ABOUT DAMP PROOF COURSES

A damp proof course is a strip of impervious material the same width as a brickwork or blockwork wall, to keep out moisture. Historically, damp proof courses were also made of impervious bricks or slates.

A damp proof course at ground level, to exclude rising damp, is laid near the bottom of the wall, at least 150mm above ground, and projecting 5mm. At high level, eg above junctions of parapet walls with a roof and at the lintel above door or window openings, a damp proof course diverts rain out of the cavity, to drain through weepholes. In cavity walls the outer edge of a damp proof course is two brick courses lower than the inner edge, to prevent entry of driving rain and both edges are built into the bed joints. Joints at laps and corners are covered with bonding tape.

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Damp proof course material comes in preformed rolls, made of a variety of flexible materials such as bitumen polymer or pitch polymer, with or without fibres. In cold weather these types should be warmed before unrolling to prevent cracking. Other materials for damp proof courses are embossed polyethylene or thin, soft super-purity aluminium sheet. A ground level damp proof course has been required by law since the Public Health Act of 1875.

All these damp proof course materials should be able to accommodate slight movements in the walling materials. They need to be jointed with care, usually by lapping at least 100mm, and, in the case of masonry, the weight of the wall is usually sufficient to seal the lap without the use of additional jointing materials. The organic felts used in some damp proof courses may be found to have perished, but this does not necessarily mean that they become ineffective as damp proof courses provided they are not disturbed by subsequent movements.

Bituminous felt damp proof courses are vulnerable to being squeezed out slightly under pressure, especially in hot weather, but the amounts exuded are usually insufficient to compromise their performance and durability. Bituminous felt damp proof courses are also relative ineffective against horizontal displacement, providing a slip plane on which the walling can move with relative ease. Polythene is common in modern buildings but plain sheet has very low shear bond and the most recent types have a moulded pattern to improve shear and flexural bonds. Higher performance damp proof courses are often formulated from a blend of pitch and polymer and these have good resistance to squeezing, though doubts have been raised on possible risks to health from volatile organic compounds (VOCs).

LEADING UK DAMP PROOF COURSE SUPPLIERS

Ruberoid is a leading supplier of damp proof courses. Ruberoid MortarMatch is a damp proof course whose ingredients do not include bitumen or pitch. The damp proof course contains a pigment. This enables the damp proof course to merge in appearance with brickwork or stonework, as opposed to the traditional black coloured damp proof course.

Click here for an easy-to-use listing of leading UK suppliers of damp proof courses, provided by Archbone.

DETAILED INFORMATION RESOURCES ON DAMP PROOF COURSES

We recommend the following professional construction directories, which include manufacturers' specifications and CAD details: Barbour Compendium at www.barbourcompendium.co.uk, RIBA Product Selector Plus at ww.productselector.co.uk, ASC Bricsnet at www.ascinfo.co.uk, Building Products Index at www.bpindex.co.uk, British Board of Agrément at www.bbacerts.co.uk, British Standards Online at www.bsonline.bsi-global.com.

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