Damp Proof Membrane Calculator

Floor DPM, cavity drainage, tanking slurry and radon barrier - with upstands and tape

Membrane Type

Upstand Height (mm) The membrane is turned up the wall - typically 150-300 mm. Set to 0 to ignore upstands.

Include DPM / radon tape 50 m rolls - for sealing joints and upstand perimeter

Joint / lap width (mm)

Waste Allowance (%)

10%

10% for regular rooms; 15-20% for awkward shapes or many internal corners.

Cost per roll

Cost per tape roll (50 m)

Labour per m²

Delivery (flat fee)

Rolls to Buy
-
rolls

Floor Area

m²

Total inc. Upstands

m²

Type	Used for
Floor DPM	Under concrete slabs, screed, beam & block floors
Radon Barrier	Radon/gas-affected areas (Part C Building Regs)
Cavity Drainage	Basements, cellars, below-ground retaining walls
Tanking Slurry	Wet rooms, below-ground walls, waterproof render base

Gauge	Typical use
250 Î¼m (1000g)	Light duty, under screed only
300 Î¼m (1200g)	Standard floor DPM - most common
500 Î¼m (2000g)	Heavy duty, commercial or contaminated ground
750 Î¼m (3000g)	Radon barrier, gas-resistant applications

Minimum requirement under Part C of Building Regulations is 300 Î¼m (1200 gauge). Radon areas typically require 500-750 Î¼m.

The membrane must be turned up at least 150 mm (Building Regs) on all walls - 300 mm is common best practice.
Laps between sheets should be at least 150 mm, taped with proprietary DPM tape.
For radon applications all joints must be sealed with radon-rated tape - do not use standard polythene tape.
Cavity drainage membranes should be installed with the studs facing the wall and lapped 50-100 mm at edges.
Tanking slurry - apply primer first, then minimum 2 brush coats. Scrub coat required on horizontal surfaces.