How to identify and deal with this watery enemy to your property

Penetrating damp is defined as moisture ingress caused by water literally ‘penetrating’ surfaces of a property and getting in from the outside. This is distinct from other forms of moisture issues such as condensation and rising damp.

A multitude of causes

Penetrating damp can be caused in various ways from a leaking roof tile allowing rainwater into brickwork or mortar in poor condition allowing water penetration.

In general, the signs you have some penetrating damp will be patches of discoloration on walls, ceilings or even floors.

To make diagnosis even harder on occasion, the damp patch may not actually be near the site of the water ingress. For example, water entering the roof through some loose tiles at the rear of the property above the main bedroom may show itself as a damp patch nearer the front above the bathroom due to the water dripping onto and travelling along a roof joist.

Call in the experts

If it’s not obvious where penetrating damp is coming from, then a thorough inspection should be undertaken. If you still can’t find it then call in an expert such as a waterproofing services company.

For example, a musty smell in the basement or cellar – and maybe some evidence of water ingress such as a damp patch on the wall – could mean moisture coming in through the brickwork due to poor or no tanking. A search for an expert in your locality such as ‘damp proofing London’ will find a company who can help in this specialism.

This type of penetrative damp – moisture coming through brickwork from the outside – is common not only in basements and cellars, but also in horizontal walls made of older brick that’s become porous with age, through damaged rendering or poor condition pebble dashing.


Since penetrating damp often gains a foothold through vulnerabilities such as failing window seals and loose tiling, it’s important to keep on top of routine maintenance and inspect regularly to stop penetrating damp before it can occur.

Perhaps once a year, conduct a thorough inspection and replace or repair vulnerabilities such as loose roof slates, poorly sealed windows and broken guttering. Attend to standing water promptly as after a while it can seep through brickwork that acts like a wick drawing the moisture in to eventually appear as damp patches on the inside.

A good idea is to check for drips or obvious leaks when it’s raining; go outside and see if there’s any signs of water trickling or running into areas it shouldn’t. For example, during a heavy downpour is that cracked gutter causing rain to saturate an outside wall? Over time it could cause a problem.

A damp audit

If you’re not sure about where moisture ingress may occur, of if you’re having a damp issue dealt with by your damp proofing experts, ask them to undertake an inspection to identify potential vulnerabilities.

The chances are some companies will look to undertake an inspection like this as part of the service when you call them in to help.


The main issues with penetrative damp; establishing when you have it and how to establish where it’s coming from, how to prevent it through full inspections.