Mould in Bournemouth Flats: Causes, Responsibility and Fixes

Mould in a Bournemouth flat almost always comes from moisture that has nowhere to go: condensation on cold surfaces, a leak from a roof, pipe or window frame, or a mix of both. The fix depends on which one you have, so the cause has to be identified before anything is cleaned, sprayed or painted. If you rent, your landlord has legal duties to investigate and repair. If you own, a survey-led diagnosis stops you paying for the wrong treatment.

This guide explains how to read the symptoms, who is responsible, what to do while you wait for repairs, and when to call a specialist.

TL;DR

• Condensation is the most common cause of mould in flats, and it peaks between October and April. Leaks, roof defects and failed window or door frames cause the rest.
• The pattern of staining, where it sits and whether it returns after cleaning tell you a great deal about the cause.
• Renting: in many cases the landlord must find the cause and fix structural defects, leaking pipes, leaking roofs and faulty guttering. Report in writing and keep photographs.
• Owning or managing a flat: get a documented survey before any treatment, so the scope of work matches the actual source of moisture.
• Do not pull up carpets or wallpaper over hidden mould, and see a GP if you feel unwell.

Table of Contents

• Why flats in Bournemouth are prone to mould
• The three main causes
• Reading the symptoms: a quick diagnostic table
• Why the cause must be found before treatment
• Who is responsible for mould in a rented flat?
• What to do now: a step-by-step plan
• If the landlord does not act
• When you need a professional survey
• A surveyor’s view
• How we can help in Bournemouth
• FAQ
• Sources

Why flats in Bournemouth are prone to mould

Bournemouth has a large stock of converted Victorian and Edwardian houses, purpose-built blocks and seafront apartments. Each has its own weak points: solid or poorly insulated walls, flat or low-pitched roofs, shared drainage, old window frames and limited ventilation in internal bathrooms and kitchens. Salt-laden coastal air and driving rain add to the exposure of external walls and roofs.

Moisture builds up in any home. BCP Council notes that an average family produces around 20 pints (11.4 litres) of moisture a day in an unvented property. In a small flat with closed windows and clothes drying indoors, that moisture settles on the coldest surfaces first: external walls, window reveals, the corners behind wardrobes and the ceiling above the shower.

The three main causes

BCP Council identifies three main causes of damp and mould: condensation, penetrating damp and rising damp. They look different and they need different repairs.

Condensation

Condensation is the most common cause of damp and mould in properties, particularly in winter, according to BCP Council. Dorset Council’s guidance explains that water vapour condenses on cold surfaces such as windows, and that persistent problems mainly occur between October and April, when temperatures are lower and homes are ventilated less.

Typical signs:

• Water droplets on windows and cold walls
• Black or grey mould in corners, on ceilings and behind furniture
• Mould that returns after cleaning, often in the same places
• Worse symptoms in bathrooms, kitchens and bedrooms

Penetrating damp

Penetrating damp is water entering from outside or from a defect. BCP Council lists roof leaks, disrepair to window or door frames and internal pipe leaks as common sources. It can show as yellowy-brown staining where water enters, damaged or misshapen plaster, localised dampness, mould, damaged decoration, or rotting floor timbers and skirting boards.

In a flat, the source is often not in your own home. A defective roof covering, blocked gutter or leaking pipe in the flat above can show up on your ceiling. Staining that spreads after rain, or a patch that stays wet when the heating is on, points to ingress rather than condensation.

Rising damp

Rising damp is moisture travelling up from the ground through masonry. BCP Council gives a maximum height of 1m. It mainly affects ground-floor flats and basement or garden-level flats. It is also often blamed wrongly. RICS advises that “rising damp” is not a conclusion, because it does not identify the source of the excess moisture, and that failure of an original damp-proof course is extremely rare. A common misdiagnosis is assuming rising damp when the real cause is something else, such as a leak, bridged damp-proof course or high ground level outside.

Our guide on rising, penetrating or condensation sets out the visual differences in more detail.

Reading the symptoms: a quick diagnostic table

The table is a starting point for your observations, not a diagnosis. Several causes can sit together: a flat with a small leak and poor ventilation will grow mould faster than either problem alone.

Why the cause must be found before treatment

Cleaning mould removes the symptom. If the moisture source remains, the mould returns. Painting over it hides the growth and often traps moisture. The sequence that works is:

1. Observe and record where and when the damp appears.
2. Find the source of moisture, by inspection and, where needed, moisture readings and leak tracing.
3. Repair the source: roof, pipe, frame, drainage or ventilation.
4. Dry the structure and treat the mould.
5. Reinstate finishes, such as replastering where plaster is damaged.
6. Re-check after a few weeks to confirm the problem has not returned.

Shelter England says landlords should check whether damp and mould come back at least six weeks after repairs, which is a sensible benchmark for owners too.

When the cause is complex, RICS recommends a JPS 2022-compliant survey by a specialist building surveyor. If your flat has had cavity or spray foam insulation fitted and damp has appeared since, BS 5250 damp surveys explain how moisture risk in insulated buildings is assessed.

Who is responsible for mould in a rented flat?

The short answer: it depends on the cause, but landlords carry most of the duty for building-related damp.

Landlord duties

Shelter England says landlords must try to find the cause of damp and fix problems such as structural defects, leaking pipes, poor ventilation, broken boilers, leaking roofs and faulty guttering. Under Section 11 of the Landlord and Tenant Act 1985, a landlord must keep the structure and exterior in repair and keep installations for water, heating and sanitation in working order. Damp caused by a roof leak therefore falls on the landlord.

RICS states that rental homes must be safe and healthy under the Housing Health and Safety Rating System (HHSRS), part of the Housing Act 2004, and that dampness and mould are listed among the highest categories of hazard.

The Homes (Fitness for Human Habitation) Act 2018 adds an implied covenant that the home is fit for human habitation at the start of and throughout the tenancy. Tenants can take legal action if it is not.

Shelter also says a landlord should not tell you to paint over mould that keeps coming back, say it is just condensation without checking, or tell you to stop everyday activities such as cooking or showering.

Rising damp is a special case. Citizens Advice explains that the landlord is likely responsible if an existing damp-proof course has failed, but may not be responsible for installing one in a home that never had one, as that can be treated as an improvement. For a fuller walkthrough, see our page on landlord responsibilities for damp and mould.

Tenant duties

Tenants must act in a tenant-like manner. Shelter’s legal guidance says this includes reporting disrepair, allowing access for repairs, ventilating, keeping furniture away from walls and heating the home properly. Following these steps also protects you if a dispute arises later.

Social housing and Awaab’s Law

If your landlord is a council or housing association, Awaab’s Law applies. The Housing Ombudsman states that it came into force in October 2025 and requires social landlords to investigate significant damp and mould hazards within 10 working days and make them safe within 5 working days. The government response adds a written summary of findings within 3 working days and investigation of emergency hazards within 24 hours.

Leasehold flats

If you own your flat on a lease, responsibility for the roof, external walls and shared pipes usually follows the lease, and often sits with the freeholder or management company, while internal finishes and your own ventilation are yours. Read your lease and report building-related causes to the managing agent in writing.

What to do now: a step-by-step plan

1. Photograph everything. Take dated photographs of each affected area, wide and close up. Note the room, size and whether it is spreading.
2. Report it in writing. The Housing Ombudsman advises reporting straight away, naming the rooms affected, saying whether it has been reported before and whether the building or outstanding repairs may be causing it.
3. Ventilate. Open windows briefly, use extractor fans while cooking and showering, and keep doors closed to the wettest rooms while they are in use.
4. Heat steadily. Keep a low, consistent heat rather than short bursts. Keep furniture a little way from external walls.
5. Do not disturb hidden mould. The Housing Ombudsman advises against pulling up carpets or wallpaper where mould is hidden, as this can release spores.
6. Speak to a GP if anyone in the home feels unwell, particularly children, older people or anyone with breathing problems.
7. Get the cause investigated if the landlord, freeholder or your own checks have not found it.

Cleaning surface mould

For small patches of surface mould, wipe with a damp cloth and dispose of it, keep the room ventilated, and do not dry-brush, which sends spores into the air. Wear gloves and avoid mixing cleaning products. Large areas, mould that keeps returning or mould behind finishes should be assessed by a specialist, because the aim is to find out why it is growing.

If the landlord does not act

Support for Tenants suggests three escalation steps if damp is not fixed within a reasonable time:

1. Send a formal written complaint with a final deadline. Two to four weeks is usually reasonable for straightforward repairs.
2. Ask BCP Council’s environmental health officers to inspect under HHSRS.
3. Consider a civil disrepair claim if the problem remains.

The Pre-Action Protocol for Housing Conditions Claims involves a letter of claim, to which the landlord has 20 working days to reply, and a single joint expert surveyor inspection. Before any claim, take advice from Shelter, Citizens Advice or a housing solicitor.

A documented survey helps at every stage. Our landlord damp and mould inspection produces written findings and a defined scope of work that a landlord, agent or tenant can act on. Our article on landlord mould responsibilities and timelines covers the legal timeline in more depth.

When you need a professional survey

Call a specialist when:

• Mould returns after cleaning and better ventilation
• Staining spreads after rain or appears below roofs, windows or bathrooms
• Skirting boards, floorboards or joists feel soft, crumbly or look cracked
• There is a musty smell with no visible source
• You are buying, letting or managing a flat and need documented findings
• A previous treatment has not worked

Timber needs particular care. Building Conservation advises that suspected rot or wood-boring insects should be investigated by an independent specialist to establish the cause and extent of damp and decay before remedial work is specified. The aim is to reduce timber moisture below 16 to 18 per cent, isolate timber from damp masonry and allow air to move around it. The Property Care Association says the first step is to find how and where water is entering, repair the defect and dry the area, and that dry rot and wet rot need different treatment. See our pages on dry rot treatment and wet rot versus dry rot.

What a good survey report should contain

• Where moisture was found, with readings and photographs
• The identified source or sources, and the evidence for them
• What is not caused by damp, and anything outside the surveyor’s remit that needs a specialist referral
• A defined scope of work, in order
• The guarantee terms in writing

A surveyor’s view

We start with what you can see. Where is the mould, what does the staining look like, when does it get worse, and what has been done before? Those answers usually narrow the cause before any equipment comes out.

In flats we see the same mistake repeatedly: treatment sold before diagnosis. A damp-proof course injected into a wall that is actually wet from a leaking gutter, or a mould wash on a ceiling that is stained by the flat above. Neither lasts.

Our process is survey first. We document the findings with photographs, set out a clear scope of work, and only then propose treatment. If something sits outside our remit, such as a structural question, we say so and refer you to the right specialist rather than stretching what we do. Where we carry out the work, it comes with a written guarantee on our workmanship and aftercare.

After more than 35 years working across Dorset, Hampshire and Wiltshire, our advice is consistent: find the moisture, fix the moisture, then deal with the mould.

Quay

How we can help in Bournemouth

Quay Point Plastering specialises in survey-led damp, mould and timber work across Dorset, Hampshire and Wiltshire, from our base in Poole. For flats, that can mean condensation and black mould treatment, positive input ventilation, penetrating damp investigation and repair, leak detection, timber treatment and replastering once the source is fixed.

Start with a damp and timber survey, or read about damp proofing in Bournemouth. You can also see our mould and damp treatments. Tell us what you can see, and we will explain what we think is happening before proposing anything. Book an inspection or call 01202 287134.

FAQ

Who is responsible for mould in a flat?

If the mould comes from a structural defect, a leaking roof, faulty guttering or leaking pipes, the landlord is responsible for repairs. Tenants are expected to ventilate and heat the home reasonably and to report problems promptly. In leasehold flats, responsibility for the building usually follows the lease.

Is mould ever the tenant’s fault?

Condensation can be made worse by drying washing indoors or not ventilating, but Shelter says a landlord should not simply blame condensation without checking the cause. Poor insulation, heating or ventilation are often building issues. A survey can separate lifestyle factors from defects.

How do I tell condensation from a leak?

Condensation appears on cold surfaces, such as external walls, windows and corners, and is worse in winter. Leaks tend to leave brown tide marks, spread after rain or stay damp regardless of the weather. Since the two can occur together, a documented inspection is the reliable way to confirm.

Can I just paint over the mould?

No. Painting hides the growth and does not remove the moisture feeding it, so the mould returns. Find and fix the source, dry the area, treat the mould and then redecorate.

Do I need a survey for a small patch?

A small patch that clears with ventilation and does not return may not need one. If it comes back, spreads, or sits near a roof, pipe or window, book an inspection so the cause is identified.

Sources

• The main causes of damp and mould in your home, BCP Council
• How to control damp, condensation and mould in your home, Dorset Council
• Damp and mould, RICS
• Damp and mould in private rented homes, Shelter England
• Damp and mould problems, Shelter England
• If you have damp or mould in your rented home, Citizens Advice
• Homes (Fitness for Human Habitation) Act 2018
• Damp and mould, Housing Ombudsman
• Awaab’s Law government response, GOV.UK
• Landlord not fixing damp, Support for Tenants
• How to handle a housing disrepair case
• Timber Decay, Building Conservation
• Guidance Document: Fungal Decay in Buildings, Property Care Association
• BS 5250 damp surveys and spray foam

Recommended

• Landlord mould responsibilities UK: the law, timelines and fixes
• Damp Proofing in Bournemouth
• Landlord responsibilities for damp and mould — what the law says
• Landlord Damp & Mould Inspection