Polythene Damp Proof Membrane DPM 1200 Gauge Black BBA (4 x 25m) is a heavy-duty, 300 micron thick polyethylene sheet engineered to create a continuous, impermeable moisture barrier beneath solid ground floors.

Primary Uses & Key Features

• Under-Slab Damp Protection: Laid directly beneath ground floor concrete slabs, screeds, or subfloor insulation to block rising groundwater vapor and dampness from penetrating the building interior.

• Building Regulations & BBA Compliance: Fully certified by the British Board of Agrément (BBA) to satisfy UK Building Regulations (Approved Document C) for ground moisture resistance in new builds and extensions.

• High Puncture & Tear Resistance: The robust 1200 gauge (300/mum) thickness resists tearing during site installation when laying over sand-blinded hardcore or handling steel reinforcement mesh.

• Radon & Soil Gas Defense: Acts as a barrier against soil dampness and assists in reducing low-level ground gas ingress when taped at joints and linked to wall DPCs.

• Large Area Coverage (100m^2): Supplied as a folded 4m x 25mroll that opens out to cover large floor footprints quickly with minimal overlapping seams.

Available for collection from our Rugby branch or local delivery using our own fleet.

Delivery is kerbside and the final offloading position is always subject to safe access and the driver’s discretion.

Please tell us before delivery about:

• Narrow roads or restricted entrances
• Parked vehicles or limited turning space
• Overhead cables, trees or other obstructions
• Soft, sloping or unsuitable ground
• Any other access concerns

Enter your postcode on the product page to check your delivery area. We’ll confirm the delivery date after your order is placed.

What is the difference between "gauge" and "microns" for DPM?

Gauge is a traditional UK measurement for polythene thickness. 1200 gauge is equivalent to 300 microns (0.3mm). This 300 micron threshold is the standard minimum thickness specified by UK Building Regulations for heavy-duty damp-proof floor membranes.

How far should DPM overlap at seams, and how is it sealed?

Overlapping sheets must overlap by at least 150mm. Seams must be double-sealed: first using double-sided jointing tape between the overlapping faces, then covered with single-sided DPM lap tape over the exposed top edge to ensure a watertight and vapor-tight joint.

How does a DPM connect to the wall DPC?

To create a continuous moisture barrier across the whole building, the DPM should be dressed up the perimeter walls and lapped with the wall DPC by at least 100mm, sealing the junction tightly with jointing tape before pouring the floor screed or concrete.

Is sand blinding necessary before laying 1200 gauge DPM over hardcore?

Yes. Compacted stone hardcore has sharp edges that can puncture the membrane under the weight of wet concrete. A layer of clean building sand or a geotextile fleece must be laid over the hardcore ("sand blinding") to create a smooth bed before laying the DPM.

What does BBA certification mean for a Damp Proof Membrane?

BBA (British Board of Agrément) certification confirms that the membrane has undergone rigorous independent testing for durability, tensile strength, and water vapor permeability, ensuring it satisfies local authority building control inspections.