the cladding. Without this cavity, moisture will be trapped and cause rot.

What batten spacing for timber cladding?

Battens should be fixed vertically at 600mm centres for horizontal cladding (or horizontally at 600mm for vertical cladding). Use 25×50mm or 38×50mm treated softwood battens. The battens create the ventilation cavity behind the cladding and provide the fixing points for the boards. Use stainless steel or galvanised fixings.

What fixings should I use for timber cladding?

Use stainless steel ring-shank nails or screws — never plain steel, which will rust and stain the timber. Annular ring-shank nails provide excellent holding power. For hardwood cladding, pre-drill to prevent splitting. Fix through the overlap (face-fixed) or secret-nail through the tongue on T&G profiles. Use 2 fixings per board at each batten.

TradeCalculator

Timber Cladding Calculator

Calculate board count by profile (shiplap, featheredge overlap), battens at 600mm centres, breather membrane and fixings.

Wall Area

Total area to clad (minus openings)

Board Width

Nominal board width before overlap

Profile

Affects overlap and effective cover

Include breather membrane

Essential for ventilated cladding systems

Price Per Board (optional)

Price Per Batten Metre (optional)

How We Calculate This

This calculator determines cladding board quantities based on the profile overlap, plus battens, breather membrane and fixings.

The formula

Effective cover = Board width - Overlap
Boards = Wall area × (1000 ÷ Effective cover)
Battens = (Wall width ÷ Spacing + 1) × Wall height
Fixings = Boards × 2 per batten crossing

Profile overlaps

Shiplap: 25mm overlap, clean modern finish
Featheredge: 40mm overlap, traditional look
Tongue & groove: 10mm overlap, tight fit
Square edge: 0mm, use for open-rainscreen systems

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.