• Danni Greenough

Damp: Causes, Prevention & Treatments



With the constant chilly temperatures and presence of water everywhere - whether it be rain or that morning frost - and our efforts to keep our homes nice and cosy inside, buildings are at risk of suffering from damp. Structural damp is when moisture gets into a building (either from outside, or from a build-up of condensation/steam) and can cause structural problems, health issues associated with mould and damage to belongings.


What are the signs of damp?

Discoloured ceilings, clammy walls, stain marks on various surfaces, flaking paint or peeling wallpaper are common, as are mould patches. Damp can cause mortar and plaster to crumble and potentially fall away, and some metal fixings to rust.




What are the different types of damp?

There are three main types of structural damp: rising damp, penetrating damp and condensation.

Rising damp - where water enters the structure from the ground via porous materials such as brick, mortar or sandstone. These materials can absorb moisture and retain it, and as more is absorbed the level slowly creeps up the wall. A tell-tale sign of rising damp is when the moisture is only found in the lower section of the wall and there are 'tide marks' where salt and minerals in the water dry at the top of the damp. (This can also be caused by other issues, so it's always worth getting a professional in to check.)

Penetrating damp - mostly caused by rain penetrating the exterior of the building, via walls, roofs and other openings (badly fitted windows, holes in brickwork, damage to roof flashing etc). This can be exacerbated if the wall is exposed to long periods of rainfall.

Condensation - created when water vapour inside the house, usually created when the humidity of a room is increased, comes into contact with cooler surfaces and builds up moisture. Bathrooms and kitchens are most at risk of this kind of damp as hot baths, showers and cooking will let out a lot of water vapour. Poorly insulated walls and little to no ventilation around windows will make it worse.



How do you prevent damp?

- Rising damp is generally prevented by a damp proof course; a standard element required in buildings since the late 1800s. It is generally a material (commonly felt or plastic) set into the wall as it is built to create a barrier and prevent ground moisture getting into the building. Make sure the existing DPC is not damaged, and that the ground level outside sits lower than the DPC so no moisture can bypass it.

- Allow air to circulate by opening windows everyday.

- Place furniture a little bit away from external walls.

- Try to heat up all of the rooms in the house equally.

- Prevent moisture build up by closing bathroom doors and opening a window when showering or install an extractor fan.

- Dry washing outside when you can or use a condenser dryer as this doesn't need a vent to outside and won't let moist air escape into your home.

- Invest in a dehumidifier to reduce humidity levels. When the humidity in a room reaches 60% or more you are likely to experience mould growth, especially if the room is 20 degrees or warmer.

- The cause of damp around the chimney breast is most likely due either the flashing around the chimney being damaged or from being blocked up. When the flue is blocked the bricks cannot breathe and moisture forms. Keep on top of this by getting your chimney regularly swept and keep fireplace vents open to allow the flue to get a good airing.

- Keep on top of maintenance jobs such as gutter cleaning and repairs to masonry and roofs, especially after heavy rain and storms.



- Make sure you use lids on saucepans when cooking, or turn on the extractor fan. Crack open a window if it does start to get too humid.

- Ensure the house is properly insulated to retain warmth.

- There are products you can buy which protect both interior and exterior (paint and masonry) to ensure breathability but prevent moisture getting in.


How do you treat damp?

- Firstly, if damp is suspected it's always best to get a qualified damp surveyor in. They can identify if it is damp or just other forms of water ingress, what kind of damp it is and then what actions you would need to take to monitor/treat it.

- Use a dehumidifier in the room/s where damp is present and make sure it's completely dry before any remedial work is started.

- Minor signs of mould on the walls can easily be wiped down with a mild detergent and then sealed in order to prevent it returning. Read our blog post on keeping mould under control here.

- If there is an issue with the DPC, then a new one may be needed. The surveyor will be able to recommend which would be best for the property.

- Interiors may need to be stripped back and treated before re-plastering and decorating.


If you do see signs of what you think may be damp - it's always best to check with an expert first. It may be something small and easily remedied, but it also may need to be monitored and investigated if there is a potential for it to be causing structural problems.

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