Penetrating damp refers to any defect that allows entry of rainwater and includes eroded pointing, brickwork, and missing or faulty flashings of chimney stacks; leaking roofs; blocked or broken gutters, fall pipes and other rain water goods; eroded pointing and frost damaged of masonry walls; cracked and blown renders; and rotten or poorly weatherproofed windows and doors.
Many of these roof slates are loose and will allow entry of rainwater. Loose slates can easily blow off a roof and are a potential health & safety risk. The weatherproofing (flashing) between the roof and the chimney stack is formed in mortar rather than lead. This mortar is cracked and will allow rain water to penetrate into the roof. Decay of the roof timbers abutting the stack is a common consequence of this defect. |
Rain water goods such as gutters and fall pipes are an important component of any dwelling and serve to remove rain water safely. Valley bottoms and gutters can become obstructed by weeds that prevent drainage and, instead, cause water to run onto the walls beneath.
Weeds obstruct the base of this valley and the gutter end preventing drainage of rainwater and allowing it to discharge onto the house walls and paths beneath. |
The end of this gutter is blocked with weeds. Efflorescent salts visible on the face of the brickwork beneath illustrate that this blockage is allowing rainwater to discharge onto the wall beneath. |
Timber gutters require regular maintenance and are prone to rot. Plastic gutters, although rot proof, are easily damaged by the weight of snow or through the careless use of ladders.
This plastic gutter has a broken bracket, causing it to sag and to discharge water onto the base of the wall. |
The timber gutter of this bay window has rotted allowing rainwater penetration and damage of the brickwork beneath. Timber gutters require regularly maintenance. |
Many older rain water systems incorporate 'hoppers' that are located on top or at intermediate points on fall pipes. Hoppers become obstructed by leaf debris and vegetation, if not cleared. Rain water pipes can also be blocked by debris and this, and other defects, often go unnoticed until dampness becomes apparent internally.
Here, either the hopper or the fall pipe is obstructed. The result is the same: rainwater, prevented from draining away has instead discharged onto the face of the wall. |
Masonry that is permanently damp such as that at the base of walls and particularly beneath a damp proof course is prone to frost damage in the winter. The water in the wall freezes and causes the surface to spall. This defect subsequently exasperates ingress of rain water and the problem worsens.
The pebbledash applied to this stone wall has deteriorated, because of rising damp and the effect of salts. The poor condition of this external coating now provides a route of entry for rain water. |
Defects to external renders are a common cause of dampness in properties. Many older properties are built with masonry that is bonded with lime mortar. It is often inappropriate to apply a modern cement renders to these older walls. Cement renders restrict evaporation and, because they are brittle in comparison with the original masonry, are prone to cracking. These cracks, even when relatively small, can allow ingress of rainwater to occur. Prevented from evaporating from the surface, this rainwater seeps through to the internal face of the wall.
Cracks in external render coatings allow ingress of water. The water it then prevented from evaporating away and seeps through to the inside face of the wall. |
Rainwater penetration can cause significant damage internally, spoiling wall decorations, plasterwork, and poses a risk of fungal decay, particularly of timbers that are built into the affected walls.
Wall decorations and plasterwork has become spoiled because of rainwater penetration resulting from defects to the balcony above. The adjacent image is an external view of this wall. |
Where rainwater penetration has resulted in salt contamination of the plaster, it is essential that appropriate action is taken to alleviate the effect of hygroscopic salts otherwise dampness will persist even after the original moisture source has been removed.
The chimney stack is in poor condition and this, along with a defect to the valley between the two roofs, is the cause of rain water penetration seen in the adjacent image. |
External doors that do not have adequate weatherproofing allow rainwater to seep beneath the door. This defect, like other forms of dampness that affect the base of ground floor walls, can sometimes be incorrectly diagnosed as rising damp. Timber windows are prone to decay allowing direct entry of rain water and cills that do not incorporate an adequate 'drip' – a groove on the underside of the cill – can allow rain water to run back on the underside of the cill, penetrating into the wall beneath.
Some buildings become so dilapidated that it can be difficult to attribute dampness to a single source. In these circumstances, serious deterioration often occurs.
A particularly severe case of penetrating damp! |
Multiple causes of dampness. |
Some sources of penetrating damp are both easy to identify and simple to rectify. However, this is not always the case. Dampness affecting the base of ground floor walls can easily be misidentified as rising damp when it may in fact be related to rainwater penetration or some other defect such as condensation. Furthermore, penetrating dampness can cause deterioration of internal plasterwork and timber decay. This consequential damage requires careful appraisal and appropriate remedial action by skilled technicians. Britannia Preservations surveyors identify all sources of dampness and provide the most appropriate solutions.
© Britannia Preservation 2011