Damp and Mould in London Rental Properties: Causes, Awaab's Law and Remediation

Damp and mould are endemic in London's older housing stock. Basement flats, Victorian terraces with failed pointing and poorly ventilated bathroom extensions all create conditions where moisture accumulates. For landlords, ignoring it is no longer an option — legally or morally.

The Main Causes of Damp in London Properties

Rising Damp

Groundwater wicks upward through porous masonry where the damp proof course (DPC) has failed or was never installed. It typically appears as a tidemark at low level on internal walls, with salting and flaking plaster. True rising damp rarely rises above one metre.

Penetrating Damp

Water enters through defects in the building envelope — failed pointing, cracked render, blocked gutters, defective flashings. This is the most common cause of damp in London properties and the one most frequently misdiagnosed as condensation.

Condensation

Warm, moisture-laden air from cooking, bathing and breathing meets cold surfaces and deposits water. In London's solid-wall Victorian properties with poor ventilation, this is a structural problem as much as a behavioural one. Black mould (Cladosporium or Aspergillus) on north-facing walls and in unventilated corners is the characteristic sign.

Plumbing Leaks

Slow leaks from waste pipes, overflow pipes and central heating circuits hidden within floor voids or wall chases can cause significant moisture accumulation before they are detected. Regular inspection is essential.

Awaab's Law: What London Landlords Must Know

Awaab's Law, enacted through the Social Housing (Regulation) Act 2023, initially applied to social housing landlords. The Renters' Rights Act 2024 extends similar hazard response obligations to the private rented sector from 2025 onwards.

Under these provisions, landlords must:

• Investigate reported damp and mould hazards within a defined timescale (expected to be 14 days for investigation, with emergency repairs within 24 hours where there is risk to health)
• Carry out repair works within a set period following investigation findings
• Keep records of reports, investigations and remediation

A property with Category 1 damp and mould hazard under the Housing Health and Safety Rating System (HHSRS) is an unlawful hazard that local authorities can require landlords to remediate under improvement notices.

Remediation: Getting It Right

The approach to remediation depends entirely on cause. Surface treatment of mould without addressing the underlying moisture source is ineffective and will not satisfy a local authority inspection.

• Penetrating damp — identify and repair the building envelope defect first (repoint, replace flashings, clear gutters). Only then redecorate.
• Rising damp — install or restore a chemical DPC, hack off and replaster with renovating plaster incorporating a salt retardant, allow to dry, redecorate.
• Condensation — improve ventilation (continuous mechanical extract ventilation in bathrooms and kitchens, trickle vents in windows), insulate cold surfaces, consider whole-house positive input ventilation.

Obtain a damp survey from an independent CSRT or CSSW qualified surveyor before commissioning remedial works. This protects you legally and ensures the correct treatment is specified.