Damp & Mould Glossary
Plain-English definitions of damp, mould, and housing compliance terms for landlords, homeowners, and estate agents.
A
Approved Document F (ventilation)
The part of the Building Regulations for England that sets ventilation standards for dwellings. Since 15 June 2022 it requires that replacement windows do not reduce a home's existing ventilation.
Awaab's Law
UK legislation requiring landlords to investigate and repair damp and mould hazards within fixed timeframes — 24 hours to investigate and make safe emergencies, 10 working days to investigate significant hazards, and 5 working days to complete safety works once a hazard is confirmed.
B
Biocidal Treatment
Chemical treatment applied to surfaces to kill mould and fungal growth. Used as part of a mould remediation process alongside physical removal. Must be combined with structural or ventilation remediation to prevent recurrence.
Black Mould
Common name for dark-coloured mould growth in properties, most often Cladosporium or Aspergillus species. Can cause respiratory irritation and allergic reactions. Requires professional treatment when covering more than one square metre.
C
CSRT
Certificated Surveyor in Remedial Treatments — the primary professional qualification for damp diagnosis issued by the PCA. A CSRT-qualified surveyor has demonstrated competence in identifying and specifying treatment for rising damp, penetrating damp, and timber decay.
Cavity Drainage System
A below-ground waterproofing method that accepts water ingress through a studded membrane, directs it to a sump and pump, and discharges it away from the building. Classified as Type C waterproofing under BS 8102.
Cold spot
A localised area of internal surface that is colder than the surrounding wall or ceiling, so it drops below the room air's dew point first and collects condensation and mould.
Condensation Mould
Mould caused by water vapour condensing on cold surfaces — typically walls, windows, and ceilings in poorly ventilated rooms. The most common form of mould in rented properties. Addressed by improving ventilation and insulation rather than damp proofing.
D
Damp-Proof Course (DPC)
A horizontal barrier built into or injected into a wall to prevent ground moisture rising upward. Modern properties have a physical DPC built during construction. Older properties may have a failed or absent DPC requiring chemical injection treatment.
Damp-Proof Membrane (DPM)
A sheet material, typically heavy-duty polyethylene, laid beneath floor slabs or behind wall finishes to prevent moisture transmission. Used in new builds and in remediation of solid floors with damp problems.
Dew point
The temperature at which air becomes saturated and water vapour starts to condense into liquid. Any surface colder than the room air's dew point will collect condensation.
dMEV (continuous mechanical extract ventilation)
A low-wattage extract fan that runs continuously at a low trickle rate and boosts automatically on humidity or occupancy, removing moisture from a wet room as it is produced.
E
H
HHSRS
Housing Health and Safety Rating System — the framework used by local councils to assess health and safety hazards in residential properties. Damp and mould is a Category 1 HHSRS hazard, the most serious category, which triggers a council's duty to act.
Hygroscopic Salts
Salts drawn to the surface of masonry by evaporating moisture, particularly associated with rising damp. Absorb moisture from the air even after the original damp source is resolved. Require salt-resistant replastering during remediation.
I
M
P
PCA (Property Care Association)
The UK's leading trade association for the damp proofing, structural waterproofing, and wood preservation industry. PCA membership indicates a contractor has met competence and financial standards.
PIV (Positive Input Ventilation)
A single-unit ventilation system typically installed in a loft space that draws fresh air in and distributes it through a central ceiling diffuser. Cost-effective and minimally disruptive. Widely used to treat condensation mould in existing rental properties.
Penetrating Damp
Damp caused by water entering a building through its external fabric — typically via failed pointing, cracked render, defective flashings, blocked gutters, or window and door seals. Can appear at any height and worsens during and after rainfall.
R
Relative humidity
The amount of water vapour in the air expressed as a percentage of the maximum the air could hold at that temperature. Warm air holds more, so relative humidity rises as air cools.
Remediation
The process of identifying, removing, treating, and preventing recurrence of damp or mould in a property. Effective remediation addresses both the symptom and the root cause. Covered by Awaab's Law timeframes for landlords.
Renters' Rights Bill
UK legislation that will extend Awaab's Law to the private rented sector, abolish Section 21 'no-fault' evictions, and introduce other tenant protections. Once enacted, all private landlords in England will face the same damp and mould obligations as social housing landlords.
Rising Damp
A type of damp caused by ground moisture rising upward through masonry via capillary action. Typically affects walls up to 1.2 metres from floor level and is characterised by tide marks, salt staining, and plaster damage.
S
T
Tanking
A waterproofing method that applies an impermeable barrier directly to walls or floors to prevent water ingress. Used in basements and below-ground rooms. Classified as Type A structural waterproofing under BS 8102.
Thermal Bridging
A point in a building's fabric where heat transfers more rapidly than through surrounding insulated areas, creating a cold spot that attracts condensation and promotes mould growth. Common at window reveals, lintels, and corners.
Trickle vent
A small controllable slot vent in the head of a window or door frame that provides a continuous background supply of outdoor air without opening the window.