Damp occurs when there is excess of unwanted moisture in the air that has no way of escaping. Excess moisture can be caused by steam when cooking, drying clothes inside the home and perspiration caused through showering and bathing.
There are 3 types of damp:
- penetrating damp
- rising damp
- condensation
Penetrating Damp
Penetrating damp is the process of moisture moving from the exterior wall of a building to the interior. It occurs when outside moisture, like wind-driven rain, impacts a building's wall. Building materials like brick are porous. They soak up rain to saturate the wall with penetrating damp.
This can happen when:
- the roof or rendering is damaged
- the gutters are blocked
- pipes are leaking or plumbing is damaged
- areas around sinks, showers or baths are damaged, such as cracked grouting or worn out sealant
Rain penetration into masonry can occur in buildings of all ages. At its most obvious, it penetrates the wall and displays as a damp patch on the internal wall. This causes discolouration, paint and wallpaper peeling and flaking. Even if it does not penetrate entirely through a wall, rainwater penetration can be damaging to a property. Wind-driven rain in masonry can cause moss growth, increased heat loss and frost damage.
Rising damp
Rising damp happens when water rises from the ground through the floor and into the walls of the building. You can often see rising damp because it leaves a tide mark low down on affected walls. Compared to penetrating damp or dampness caused by excess condensation, rising damp is relatively rare. In older buildings over 100 years, it is often caused by a faulty or missing DPC (Damp proof course). In newer buildings, rising damp is often caused by adjoining structures that introduce moisture above the DPC.
Internal signs of rising damp:
Dampness in walls originates from a variety of different sources. It is therefore important to find out exactly where the dampness comes from to save time and money on the wrong treatment. Internally, the rising damp can be identified by looking at the following signs:
- Efflorescent salts at ground level on external walls
- Damp sections of wall
- Flaking or bubbling plaster
- A stale, mouldy, musty smell
- A damp tide mark around 1m up the wall
External signs:
- Rusting metal fastenings
- Efflorescent salts on brick walls
- Spalling bricks and mortar
- A damp patch rising from the ground
What causes rising damp?
Rising damp is often the cause of structural damage in buildings. Internally rising groundwater saturates walls and pollutants. Saltpetre, which is contained in water, damages building materials. With time, constant dampness in walls can lead to mould, blistering, the peeling of paint and wallpaper and damaged render.
In older buildings, this type of damp is often caused by a damaged DPC or the lack thereof. Relevant building regulations for damp-proof courses were developed in the early 1900’s. However, these were not always adhered to. As a result, some of these DPCs become damaged over time.
Condensation
Condensation is by far the most common cause of dampness in buildings, probably accounting for the majority of damp problems reported. It affects both old and new buildings, but it appears to be a significant problem where the building has been modernised.
Condensation is directly associated with mould growth. It is this that the occupier sees first, and it gives an indication of the potential scale of the problem. The mould is usually found on decorative surfaces, especially wallpapers, where it can cause severe and permanent spoiling. In many cases, the mould and its spores (‘seeds’) give rise to complaints about health, and cause the “musty” odour frequently associated with a damp house.
What is the condensation caused by?
If humidity is high enough, the accumulated moisture in the air is deposited on cold impenetrable surfaces. This can cause condensation on the outside and inside of windows. Condensation can also form inside double-glazing, although that is usually caused by a failure of the seal between the two window panes. Condensation can also affect penetrable surfaces, such as wallpaper and plaster. The perfect conditions for condensation to manifest are:
- warm rising air
- falling temperatures
- cool surfaces
Warm air holds more moisture than cold air and when it rises, so do the suspended water molecules that are contained. As temperatures fall, the air can no longer hold all of its moisture, so it will find surrounding cool surfaces to transfer this moisture onto. Condensation is very much a seasonal problem, occurring during the colder months – October to April. During the summer, the problem is seen to go away.
During the winter, ventilation of the house is usually low (due to windows and doors being closed, draught-proofing takes place). This allows build up of water vapour in the house, which, in some cases is sufficient to cause condensation. This condensation becomes apparent from the following symptoms:
- Water droplets form on cold, impervious surfaces such as glass and paint.
- Slightly damp wallpaper (often not noticed).
- Development of moulds, usually black mould.
Condensation is common in areas where there is little air movement, such as:
- behind furniture
- in cupboards
- under work surfaces
- on north facing walls
- in corners
If a property doesn't have good ventilation and heating, condensation can cause mould. Mould is a type of fungus which grows in damp conditions. Its spores can make some medical conditions worse, such as:
- respiratory infections
- allergies
- asthma
How to prevent condensation and mould growth
- Reduce moisture by wiping any damp or wet windows, sills, walls and surfaces with a paper towel and throwing it away.
Heating
- Keep low, background heating on all day if possible and a window slightly open (warm air can hold more moisture so you're less likely to have condensation).
- Don't put heating on for short periods of time (this will make the problem worse because the air heats and cools quickly).
- Don't use liquid, propane gas or paraffin heaters because they produce a lot of water vapour.
Help air move around
- Leave doors open unless you're cooking, having a shower or bath, or drying clothes.
- Keep furniture away from walls, particularly external walls, if possible.
- Don't overfill cupboards and wardrobes.
- Don't block air-bricks or vents.
- Don't completely block chimneys, leave a hole and fit an air vent.
- Keep a window slightly open, if possible, because this will help moisture escape.
- Keep trickle vents open if you have them. A trickle vent is a small slot above a window or door that allows air in and out when the door or window is closed.
It might seem strange to keep the heating on with a window slightly open, but it helps because you're letting air that's full of moisture out and dry air in. Dry air is easier and cheaper to heat.
Cooking
- Close the kitchen door.
- Open a window or put the extractor fan on.
- Cover pans with lids.
- Don't leave pans or the kettle boiling longer than needed.
Having a shower or bath
- Close the bathroom door.
- Open a window or put the extractor fan on.
- Leave the window open or fan on until all the moisture has gone from the windows and walls.
- When you have a bath, put some cold water in the bath first and then add hot water. This will reduce the amount of steam produced.
Drying clothes
- Dry clothes outdoors if possible.
- If you have to dry clothes indoors:
- put them in a room with the door shut and heating on
- open a window (or put the extractor fan on if they're in the bathroom)
- If you use a vented tumble dryer, make sure it has a hosepipe taking the moisture outside.
Mould
- Remove any mould as soon as you see it.
- Clean the area with soapy water or a fungicidal wash (follow any instructions carefully).
- Don't brush or vacuum the area because it can disturb mould spores.
- Dry the area thoroughly.
- Paint the area with a fungicidal paint. Don't use ordinary paint or wallpaper.
The most crutial thing when dealing with any type of dampness is to react promptly. Water can make a lot of damage to your property, thats why it is important to notice early signs. Share this article with your tenants and ask them to report anything suspicious as soon as possible.
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