If you live in one of Britain’s beautiful older buildings the chances are you’ve had to deal with damp as some point. If you’re lucky enough to have a cellar, this might have felt like a real uphill struggle. We’re here to help!
Damp isn’t just a cosmetic inconvenience. It can cause serious deterioration of plaster and stonework, rot wood and also be a health hazard for you and your family. There are also plenty of advertised “treatments” for damp that actually cause more harm to old buildings than good.
For example, becoming reliant on electrical moisture meters frequently leads to unnecessary expense and damage through the retrospective installation in walls of horizontal damp proof barriers (damp proof courses or DPCs). Equally the harm done by modern solutions that aim to seal old walls rather than improve their ability to breathe is underestimated. An appreciation of how the basic construction of old buildings differs from that of new ones will help you avoid such misguided remedies.
The Main Causes of Damp
If you’ve got damp in your cellar, the likely culprit will be one of these:
- Internal spillage. The common cause of this is overflowing or badly sealed baths or showers, burst pipes, leaking pipe joints, leaks from washing machines or dishwashers or accidental spills.
- Air moisture condensation. Measures to insulate old houses – whilst helping keep the warmth in and the weather out – can have the detrimental effect of sealing in all the moisture produced in your home. Everything from steam from the kettle to the moisture in our breath (best not to dwell on that too long) is trapped in the house by double glazing and insulation. To make matters worse, interstitial condensation within the pores of materials reduces thermal insulation and further increases the risk of condensation – driving the problem further.
- Penetrating damp. Roofs, chimneys, parapets and other exposed parts of a building are most susceptible to rain penetration, especially without regular maintenance. Junctions in roofs are potential trouble spots. Water will always find defective lead flashings, mortar fillets, ridges or hips. Poorly maintained rainwater fittings and leaks from parapet and valley gutters can cause significant damage the structure of your roof.
- Below ground damp. Most common in your cellar. Floors can become damp where the evaporation of moisture from below is prevented by something such as vinyl sheet, rubber-backed carpets or other impervious coverings. New concrete floors or impervious coverings also drive excess moisture into the bases of nearby walls where it rises by capillary action. DPCs were not compulsory in walls prior to 1875. In addition to rising damp, below ground moisture can result in problems where ground levels around your building rise unduly.
Tackling Damp In Your Cellar
Damp can be particularly troublesome in cellars but increased ventilation (including opening up redundant flues), re-pointing and lowering the water table locally can be effective. Failing this, it may be worth considering a dry lining system. Tanking (applying waterproof linings to walls and floors) is not recommended in old buildings.
The best – and most straightforward – way to deal with rising damp is to get a bit of ventilation to your cellar. Let the room breathe as much as you can. Replacing hard cement render by using a more suitable lime-based mortar often improves a damp wall and allows rising damp to dry out.
Where a floor has a modern damp-proof membrane (horizontal barrier or DPM) that is displacing moisture to the bottoms of walls, you could replace this completely with a breathable construction or to at least provide a breathing zone for evaporation around the perimeter of the room.
The second step you can take is to tackle the source of moisture. French drains can be an effective and relatively inexpensive answer. Remember not to install them directly against walls and rodding points must be provided. Without this blockages can effectively convert them into a sump and increase dampness.
Although retrofit damp proof courses can sometimes work in old houses always consider whether rising damp is actually too minor to matter and, if it is significant, whether less invasive measures could work before you do anything too drastic. Where any timber is at risk of decay, for example, you might be able to simply isolate it. Similarly, the eradication of any contributing moisture from other sources such as rainsplash off closely abutting patios could obviate the need for more extensive remedial treatment.