Rising damp in Doncaster: damp proof course checks and fixes

“Rising damp” is one of the first phrases people reach for when they see a damp patch low on a wall, and one of the most often misdiagnosed. GOV.UK guidance describes rising damp as moisture from the ground rising through walls and floors in contact with it, and says it is usually found in older properties and is often misdiagnosed. This guide explains how a damp proof course (DPC) is meant to work in a Doncaster brick house, what commonly stops it working, and what to check before you agree to any treatment. It is general information, not a diagnosis. If you are not sure which kind of damp you have, start with our checklist on condensation vs rising damp.

What rising damp is

Bricks, stone and mortar are porous. Where a wall sits in wet ground, water can move up through the pores by capillary action. As it evaporates from the wall surface it leaves salts behind, which is why rising damp typically shows as a “tide mark” low on the wall with white, powdery deposits, crumbling plaster and decaying skirting boards. Wikipedia’s summary of the research notes the rise is rarely above about 1.5 metres, and that wall stains and moisture meter readings are easy to misread.

What a damp proof course does

A DPC is a waterproof layer built into a wall near the bottom: slate, bitumen felt, engineering bricks or, in newer houses, plastic. It stops ground moisture travelling any higher. A requirement for a DPC was introduced by the Public Health Act 1875, so most Doncaster houses, from Victorian terraces to 1930s semis and post-war estates, should have one, though older materials can crack or decay. You can often spot it as a thin line in the mortar a few brick courses above the ground. Building regulations guidance for new work (Approved Document C) says the DPC in an external wall should be at least 150mm above the level of the adjoining ground. That gap matters: it stops rain splashing up and soaking the wall above the DPC.

How a DPC gets bridged

Most damp low on a wall in a house that has a DPC comes from something letting moisture around it rather than the DPC itself failing. GOV.UK lists a bridged (compromised) damp proof course among the outside checks for any damp problem. Look for:

Raised ground. Paths, patios, driveways or flower beds built up to, or above, the DPC line.
Render or pebbledash carried down over the DPC to the ground, giving water a path up the face.
Debris in the cavity. In cavity walls, mortar droppings or rubble at the bottom of the cavity can bridge the inner and outer walls.
Internal changes. A new solid floor laid higher than the old one, or plaster taken down to the floor slab.
Leaks at low level. A dripping outside tap, overflowing gully or leaking pipe keeping the base of the wall wet.

Low, wet ground in parts of Doncaster

Some of the borough sits on very low ground. Hatfield Chase, to the east of Doncaster, is less than 10 feet (3 metres) above sea level apart from the Isle of Axholme, was drained from 1626 and still relies on pumping stations maintained by the Environment Agency and the local drainage board. In November 2019, flooding mainly affected Bentley, Scawthorpe, Fishlake, Conisbrough and Tickhill; our local guides for Thorne, Hatfield and Fishlake, Conisbrough and Mexborough and Rossington, Bawtry and Tickhill cover those areas. Wet ground or a recent flood does not mean a DPC has failed, but it can keep the base of walls wetter for longer, so drainage, ground levels and air bricks deserve a careful look. If your home flooded, see our guide to damp after flooding in Doncaster before anyone recommends a new DPC.

Things that look like rising damp but are not

Condensation on cold walls behind furniture, often low down and worse in winter. See black mould causes.
Penetrating damp from gutters, downpipes or open joints, which can run down inside a wall and collect at the bottom. See penetrating damp.
Plumbing leaks in floors, kitchens and bathrooms.
Salts left in old plaster, which can draw moisture from the air even after the original cause has gone.

Is chemical DPC injection the answer?

Injecting a chemical DPC into a brick wall is a common recommendation. Where a survey shows the original DPC is missing or has failed, and the other causes above have been ruled out, it may be part of the fix. But it will not help if the real cause is a bridged DPC, a leak or condensation, and replastering with the wrong materials can trap moisture. Ask for the evidence behind any recommendation, in writing, and compare more than one opinion. Our damp survey cost guide explains what a good survey should include. Doncaster also has cellared houses where the problem is below ground; see cellar damp and tanking.

What you can check yourself

Find the DPC line outside and measure the gap to the ground: it should be clear, not buried.
Look for render, paving or soil bridging it, and clear soil or debris away from the wall where you safely can.
Make sure air bricks are not blocked or buried.
Check outside taps, gullies and downpipes near the damp patch.
Take dated photos of the inside and outside of the same wall, with a tape measure showing the height of the damp.

Questions to ask a surveyor

What moisture readings and tests did you take, and where?
Have you ruled out a bridged DPC, raised ground, leaks and condensation?
If you recommend injection, why, and what plaster do you specify afterwards?
Who backs any guarantee, and what does it cover?

Need help?

If the damp keeps coming back or you cannot find the cause, tell us what you can see using the enquiry form. With your consent, we will pass your enquiry to a local damp and mould business that covers your part of Doncaster. You can also find your area on our Doncaster areas and DN postcodes page. If you rent, see damp and mould in rented homes.

Sources and further reading

GOV.UK: understanding and addressing the health risks of damp and mould in the home; GOV.UK: Approved Document C (site preparation and resistance to moisture); Wikipedia: rising damp; Wikipedia: damp-proof course; Wikipedia: Hatfield Chase; RAB Consultants: Doncaster Section 19 flood investigation.

Related guides

Frequently asked questions

How do I know if I have rising damp?

Rising damp usually shows as a tide mark low on the wall, rarely more than about 1.5 metres up, with white salts, crumbling plaster and decaying skirting boards, and it is there all year. Condensation, leaks and a bridged damp proof course can look similar, so only a survey can confirm it.

Do older Doncaster houses have a damp proof course?

Most should. A requirement for a damp proof course came in with the Public Health Act 1875, so Victorian terraces, inter-war semis and later houses were usually built with one. Older slate or bitumen DPCs can crack or decay, and many are bridged by raised paths, render or debris.

What does it mean if my damp proof course is bridged?

Something lets ground moisture get around the DPC, such as soil, paving or render above the DPC line, or rubble in the cavity. Building regulations guidance for new work puts the DPC at least 150mm above the adjoining ground, so the fix is often to lower or clear the ground rather than inject a new DPC.

Is a chemical damp proof course injection worth it?

Only if a survey shows the original DPC is missing or has failed and other causes have been ruled out. It will not cure condensation, leaks or a bridged DPC. Ask for the readings and reasons in writing and get more than one opinion before agreeing.