Headshot of Professor Michael Parrett.

Professor Michael Parrett FRICS

Consultant Building Pathologist, Michael Parrett Associates

RICS would like to thank Professor Michael Parrett FRICS for his help producing this consumer guide and for providing the photographs.

This consumer guide helps owners and occupiers of residential property to manage and maintain their homes.

What is ‘damp’ in buildings?

Damp can be described as ‘excess moisture that should not be there’.  

If any part of your home

  • is not dry to the touch
  • has mould growth or
  • has a musty smell

you should investigate.

Damp comes from many sources and can take different forms:

Penetrating damp occurs when water moves from one side of a wall, ceiling, roof or floor to the other.

Examples:

  • a broken tile causing a leaking roof
  • broken sealant around a window letting rainwater in.

Penetrating damp, 'rising damp' and condensation are not causes of damp but are different ways moisture moves through, or onto, parts of a building.

To solve a damp problem, you first need to find where the moisture is coming from.

What causes damp?

Finding the cause(s) of a damp problem can sometimes be complex, and it is best to contact a specialist building surveyor and ask for a Joint Position Statement (JPS 2022)-compliant survey.

However, anyone can investigate and look for problems. For example, you could go outside in the rain and see whether your gutters are overflowing. If something doesn’t look right, it usually isn’t right.

Check for:

  • leaking and/or blocked gutters and rainwater pipes
  • ill-fitting doors and windows
  • roofing defects, such as poor roof flashings and dislodged or broken roof tiles
  • open chimney pots
  • poor external pointing
  • cracked external wall render
  • raised ground levels next to walls
  • excess rubble under suspended ground floors. This can stop ventilation under the floor and make floor timbers wet, bridge the damp-proof course and block low-level through-wall air vents.
  • failed underground drainage
  • leaking water main supply pipes
  • bridged cavity walls, i.e. physical blockages such as rubble in the cavity wall void
  • blocked low-level through-wall vents for suspended floors
  • broken sealant or mortar around windows and doors
  • internal plumbing leaks, e.g. below baths or broken mastic seals around showers
  • flooding
  • high local water table.

What causes condensation?

When indoor temperatures drop or humidity is high, water vapour in the air turns into liquid droplets on the coldest surfaces in a room. This is commonly seen as condensation on windows, walls or other surfaces.

This can lead to mould growth forming over time on surfaces, typically:

  • around windows
  • on external walls and
  • on ceilings close to external walls.

Things that can increase condensation in your home are:

  • drying clothes over radiators
  • not closing kitchen and bathroom doors or not opening windows during cooking and bathing/showering
  • not covering pots when cooking
  • incorrectly vented tumble dryers or ‘recirculating-only’ cooker hoods (i.e. directing the moisture inside rather than outside)
  • poor ventilation, especially in bathrooms and kitchens
  • not heating your home sufficiently
  • overcrowding (people produce moisture, so the more people in a home, the more moisture is produced).

How do I minimise condensation?

Firstly identify the source of the moisture.

Finding the source requires a methodical approach over time and you may need professional help.

Fix defects in the property.

Use windows and extractor fans for ventilation.

  • This is especially important after cooking, bathing, showering or drying clothes.
  • Windows do not need to be open all the time to improve ventilation – about 5 minutes for every hour you’re in a room is enough. Or you can allow a small amount of ventilation using:
    • trickle vents on modern windows (trickle vents are small devices, often fitted at the top of the window, that allow fresh air to circulate naturally through a room), or
    • the secure window latch.

Opening windows does not always work when there is high humidity outside, so use extractor fans too.

Always use extractor fans while cooking, bathing or showering.

Check the ventilation systems in your home.

  • Fit bathrooms and kitchens with mechanical air extractors that can cope during peak periods: cooking, washing, bathing, showering and drying clothes indoors.
  • Check extractors are of the right size and working well, and make sure that you clean them regularly.
  • If you use a tumble dryer, check that it is fitted with an external vent or condensate system.
  • There may be air vents in bedrooms and cupboards. Do not block these up as they allow fresh air to circulate and reduce condensation. 

Keep kitchen and bathroom doors closed and windows open when in use. 

Cover pots and pans where possible during cooking.

Maintain internal heat levels.

Keep your home well-ventilated and maintain internal heat levels, ideally between 18C and 21C.

This will reduce the likelihood of condensation and mould spores forming.

Internal temperatures below 18C may impact the health of pre-school-aged children, the elderly and those with existing health conditions.

Fuel poverty:

For those struggling to pay heating bills, there is advice from various platforms to 'heat the person, not the home'. However, not heating your home adequately can contribute to condensation and mould issues. If you can only heat yourself, remember that your home still needs ventilation.

Consider upgrading your windows.

If you own your home, you can address heat loss by upgrading your windows (especially if you upgrade from single-glazing to double- or triple-glazing or secondary glazing) − but remember that this will not address the source or amount of moisture in your home.

You may also need to increase ventilation, as modern windows have tighter air seals than older, draughty windows.

Finally, regularly wipe up condensation.

Wipe off daily with a dry cloth or sponge from around cooler places, like window areas and tiled wall surfaces in bathrooms and kitchens. This helps prevent mould growth. 

If you are renting your home, report any concerns to your landlord or managing agent.

If you are finding it difficult to heat your home, you may be entitled to government help.

Citizens Advice’s page Struggling to pay your bills has links to other organisations that can help.

What is mould?

The term mould describes fungi that thrive in damp conditions.

There are thousands of different mould species found in the home. The most serious are those that release mycotoxins.

Mycotoxins are extremely harmful poisons, which can be inhaled, eaten or absorbed directly through the skin. They can lead to poisoning, and in the long term can cause certain cancers and immunosuppression-related illnesses. Asthma and other severe respiratory conditions can also be triggered.

How do I control and remove mould growth?

The first step is to identify and remedy the source of moisture. Mould treatments can only address the symptoms of dampness, not the underlying causes. These need to be properly understood and often require an independent chartered building surveyor who specialises in building pathology to investigate.

It is essential to remove mould in your home promptly and daily to reduce health risks. For hard surfaces, use mould and mildew cleaning products (which are more effective and safer than bleach) and leave them to dry completely.

Mould removal itself presents a health risk, so during cleaning:

  • wear protective clothing such as gloves, mask and goggles
  • keep doors shut (so spores don’t spread) and keep windows open (for ventilation).

Lock cleaning products away and keep them well out of the way of children, as they can be very harmful if ingested.

Larger areas of mould (such as a substantive part of a whole wall or ceiling) should only be addressed by qualified professionals. If you are renting your home, tell your landlord or managing agent about any mould that is causing you concern.

Absorbent materials such as carpets, soft furnishings and ceiling tiles might need specialist cleaning if they become mouldy. It may be difficult or impossible to remove the mould completely.

Moisture can migrate from kitchens and bathrooms and then condense on cold external wall surfaces.

In this case, there was also water coming through the solid floor from the ground below. This raised humidity levels and caused the secondary problem of condensation.

Repair, maintain, manage

No home is completely immune from condensation and mould formation. They are natural processes and require managing.

Repairs, maintenance and management apply to everyone to differing degrees, whether a homeowner, tenant or landlord.

Do:

carry out regular maintenance to keep your building as dry as possible, for example:

  • clear gutters, downpipes and drains
  • repair leaking pipes, baths, sinks and toilets
  • replace broken mastic seals around showers, baths and sinks
  • cut back overgrown trees and vegetation
  • clean extractor fans (including ducting and vent covers)
  • maintain doors and windows
  • check for water splashing off hard surfaces back up against walls outside. 

Do not install expensive damp-proofing measures without carrying out routine maintenance work, or considering what has changed and addressing that, first. In some types of home (for example older buildings with solid walls), damp-proofing measures may not be appropriate and may exacerbate damp issues. 

Always seek advice from a building surveyor before making changes to your home or garden. This avoids the risk of creating problems. For example:

  • installing a new path or decking area could raise ground levels and block air vents
  • using modern cement in mortar or render on older buildings can trap moisture in walls, making any damp problem worse.

Remember that changes to a building may require local authority planning consent and/or building regulations approval using an approved certified contractor. 

Size/volume matters. The volume of space inside a property stays the same, but the number of people (and pets) living there changes. Where homes accommodate more people, more consideration of moisture management , e.g. additional ventilation, may be required.

Seeking professional help

Always take a holistic and proactive view when trying to solve a damp problem in the home. Think about all the sources of moisture, and think about whether you can make any small modifications to your daily routine to reduce moisture.

If there is a significant damp and mould issue, it’s critical to approach the right kind of building surveyor.RICS membership does not automatically mean a surveyor is suitably experienced in damp and mould. There are many different kinds of RICS members: valuers, quantity surveyors, etc.

  • RICS membership does not automatically mean a surveyor is suitably experienced in damp and mould. There are many different kinds of RICS members: valuers, quantity surveyors, etc.
  • Look for an AssocRICS/MRICS/FRICS building surveyor who has suitable experience in building pathology and the moisture issues described. Pathology is a specialism that focuses on the science of the causes and effects of how buildings fail.
  • An experienced local building surveyor will be familiar with local building techniques and materials, and will fully understand the construction weaknesses of different types of buildings. Ask to see the surveyor’s CV and ask about their experience in this work.
  • Search for local specialists on RICS’ Find a Surveyor under the category Residential/Maintenance/Interior, and ask about their experience in building pathology.
  • When instructing a surveyor, RICS advises you to ask for a Joint Position Statement 2022 (JPS22)-compliant inspection.
     

A JPS 2022-compliant inspection report will give you an unbiased professional opinion from someone who does not have a commercial interest in selling you a product. The report will only suggest remedial works that are proportionate and that respect the nature of the property.

Be wary of any surveyor or commercial specialist who uses only a damp meter to diagnose the source of dampness, especially in hard walls and solid floors.

Damp meters test an electric current through a material. They are accurate for measuring moisture levels in timber, but in other materials may register high readings from other conductive materials, not just moisture.

Advice for landlords

Landlords must make sure their rental homes are safe and healthy for people to live in (see government guidance for landlords). This legal duty comes through the housing health and safety rating system (HHSRS), which is part of the Housing Act 2004. The HHSRS lists 29 hazards in the home. Dampness and mould are listed among the highest categories of hazard.

Do:

inspect the condition of the property at regular intervals

thoroughly and promptly investigate any concerns raised by the tenant, and fix any defects that are causing damp and mould

carry out regular maintenance to keep the property in good condition

ensure appropriate and sufficient insulation and draught proofing are in place

ensure ventilation such as windows, vents and fans are working to the current standards, for example, see Approved Document F for new buildings

ensure tenants know how to use the heating system and thermostatic controls efficiently

use void periods between tenancies to replace any faulty fans or upgrade existing fans with improved trickle-fed humidistat units.

From October 2025, if a tenant reports mould or dampness, registered social landlords (councils and housing associations) must:

  • tackle emergency cases within 24 hours
  • inspect, report and outline remediation for damp and mould that present significant risk of harm within 10 days, and
  • begin repair works within 5 working days.

(See Awaab’s Law, part of the Social Housing Regulations Act 2023).

One of the most important aspects to consider is occupiers’ health.

In most instances, practical, low-cost measures can solve the problem, e.g. general maintenance of the home and slight changes in the way occupants do things, like closing doors to the bathroom when showering.

However, it is unavoidable that everyday tasks such as cooking, bathing, washing and drying laundry will produce indoor moisture. Many factors are outside of the control of tenants, such as overcrowding or a lack of space to adequately dry clothing. These can be challenging to address and/or require ongoing management.

Do:

listen carefully to what tenants think is causing the problem. It could be that damp and mould only appeared from a particular time, which may mean something has changed, e.g. an escape of water or an increase in the number of residents.

take reasonable steps in partnership with residents. Consider:

  • improving ventilation
  • making energy-saving improvements.

Fuel poverty is a significant factor causing low heat levels, and must be considered when discussing and implementing solutions.

Don’t:

assume that you have met your responsibilities. For instance, the mere presence of an extractor fan does not automatically mean the ventilation is satisfactory, without any evidence that the fan is performing to the required standard.

Advice for tenants

Do:

find out what you have responsibility for. Carefully check your conditions of tenancy, and if you are a leaseholder, check the terms of your lease. Your responsibility to address issues could depend on your situation and occupation rights as a tenant.

report any concerns you have about damp or maintenance issues to your landlord promptly.

If you have HHSRS-related concerns, contact your local council's environmental health team. Your local authority can take action against landlords for non-compliance.