Condensation affects a lot of homes in the UK, and if severe enough it can even lead to damp and mould problems in homes. But what causes condensation? What does it look like, and how can you prevent it from becoming a problem in your home?

Key Findings

Two people can produce 12.5 litres of condensation per day through normal activities like breathing, bathing, and boiling a kettle.
Having damp in your home can devalue the property by up to 10%, and severe cases can even reduce your home’s value by up to 53%.
Damp and mould can increase the risk of health problems like respiratory conditions, skin rashes and runny noses.
You will usually see condensation appear on cold surfaces like windows, walls, and mirrors.
Condensation forms at a dew point which changes depending on the temperature and humidity of a room.
Methods of reducing condensation in your home include increasing ventilation, drying clothes outside, and maintaining a consistently warm temperature.
Installing double or triple glazing can reduce heat loss from a room by 56%, reducing the amount of condensation that appears on windows.

What is condensation?
Where does condensation appear?
What causes condensation?
What is the dew point for condensation?
How much condensation do people produce?
Damp and mould as a result of condensation
Tips for preventing and reducing condensation
Sources

What is condensation?

Condensation is water that collects as droplets on cold surfaces like windows and walls when humid air comes into contact with them. The cold surfaces cause water vapour in the air to cool and become water.

What condensation looks like

Below you can see the typical signs of condensation to look out for in your home. These include water droplets on windows, peeling wallpaper and damp smells.

Signs of condensation in the home Homebrite

Where does condensation appear?

Condensation usually appears on cold, non-permeable surfaces. This can include windows, walls, mirrors and tiles. In your home, you’ll usually see the most condensation in rooms like kitchens and bathrooms as more moisture is produced in these rooms from cooking, showering and bathing.

Condensation on windows

You’ll often see condensation on windows because they provide an impermeable surface that is typically colder than the air inside your home. This is usually because the air outside your home is colder than the air inside, making the surface of the window colder.

Condensation in your loft

Just like other areas in your home, condensation can form in the loft due to condensation from excess moisture in the air and a lack of ventilation.

Things that can cause condensation to build up in the loft include:

Insulation being laid down in the loft which causes the loft space to be colder than the rest of the house and increases the chances of moist air depositing as condensation on cold surfaces in the loft.
Ventilation in the roof has been blocked by household items and boxes being stored in the loft, preventing fresh air from circulating.
Steam from showering and bathing rising into the loft due to a lack of ventilation.
Hot water tanks in the loft releasing steam and warm, moist air into the loft

What causes condensation?

Condensation is caused by the air being too humid and this warm air hits a cold surface. The air then cools quickly and turns from water vapour into water droplets.

A number of things in your home can cause condensation to form. Examples include:

Cooking – Steam coming from boiling pans, kettles, and ovens adds excess moisture to the air in your kitchen, and if the windows and tiles in the room are cold, condensation can start to form.
Showering or bathing – Running a hot shower or bath for a prolonged period produces a lot of steam, usually in a smaller space than other rooms in the house. This steam collects as water droplets on windows, tiles and the corners of the bathroom.
Drying clothes – If you dry clothes in a tumble dryer or hang them up to dry inside without enough ventilation, this will release moisture into the air that can collect as condensation.

What is the dew point for condensation?

The dew point is defined as the temperature at which condensation occurs. This temperature varies depending on humidity and atmospheric pressure. When the air is cooled below the dew point, its capacity to hold moisture reduces, and airborne water vapour condenses into liquid. [1]

Calculating the dew point in your home

As we mentioned, the dew point at any given time depends on the Relative Humidity (RH), and can be calculated using the current air temperature and the RH percentage.

The dew point chart below shows the dew points for different combinations of temperature and Relative Humidity.

For example, if the air temperature was 18°C and the Relative Humidity was 80%, the dew point would be 14.56°C. This means that, in these conditions, water vapour in the air would start turning into water droplets when the air hits temperatures of 14.56°C or lower.

So, if the air in your living room is at a temperature of 18°C with 80% Relative Humidity, and your window temperature is below 14.56°C, condensation will start to appear on your window.

Air Temp (Celsius)	Relative Humidity %
	45%	50%	55%	60%	65%	70%	75%	80%	85%	90%	95%
2°C	-7.77	-6.56	-5.43	-4.4	-3.16	-2.48	-1.77	-0.98	-0.26	0.47	1.2
4°C	-6.11	-4.88	-3.69	-2.61	-1.79	-0.88	-0.09	0.78	1.62	2.44	3.2
6°C	-4.49	-3.07	-2.1	-1.05	-0.08	0.85	1.86	2.72	3.62	4.48	5.38
8°C	-2.69	-1.61	-0.44	0.67	1.8	2.83	3.82	4.77	5.66	6.48	7.32
10°C	-1.26	0.02	1.31	2.53	3.74	4.79	5.82	6.79	7.65	8.45	9.31
12°C	0.35	1.84	3.19	4.46	5.63	6.74	7.75	8.69	9.6	10.48	11.33
14°C	2.2	3.76	5.1	6.4	7.58	8.67	9.7	10.71	11.64	12.55	13.36
15°C	3.12	4.65	6.07	7.36	8.52	9.63	10.7	11.69	12.62	13.52	14.42
16°C	4.07	5.59	6.98	8.29	9.47	10.61	11.68	12.66	13.63	14.58	15.54
17°C	5	6.48	7.92	9.18	10.39	11.48	12.54	13.57	14.5	15.36	16.19
18°C	5.9	7.43	8.83	10.12	11.33	12.44	13.48	14.56	15.41	16.31	17.25
19°C	6.8	8.33	9.75	11.09	12.26	13.37	14.49	15.47	16.4	17.37	18.22
20°C	7.73	9.3	10.72	12	13.22	14.4	15.48	16.46	17.44	18.36	19.18
21°C	8.6	10.22	11.59	12.92	14.21	15.36	16.4	17.44	18.41	19.27	20.19
22°C	9.54	11.16	12.52	13.89	15.19	16.27	17.41	18.42	19.39	20.28	21.22
23°C	10.44	12.02	13.47	14.87	16.04	17.29	18.37	19.37	20.37	21.34	22.23
24°C	11.34	12.93	14.44	15.73	17.06	18.21	19.22	20.33	21.37	22.32	23.18
25°C	12.2	13.83	15.37	16.69	17.99	19.11	20.24	21.35	22.27	23.3	24.22
26°C	13.15	14.84	16.26	17.67	18.9	20.09	21.29	22.32	23.32	24.31	25.16
27°C	14.08	15.68	17.24	18.57	19.83	21.11	22.23	23.31	24.32	25.22	26.1
28°C	14.96	16.61	18.14	19.38	20.86	22.07	23.18	24.28	25.25	26.2	27.18
29°C	15.85	17.58	19.04	20.48	21.83	22.97	24.2	25.23	26.21	27.26	28.18
30°C	16.79	18.44	19.96	21.44	23.71	23.94	25.11	26.1	27.21	28.19	29.09
32°C	18.62	20.28	21.9	23.26	24.65	25.79	27.08	28.24	29.23	30.16	31.17
34°C	20.42	22.19	23.77	25.19	26.54	27.85	28.94	30.09	31.19	32.13	33.11
36°C	22.23	24.08	25.5	27	28.41	29.65	30.88	31.97	33.05	34.23	35.06
38°C	23.97	25.74	27.44	28.87	30.31	31.62	32.78	33.96	35.01	36.05	37.03
40°C	25.79	27.66	29.22	30.81	32.16	33.48	34.69	35.86	36.98	38.05	39.11
45°C	30.29	32.17	33.86	35.38	36.85	38.24	39.54	40.74	41.87	42.97	44.03
50°C	34.76	36.63	38.46	40.09	41.58	42.99	44.33	45.55	46.75	47.9	48.98

Source [2]

Below is the formula for calculating the dew point:

Td = T – ((100 – RH)/5.) where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in per cent). [3]

How much condensation do people produce?

A lot of our daily activities add moisture to the air, things like washing and drying clothes, boiling kettles and even just breathing all add water vapour to the air.

A typical two-person household can produce 12.5 litres of moisture in a home in one day by completing some of the normal household activities shown below.

Activity	Amount of moisture produced
Two people active during the day	1.7 litres
Two people sleeping	0.5 litres
Boiling a kettle or cooking	3.4 litres
Having a shower or bath	1.3 litres
Washing clothes	0.5 litres
Drying clothes	5.1 litres
Total	12.5 litres

Source [4]

Damp and mould as a result of condensation

In England, 3.5% of homes have some sort of damp problem, and condensation is one of the most common causes of dampness.

When condensation can’t dry out, mould can start to form on walls, around windows and behind furniture. Living in a home with mould can cause a number of health concerns like respiratory infections, skin rashes, and red eyes. It is estimated that the NHS could save over £38 million per year if hazards related to dampness in homes were rectified.

Financial impacts of condensation and damp

If you experience a small amount of condensation in your home, it’s unlikely to cause serious problems. However, if the problem is more serious and results in damp, this can reduce the value of your property by up to 10%. In very severe cases of dampness, your property could be devalued by up to 53%. [5]

Tips for preventing and reducing condensation

While condensation is a normal thing to see in your home, it can be an inconvenience, especially if it leads to damp and mould. There are some steps you can take to reduce condensation build-up and prevent moisture from causing more serious issues.

Insulation to prevent condensation

Insulating your home can help reduce the risk of condensation as it makes the house warmer, preventing moist air from hitting cold walls and windows which would ultimately cause condensation to build up. As long as the insulation is installed correctly, consistently, and with adequate ventilation throughout the house, it should help reduce the amount of condensation that appears.

Insulation should not be used as a solution to an existing damp problem. For example, if you have a leaking roof that is causing damp, installing insulation into the wall will just divert the water elsewhere, maintaining the damp problem.

Condensation can still be found in uninsulated parts of the house, so it’s important to ensure that your home is thoroughly insulated. [6]

Types of insulation

Adding insulation to your home helps reduce condensation by simply keeping your home warmer. The type of insulation that works best will depend on each home, how it is built, and whether there are any existing issues. Some of the insulation options to consider include:

Type of insulation	Description	Heat loss reduction
Cavity wall insulation	The gaps between the two layers of your wall are filled with an insulating substance like foam or fibre.	Up to 33%
Solid wall insulation	For homes without cavity walls – a layer of insulation is added to either the inside or outside of the wall, and covered with plasterboard or cladding.	Up to 60%
Double glazing or triple glazing	Windows made of two or three layers of glass which retain more heat than old-style single glazing.	Up to 56%
Loft insulation	Either fibreglass or spray foam insulation is applied to the joists and/or rafters in your loft space.	Up to 50%
Floor insulation	Spray foam or insulation boards are installed beneath the floor.	Up to 15%

Sources [7] [8]

Maintaining a consistently warm temperature

Keeping your home consistently warm helps reduce any sudden drops in temperature that lead to condensation forming on cold walls and windows. This doesn’t mean you need to keep your heating on all the time, you can leave it on in the background or have it set to come on at certain times when the house may drop in temperature.

It’s also important to maintain an even temperature throughout the house as heating some rooms and leaving others cold can make condensation worse.

What temperature should I have in my house to prevent condensation?

Letting rooms in your house become too cold is one of the main reasons why condensation forms and can lead to problems with damp and mould.

Keeping rooms above 15°C is a good place to start if you’re trying to prevent condensation in your home.

Increase ventilation

Ventilation is one of the key differences between homes that produce a lot of condensation and those that don’t. Make sure you use your kitchen extractor fan when cooking, and use a bathroom extractor fan when showering or running a bath. If you don’t have extractor fans, consider installing them, or alternatively open a window or door when cooking or bathing.

Reduce the amount of water vapour in the air

As we mentioned, water vapour and steam are produced through a number of everyday activities in the home. Some things you can do to reduce the amount of water vapour that ends up in the air include:

Drying clothes outside if you can – Water vapour is produced by clothes air drying or tumble drying in the home, line drying clothes outside ensures that this water isn’t trapped in the air in your home.
Keeping lids on pots and pans – Steam from cooking can land on windows and walls as condensation, keeping lids on boiling pans means water vapour stays inside the pan instead of in the air.
Closing kitchen and bathroom doors – When cooking or bathing, keeping the kitchen and bathroom doors closed can help prevent water vapour from entering other areas of the house and creating condensation on cold surfaces.