What Causes Damp in a House? | Damp & Mould Hub

Damp in a house always comes down to moisture that shouldn’t be there — but where that moisture comes from varies, and so does the fix. This guide runs through the causes, how to spot which one you have, and how to put it right.

General guidance. Persistent or unexplained damp is worth getting diagnosed — see damp and mould survey explained.

The causes of damp, in order of likelihood

Condensation (most common)

Moisture generated inside the home — cooking, showering, drying clothes, breathing — settling on cold surfaces. It’s behind most household damp and mould. See condensation explained.

Penetrating damp

Water getting in from outside through a defect: a leaking roof or gutter, cracked render, failed pointing, or gaps around windows. Usually a localised patch that worsens after rain.

Rising damp

Ground moisture rising up through walls where the damp-proof course is missing, failed or bridged. Concentrated at the base of walls. See rising damp explained.

Leaks

Plumbing leaks, an overflow, or rainwater ingress can create sudden, localised damp — often mistaken for one of the above.

Cold spots and poor insulation

Not a moisture source themselves, but cold surfaces and “thermal bridges” give condensation somewhere to form.

How to spot the cause

What you see	Likely cause
Damp on windows, mould in corners	Condensation
Patch that worsens after rain	Penetrating damp
Damp at base of walls, tide mark	Rising damp
Sudden patch near pipes/bathroom	A leak

These are starting points — symptoms overlap and homes often have more than one cause. More detail in the types of damp explained.

How to fix damp in a house

The fix follows the cause:

Condensation → manage moisture, ventilate, keep steady warmth.
Penetrating damp → repair the external defect letting water in.
Rising damp → address the damp-proofing and any bridging.
Leak → trace and repair, then dry out.

Treating the wrong cause is the classic, costly mistake — which is why diagnosis comes first.

When to get a survey

If you can’t pin down the cause, or damp keeps returning, an independent damp and mould surveyor will diagnose it properly. Renting? Your landlord is usually responsible — see your rights as a tenant.

Frequently asked questions

What causes damp in a house?

Damp comes from moisture either generated inside the home (condensation) or entering it (penetrating damp through defects, rising damp from the ground, or leaks). Cold surfaces and poor ventilation make condensation worse.

How do I fix damp in a house?

Identify the cause first. Condensation is fixed by managing moisture, ventilation and warmth; penetrating damp by repairing the defect letting water in; rising damp by addressing the damp-proofing. The wrong fix wastes money.

How do I stop damp in my house?

For the most common type — condensation — reduce indoor moisture, ventilate well and keep a steady background warmth. For other types, fix the underlying defect. Persistent damp is worth getting diagnosed.

Is damp dangerous to health?

Damp itself, and the mould it encourages, can affect health — particularly for children, older people and those with respiratory conditions. See is mould dangerous?