What Causes Damp in Houses?

Unfortunately, dampness is a common occurrence for many UK homeowners and landlords. It’s a serious problem, which can accelerate chronic health conditions like asthma and damage the fabric of buildings. The good news is that in most cases, it’s pretty easy to fix.

We talk about the three main types of damp your home could be affected by and how to identify them so you can then choose the proper treatment. 


This is the most common type of damp, occurring when warm moist air contacts a cold surface and condenses. It can also happen in hidden wall spaces, floor cavities or roofs, causing structural damage and mould growth. This is serious, as homeowners can’t usually see the damage until it’s wreaked havoc.

Affecting around one in five UK homes, it’s confused in many cases with rising damp, which is more severe.

It’s caused by daily activities such as washing, bathing or cooking, which can add as much as four pints of water into the air. New homes tend to suffer more as they’re well-sealed and can’t breathe as much as traditional properties.

Inadequate heating is another cause. As warm air holds much moisture, this condenses on cooler surfaces, which can be made worse when heating fluctuates frequently. 

The final cause of condensation is inadequate ventilation. Homes that allow good airflow enables moisture-laden air to escape. However, poorly ventilated homes allow warm air to condense on cold surfaces, typically windows and external walls. 

The tell-tale signs of condensation include moisture on windows, damp patches on walls, mould, water on window sills, peeling wallpaper or a wet, musky smell.

Rising Damp

Rising damp happens when groundwater surrounding a property rises through brickwork through capillary action. This results in damp and mould, which appears around one meter up the wall.

Damp-proof courses, and damp-proof membranes found in newer properties, are usually enough to prevent rising dampness. 

Damp-proof courses are usually a slate, bitumen or plastic barrier embedded between brickwork in homes built after 1930. In older properties, these can fail, causing rising damp. 

This is often due to ‘bridging’, when debris within the wall cavity allows dampness to pass the DPC. Ground levels too elevated, overlapping renders or incorrect cavity wall insulation are other reasons this can happen. 

If you suspect your home doesn’t have a DPC, examine an outside wall to see if a black line about three bricks above ground exists. If not, your property doesn’t have a DPC. 

If you think your home could be suffering from rising damp, a telltale sign to look for is tide marks on internal walls to a height of around one meter.

Other things to look for inside include dark patches, stained or peeling wallpaper, blistering paint, blistered and flaking plaster, efflorescence or decaying skirting boards. Outside, you may notice salts on the wall or crumbling mortar. 

Penetrating Damp

This form of damp, which is common in older properties, happens when water penetrates a building’s structure, typically affecting upstairs rooms as water moves horizontally. 

Frequently occurring due to poor outside render or blocked gutters, it can damage a building’s structure and saturate cavity wall insulation, prolonging the issue even more.

There are several reasons for penetrating damp. Building faults are common reasons, like cracks in masonry, mortar joints, or render. However, plumbing leaks or too highly elevated ground levels can also be to blame.

If you suspect your home is suffering from penetrating damp, look for damp stains on plaster or wet patches which worsen after heavy rain. Also, look for green growth on outside walls, damp and mould in unusual places, or timber decay.