Cladding Calculator — How Much Cladding Do I Need?

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).