Why is the damp worse in one room only?

Because the cause is local. A single wet room usually points to a defect above or beside it, a gutter, a chimney, a blocked gully or a cold external corner, rather than a whole house problem.

Will a dehumidifier solve it?

It manages condensation while it runs and does nothing about water entering from outside. It is a useful diagnostic and a poor cure.

Is black mould always condensation?

It usually indicates condensation because mould needs a surface that stays cool and humid, but a penetrating leak can create the same conditions. The pattern and timing tell you which.

Can insulation make damp worse?

Badly specified insulation can, by moving the cold surface into the middle of the construction or by trapping moisture in a solid wall. Vapour open systems and careful junction detailing avoid it.

Diagnosis · Cornwall

Damp in old Cornish homes, diagnosing the cause before spending money on the symptom

Damp is the most commonly misdiagnosed defect in Cornish housing, partly because the climate provides plenty of all three kinds and partly because the cheapest available answer, an injected chemical course and a coat of waterproof render, is sold as a cure for everything. The three mechanisms behave differently, appear in different places and respond to completely different work.

Book a free consultation See built work

Free · No obligation

Ask us about your project

A free first conversation — no obligation, no sales calls.

Penetrating damp

Water arrives from outside through a defect. On the exposed western side of a Cornish house that is often wind driven rain finding cracked render, failed pointing, a blocked gutter or a redundant chimney with no cap. The tell is that it worsens within hours of driving rain from a particular direction and dries back afterwards, and that the affected patch usually sits at a specific height or beside a specific feature rather than running along the whole wall.

Check gutters and downpipes during actual rain rather than on a dry day
Look at the prevailing weather face first, typically the south west elevation
Suspect chimneys, parapets, abutments and anywhere two materials meet
Cracked cement render is a common cause dressed up as a cure

Condensation

Moisture generated inside the house lands on the coldest surface it can find. It shows as black mould in corners, behind furniture on external walls, around window reveals and in unheated bedrooms. It is a function of moisture production, ventilation and surface temperature, so it responds to extract fans that actually run, background ventilation, gentler continuous heating and insulation that raises the temperature of cold spots. It does not respond to anything injected into a wall.

Rising damp and what usually turns out to be happening instead

True rising damp exists but is far less common than the industry implies, and in solid walled Cornish buildings the usual culprit is a raised external ground level, a cement plinth or a concrete path bridging the base of the wall. Before accepting a diagnosis, look at where the ground sits relative to the internal floor, and whether a modern impermeable finish is holding water in a wall that used to dry freely.

A sensible order of work

Fix water getting in, then let the fabric dry, then improve ventilation and warmth, and only then consider finishes. Work in that order and most cases resolve without a specialist chemical treatment. Work in the reverse order, sealing the wall first, and the problem usually reappears one or two winters later in a slightly different place.

Frequently asked

Straight answers.

Why is the damp worse in one room only?: Because the cause is local. A single wet room usually points to a defect above or beside it, a gutter, a chimney, a blocked gully or a cold external corner, rather than a whole house problem.
Will a dehumidifier solve it?: It manages condensation while it runs and does nothing about water entering from outside. It is a useful diagnostic and a poor cure.
Is black mould always condensation?: It usually indicates condensation because mould needs a surface that stays cool and humid, but a penetrating leak can create the same conditions. The pattern and timing tell you which.
Can insulation make damp worse?: Badly specified insulation can, by moving the cold surface into the middle of the construction or by trapping moisture in a solid wall. Vapour open systems and careful junction detailing avoid it.

Trying to work out where the damp is coming from?

Send photographs, the address and when it appears. We will tell you which of the three mechanisms it looks like before anyone quotes you for treatment.

Free · No obligation

Book your free consultation

Tell us about your project — we usually reply within 2 hours (working day).