Blocked gutters and damp walls: tracing the cause properly
A striking number of homeowners spend four figures on chemical damp treatment for a wall that is wet because a gutter joint fifteen feet above it has been dripping since 2019.
Damp that appears on an internal wall after heavy rain, high up or in a vertical stripe, is usually rainwater from an overflowing gutter or a split downpipe rather than rising damp. Fix the rainwater goods first — it costs a fraction of any damp-proofing treatment and resolves most cases.
How to tell rainwater damp from the alternatives
Rainwater damp follows the weather: it darkens during and after rain and dries back in a settled spell. It usually sits high on the wall or in a vertical band, often near a corner or beside a chimney breast. Rising damp is confined to the bottom metre or so of a wall and often shows a tide mark with salt crystals. Condensation appears on cold surfaces and in corners, is worst in winter, and comes with black spot mould rather than a stain. Getting this diagnosis right is the whole job — the three have completely different fixes.
The specific failures that cause it
In order of how often we find them: a blocked gutter overflowing at the same point every downpour; a leaking gutter union dripping onto one spot; a split or displaced downpipe spraying against the wall; a downpipe discharging onto the ground next to the wall instead of into a gulley; a blocked gulley backing up at the base; and a hidden box gutter behind a parapet overflowing internally. All six are visible in the rain, which is why we ask people to take a photo mid-downpour if they can do it safely from a window.
Why solid walls suffer more
Most pre-1930s houses round Hampton, Twickenham and Teddington have solid brick walls with no cavity. There's nothing to stop water that's soaked into the outer face reaching the inner. A cavity wall tolerates a leaking gutter for far longer because the cavity breaks the path — until debris or a mortar snot bridges it, at which point you get a very localised damp patch that looks mysterious until someone works out where the bridge is.
What the water does to the brickwork
Persistently wet brick fails in frost: water in the pores expands, the face spalls off, and the exposed core absorbs even faster. Wet pointing washes out, which lets in more water again. This is a compounding problem, so the useful thing to know is that the repointing bill scales with how long the gutter has been ignored. Sorting the rainwater goods early is the cheap intervention; repointing a saturated elevation is the expensive one.
The sensible order of works
One: clear and repair the rainwater goods and confirm the whole run flows and discharges properly. Two: let the wall dry — a saturated solid wall needs weeks to months, not days, so resist the urge to redecorate immediately. Three: repoint any washed-out or spalled brickwork. Four: only then, if the damp persists through a dry spell, investigate other causes. Any contractor who wants to inject a damp course before step one has been done is skipping the diagnosis.
What it typically costs
Clearance and flushing: £80–£150. New gutter unions and brackets on an otherwise sound run: £120–£300. Replacing a downpipe: £150–£350. A full uPVC gutter and downpipe replacement on a semi: usually £700–£1,300. Repointing a damaged section of elevation: from £400 depending on area and access. Set that against typical damp-proofing quotes and the case for looking at the roofline first makes itself.
Internal damp that isn't the gutter
We do find other causes and we say so. A cracked chimney flaunching sends water down inside a stack and out through the breast. A failed lead apron behind a bay roof runs into the wall head. Missing verge mortar at a gable soaks the top corner of an upstairs room. Penetrating damp around window heads is often a failed lintel detail rather than anything to do with the roof at all. The point is to identify the entry path before spending money.
Getting it looked at
We survey damp-with-a-suspected-rainwater-cause across Hampton, Hampton Hill, Teddington, Twickenham, Whitton, Richmond and the surrounding KT and TW postcodes. It's a free visit, we photograph the roofline and the affected elevation, and if the cause turns out to be nothing to do with the roof we'll tell you that plainly rather than sell you gutters you don't need.
FAQs
Yes, and it's one of the most common causes we see. Water overtopping the same spot repeatedly saturates the masonry, and on a solid brick wall that reaches the inside face.
A solid brick wall can take several weeks to a few months, depending on thickness, weather and ventilation. Don't replaster or redecorate until it's genuinely dry or you'll trap the moisture.
Rule out rainwater ingress first. It's far cheaper to fix and it's the actual cause in a large share of the cases we're called to.
We handle the rainwater goods and associated repointing. Where a wall needs specialist masonry work beyond that, we'll tell you and point you at someone who does it properly.
Related reading
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- How often to clean your gutters (and what happens if you don't)Maintenance & seasonal
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