For many UK homes, 40% to 60% relative humidity is a useful general range. Relative humidity is often shortened to RH.
A reading between 40% and 60% is usually a reasonable result, but no percentage can guarantee that condensation or mould will not develop. Room temperature, ventilation, insulation and the temperature of walls and windows also matter.
A short rise after cooking, showering or bathing can be normal. Take a closer look if humidity:
- Remains above 60% for prolonged periods
- Repeatedly rises after normal household activities
- Is still high the following morning
- Appears alongside condensation, damp or mould
- Is much higher in one room than elsewhere
As a broad guide:
- Below 30% RH: The room may feel dry or uncomfortable.
- 30% to 40% RH: This can be acceptable, particularly during colder weather.
- 40% to 60% RH: A practical range for many homes.
- Above 60% RH: Monitor how long it remains high and check for signs of excess moisture.
A cold window, external wall or corner can develop condensation even when a hygrometer in the centre of the room reads below 60% RH.
What should you do about a high reading?
Do not judge the room from one reading taken immediately after cooking or showering. Monitor the humidity and temperature over several days.
Use extractor fans, keep permanent vents clear and reduce avoidable moisture. Check for leaks if one room is consistently more humid than others.
If high readings, condensation, damp or mould keep returning, the underlying cause may need further investigation.
What relative humidity means
Relative humidity describes how much water vapour is in the air compared with the maximum amount it could hold at its current temperature.
The reading changes as the temperature changes. If air cools without losing moisture, its relative humidity rises.
This helps explain why condensation forms on cold windows and walls. The air beside a cold surface may cool enough for some of its water vapour to become droplets.
Condensation on a window does not necessarily mean the entire room is saturated. It means the glass is cold enough for condensation to form in the air immediately beside it.
How to measure humidity at home
A hygrometer measures relative humidity. Many digital hygrometers also display the room temperature.
Place the hygrometer in a part of the room that represents normal conditions:
- Keep it away from radiators, fires and direct heat.
- Do not put it beside an open window or external door.
- Keep it out of direct sunlight.
- Avoid placing it immediately beside a shower, kettle or tumble dryer.
- Allow it time to adjust after moving it.
- Follow the manufacturer’s instructions.
Take readings in more than one room where possible. Bedrooms may become more humid overnight, while kitchens and bathrooms experience short increases during normal use.
Monitor the pattern
Check the humidity and temperature over several days. Useful times include:
- First thing in the morning in bedrooms
- Before and after showering
- During and after cooking
- While drying washing indoors
- During periods of cold or wet weather
A bathroom reading may rise sharply after a shower and then fall as moist air is removed. The time this takes will depend on the room, outdoor conditions and performance of the ventilation.
Check the extractor fan and vents if the room remains humid for a prolonged period or still feels damp the following morning.
Also look for:
- Regular condensation on windows
- Mould around frames or in corners
- Damp patches on walls or ceilings
- Musty smells
- Peeling paint or wallpaper
- Moisture behind furniture
- Damp inside wardrobes
A hygrometer can identify a pattern, but it cannot diagnose the source of damp.
What causes high humidity?
Daily activities release water vapour into the air. Humidity rises when moisture is produced faster than the home removes it.
Common sources include:
- Cooking and boiling water
- Showering and bathing
- Drying clothes indoors
- Breathing and perspiration
- A large number of houseplants
- Limited or obstructed ventilation
- Appliances that are incorrectly installed or used
High humidity, damp and mould should not automatically be attributed to household behaviour. Property-related causes can include:
- Leaking pipes or appliances
- Roof or gutter defects
- Damaged downpipes
- Water entering around windows or doors
- Defective render or pointing
- Inadequate or faulty ventilation
- Cold surfaces associated with insulation gaps
- Other forms of water ingress
Persistent patches, damaged plaster or moisture that becomes worse after rain may need to be investigated.
How to reduce humidity in your home
Start by controlling moisture at its source and using the home’s ventilation as intended.
Use existing ventilation
- Use kitchen and bathroom extractor fans while producing steam.
- Allow fans to continue running afterwards if they are designed to do so.
- Keep purpose-designed trickle vents open and unobstructed.
- Do not cover permanent ventilation grilles.
- Clean extractor fan covers and filters as instructed.
- Keep curtains, furniture and belongings away from vents.
- Follow the instructions for any whole-home ventilation system.
The government’s existing home ventilation guide provides more information about using and maintaining household ventilation.
Opening windows can provide extra airflow when it is safe and suitable. It should not replace working extractor fans, trickle vents or permanent ventilation.
Do not cover or alter permanent ventilation without suitable advice.
Reduce avoidable moisture
- Keep lids on pans where practical.
- Use the kitchen extractor while cooking.
- Keep kitchen and bathroom doors closed while producing steam.
- Remove excess water from shower screens and window sills.
- Avoid leaving wet towels in rooms with limited ventilation.
- Dry clothes outdoors where practical.
- If washing must be dried indoors, use a suitably ventilated room.
- Avoid placing wet washing directly on radiators.
- Use tumble dryers according to the manufacturer’s instructions.
- Empty appliance water containers and clean filters when required.
- Report or repair plumbing, roof and gutter leaks.
Check cold and poorly ventilated areas
Moisture can collect behind wardrobes, beds and sofas positioned against external walls.
Where space allows, leave a small gap behind large furniture. Check these areas periodically and make sure furniture or stored belongings are not blocking vents.
Very cold walls and windows are more likely to experience condensation. Where affordable and practical, maintaining a reasonably steady indoor temperature may help.
Heating does not remove water vapour. Moisture still needs to be controlled at its source or removed through ventilation or dehumidification.
Humidity in winter and summer
The general range of 40% to 60% RH remains useful throughout the year, but seasonal conditions affect how humidity behaves.
During winter
Condensation is often more noticeable because windows and external walls become colder. People may also spend more time indoors, keep windows closed and dry more washing inside.
During colder weather:
- Keep trickle vents clear.
- Use extractor fans while cooking or bathing.
- Check bedroom humidity in the morning.
- Look for condensation around windows and external walls.
- Investigate damp that repeatedly appears in the same place.
If the reading is consistently very low, check the hygrometer before adding moisture. Unnecessary humidifier use could increase condensation on colder surfaces.
During summer
Indoor humidity may rise during warm, wet or muggy weather. Opening windows will not always reduce it because the outdoor air may already contain a considerable amount of moisture.
Continue using extractor fans during cooking and bathing. Avoid drying large amounts of washing in closed rooms and check for a leak if one room remains much more humid than the others.
Do dehumidifiers work?
A dehumidifier removes water from the air and collects it in a tank or through a suitable drainage arrangement.
It may help when humidity remains high, when washing must be dried indoors or while an area dries after a repaired leak.
A dehumidifier may:
- Reduce persistent high humidity
- Help washing dry more quickly
- Limit condensation
- Make a humid room feel more comfortable
- Support drying after a repaired leak
- Reduce musty smells linked to excess moisture
It cannot stop water entering a property or permanently compensate for faulty ventilation.
Choose and use an appliance according to the manufacturer’s instructions. Check the recommended room size, operating temperature, noise level, maintenance requirements and power consumption.
Keep its air inlet and outlet clear. Stop using it if the plug, cable or casing appears damaged. Current electrical appliance notices can be checked through the government’s product safety alerts, reports and recalls.
When damp or mould needs further investigation
Everyday changes can help reduce condensation, but they cannot replace maintenance or repairs.
Further investigation may be appropriate if:
- Mould returns after it has been removed.
- Damp patches continue to grow.
- Water appears during or after rainfall.
- Plaster becomes stained, soft or damaged.
- A room smells persistently musty.
- Humidity remains high despite working ventilation.
- An extractor fan or ventilation system is not working.
- You suspect a roof, gutter, window or plumbing leak.
- Damp is damaging belongings or decoration.
The government’s guidance on the health risks of damp and mould provides further information.
If you rent your home, report damp, mould, leaks and ventilation faults through the process provided by your landlord or managing agent. Keep photographs, dates and copies of reports or responses.
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Keeping humidity under control
For many UK homes, 40% to 60% RH is a useful general guide. Consider the reading alongside room temperature, how long it remains high and whether there is condensation, damp or mould.
Monitor conditions over time, reduce avoidable moisture and use the home’s ventilation as intended. A dehumidifier may help with excess moisture, but it cannot replace suitable ventilation, maintenance or repairs.
If humidity, damp or mould keeps returning, report the problem or arrange for the underlying cause to be investigated.
This article provides general information about household humidity, condensation and damp. It is not medical or legal advice and should not be used to diagnose a health condition, determine legal responsibility or assess the condition of a property.
