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What is Penetrating Damp?

Penetrating damp is the term given to rainwater that passes through the walls or roof of a building. It may be nothing more than the appearance of a damp patch, but if left unchecked, the consequences can be very severe, costly and difficult to repair.

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Main causes of penetrating damp

Penetrating damp (or rainwater penetration) can occur for a great many reasons, but the overarching causes will usually be one or more of the following. 

  1. Inadequate repair and maintenance
  2. Deterioration of construction materials
  3. Damage 
  4. Design 

The location and orientation of a building will also be important. High levels of exposure to wind driven rain or very high levels of rainfall also have an effect on the likelihood, frequency and severity of damp penetration. To learn more about the causes, expand the options below.

+ More about Cause 1 - Repair and Maintenance >>

Well maintained buildings are generally much less likely to be affected than those that are neglected. Blocked guttering and defective fall pipes are a common cause or water ingress but poor pointing, defective roof coverings, and flashings though sometimes less obvious are also important.

Regular inspections, cleaning and repairs should be scheduled by every homeowner to help prevent penetrating dampness and to address issues before the consequences of water ingress become severe.

+ More about Cause 2 - Deterioration of construction materials >>

Many of the things used to hold buildings together deteriorate over time. Wind, rain, ice and sunlight  can effect renders, paints, sealants and even bricks, stone and mortar that constitute the building. Some break down rapidly and predictably, some incredibly slowly and inconsistently.  

Scheduled inspections of the building should highlight the need for any repairs that will prevent rainwater water ingress and the unwanted effects of penetrating dampness.

+ More about Cause 3 - Damage >>

Buildings can suffer from impact damage caused by trees, subsidence, shrinkage or things bumping into them. Even alteration where holes are made or pipes or services removed can be an issue. These impacts can result in cracks or holes in the structure. Holes in the water resisting envelope of the building can and do result in rainwater ingress.

+ More about Cause 4 - Design >>

When any home/building is planned & designed, its use, location and orientation is all considered. This is not just important aesthetically, but is essential if it is to resist the rain and wind that try to drive water into it.

Fashion and taste as well as practicality drive building design. Occasionally, architectural features can be a vector for penetrating dampness. Solid wall construction, parapet walls, raised brick features, rainwater pipes and even material choice can all increase the susceptibility of buildings to water penetration.

What to look out for

Where the effects of penetrating damp are seen within the home/building, they will usually first present themselves as damp patches on ceilings or walls. Water running in around the window reveals (the timber surrounding of the window unit, i.e windowsills) or even puddling is now common where problems are severe. You may also see deterioration of decorative finishes, decay in important wooden structural and decorative elements. 

In any event it is advised that the full extent and the likely implications of any penetrating dampness are evaluated and assessed by an expert. 

Finding the source of the damp issue

Like all damp problems, it is important that the source of the penetrating dampness is identified and that the progress of the water as it moves through the building is traced and investigated. To help homeowners find the source, we have pulled together a simple guide below. However, if you are concerned, we do suggest engaging the services of a trained and competent specialist who can assess, evaluate and conduct any necessary diagnostic investigations.

The Roof - potential causes of the dampness

  • Blocked gutters, especially in the hidden valleys of the roof or defective rainwater goods.
  • Defective surfacing to valley gutters and flat roofs.
  • Missing, broken, displaced or loose tiles or other roof coverings.
  • Faulty flashing around chimneys.

Penetrating damp - checking the roof - PCA

Penetrating damp - checking the walls - PCA

The Walls - potential causes of the dampness

  • Deterioration of mortar in brickwork joints.
  • Spalling of brickwork 
  • Bridging over the damp proof course by soil in flower beds, plinths, etc.
  • Blocked air-bricks.
  • Cracked or broken pipes, both water pipes and waste pipes.
  • Defective detailing and design around window frames and doors (cavity trays - throats to sills).
  • Continued overflow from cisterns or water tanks.

Ivy or other climbing plants may hide many of the above faults and roots may undermine foundations causing breaks in damp courses. Roots of nearby trees may cause similar damage to foundations and damp-courses.

Internal Investigation

Look for the evidence of moisture penetration where the outside inspection has identified faults. In addition a number of potential causes of dampness will not be visible from the outside:

  • Where a impervious membrane is punctured or of poor quality or where no membrane is fitted.
  • Condensation normally caused by high levels of mositure from bathroom and kitchen use. This is especially important in uninsulated and/or poorly ventilated buildings and is often the cause of decay.
  • Trapping of flood-water in under-floor space and over concrete.
  • Plumbing defects and defective toilets, either from fracture of the pan or, more commonly, defects in the plumbing unions.

Adequate sub-floor ventilation is important and careful attention must be given to clearing blocked air vents or air-holes in sleeper walls. Pockets of dead air favour fungal growth and should be eliminated. Steps must be taken to dry out existing dampness and to prevent further entry of water in addition to the eradication of the fungus and repair of damage caused. Where there is any doubt about the causes source or risks associated with water ingress, ask the advice of a reputable company.

Penetrating damp - Internal Investigation - PCA

Options to resolve penetrating damp

If dampness becomes apparent in your property (whether it be penetrating damp or not) then action should be taken quickly and without delay. Hesitation to address the issue quickly may result in greater and more costly damage. Any defect permitting access of moisture/damp into the fabric of a building must be remedied or treated. Further entry of water must be prevented and the area affected by water dried out.

Hopefully, some of the tips above have given you a good indication towards the defect/source of the penetrating damp issue to allow you to tackle the root cause. However, depending on conditions & on how long the problem has existed for, there may be damage to the internal fabric of the building and potentially risk of fungal decay such as wet rot or dry rot.  

We would suggest in order to identify the defects, a detailed inspection should be undertaken by a competent specialist.

More about penetrating damp treatment >>

Find local penetrating damp specialists

If you are looking to find a damp related specialist to investigate a potential penetrating damp issue, then you can use the search tool below to find local & qualified damp specialists near you.  Simply put in your postcode and run a search.

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Professional Damp Guidance

For professional tradesmen or contractors looking to find out more technical detail about penetrating damp and other forms of dampness, visit our professional guidance section.

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