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DPC Calculator — Damp Proof Course Lengths & Rolls
Calculate damp proof course quantities for walls, cavity trays and stepped DPC. UK standard roll sizes.
Length of wall requiring DPC
Number of walls with the same dimensions
Above windows, doors and abutments
Adds 10% for cutting and fitting
Typical site allowance for cutting and offcuts (rule of thumb ~10%); no British Standard sets a fixed DPC wastage figure.
Enter your supplier price for a cost estimate
How We Calculate This
This calculator works out the total length of DPC needed for your project, including allowances for overlaps at joints (100mm per join, the BS 8215:1991 minimum lap in runs) and wastage, then converts this to standard roll quantities.
The formula
Total DPC = (Wall length + Join overlaps) × Wastage factor
Rolls needed = Total DPC length ÷ Roll length
Cavity tray = (Opening width + 300mm) per opening
Standard UK DPC sizes
- 112.5mm wide: Standard single leaf — 30m rolls
- 225mm wide: Wide walls / double leaf — 30m rolls
- 300mm wide: Stepped DPC — 30m rolls
- 450mm wide: Below ground / wide walls — 30m rolls
- Pitch polymer: 20m rolls (higher specification)
- Lead DPC: 3m strips (premium, cavity trays)
Overlap DPC joints by 100mm minimum in runs (BS 8215:1991), with full laps at angles. At corners, fold the DPC — never cut and butt. DPC must be bedded on a full mortar bed and pointed flush with the wall face. Lead DPC is used for stepped DPCs and cavity trays rather than continuous horizontal runs.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.