Dampness is a serious problem in some homes.

Common causes of this are:  

• rain water leaking from pipes, gutters, wastes or overflows
• rain water coming in through a crack in the wall, a gap in a window or a missing roof tile (this is known as ‘rain penetration’)  
• rising damp which leaves a ‘tidemark’ on the wall, about a metre above the floor

These kinds of dampness are treated by having the fault repaired by a tradesperson or as a DIY job; rising damp certainly requires a professional builder.

If a home has dampness and none of these problems applies, it is likely that the house is suffering from CONDENSATION: it is estimated that 70% of all dampness is down to condensation. Indeed, one in five British homes experiences some condensation-related problems during the winter months.

A page of advice and a video from the Energy Saving Trust on fixing damp and condensation Fixing damp and condensation - Energy Saving Trust 

What is condensation and what causes it?

There is always moisture (more accurately, water vapour) in the air, but normally it is invisible. Human activities like bathing, showering, cooking, boiling a kettle, drying clothes or breathing generate warm humid air (i.e. air holding a lot of water vapour). This warm  humid air is drawn to cold areas by heat transfer and it then cools down quickly when it collides with cold air (in unheated rooms) or hits a cold surface (window panes or cold walls), especially a surface where there is little movement of air. As the humid air cools, the water it holds condenses out of it (i.e. it changes from water vapour to liquid water) and forms droplets on the cold surface.

While condensation is rarely a problem in the summer, the amount of water in the air (otherwise known as the humidity) inside our homes is higher during colder months. This is because we tend to have the heating turned up high and the windows closed.

In summary, condensation is caused by four things:

• H - Not enough Heating – more water vapour is held in warmer air than cold air
• I -  Not enough Insulation – the home can’t retain heat and has cold surfaces
• V - Not enough Ventilation – the moist air can’t escape
• E - Excess moisture – steam in the kitchen and bathroom, drying laundry

What are the effects of condensation?

If not dealt with quickly, condensation develops into condensation dampness, causing major   problems:

• a musty smell
• damage to interior decoration e.g. peeling wallpaper
• damage to property e.g. rotting window frames – ultimately this can damage the structural integrity of the home 
• mildew, fungus or black mould on walls, carpets, bedding or clothes 
• infestations of dust mites

Mildew, fungus and mould cause many health problems including sinus problems and skin rashes, as well as serious respiratory conditions like asthma and bronchitis. These are especially severe for people with existing skin conditions, compromised immune systems, or who already have respiratory difficulties. Children and the elderly can be especially affected.   

How can a householder prevent or reduce condensation?

Preventing condensation in the first place is far easier than trying to take remedial action to deal with its effects. To tackle it you need to:   

generate less moisture (tackle the ‘E’ in HIVE) 

• avoid using paraffin or bottled gas heaters – they produce a vast amount of water vapour
• cover pots and saucepans when cooking
• dry laundry outdoors if possible; or at least hang it in a room, shut the door and open the window
• vent a tumble dryer to the outside or buy a DIY ‘self-condensing’ dryer kit

let the moisture out (tackle the ‘V’ in HIVE)

• leave ‘trickle’ vents open whenever someone is in the room – these are small vents in the

frames of modern windows

• air the rooms people use a lot, especially bedrooms: much moisture is caused by breathing
• use extractor fans in bathrooms and kitchens when cooking or drying laundry
• open windows when they steam up
• close internal kitchen and bathroom doors when steam is being produced
• air cupboards and wardrobes and avoid putting too much in them as this stops air circulating
• leave a gap between furniture and walls to allow air to circulate.

insulate the home (tackle the ‘I’ in HIVE)

• fit wall and loft insulation to make the outside walls and ceiling warmer
• draught-proof internal kitchen and bathroom doors to help keep moisture from spreading

heat the home adequately (tackle the ‘H’ in HIVE)

• keep temperatures in all of the rooms above 15°C to cut down the risk of condensation forming on walls and fabrics  

but please DO NOT:

• block air bricks, trickle vents or chimneys
• draught-proof windows in rooms where there is condensation or mould
• draught-proof windows in kitchens or bathrooms unless the window has a trickle vent or there is an extractor fan

Here is an advice video from a housing association (691) How To Prevent Damp, Mould and Condensation | 'How To' Guides with Sanctuary Housing - YouTube