Damp Proof Course Calculator

About this calculator

A damp proof course (DPC) is a continuous horizontal barrier built into a wall to stop rising damp from moving up from the ground into the brickwork above, and “continuous” is the operative word — every joint where one roll ends and the next begins must overlap, typically by around 100mm at horizontal joins and more at corners, or the barrier isn’t actually continuous. Total DPC length needed is therefore wall perimeter plus the extra length consumed by these laps, not simply the bare perimeter measurement.

Builders and DIY renovators calculate DPC length, roll count and total cost before ordering because DPC membrane is sold in fixed roll lengths, and underestimating the lap allowance is a common reason a job runs short mid-installation — a gap in the DPC anywhere along the wall defeats its purpose, since damp will simply rise through the unprotected section.

This calculator takes your wall perimeter, roll length and roll price, and returns exactly how many rolls you need — laps included — and the total cost.