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Cladding Calculator — How Much Cladding Do I Need?
Calculate cladding boards, battens, breather membrane and fixings for external wall cladding (plus counter-battens for vertical cladding). UK standard profiles.
Total length of wall to be clad
Height of area to be clad
Nominal board face width
Standard lengths: 2.4m, 3.0m, 3.6m, 4.8m
Board-to-board overlap
Adds 10% extra for cutting and waste
10% standard; 15% for walls with many openings
Enter price per board for a cost estimate
Vertical batten centres in metres. 400–500mm recommended (TDCA / Vastern Timber); 600mm is the maximum, ≤400mm for diagonal boards.
Overlap allowance for breather membrane (default 1.15)
Safety notice
Structural elements must be designed or checked by a structural engineer before construction. Treat these figures as initial guidance for planning and budgeting, not a structural design.
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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, breather membrane and fixings (plus counter-battens for vertical cladding).
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: For horizontal cladding, vertical treated-softwood battens at 400–500mm centres (600mm max). This single layer forms the ventilated cavity, so counter-battens are only needed for vertical (board-on-board) cladding.
- Breather membrane: Wall area + 15% for overlaps. Standard wall-wrap rolls (e.g. Tyvek Supro) are 1.5m × 50m = 75 m².
- Fixings: One stainless-steel fixing where each board crosses each vertical batten (TDCA single-fix rule), allowing the board to move.
Standards
External timber cladding is specified to BS 8605-1:2014 and installed per the guidance in BS 8605-2:2014 and the TDCA Timber Cladding Handbook (battens, cavity, breather membrane, fixings). Wind-driven-rain exposure is assessed using BS 8104:1992, and moisture resistance is covered by Approved Document C. Treat timber to BS 8417:2024 (external cladding = Use Class 3).
Frequently Asked Questions
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.
Horizontal cladding (shiplap, featheredge, fibre cement) fixes to vertical battens — typically 25×50mm or 38×50mm treated softwood at 400–500mm centres (600mm maximum). That single vertical batten layer creates the drained, ventilated cavity behind the cladding, so no counter-battens are needed. Vertical (board-on-board) cladding is the reverse: horizontal battens over vertical counter-battens. The ventilation gap prevents moisture build-up and is recommended by BS 8605-2:2014 and the TDCA Timber Cladding Handbook, with the moisture-resistance principle set out in Approved Document C. See our Wall Cladding Calculator for a full materials list including battens and membrane.
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.
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.
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.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.