types of damp

4 Types of Damp You Must Avoid (and how to treat them)

Damp is an issue you can’t ignore if you care about your health and well-being, and if you want to know how to treat it, you must first understand the different types of damp.

I’ve carried out countless house surveys over the years, some for potential buyers but primarily for concerned homeowners who have a problem with cracks in walls or dampness inside the house. The first thing to do is identify the cause and then provide a remedy.

In this article, I’ll tell you about the 4 types of damp, their common causes and what you should do to eradicate the problem.

Types of Damp and How To Treat Them

Understanding the cause and extent of a problem is the first step towards resolving it. With damp, you must start with the basics.

What is Damp?

When we talk about damp, we refer to moisture within the structure, be it on the surface of walls and ceilings or in the air. Damp problems may be caused by a combination of these or all three.

Types of Damp

There are 4 types of damp you should be concerned about: Condensation, Rising Damp, Penetrating Damp, and damp caused by Water Systems/Leaks.


wiping off condensation

Condensation is the most common form of damp and appears on glass surfaces as tiny water droplets. 

It’s virtually impossible to eliminate condensation because the air within your home is full of moisture from various sources, including breathing, bathing, cooking and cleaning.

When the moisture-laden air meets a cooler surface, the moisture condenses, damping the surface. Sometimes this can occur beneath the surface, in the structure itself, and this is known as interstitial condensation and is more difficult to recognise. Read this article by Designing Buildings to find out more.

Condensation on glass is not usually a problem until it runs down and lands on a horizontal surface, such as a window frame. If left there, this can lead to mould growth and, ultimately, rot.

Rising Damp

flaking paint on the exterior wall indicating rising damp

Rising damp is caused by capillary action. I.e. moisture in the masonry below ground rises through the porous brickwork and mortar joints. 

Typically, the wall’s damp proof course (DPC) prevents this. However, if the DPC is defective, missing, or bridged by rendering, damp will rise into your home.

You may also experience rising damp through a concrete floor if this is laid directly onto the ground with no damp-proof membrane.

Penetrating Damp

interior decay

Penetrating damp is similar to rising damp in that it is usually caused by capillary action — this time horizontally through the wall. As with rising damp, the absence of a functioning damp-proof course around openings in the wall causes this issue.

Penetrating damp may also result from poorly fitting doors and window frames, allowing driven rain to penetrate inside.

Water Systems/Leaks

Water comes into your house through a series of pipes that feed all your appliances, such as the central heating boiler, washing machine, showers and taps in your kitchen sink and wash basins.

Each of these can potentially create or contribute to a damp issue. This moisture can be in the form of water vapour (e.g. boiling water) or water in its liquid form (e.g. leaks).

Causes of Damp

Common causes include; Condensation (see above), Faulty Plumbing, Leaking Roofs, Lack of or Defective Damp Proof Membranes, and Defective Building Work.

Faulty Plumbing

female hand cleaning leaked water from faulty plumbing

Leaking pipework, dripping taps, and faulty sealant around baths and showers contribute to damp problems, either by direct water damage or by adding moisture to the air.

Leaking Roof

Stains on a ceiling are a sure sign of problems above, often due to missing roof tiles, inadequate flashing around a chimney or a blocked gutter.

Modern homes have an underfelt that stops water from dripping onto the ceiling below. However, this membrane isn’t intended as a first-line defence against water penetration. In high winds, water can be blown up the roof and enter through the joints in the felt.

Lack of or Defective Damp Proof Membrane

When I say “damp-proof membrane”, I refer to damp-proof courses, vapour barriers and breathable membranes.

If damp-proof membranes are missing or damaged, this provides a direct route for damp to penetrate the outer fabric of the building and reach the inside.

Defective Building Work

Building defects such as bridged cavities in walls or defective pointing in brickwork can lead to penetrating damp.

Cavity wall construction is perfect for keeping out driven rain, but if mortar drops down the cavity during construction, it forms a bridge when it hits a wall tie. This bridge allows water to cross over to the inner leaf of your home.

The mortar can become soft and porous in older houses with solid brick walls. Constant freezing and expansion of water in the brick can force off brick faces — known as spalling — allowing moisture to penetrate the inner surface.

Effects of Damp

Damp can manifest in different ways, some more serious than others.

Mould Growth

wall with mould

Those horrible black patches on walls and ceilings come from a fungus that thrives in damp or humid conditions. 

Spores from the fungus become airborne, helping it spread to other parts of the room and into your lungs, leading to the next problem — Ill health.

Ill health

Damp conditions and fungal spores lead to sickness. I.e. as the microscopic spores become airborne, you breathe them in, which can lead to asthma, nasal congestion and even pneumonia.

Wet and Dry Rot

Closeup of a rotten old wooden window frame

Even wood treated with a preservative can rot if it’s in constant direct contact with a damp wall. Windows, door frames and floor joists built into walls below the DPC are especially prone to attack.

Wet and dry rot are both forms of fungal growth, the difference being the wood’s moisture content (MC). 

Wet rot requires an MC of 50% or more, whereas dry rot will thrive at an MC of less than 30%. However, they both need moisture to be present, so if you remove the source of damp, the rot will stop.

If you want to learn more about these forms of decay, check out this Timberwise guide.

Peeling Paint or Wallpaper

hand of a woman peeling wallpaper on a wall with mould buildup

Painting or papering over damp walls and ceilings is useless — it just won’t stick! And if you find you have a damp problem after decorating, you’ll probably have to redo it.

When you paint or paper a wall, any moisture in that wall becomes trapped, and with nowhere to go, it causes the surface to bubble.

Stained Plaster

identifying damp

After a water leak or damp penetration issue, it is common to see stains on plaster surfaces. 

These stains are difficult to remove and may return after repainting. The only way to avoid this is to use a stain blocker. A good, heavily pigmented stain block kills off spores, preventing them from reaching the surface.

Once you’ve applied the stain block, paint the walls with anti-mould paint for further protection.

Treating Damp

Having identified the problem, you must cure it. Our article on How to Treat Damp Walls Before Painting contains valuable information.

Treat at Source, Don’t Cover Up

Once you’ve established why you have a damp problem, you must treat the source of the issue. If you try to hide it, the problem will return and cause more damage. For example, joists built into or in contact with damp walls will rot, leading to collapse if untreated.

If you have a problem with rising or penetrating damp, you may have to call in the professionals. Fixing this issue is particularly important if you intend to sell your property soon because when a prospective buyer has a survey, these problems will appear. 

Any treatment to eradicate a damp problem must have an insurance-backed guarantee. Your DIY efforts to solve the problem won’t be enough to satisfy a mortgage broker.

To learn more about the cost of treating damp, our guide to damp proofing costs will give you all the information you need.

Increase Ventilation

Good air ventilation is required to combat condensation. Opening a window or a trickle vent will help, and if you can’t do that, introduce an extractor fan.

One of the problems of modern, almost airtight, construction is the lack of natural ventilation, which is why many homes now incorporate a Mechanical Ventilation with Heat Recovery (MVHR) system. Read more on this and the need for condensation traps in ventilation pipe runs in our guide to fitting a condensation trap.

Reduce Moisture in the Air

Removing moisture sources is the best way to reduce the air’s moisture content. 

An extractor fan over the cooker moves lots of moisture outside, and fans in shower rooms are essential. Placing washing machines and tumble dryers in an outside space (e.g. a garage) also helps.

Consider using a portable dehumidifier if you can’t do any of these things. A low-cost model can remove between 10 and 20 litres per day (the equivalent of up to 250m2 of floor space) — that’s a lot of moisture! 

Fix That Leak!

It should go without saying, but the longer you leave a leaking pipe, the worse the problem gets. The same goes for a leaking roof. Remember, a stitch in time saves nine!

So don’t keep mopping up the mess or leaving a bucket under the leak. Fix it before it causes more damage!

Final Thoughts

You should now know how much of a problem damp is and how to deal with different types of damp. If you’re still unsure what to do, call in the professionals. 

Pro Tip: It’s better to look for an independent damp surveyor than use a company specialising in one form of remedial work. Only a top-rated independent damp professional will provide an unbiased opinion you can trust.