Last Updated on
Have you discovered an issue with damp in your home? Whether it be a slight musty smell, an obvious patch of mould or a tide mark, it's time to tackle the problem.
But how do you know if you need a full damp-proof course? What is it, and how much is it likely to cost? We've got everything you need to know when it comes to the cost of damp-proofing. Read on for the complete guide.
How do you know if you have damp? Apart from the obvious, there are certain things to look out for. Although, the signs may indicate that it's not so much a small problem that can be resolved yourself, but rather a big issue that might need the aid of a professional.
Patches of black mould are a huge giveaway and can cause respiratory issues over the long term. Other indications of a problem with damp include peeling paint or wallpaper, crumbling skirting boards, tidemarks and salty deposits on the walls or floor.
Left untreated, a serious issue with damp can rot, damage plaster and affect the structure and stability of your property.
Before deciding whether your property needs damp-proofing, you need to determine what type of damp it is, the cause of the issue, and what you might be able to do to counteract it.
There are three different types of damp; condensation, penetrating damp or rising damp. Unless you know for definite where the problem originates, it's a good idea to go through a process of elimination first, to avoid any excessive and unnecessary expense.
With condensation being the easiest problem to resolve, it's the obvious place to start. Without proper ventilation, moisture builds within your home or property, resulting in mould spores and mildew, as indicated in case study #1 from the Job Prices website.
Simple things like opening windows more often, drying clothes outside rather than in, and using extractor fans in bathrooms and kitchens will help to reduce the level of moisture in the air.
According to Which?, simply keeping your heating on constant at a lower temperature can help prevent damp. You could also invest in a dehumidifier to reduce and control humidity.
As the heading suggests, there's water coming in somewhere it's not supposed to be. This could be caused by a range of problems, some of which can be rectified and prevented from happening in the first place.
Things you can check include guttering and down-pipes. Blockages can cause rainwater to bypass pipes, resulting in prolonged contact with the external walls.
Furthermore, there may be hairline cracks in the rendering or brickwork, and moisture seeping into the structure of the building can cause significant damage.
If your property has a cavity wall, there may be debris lodged between the outer and inner walls, creating a bridging effect. Similarly, cavity wall insulation could also pass moisture to the inner walls where the outer wall has deteriorated through driving wind and rain.
Other causes of penetrating damp might be leaks in the roof from missing slate or tiles. Internally, you could have an issue with a leaking pipe, cracks in the tiles or grout, or leaks from the shower or bath.
Rising damp is generally caused by moisture below the ground which rises up and seeps into the walls. Though relatively uncommon, it is an issue that can cause complications and be the most problematic to deal with.
Check your existing damp-proof course around the outside of the house, which should sit 150mm/6" above ground level (see diagram above).
Building regulations made them compulsory for all houses built after 1875, so if your property was built before then, it may not have one. There should be a thin strip or a grill at the base of the wall to indicate the presence of the DPC.
If the soil level is higher than the damp-proof course, this will need to be dug out again. Similarly, if a patio has been installed above the DPC, this will need lowering.
If condensation, leaky guttering or missing roof tiles have been eliminated as the cause of the issue, you'll need to consider other options. The type of treatment you need will undoubtedly depend on the severity of the problem.
Penetrating damp through porous bricks can be treated with a limewash or silicone water-repellent, still allowing the walls to breathe, but if there is an interim issue such as wet cavity wall insulation, this will need to be resolved prior to any application.
Rising damp can be resolved by injecting a damp-proof course (DPC) chemical gel or paste into the base of the walls, at a minimum of 15cm/6" above ground.
It's worth bearing in mind that depending on the severity of the problem and whether the floor is affected, it might be a case of repairing the existing damp proof course and membrane.
A chemical DPC is generally the most cost effective and DIY-friendly type of damp proofing. The water-repelling chemical paste or cream is injected directly into the wall along the mortar-course, as demonstrated in the video below. A quality DPC should be effective in preventing damp from creeping up the wall; IF this is the root problem of the issue.
While it is possible to attempt to do this yourself, personally I would recommend hiring a professional. If you did decide to DIY, you can expect to pay around £20 for a 310ml Dryzone cartridge – or around £30 for a 600ml cartridge – and should follow the instructions very carefully.
Bear in mind that you may also need to remove and replace existing plaster and consider the costs associated with this.
To work out the quantity of chemical DPC you may need, use the table below as a guide. Prices and figures obtained from householdquotes.co.uk.
Width of Wall
4.5" single wall
9" thick cavity or double solid wall
4.5m (double if required on both sides)
8" thick filled or solid wall
Note: scroll left/right to view the entire table above
For a step-by-step guide to installing a DPC cream, check out this guide from Skilled Build.
Before rushing out and stocking up on chemical DPC and other tools, it's best to be sure on the course of action you need to take. If you've checked everything and still can't determine the exact cause of the problem, and aren't confident in tackling the issue yourself, what's the next step?
If you want to go direct to a damp-proof specialist, you might want to look at getting an independent survey done first, which will cost between £150 – £300.
A surveyor will be able to conduct an investigation and discover the cause. They'll also advise on a course of action and provide a ball-park guide-price, thus avoiding any potentially unnecessary and extensive work. At this point, you can then contact a professional to complete the work required.
For the more common problems and resolutions when it comes to rising and penetrating damp, the table below provides an insight into the type of costs you could you be facing. The data indicates costs for soil excavation and laying any external surfaces, new DPC, and silicone injection into the walls.
Prices sourced from homeadviceguide.com and will vary depending on your location within the country as well as the size of your property and the work required.
Problem: Ground level higher than existing damp proof course
Ground excavation – one wall
Ground excavation – whole house
Ground excavation & installing gravel path – one wall
Ground excavation & installing gravel path – whole house
Ground excavation & installing concrete slabs – one wall
Ground excavation & installing concrete slabs – whole house
Ground excavation & installing concrete path – one wall
Ground excavation & installing concrete path – whole house
Problem: Damaged (or non-existent) DPC
Silicone injection damp proofing – one wall
Silicone injection damp proofing – whole house
Insert new damp-proof course – one wall
Insert new damp-proof course - whole house
The above information should help to determine the root of your problem and decipher the level of work required to make your home fully damp-proof. If there is an underlying issue of damp in your property, just papering over the cracks (so to speak) won't solve the problem.
If you're a property expert or DIY enthusiast, you might be confident enough to attempt a chemical injection DPC. But for a big job that requires a professional, contact Rated People.
Have you had experience with damp before? What was the outcome? Let us know in the comments below, and if you liked this article, please share.
Fiona Chapman is a copywriter and lifestyle blogger. With a keen interest in property and home decor, she’s passionate about keeping costs down. When not writing you’ll find her working on her latest craft, or chasing her unruly children