Yorkshire Dampcourse home page :: Penetrating Damp

Penetrating Damp

There are three forms of dampness that affect buildings:-

  • rising dampness
  • condensation
  • penetrating dampness

We cover penetrating dampness here.

Penetrating damp

Penetrating dampness is defined as the entry of water into a property. This includes leaking roofs, defective guttering, entry of water through defective windows, poor pointing, spalled brickwork and down chimneys. It can include leaks from plumbing or drainage systems, either inside or outside a building, entry of water through earth retaining walls or into cellars below ground level.

In all cases the solution to penetrating dampness is to eliminate the moisture at the source and allow the area to dry out – easily done in some cases, but impossible in others without going to extremes of cost. For example, a leaking gutter can be easily repaired, but the penetration of water from a high external ground level into a cellar is more difficult to deal with. The following specialists will provide the repairs/remedial works needed to eliminate penetrating dampness:-



Problem Area


Roof, guttering, roof gullies, down-piping, chimneys Roofer
Pipes and internal drainage Plumber
Brickwork, pointing, external drainage, windows, path and ground level reduction Builder
Plaster, other wall linings Plasterer / Damp-proofer
Basement/cellar water-proofing Damp-proofer

Seriously leaking guttering pipework

Penetrating dampness causes several main problems :-

  • damage to masonry, plaster, paint work; mostly by staining, which sometimes requires replastering
  • moisture in timbers; which can lead to decay by wood rot or insect attack
  • cold, wet internal surfaces on which condensation can occur.

Having eliminated penetrating dampness and allowed a period of drying out, repairs to timbers and plaster should be undertaken. This may include timber replacement or in-situ timber treatments. Only suitable renovating plaster should be used for replastering as conventional plasters are not formulated to deal with residual moisture or salt contamination (for example dark staining salts in chimney breasts). Areas that have become very damp and those subject to heavy salt contamination (chimney breasts) may require dry-lining (application of plasterboard over a damp-proof membrane) or tanking / structural waterproofing.  



Leaking soil pipe

 Left in this condition for long enough, this leaking soil pipe will not only cause a hygiene problem, but also lead to internal penetrating damp.

Problems like this should be sorted out as soon as they are noticed.

To notice them, you have to wander around your house and LOOK. Sounds obvious; but inspect everything - up, down, left, right and centre. The best time to do this is just after rain, and for guttering problems during rain.

Getting the things outside the house right, and this includes the roof covering, will ensure the house stays weatherproof. 




Condensation, penetrating and rising damp - all in one goIt's rare to find all three types of damp located in one area - but this is probably it.

The overhead guttering outside was leaking badly. The 9 inch solid wall was so poorly pointed water could easily get through the wall.

The wall had no damp proof course and external ground levels were too high.

Internal growth of black spot mould is an indication of the occurrence of condensation.

The trouble is you need to eliminate all of them - one by one to solve the damp problem inside. 




The significance of long periods of rain and its affects on properties is seen in the photo below. Penetrating damp to gable wall




















The "shadow" of the wet bricks below the over-hanging roof can be seen clearly, with all the brick work in the dark areas being saturated with water.

The wall will be drying out - losing water by evaporation - and this is an energy consuming process, the energy for which comes from the wall. The result is that the wall temperature falls significantly and will therefore form a heat sink for the heat inside the house. This makes cavity wall insulation very important on this wall, but there can only be about 50 mm of it in the cavity, so that the insulation value is small.

It would have been better for the wall to never get wet in the first place, and this can be ahieved by silicone or acrylic masonry water repellants applied directly to the brick surface. To find out more about this, click here. 


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