How Long Does Damp Proof Course Last?
A damp proof course should last for a good 20 to 25 years.
However, they can fail and lead to rising damp and ongoing issues where water moves through your walls and floors, leaving water stains and causing plaster to peel.
The original damp proof course installed during construction is usually a plastic membrane, placed at the base of walls as a protective shield.
Chemical damp proof courses are more common for replacement damp proof courses and usually come with a 20-year guarantee.
Signs That You Need a Damp Proof Course
There are some forewarnings to look out for, which indicate that your property may be experiencing the start of damp problems:
- Watermarks and stains appearing on walls.
- Peeling wall surfaces and plaster.
- Deterioration to skirting boards and wood.
- Black spot mould on interior walls.
These issues could also be down to other damp problems, such as a build-up of condensation without sufficient ventilation, so they aren't necessarily a reason to immediately schedule a new damp proof course.
That said, without damp proofing treatments, you could see visual damage to your internal walls, find that your property market value decreases, and even experience rot in your timbers.
Most of the severe potential impacts occur after several years of untreated dampness.
Still, the potential for structural damage means that it is strongly advisable to seek professional advice if you suspect your damp proof course is failing.
How Long Will My Damp Proof Course Remain Effective?
A lot depends on the type of damp proof course you have, when it was carried out, and your property type.
Conventional damp proof course membranes, or DPMs, are broader in surface area than chemical damp proof courses, or DPCs.
Membranes are sheets of polythene that cover a wider space than the walls, laid under concrete slabs to prevent moisture from rising through the concrete and reaching the building timbers or masonry.
It's unusual to replace a DPM because these membranes are primarily laid during initial construction phases and are expected to last around 25 to 30 years.
Repairing or replacing a DPM is a tough job, whereby a contractor would need to dig down under the foundations, so a DPC is usually far more cost-effective.
A DPC differs because the damp proof course involves:
- Drilling a series of holes along the base of the wall affected by damp.
- Implementing a barrier at around 150 mm from floor level, alongside the mortar joints.
- Injecting a silicone-based solution, which draws water from your brickwork.
Chemical damp proofing uses a cream to coat the bricks with a layer of solution to stop water from continuing further upwards into the property.
Most DPCs come with a 20 or 30-year guarantee, but poor installation or property damage can inhibit the ability of the treatment to remain effective against dampness.
Do I Need a Professional to Install a New Damp Proof Course?
When a damp proof course begins to fail, it is important to remedy this as soon as is practicably possible to avoid water ingress, mould and damp which, as we've seen, can be disastrous if untreated.
While there are DIY damp proof course kits, it's usually recommended you work with a professional given the crucial nature of this protection.
The process normally follows these steps:
- Identify the walls with damp, and inspect the integrity of the existing damp proof course to establish whether a repair or replacement is necessary.
- Install a chemical DPC using a silicone-based solution.
- Inject the DPC cream, leaving it for a requisite period to fill in correctly.
Contractors will use several techniques and instruments to evaluate the severity of any damp issues and make suggestions for suitable solutions.
In some cases, your damp proof course may be functioning perfectly, and another structural problem or internal defect in your plumbing or piping may be to blame.
Hence, it may be far more cost-effective to assess the situation before investing in a new damp proof course.
Frequently Asked Questions - How Long Does a Damp Proof Course Last?
If you have any further questions about a damp proof course, we've answered some of the most common queries here.
How Much Does a Damp Proof Course Cost?
The costs depend on whether you're having a membrane or chemical damp proof course, the age of your property, and any repair works needed to address issues caused by damp.
Prices also vary, depending on where you have damp problems in the property.
Averages in the UK are about £320 for a terraced house, up to £1,500 for a detached property.
What Types of Damp Proof Course Can I Choose Between?
We've looked here primarily at chemical damp proof courses and membranes installed during construction, but there are other alternatives:
- Mortar injection damp proof courses are used in stone walls, with a similar drilling and injection method to chemical damp proofing, but with a cement-based mortar.
- Electro-osmosis damp proof systems are more technical and run an electrical charge through wires in the wall. This wiring is earthed to the ground, reversing the capillary action that is the basis of rising damp and pulling the moisture back into the soil.
If you have a period home or a property built from anything other than standard bricks and mortar, specialist advice is often necessary to select the appropriate damp proofing treatment.
Why Do I Need to Have Plaster Removed to Install a New Damp Proof Course?
Rising damp causes no end of problems, not limited to aesthetic damage to your walls. Moisture entering your property from the ground includes nitrates, chlorides and hygroscopic salts.
These salts suck in further moisture and contaminate your plaster, which is already a porous substance.
Even after a damp proof course, contaminated plaster will still be susceptible to dangerous levels of damp, so it's important to strip this back and replace it.
Usually, plaster only needs to be removed up to one metre from floor level, given that this is the typical height to which damp will rise.
References:
- https://www.timberwise.co.uk/damp-proofing/course/
- https://thedampbuster.com/how-long-does-a-chemical-dpc-last/
- https://www.travisperkins.co.uk/trade-corner/damp-proof-course-and-membrane-advice
- https://www.richardsonandstarling.co.uk/damp-proofing/faq/
By Johnny Fuller
Home Improvement editor at NWrenovations.com
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