Skirting boards swell when the wood behind them stays wet. The usual causes are a leaking pipe under the floor, a damp concrete screed or rising damp in an older solid wall. A one-off spill dries in days. If the swelling grows, the paint keeps bubbling or a tide mark climbs the wall, water is still arriving and the source needs tracing.
You noticed it while hoovering. The skirting board in the hall has gone soft and puffy along the bottom edge, or the paint just above it has lifted into little blisters. Nothing has been spilt there, the ceiling is dry and there is no obvious drip. It is a small thing to look at, but skirting rarely swells on its own. Something below or behind it is wet, and has been for a while.
This guide works through the likely causes in the order we tend to find them, what each one looks like, and the simple checks you can do before deciding whether it is a job for water leak detection or a damp specialist.
Why the skirting is the first thing to show
Skirting sits at the junction of wall and floor, which is the lowest point in the room and the first place moisture collects. Most modern skirting is MDF, which soaks up water like a sponge and swells permanently. Softwood skirting swells too, but often more slowly. Paint on the wall above it blisters because moisture is pushing through the plaster from behind, and the paint film is the only thing stopping it evaporating.
So the skirting is a messenger, not the problem. The question is where the water is coming from, and there are only a few realistic answers.
The four usual causes
1. A pipe leaking under the floor
Hot and cold supply pipes and central heating pipes are routinely buried in or under ground floors. When a joint weeps or a pipe corrodes, the water spreads sideways through the screed or along the underside of floorboards until it meets a wall. The skirting on that wall is the first thing to go.
Tell-tale signs: the damage is on one wall or in one corner rather than all round the room, it is worse near where pipes would run (towards a radiator, the kitchen, the bathroom above), and it keeps getting worse however much you ventilate. If the wet area is warm to the touch it is very likely the heating circuit. Our guide to a warm patch on the floor covers that scenario in detail.
2. Damp screed or a wet sub-floor
Concrete floors in extensions and 1960s to 1980s houses were laid with a damp-proof membrane that can fail, be bridged, or have been missed at the edges. Ground moisture then rises through the slab and shows at the perimeter. In Cornwall, with our high water table in valley bottoms and heavy winter rain, this is common in converted outbuildings and older bungalows around Camborne and Redruth.
Tell-tale signs: the damp is fairly even round the whole room or along an outside wall, it is worse in winter and eases in a dry summer, and there is no single wet point. A leak is usually lopsided. Ground damp is usually spread out.
3. Rising damp in an older solid wall
Granite and cob cottages often have no damp-proof course at all, or a slate one that has been bridged by a raised path, a render skirt or a later concrete floor. Moisture climbs the wall by capillary action, typically to around a metre, and leaves a horizontal tide mark with salt crystals on the plaster.
Tell-tale signs: a level band of staining that stops at roughly the same height along the wall, a fluffy white salt deposit, and skirting that is damp along its whole length rather than swollen in one spot. Our piece on rising damp or a leak in a Cornish cottage goes deeper on telling the two apart.
4. A one-off spill or flood
A washing machine that overflowed, a dropped bucket, a burst in the flat above that was fixed months ago. The skirting swelled at the time and has simply never recovered, because MDF does not shrink back. If the wall above is dry, the swelling is not spreading and there is no tide mark creeping up, this is probably old damage and a replacement board is all that is needed.
The tide mark: the most useful clue on the wall
Look at the boundary between wet and dry plaster above the skirting. Its shape tells you a lot.
- A rising arc from one point. Water is coming from a single source at floor level and spreading out. That is the signature of a pipe leak.
- A flat horizontal line. Moisture is rising evenly from the ground. That points to rising damp or a failed floor membrane.
- A mark that has moved up since last month. The source is still active. Mark the edge with a pencil and date it. If the line climbs, do not wait for it to stop.
- A mark that is fading at the edges. The wall is drying out. Whatever caused it may have stopped, or may have been repaired without anyone connecting the two.
Checks you can do this weekend
- Press the board. Wet MDF feels spongy and cold. Old dried swelling feels crumbly and warm. Cold and spongy means water is still present.
- Read the water meter. Turn off every tap and appliance, note the reading, leave it two hours and check again. Movement with nothing running points to a supply pipe leak. The overnight meter test explains how to do this properly.
- Watch the boiler gauge. A sealed heating system should hold pressure at about 1 to 1.5 bar when cold. If you keep topping it up, the heating circuit is losing water somewhere, and a swollen skirting near a pipe run is a strong candidate.
- Check outside. Is the ground level outside the affected wall higher than the floor inside? Is a downpipe discharging next to it? Has a path been laid over the damp course? These bridge the damp-proofing and mimic a leak.
- Feel for warmth. Hand flat on the floor near the skirting, then a metre away. A distinct warm zone on a cold morning usually means a heating pipe below.
| What you notice | Most likely cause | What to do |
|---|---|---|
| Swelling in one corner, spreading, floor warm | Heating pipe leak under the floor | Check boiler pressure, book a trace |
| Swelling near kitchen or bathroom, meter moves | Supply pipe leak | Meter test, then a trace |
| Even damp along an outside wall, salt line | Rising damp or bridged DPC | Check ground levels, damp survey |
| Whole room perimeter damp in winter only | Failed floor membrane | Floor moisture test, builder |
| Old, dry, not spreading | Historic spill or repaired leak | Replace the board |
What a thermal camera shows at floor level
This is the point where guessing stops. A thermal imaging camera does not see water, it sees temperature, and wet materials hold a different temperature from dry ones. Pointed along a floor and up the base of a wall, it reveals the true extent of the moisture, which is nearly always larger than the visible swelling suggests.
On a heating leak, the camera shows a warm plume with the pipe route running through it and the hottest point close to the failure. On a cold supply leak, it shows a cool shadow spreading from one spot. On rising damp, it shows a cool band across the whole width of the wall with no focal point. Three different pictures for three different problems, taken without lifting a single board.
We back the camera with a moisture meter to map how far the damp extends, and where a pipe is suspected, acoustic listening and tracer gas to pin the exact point. A floor-level leak in a Truro terrace can then be opened up in one small area rather than the whole hallway being dug out on a hunch.
Why it matters for your insurance
Escape of water from a pipe is normally covered by buildings insurance, and the cost of finding and reaching that pipe often falls under the trace and access section of the policy. Rising damp and a failed floor membrane are not sudden events, so they are generally treated as maintenance and not covered. Getting the diagnosis right, in writing, before anyone starts ripping out flooring is what keeps a valid claim on track. Our report gives the insurer the source, the method and the photographs they ask for.
If the swelling has been there a long time, read up on how insurers treat gradual damage before you make the call, so you know what to expect.
Frequently asked questions
Can swollen skirting boards be dried out and saved?
Softwood skirting sometimes recovers once the source is fixed and the wall has dried, though it may need refixing and repainting. MDF does not shrink back once it has swelled. The important thing is to fix the water source first, otherwise the replacement board will go the same way.
How do I know if the leak is under the floor or in the wall?
Water from a wall leak tends to run down and pool, so the wall is wet from a point above the skirting and the floor is only damp beneath. Water from a floor leak wets the skirting first and the wall above only as it wicks upward. A thermal camera makes the difference obvious.
Why is the paint bubbling but the wall feels dry?
Blistered paint means moisture was pushing through at some point. Plaster can feel dry to the hand while still holding water a few centimetres in, which a meter will show. If the blisters are old and not multiplying, the source may have stopped. If new ones keep appearing, water is still arriving.
Will home insurance cover swollen skirting?
If a pipe leak caused it, the resulting damage is usually covered under escape of water, and finding the pipe often comes under trace and access. Rising damp, condensation and a worn floor membrane are normally excluded as gradual or maintenance issues. Check your policy schedule and get the cause confirmed in writing.
Should I take the skirting off to look?
You can, but it rarely tells you much beyond confirming the wall is wet, and it can disturb evidence an assessor might want to see. A non-invasive survey finds the source without opening anything up, and then the repair is limited to the right spot.
Find what is wetting your skirting
If the swelling is spreading or the tide mark keeps climbing, we can survey the floor and wall without lifting a board and tell you whether it is a pipe, the ground or an old spill. We provide leak detection across Cornwall with a report your insurer can use.
