The Landlord Damp Diagnosis Checklist
A 5-step framework to identify whether your damp is condensation, rising or penetrating — before spending on the wrong repair. Written for London landlords and managing agents.
Most Damp Repairs Fail Because of the First Step, Not the Last
By the time damp is visible internally, three things are already true: the source has been active for weeks at minimum, the masonry behind is saturated, and at least two trades will turn up to quote — each pointing at a different cause.
This guide gives you a structured way to triage the symptom before authorising any spend. Get the diagnosis right and the repair is usually a fraction of the price; get it wrong and the damp returns, often after the redecoration cheque has cleared.
The checklist takes about 15 minutes for a single room. Walk through it before calling any contractor.
Five Steps to a Working Diagnosis
Map Every Damp Spot
Photograph every damp area in the property. Note: which room, which wall (external or internal), height above floor, ceiling proximity, and what is directly above (the flat above? the roof? a parapet? a hopper?).
Why it matters: the pattern tells you the cause faster than any single reading. Damp confined to top-floor flats below a parapet is almost always external. Damp around windows and corners is often condensation. Damp at floor level on a ground-floor party wall is often rising.
Correlate With Weather and Lifestyle
Ask the tenant: when does the damp get worse? After heavy rain? In cold weather when heating is on? When laundry is dried inside? After a thaw following a freeze? Note which trigger is reported.
Why it matters: rain-correlated damp is penetrating; cold-and-condensation correlated damp is condensation; freeze-thaw correlated damp is usually a pointing or render defect on an exposed elevation. The tenant's pattern report is diagnostic — take it seriously.
Look at the Outside
Walk to the external face of the building above and around the internal damp. Look for: failed pointing, cracked render, lifted lead, blocked or overflowing hoppers, vegetation growing in joints, cracked coping stones, missing flashings, blocked overflows.
Why it matters: 80% of penetrating damp problems are visible externally. If you cannot see far enough up — and from the pavement you usually can't — that is the moment to commission a rope access inspection rather than guess.
Take Comparison Moisture Readings
Use a resistive moisture meter (£40 from any builders' merchant). Take readings on the damp area, then on a known-dry wall in another room. Compare. A differential of 5 percentage points or more confirms abnormal moisture.
Why it matters: the relative reading matters far more than the absolute. Old buildings run higher than new ones; lime plaster reads differently from gypsum. The differential tells you whether you have a real damp problem or a normal background reading on an old wall.
Resolve the Source Before Redecorating
Once cause is identified — penetrating, rising or condensation — fix that first. Allow drying time (often weeks). Then redecorate. Apply mould-resistant emulsion. Treat any visible mould with appropriate fungicide before painting.
Why it matters: the most common single reason for damp recurrence is redecorating before drying out. Paint applied to wet plaster will blister; the staining will return within a season; the tenant will reasonably conclude that you have not addressed the issue.
The Three Common Damp Types — Compared
Condensation
Pattern: corners, around windows, in kitchens and bathrooms; worse in winter.
Cause: warm moist air meeting cold surfaces. Usually a heating, ventilation or insulation issue.
Fix: ventilation, dehumidification, anti-condensation paint, insulation upgrades.
Penetrating Damp
Pattern: localised; correlates with rainfall; often follows visible external defects.
Cause: water entering through the building envelope — failed pointing, cracked render, lifted lead, blocked hopper.
Fix: external repair to source, allow drying, internal redecoration.
Rising Damp
Pattern: ground floor only; up to ~1m height; often with a tide line.
Cause: failed or absent damp-proof course allowing groundwater to be drawn up by capillary action.
Fix: chemical DPC injection, replastering with salt-resistant render, drainage improvements.
When to Call a Specialist
Step 3 Reveals Defects at Height
If the external inspection shows defects above ground floor — failed coping, cracked parapet, lifted lead — a rope access investigation is the fastest, cheapest way to confirm and quote a fix.
Damp Has Returned After Redecoration
If the tenant has reported the same damp twice within 18 months, the source was not addressed. Time for a structured external investigation.
Pre-Disrepair-Claim Posture
A documented investigation report — with photographs and a recommended repair — is your best protection if a tenant escalates a damp complaint into a disrepair claim.
Damp Investigation From £350+VAT
A typical London damp investigation includes a half-day external inspection, photographs, written diagnosis and a costed repair plan. We bring the diagnostic checklist to the building so you do not have to.