In over a decade of surveying Victorian houses across Acton, Ealing, and West London, I've looked at hundreds of damp walls. I've seen buyers panic about moisture readings that were completely benign, and I've seen buyers brushed off with "it's just condensation" when there was actually a serious defect requiring immediate action. Here's how to tell the difference.
A moisture meter is one of the surveyor's key tools — but it needs to be used and interpreted correctly.
The Three Main Types of Damp
When a surveyor flags dampness in a Victorian property, it's almost always one of three things:
1. Rising Damp
This is what most people mean when they say "damp." Rising damp occurs when groundwater is drawn up through masonry by capillary action, past a failed or absent damp proof course (DPC). In Victorian houses, the DPC was typically a course of slate, bitumen felt, or engineering bricks — and after 100+ years, it can fail.
True rising damp produces a characteristic "tide mark" pattern — damp to a height of about 1 metre, with efflorescent salt deposits on the wall surface. It's usually worse in autumn and winter. The treatment is to install a new chemical DPC — though the diagnosis needs to be correct first, because rising damp is often misdiagnosed.
2. Penetrating Damp
Penetrating damp is by far the most common type we find in Victorian houses across Acton. It's caused by water getting in from outside — usually through a defect rather than through the wall itself. The most common causes in West London Victorian properties are:
- Blocked or leaking gutters and downpipes (the number one cause)
- Failed pointing or mortar joints in the brickwork
- Defective or missing flashings at roof junctions
- Failed seals around windows and doors
- Cracked or damaged render
The key distinction is that penetrating damp follows the defect. Fix the defect, and the damp goes away. Unlike rising damp, the solution doesn't require chemical treatment — it requires finding and fixing the source.
3. Condensation
Condensation is the most misunderstood form of dampness. It's not a defect in the building fabric — it's a symptom of lifestyle, ventilation, and thermal performance. In an unheated Victorian house with minimal insulation, warm moist air from cooking, bathing, and breathing hits cold surfaces and condenses.
Condensation mould (typically black mould on cold corners, behind furniture, and around window reveals) is often mistaken for rising or penetrating damp. The fix is ventilation and heating — not damp treatment. A knowledgeable surveyor will distinguish between the two; a cowboy damp proofer will sell you an expensive chemical injection regardless.
The Damp Industry Problem
I need to be honest with you about something: the damp proofing industry has a poor reputation for diagnosing rising damp where none exists. RICS research has shown that many properties "diagnosed" with rising damp by damp treatment companies actually have penetrating damp or condensation — which requires very different (and usually cheaper) treatment.
Always get an independent structural survey before instructing any damp treatment company. A RICS surveyor has no financial interest in what treatment you choose — a damp proofing company does.
What Happens When Our Survey Flags Damp?
When we find dampness in a Victorian property, here's our process:
- We use a calibrated moisture meter to measure moisture levels at multiple heights and locations.
- We inspect externally for potential sources — gutters, downpipes, flashings, pointing.
- We inspect the roof space and any flat roof elements that might be sources.
- We consider the pattern of the dampness — height, location, seasonality (based on what we're told).
- We give our diagnosis and recommendation — not just "dampness noted" but "penetrating damp from blocked valley gutter — clear gutter and inspect flashings."
That specificity is what distinguishes a good survey report from a useless one — and it's what can help you renegotiate the price or ask the seller to fix the source before completion.
Should Damp Put You Off Buying?
Almost never — as long as you know what you're dealing with. Most dampness in Victorian properties is repairable. The question is: how much will it cost, and who pays? Use the survey report to get quotes for the remedial works, then use those quotes to either renegotiate the price or request that the seller fixes the issue before exchange. Our guide to renegotiating after a survey explains exactly how to do this.
