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Damp proof membranes and damp-proof course are designed to preventing damp rising from the ground and into the property. It also plays a vital part in preventing ground gases from entering the property. Attention to detail is critical to its success.
Preparation for the installation of the DPM must be complete before commencement.
Block and beam fully grouted with no gaps around the penetrations.
Free from debris and other materials which could puncture the membrane.
Damp proof membrane laid across the block and beam.
Pulled tort with limited folds and joints.
Ballast carefully placed on top of the membrane to prevent movement.
Damp proof membranes require sealed laps of 300mm or as per the manufacturer’s recommendations.
Gas membranes require the laps to be sealed.
At party walls the membrane must form within the cavity to a minimum depth of 225mm.
This is to comply with Robust details.
Internal and external corners must be fixed and sealed as per the design.
Prefabricated corners can be used.
Penetrations require an appropriate seal.
Seals need to be complete around both base and pipe.
Approved tape should be applied to the membrane the pipe work or ducting penetration.
Mechanical fixing used around the pipe/duct to secure the “top hat”.
Unless stated in the design, DPM must have a minimum lap of 90mm on to the internal leaf of the external wall.
DPC over laps the DPM on the internal leaf.
DPC on the external leaf must be placed flush with the external face of the brick or over hang slightly.
Gas membranes must be cut flush with the external face of the brick of the external leaf.
A cavity tray must be provided, and weep holes installed to allow moisture that enters the cavity to egress.
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