Dealing with Damp

Dealing with Damp

Dealing with Damp A damp home is more than just unpleasant to live in, over time it will cause considerable damage to the property. Perpetually damp properties may also pose health risks for occupants and damage interior furnishings such as carpeting, furniture and window treatments. Making your home damp-free creates a more pleasant and healthy environment to live in and will help you to avoid problems like infestations of rot and mould in the house.

Types of Damp

Three different types of damp are attributed to outside influences, all of which can adversely affect your home.

Rising damp

As its name implies, rising damp is water coming up from the ground and absorbed into the walls of the house. Most houses built after 1920 are protected from rising damp by a physical barrier called a damp-proof course (DPC), which prevents damp from rising above a certain level. However a DPC can fail or be bridged in various ways. For example, a wood pile, or pile of earth, resting against an outside wall above the DPC level is all that is needed to conduct moisture.

Penetrating damp

Even if the DPC is in perfect condition some houses still suffer from damp walls, which can damage the flooring. In general, this tends only to affect one or two walls. If there are walls in your house that face the prevailing winds and only appear to get damp during or after a rain shower, they will almost certainly be suffering from penetrating damp. Solid walls are at greatest risk as there is no cavity for the moisture to cross. Once it has found its way into the wall, the damp will come through to the inside where it will be absorbed by flooring joists and boards. Unlike rising damp, which comes up from the ground and so only affects floors at ground level, penetrating damp can affect floor joists at any level. Porous bricks, damaged pointing, defective rendering or even a continuously leaking overflow can cause penetrating damp.


When warm, moist air meets a cold surface the air cools, and condensation is the tiny liquid droplets that form when the warm air is no longer able to hold the moisture. This is no less damaging to the structure of the building than penetrating or rising damp. More insidious than any other type of damp, it is often the most difficult to treat effectively. The root causes of condensation are usually poor ventilation, poor insulation, or a lack of heat. Unlagged water pipes in floor spaces also attract condensation and drips from these are often mistaken for leaking pipes. Adding heat to a room helps the air to absorb more moisture and will in part halt the condensation. Avoid paraffin and gas blower heaters as these use fuel composed of 50% water, which will only increase the amount of moisture in the air.

Tackling Damp

The most important first step towards dealing with damp is to identify the source of the problem.

Minor repairs

Often it is best to call in a specialist, but before going to that expense first check that the damp is not being caused by a small problem that can be cured with a minor repair. Cracks in masonry, broken and missing render or leaking pipes are some of the most common causes of damp. Such problems are easy to correct, and fixing a leaking pipe is much less expensive than replacing or installing a damp-proof course.

Dealing with a failed DPC

If your house does not include a damp-proof course or it has failed, a new DPC can be installed by injecting waterproof chemicals into the masonry at DPC level. This is usually carried out by damp treatment firms, but it is possible to hire the equipment and buy the chemicals if you are confident enough to tackle the job yourself. Injecting the damp-proofing chemicals is a two-stage task that involves drilling holes through the brickwork 150mm (6in) apart, first to a depth of 75mm (3in), at which point fluid is injected, then drilling to 150mm (6in) in solid walls and 200mm (8in) in cavity walls, and repeating the injection process.

Safety Advice

Some damp-proofing chemicals are poisonous – follow the instructions and always exercise caution.

Anatomy of a Damp-Proof Course

Since the late 19th century, most houses have been built with a waterproof layer designed to guard against rising damp. Called the damp-proof course (DPC), this layer is normally built into walls about 150mm (6in) above the ground level and will often show as a black line in the brick-or stonework. DPCs in newer houses are formed from a strong strip of plastic and in older houses they are often made from two layers of slate or dense water-resistant engineering bricks. Air bricks fitted at intervals in a wall represent another method of tackling damp in the home.

These work by improving ventilation from the space underneath a floor.

15. December 2010 by admin
Categories: Damp | Tags: | Comments Off on Dealing with Damp


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