In this guide
If a damp patch on an inside wall appears or darkens a day or two after heavy rain, then fades again in a dry spell, you're almost certainly looking at penetrating damp: rainwater getting through the outside of the building. It's one of the most common damp problems we see across Birmingham, Solihull, Wolverhampton and Walsall once the autumn weather sets in. The good news is that it usually has one clear cause outside, and fixing that cause is what fixes the wall. This guide from the Property Edge damp team walks you through how to narrow it down.
Is it really penetrating damp?
There are three main types of damp in a house, and each has a different fix, so it's worth being sure before spending anything. Our guide to spotting rising damp covers all three in detail, but as a rough rule:
- Penetrating damp: a localised patch, often on an outside wall and often higher up — round a window, under a gutter, beside a chimney breast. It gets worse after rain, especially wind-driven rain, and better in dry weather.
- Rising damp: confined to the bottom metre or so of a ground-floor wall, usually with a tide mark and white salt deposits. It doesn't come and go with each shower.
- Condensation: black spotty mould in corners, behind furniture and around windows, worse in cold weather and in rooms where washing is dried or people sleep. It tracks the heating and the humidity, not the rain. See how to stop condensation and black mould.
One simple test: take a photo of the patch with the date, then compare it after the next proper downpour and after a dry week. If it changes with the rain, look outside first.
The usual culprits, in the order we check them
1. Gutters and downpipes
By far the most common cause. A gutter blocked with leaves or moss, a sagging section, a leaking joint or a cracked downpipe can pour water down the same few square metres of brickwork every time it rains. Stand outside during a heavy shower (with an umbrella, not a ladder) and watch: water spilling over the front edge, dripping from a joint, or a dark wet stripe down the bricks lines up very neatly with a patch inside. Our autumn gutter guide covers what to look for.
2. Worn pointing and porous brickwork
Much of the Victorian and Edwardian housing in Birmingham and the Black Country has solid brick walls with no cavity, so the brick and mortar are the only thing keeping the weather out. Mortar joints that have eroded, cracked or fallen out let water soak deep into the wall. Bricks that have 'spalled' (the face has flaked off, often from frost) soak up water much more readily. Look for recessed or crumbling joints and flaky brick faces on the wall behind the patch.
3. Cracked render
Render looks like a waterproof coat, but once it cracks, water runs in behind it and can't easily dry out again — so a rendered wall can stay damp long after the rain stops. Hairline cracks, bulging patches that sound hollow when tapped, and render that's been taken down to ground level (bridging the damp-proof course) are all worth noting.
4. Windows, sills and doors
A damp patch below or beside a window often traces back to the window itself: failed sealant round the frame, a sill with no drip groove underneath (so water runs back into the wall), or a cracked sill. If the patch spreads from the corners of the window reveal, start here. Replacing tired sealant is often a small job; if the frames themselves have failed, that's a windows and doors conversation.
5. Chimneys and roofs
Patches high on a wall, on an upstairs ceiling edge or on a chimney breast usually point upwards — to flashing, the chimney stack, or slipped tiles. We've covered these separately in damp on a chimney breast and why a roof leaks.
6. Problems inside a cavity wall
Most homes built from roughly the 1930s onwards have cavity walls: two layers of masonry with a gap between them, designed so rain that gets through the outer layer runs down inside the cavity rather than across to the inner wall. That only works if nothing bridges the gap. Mortar droppings left on wall ties during building, debris at the bottom of the cavity, or in some cases cavity wall insulation that's become wet or isn't suited to a very exposed wall can all carry water across. This one can't be diagnosed from the outside — it usually needs an inspection, sometimes with a small camera through a drilled hole.
What you can safely do yourself
- Keep a dated photo record of the patch inside and the wall outside, before and after rain.
- Check gutters and downpipes from the ground during a downpour. Clear ground-level gullies and drains of leaves so water can get away.
- Make sure air bricks low down on the outside wall are clear and that soil, paving or planters aren't banked up against the wall above the damp-proof course.
- Keep the room heated and ventilated while the wall dries. Damp plaster takes weeks, sometimes months, to dry out fully.
- Leave anything that needs a ladder, scaffolding or a roof to someone with the right access equipment.
What a repair usually involves
Most penetrating damp repairs are about the outside of the building, and many are modest: re-fixing or replacing a run of gutter, repointing a section of wall, cutting out and replacing a few spalled bricks, repairing render, or resealing a window. Once the source is fixed, the inside wall is left to dry, and only then is any damaged plaster cut out and replaced and the room redecorated. Re-plastering before the wall has dried, or before the leak has been fixed, is wasted money.
Renting or letting the property?
As general guidance, landlords in England are responsible for keeping the structure and exterior of a rented home in repair, including walls, gutters, drains and windows, under Section 11 of the Landlord and Tenant Act 1985, and homes must be fit to live in, which covers serious damp. Social landlords also now have fixed timescales for investigating and fixing damp and mould hazards under Awaab's Law. Tenants should report damp in writing, with photos, as soon as it appears; landlords and agents should get the external cause found quickly rather than treating it as a decorating job. Our guide to who fixes what between landlord and tenant has more, and we work with HMO landlords and agents across the region. This is general guidance, not legal advice.
Getting it sorted
If a damp patch keeps coming back with the rain, it won't fix itself, and every wet winter it's left makes the repair bigger. Book a damp survey anywhere across Birmingham, Solihull, Wolverhampton, Walsall, Dudley and the wider Midlands, or get in touch with photos of the patch and the outside wall and we'll give you an honest first view of what it's likely to be.