How much does it cost to repair damp?

Damp

How much does it cost to repair damp?

Article 4 of 5

Find out the typical cost of different types of damp treatment so you know how much you should be paying to stop damp in its tracks. 

Repairing your home's damp problem can be expensive. Here we look at typical costs and give you expert advice to make sure you don't end up spending more than you need to.

Damp proofing costs can run into thousands of pounds, as the most extreme remedial works significantly affect your home's structure and may be the only solution if you want to banish damp for good. 

Costs for dealing with damp

We've worked with the Royal Institution of Chartered Surveyors, which publishes average building work and repair costs, to bring you the average cost for a range of different damp treatments, from repairing a damp-proof course with silicone to laying an entirely new damp-proof membrane.

And to give you a more realistic idea of what treatments might cost you, we've provided prices for terraced, semi-detached and detached houses, as well as the costs for treating just one wall or one area.

Which? members can log in now to see all the prices in the tables below, as well as findings from our damp investigation, which revealed bad practice from a number of damp specialist companies. 

If you're not a Which? member, you can gain instant access to all this information, and our investigation findings, with a £1 trial subscription to Which?.

Problem: ground level is above the existing damp-proof course
Solution: excavate soil as necessary to ensure the ground level is at least 15cm below the damp-proof course
Work needed Terraced house Semi-detached house Detached house
Excavate soil only - one wall Subscriber only content Subscriber only content Subscriber only content
Excavate soil only - whole house Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay new gravel path - one wall Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay new gravel path - whole house Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay concrete paving slabs - one wall Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay concrete paving slabs - whole house Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay 10cm thick concrete path - one wall Subscriber only content Subscriber only content Subscriber only content
Excavate soil and lay 10cm thick concrete path - whole house Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016.
Problem: DPC is damaged or non-existent
Solution: create a damp barrier with silicone or insert new DPC
Work needed Terraced house Semi-detached house Detached house
Inject silicone damp-proofing - one wall Subscriber only content Subscriber only content Subscriber only content
Inject silicone damp-proofing - whole house Subscriber only content Subscriber only content Subscriber only content
Insert new DPC - one wall Subscriber only content Subscriber only content Subscriber only content
Insert new DPC - whole house Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016. Injecting silicone involves drilling into the walls. Inserting a DPC (Hessian-based bitumen in this case) would involve cutting two courses into the brickwork, inserting the new DPC, pointing in mortar and restoring the brickwork to make it look like it did before.
Problem: blocked cavity walls are allowing damp to reach the inner walls from outer walls
Solution: clear blocked cavities
Work needed One area Two areas Three areas Five areas
Clear out cavities in isolated areas less than three metres above ground level Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Clear out cavities in isolated areas higher than three metres above ground level Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016. This work includes cutting out three bricks and renewing them to match the existing.
Problem: insufficient damp-proofing in walls at different heights
Solution: create a damp barrier within the walls at different levels
Work needed at low level (no scaffolding) One metre wall Two metre wall Three metre wall Five metre wall
Insert cavity tray (used to stop water from the outer wall reaching the inner wall) Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Insert stepped cavity tray (a more complex tray usually used where the roof meets the wall) Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Insert new damp-proof barrier/course where there is a 'weakness' in the wall (such as a joint) that may allow water in Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Work needed at high level (scaffolding) Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Insert cavity tray (used to stop water from the outer wall reaching the inner wall) Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Insert stepped cavity tray (a more complex tray usually used where the roof meets the wall) Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Insert new damp-proof barrier/course where there is a 'weakness' in the wall (such as a joint) that may allow water in Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016. Where a cavity tray or damp proof barrier is inserted, the cost includes removing bricks, replacing them and making them match the existing bricks. The damp-proof barrier/course is added in the coping area. The costs for the cavity trays quoted are made from polypropylene. The stepped one is also made from led.
Problem: damaged exterior surfaces are allowing damp to penetrate through walls
Solution: apply waterproof paint to exterior walls
Work needed Area one m2 Area two m2 Area three m2 Area five m2
One coat of exterior paint in isolated areas less than three metres above ground level Subscriber only content Subscriber only content Subscriber only content Subscriber only content
One coat of exterior paint in isolated areas higher than three metres above ground level Subscriber only content Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016.

Problem: internal walls are damp

Solution: 'seal' the walls (often called tanking) in damp-proofing material
Work needed 3 x 3 metre room 4 x 4 metre room 8 x 4 metre room
Remove damp/damaged walls and coverings, recover in damp-proof material to 1.2 metres high and decorate to full height Subscriber only content Subscriber only content Subscriber only content
Remove damp/damaged walls and coverings, recover entire wall, from floor to ceiling, in damp-proof material and decorate Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016. The material used for sealing the walls in this case is asphalt, a thick liquid. Jobs quoted above include removing old plaster, clearing out joints and brickwork/blockwork, applying three cots of asphalt tanking, rendering (with cement and sand), refixing or installing new skirting and decorating.

Problem: floors are damp

Solution: 'seal' the floor (often called tanking) in damp-proofing material
Work needed 3 x 3 metre room 4 x 4 metre room 8 x 4 metre room
Remove flooring, screed (concrete under the floor) and skirting, then lay membrane. Reinstate screed, refix skirting and lay new flooring Subscriber only content Subscriber only content Subscriber only content
Remove flooring, screed (concrete under the floor) and skirting, then coat twice with asphalt, a thick liquid. Reinstate screed, refix skirting and lay new flooring Subscriber only content Subscriber only content Subscriber only content
Table notes: Costs correct April 2016. Membrane used in this case is 500 gauge bitumen coated polyethylene.

About these costs

To arrive at the average prices above, RICS uses cost data from its Building Cost Information Service (BCIS) database, where costs are collated from a variety of sources and analysed. 

Material costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average. Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. 

Damp jargon buster

We've explained some of the common damp treatment terms below, but it's also worth visiting our pages on condensation, rising damp and penetrating damp for more details.

Damp jargon buster
Word or phrase Explanation
Damp-proof course (DPC) A horizontal strip, often made from plastic or bitumen felts, built into the wall at the height of at least 15cm above ground level.
Damp-proof membrane (DPM) A sheet of material, impervious to water, laid under the concrete floor. This should be connected with the damp-proof course so that the house is effectively sealed and protected from ground water.
Silicone damp-proof barrier Instead of inserting a new damp-proof course, silicone is sometimes injected into a wall to create a barrier.
Cavity tray Used in a cavity wall to act as a way to drain any water away from the inner wall to the outside through 'weep' holes (holes in a part of the outer wall). These are usually used around places where something 'interrupts' the wall, such as windows. These come in many different forms, depending on where they are in the wall, and made of many different materials.
Tanking Covering an entire damp area, such as a whole wall or floor, in damp-proof material (either a membrane or liquid), to effectively 'seal' the area and protect it from moisture.

Get professional damp-proofing help if needed

Many of the problems and solutions above require specialist help. So to make sure you're not overcharged, you should get quotes from at least three companies (some do charge for a damp report, but you get this back if you use the company) and seek advice from an independent damp specialist if there are inconsistencies in the work recommended. 

That way, you'll find out whether or not the treatment is absolutely necessary and will be able to weed out any firms that charge over the odds.

In our undercover damp-proofing investigation (see below), we found that households could be spending hundreds of pounds on unnecessary damp-proofing treatment.

Damp-proofing investigation

In a snapshot assessment in 2012, Which? invited 11 damp-proofing companies to two houses with a total of three potential damp problems. These visits were then analysed by three damp-proofing experts, who found that in two thirds of cases the companies recommended unnecessary or inappropriate treatment, or missed the problem completely.

Five of the 11 damp companies that visited the first property recommended completely unnecessary treatment according to the experts – some costing as much as £1,440 – when essentially they should have suggested asking a plumber to fix a leak.

In the second property, only two of the 11 companies recommended a suitable solution for the penetrating damp problem in the hallway. In this property five companies also failed to notice the likely damp penetration/rising damp problem at the front of the house. Of those who did identify it, only four recommended a suitable treatment.

Which? members can log in now to see the full findings from our investigation as well as all the prices in the tables below. If you're not a Which? member, you can gain instant access to all this information and thousands of reviews with a trial subscription to Which?.