Penetrating and Rising Damp

Penetrating Damp

Penetrating damp occurs when moisture seeps in from the external walls to the internal walls, it is usually caused by construction that has failed and occurs at a high level of the property.

• Blocked guttering, hoppers or down-pipes. These will overflow when blocked and saturate the adjacent wall
• Unused chimneys that are capped or sealed, which has defective haunching will allow water to enter the chimney and saturate the building
• Where flashing on a building fails leaks will occur, this leak can lead to penetrating damp
• Valley gutters that are not lined appropriately and are not carried 200mm up the pitch roof on either side of the valley, under the slates or tiles can cause penetrating damp to a building if snow or ice accumulates in the valley
• Cavity walls that have a bridge; caused by rubbish left in the cavity or mortar that has been left on wall ties or insulation batts during construction, can cause penetrating damp if the wall experiences driving rain. Water can cross the cavity to the internal wall and saturate the inner masonry leaf and then onto the inner plaster.

How to spot penetrating damp

Damp will occur in certain areas of a wall or ceiling, however leaks can cause the same localised damp pattern. Therefore a professional should be brought in to determine the problem.

How can I get rid of it?

A professional builder or contractor will need to complete repairs on the property to solve the penetrating damp source.

Rising Damp

Rising damp usually occurs in properties built before 1930's and build with brickwork, stone and plaster (absorbent materials), it is rare in newer buildings. It is caused by moisture in the ground around and under the property rising up within external and internal walls, causing internal decoration to become damaged and lead to mould growth.

All new properties are built with a damp proof course, which prevents ground moisture rising into the property; however it can occur in newer buildings if the damp proof course becomes defective.

How to spot rising damp

Dampness, mould growth and staining will be visible along the lower part of the external or internal wall. Internally damp will be seen approximately one metre above the ground floor level. If a property with a damp proof course experiences rising damp, the pattern will be visible in remote areas where the damp proof has failed.

How can I get rid of it?

If a damp proof course has failed, it can simply be cut and replaced in the section that has failed. If a property does not have a damp proof course, one can be introduced by a professional who can inject the external walls, the chemicals injected will be absorbed and form a barrier. It is necessary with this process to ensure all internal plaster from the affected walls are removed before the damp proof course is introduced, once the external walls have been treated new internal, waterproof plaster can be applied internally.

If a damp proof membrane is missing it may be possible to fix on top of a concrete ground floor slab, a polythene damp proof membrane or a sealing compound. It must be noted that with this method the floor of the property will have to be replaced, however floor insulation could be installed at the same time.

If your property is listed it may not be possible to inject a damp proof course or replace a floor, therefore actions will need to be taken to manage the problem such as externally applying lime wash and keeping rooms well ventilated and heated.

Please also see Condensation and Mould

If you live in rented accomodation you can request a visit from the Energy Awareness Officer. Please mention mould on your request.


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Modified: 2014-10-09
Published: Tue, 11 Nov 2014 11:43:46
Author: Martin Fitzpatrick
Editor: Allison.Helyer
LGSL PID: 880
RDCMS ID: 28466