Mould and Condensation in London Victorian Terraces: Causes, Treatment, and Prevention

CORRECTLY DIAGNOSING THE TYPE OF DAMP AFFECTING A LONDON VICTORIAN TERRACE IS THE MOST IMPORTANT FIRST STEP IN ADDRESSING IT — BECAUSE CONDENSATION DAMP AND PENETRATING OR RISING DAMP HAVE VERY DIFFERENT CAUSES AND VERY DIFFERENT TREATMENTS: CONDENSATION DAMP: CAUSED BY MOISTURE IN THE INDOOR AIR (GENERATED BY COOKING, BATHING, DRYING CLOTHES, BREATHING, AND OTHER HOUSEHOLD ACTIVITIES — A FAMILY OF 4 GENERATES APPROXIMATELY 10-15 LITRES OF MOISTURE PER DAY THROUGH NORMAL HOUSEHOLD ACTIVITIES) COMING INTO CONTACT WITH COLD SURFACES (SINGLE-GLAZED WINDOWS, UNINSULATED EXTERNAL WALLS — PARTICULARLY AT COLD THERMAL BRIDGES SUCH AS WALL-FLOOR JUNCTIONS, REVEALS AROUND WINDOWS AND DOORS, WINDOW LINTELS, AND STRUCTURAL MEMBERS EMBEDDED IN THE WALL) AND CONDENSING ON THOSE SURFACES — THE CONDENSED WATER PROVIDES AN IDEAL MEDIUM FOR MOULD SPORE GERMINATION AND GROWTH; IDENTIFYING CONDENSATION DAMP (VS RISING DAMP OR PENETRATING DAMP): LOCATION OF DAMP: CONDENSATION DAMP IS MOST COMMONLY FOUND IN CORNERS OF ROOMS (WHERE TWO EXTERNAL WALLS MEET — A THERMAL BRIDGE — THE CORNER IS COLDER THAN THE ADJACENT WALL SURFACES), BEHIND FURNITURE PUSHED AGAINST EXTERNAL WALLS (FURNITURE INTERRUPTS AIRFLOW ACROSS THE WALL SURFACE — THE WALL BEHIND FURNITURE IS COLDER AND MORE LIKELY TO BE BELOW THE DEWPOINT), ON OR BELOW WINDOW CILLS (COLD CONDENSING SURFACE), AND IN BATHROOMS AND KITCHENS (HIGH MOISTURE-GENERATING ROOMS); PENETRATING DAMP: WET PATCHES ON WALLS THAT CORRESPOND TO EXTERNAL DEFECTS (CRACKED RENDER, FAILED POINTING, DEFECTIVE FLASHING, LEAKING GUTTER) — TYPICALLY APPEAR DURING OR AFTER RAINFALL — DAMP PATCHES ARE LOCALISED AND CORRESPOND IN POSITION TO THE EXTERNAL DEFECT; RISING DAMP: DAMP AT LOW LEVEL (BOTTOM 1-1.2M OF WALL — RARELY HIGHER) — TYPICALLY WITH SALT STAINING (HYGROSCOPIC SALTS DEPOSITED ON THE WALL SURFACE AS THE WATER EVAPORATES) — TIDE MARK — OFTEN DIAGNOSED INCORRECTLY BY DAMP PROOF INJECTION CONTRACTORS (NOTE: GENUINE RISING DAMP IS CONSIDERABLY LESS COMMON THAN CONDENSATION DAMP — MANY WALLS DIAGNOSED AS RISING DAMP ARE IN FACT CONDENSATION DAMP AT LOW LEVEL OR PENETRATING DAMP FROM RAISED EXTERNAL GROUND LEVEL); CONDENSATION IS THE MOST COMMON CAUSE OF DAMP IN LONDON VICTORIAN TERRACES — THE BUILDINGS RESEARCH ESTABLISHMENT (BRE) ESTIMATES THAT CONDENSATION ACCOUNTS FOR THE MAJORITY OF DAMP COMPLAINTS IN THE UK HOUSING STOCK — FAR MORE COMMON THAN RISING DAMP.

LONDON VICTORIAN TERRACES WERE BUILT WITHOUT INSULATION IN THE EXTERNAL WALLS (THE ORIGINAL SOLID BRICK WALLS ARE TYPICALLY 215-225MM OF SOLID BRICKWORK — NO CAVITY, NO INSULATION) — AS A RESULT, THE U-VALUE (HEAT TRANSMITTANCE COEFFICIENT) OF THE ORIGINAL UNINSULATED SOLID BRICK WALL IS APPROXIMATELY 2.0-2.3 W/M²K — COMPARED WITH PART L 2021 TARGET 0.18 W/M²K FOR NEW EXTERNAL WALLS — MEANING THE ORIGINAL VICTORIAN TERRACE EXTERNAL WALL LOSES HEAT AT 10-12 TIMES THE RATE OF A MODERN WELL-INSULATED WALL — THE INNER FACE OF THE WALL IS CORRESPONDINGLY COLD IN WINTER.

KEY CAUSES OF CONDENSATION IN LONDON VICTORIAN TERRACES: (1) THERMAL BRIDGING (THE MOST IMPORTANT CAUSE OF LOCALISED COLD SPOTS AND CONDENSATION): A THERMAL BRIDGE IS A PATH OF LOW THERMAL RESISTANCE IN THE BUILDING ENVELOPE — THROUGH WHICH HEAT IS LOST AT A HIGHER RATE THAN THE SURROUNDING WALL — THE INNER SURFACE OF A THERMAL BRIDGE IS COLDER THAN THE SURROUNDING SURFACE — AND IF IT IS BELOW THE DEWPOINT OF THE INDOOR AIR, CONDENSATION WILL FORM ON IT; COMMON THERMAL BRIDGES IN LONDON VICTORIAN TERRACES: CORNERS OF ROOMS (WHERE TWO EXTERNAL WALLS MEET — THE GEOMETRY CONCENTRATES HEAT LOSS AND REDUCES THE TEMPERATURE OF THE INTERNAL CORNER SURFACE — THIS IS WHY MOULD MOST COMMONLY APPEARS IN THE CORNERS OF BEDROOMS AND LIVING ROOMS); WINDOW AND DOOR REVEALS (THE SOLID BRICK REVEAL ON EITHER SIDE OF A WINDOW OPENING IS NARROWER THAN THE MAIN WALL — THE THERMAL RESISTANCE OF THE REVEAL IS LOWER — THE REVEAL SURFACE IS COLDER — CONDENSATION AND MOULD ARE COMMON ON WINDOW AND DOOR REVEALS IN VICTORIAN TERRACES); WINDOW LINTELS (CAST IRON OR STONE LINTELS ABOVE WINDOW OPENINGS ARE HIGHLY CONDUCTIVE — THEY CREATE A COLD STRIPE ACROSS THE TOP OF THE WINDOW OPENING — CONDENSATION IS COMMON ON THE PLASTER IMMEDIATELY BELOW A CAST IRON LINTEL); FLOOR WALL JUNCTION (THE JUNCTION BETWEEN THE GROUND FLOOR SLAB OR SUSPENDED FLOOR AND THE EXTERNAL WALL — A STRUCTURAL THERMAL BRIDGE); (2) POOR OR ABSENT VENTILATION: IN THE ORIGINAL VICTORIAN TERRACE, VENTILATION WAS PROVIDED BY THE OPEN CHIMNEY FLUES (OPEN FIRES CREATED A POWERFUL NATURAL VENTILATION DRAUGHT — THE TYPICAL VICTORIAN TERRACE WITH A FIRE IN EVERY ROOM EXCHANGED ITS AIR APPROXIMATELY 3-5 TIMES PER HOUR THROUGH CHIMNEY VENTILATION); IN THE MODERN VICTORIAN TERRACE WHERE ALL FIREPLACES HAVE BEEN SEALED AND REPLACED WITH CENTRAL HEATING, THE NATURAL CHIMNEY DRAUGHT IS LOST — THE AIR CHANGE RATE IN A SEALED VICTORIAN TERRACE CAN FALL TO AS LOW AS 0.1-0.3 AIR CHANGES PER HOUR (PART F 2021 MINIMUM IS 0.5 ACH FOR A HOUSE) — THE RESULT IS MOISTURE ACCUMULATION IN THE INDOOR AIR; (3) LIFESTYLE FACTORS: DRYING CLOTHES INDOORS (ONE OF THE HIGHEST MOISTURE LOADS — A SINGLE LOAD OF WASHING RELEASES APPROXIMATELY 2 LITRES OF WATER INTO THE INDOOR AIR AS IT DRIES); COOKING WITHOUT AN EXTRACTOR FAN (OR WITH AN EXTRACTOR FAN THAT RECIRCULATES RATHER THAN EXTRACTS TO OUTSIDE); BATHING AND SHOWERING WITHOUT ADEQUATE BATHROOM EXTRACT VENTILATION; KEEPING THE HOUSE VERY WARM (HIGH INDOOR TEMPERATURES ALLOW THE AIR TO HOLD MORE MOISTURE — WHEN THE AIR CONTACTS A COLD SURFACE, MORE MOISTURE CONDENSES OUT); (4) INSUFFICIENT HEATING: ROOMS THAT ARE POORLY HEATED OR UNHEATED (SPARE BEDROOMS, HALLWAYS, CORNERS OF ROOMS) HAVE COLD WALL SURFACES THAT ARE MORE LIKELY TO SUPPORT CONDENSATION.

THE MOULD MOST COMMONLY ASSOCIATED WITH CONDENSATION DAMP IN LONDON VICTORIAN TERRACES IS CLADOSPORIUM SPHAEROSPERMUM AND ALTERNARIA ALTERNATA (BLACK MOULD — THE COMMON BLACK-GREEN MOULD GROWTH VISIBLE ON WALLS AND WINDOW CILLS IN CONDENSATION-AFFECTED ROOMS) AND STACHYBOTRYS CHARTARUM (TOXIC BLACK MOULD — LESS COMMON — ASSOCIATED WITH PROLONGED AND SEVERE WATER DAMAGE AND HIGH MOISTURE — PRODUCES MYCOTOXINS THAT CAN CAUSE SERIOUS RESPIRATORY EFFECTS).

IDENTIFYING MOULD FROM CONDENSATION: BLACK OR DARK GREEN MOULD PATCHES (CLADOSPORIUM — THE MOST COMMON CONDENSATION MOULD IN UK HOMES): APPEARS AS BLACK OR DARK GREY-GREEN PATCHES ON WALL SURFACES — PARTICULARLY IN CORNERS OF ROOMS, ON NORTH-FACING EXTERNAL WALLS, ON WINDOW CILLS AND FRAMES, IN BATHROOMS AND KITCHENS, AND BEHIND FURNITURE PUSHED AGAINST EXTERNAL WALLS; MUSTY SMELL: A CHARACTERISTIC MUSTY, EARTHY SMELL IN AFFECTED ROOMS — CAUSED BY MICROBIAL VOLATILE ORGANIC COMPOUNDS (MVOCs) PRODUCED BY MOULD GROWTH; CONDENSATION ON WINDOWS: SINGLE-GLAZED OR DOUBLE-GLAZED WINDOWS WITH FAILED EDGE SEALS (MISTED GLASS) ARE A COMMON SITE OF VISIBLE CONDENSATION IN COLD WEATHER — THE COLD GLASS SURFACE IS BELOW THE DEWPOINT OF THE INDOOR AIR; HEALTH EFFECTS OF MOULD IN A LONDON HOME: RESPIRATORY EFFECTS: MOULD SPORES ARE ALLERGENS — EXPOSURE TO ELEVATED MOULD SPORE COUNTS IN INDOOR AIR CAUSES OR EXACERBATES RESPIRATORY CONDITIONS INCLUDING ASTHMA, RHINITIS, AND ALLERGIC BRONCHOPULMONARY ASPERGILLOSIS (ABPA — A SERIOUS ASTHMA COMPLICATION) — NHS GUIDANCE (NHS ENGLAND GUIDANCE ON DAMP AND MOULD — OCTOBER 2023 — PUBLISHED FOLLOWING THE INQUEST INTO THE DEATH OF AWAAB ISHAK FROM PROLONGED MOULD EXPOSURE IN A SOCIAL HOUSING PROPERTY IN ROCHDALE) STATES THAT DAMP AND MOULD CAN CAUSE SERIOUS HEALTH EFFECTS INCLUDING RESPIRATORY ILLNESS AND THAT LANDLORDS HAVE A LEGAL OBLIGATION TO ADDRESS DAMP AND MOULD PROMPTLY; SKIN AND EYE IRRITATION: MOULD EXPOSURE CAN CAUSE SKIN RASHES AND EYE IRRITATION IN SENSITIVE INDIVIDUALS; MYCOTOXINS: STACHYBOTRYS CHARTARUM (TOXIC BLACK MOULD — LESS COMMON IN CONDENSATION-ONLY SCENARIOS — MORE ASSOCIATED WITH PROLONGED SEVERE WATER DAMAGE) PRODUCES TRICHOTHECENE MYCOTOXINS THAT CAN CAUSE MORE SERIOUS HEALTH EFFECTS — IF A LARGE AREA OF DARK SLIMY (NOT POWDERY) BLACK MOULD IS PRESENT, PARTICULARLY AFTER A FLOOD OR PROLONGED SEVERE DAMP, SPECIALIST MOULD REMEDIATION SHOULD BE CONSIDERED.

MOULD TREATMENT IN A LONDON VICTORIAN TERRACE MUST ADDRESS BOTH THE SURFACE MOULD (TO REMOVE THE EXISTING GROWTH AND PREVENT REGROWTH) AND THE UNDERLYING CAUSE (THE CONDENSATION — WITHOUT ADDRESSING THE CAUSE, SURFACE TREATMENT ALONE WILL NOT PREVENT MOULD RETURNING): SURFACE MOULD REMOVAL (EXISTING MOULD GROWTH ON WALL AND CEILING SURFACES — APPROPRIATE PROTECTIVE EQUIPMENT: FFP2 MASK, NITRILE GLOVES, EYE PROTECTION — BEFORE REMOVING MOULD, DAMP SPRAY THE AFFECTED SURFACE TO REDUCE AIRBORNE SPORE RELEASE): DILUTED BLEACH SOLUTION (1 PART HOUSEHOLD BLEACH — DOMESTOS OR SIMILAR — TO 10 PARTS WATER) — APPLY TO MOULD-AFFECTED SURFACES WITH A SPONGE OR CLOTH — LEAVE FOR 10-15 MINUTES — WIPE CLEAN — THE SODIUM HYPOCHLORITE IN BLEACH IS AN EFFECTIVE BIOCIDE AGAINST MOULD SPORES — APPROPRIATE FOR NON-POROUS SURFACES (TILES, SEALED PAINT) — LESS EFFECTIVE ON POROUS SURFACES (PLASTER, MASONRY) WHERE MOULD HAS PENETRATED BELOW THE SURFACE; SPECIALIST MOULD CLEANER (DETTOL MOULD AND MILDEW REMOVER, KILROCK MOULD AND MILDEW KILLER, OR PROFESSIONAL PRODUCTS SUCH AS BIOMASTER BIOCIDAL MOULD TREATMENT — QUATERNARY AMMONIUM COMPOUND-BASED BIOCIDE — MORE EFFECTIVE ON POROUS SURFACES THAN BLEACH ALONE); FUNGICIDAL PAINT (DULUX TRADE MOULDSHIELD OR LEYLAND TRADE MOULD-PROOF EMULSION — PAINTS CONTAINING A FUNGICIDE (TYPICALLY ZINC OXIDE OR ANTIMICROBIAL ADDITIVES) THAT INHIBIT MOULD GROWTH ON THE PAINTED SURFACE — APPROPRIATE AS A FOLLOW-UP TO SURFACE MOULD REMOVAL — NOT A SUBSTITUTE FOR ADDRESSING THE UNDERLYING CONDENSATION CAUSE); FOR SEVERE MOULD ON PLASTER (WHERE THE MOULD HAS PENETRATED DEEPLY INTO THE PLASTER SUBSTRATE AND CANNOT BE REMOVED BY SURFACE CLEANING): HACK OFF THE AFFECTED PLASTER — TREAT THE MASONRY SURFACE WITH BIOCIDAL MOULD TREATMENT (WYKAMOL FUNGICIDAL WASH OR SOVEREIGN PX FUNGICIDE — DILUTED AS DIRECTED — TWO COATS) — ALLOW TO DRY — RE-PLASTER WITH SAND-CEMENT RENDER + FINISH (OR BRITISH GYPSUM RENOVATING PLASTER WHERE HYGROSCOPIC SALTS ARE ALSO PRESENT).

THE THREE PILLARS OF CONDENSATION PREVENTION IN A LONDON VICTORIAN TERRACE ARE: (1) REDUCE MOISTURE GENERATION; (2) INCREASE VENTILATION TO REMOVE MOISTURE FROM THE INDOOR AIR; (3) RAISE THE TEMPERATURE OF COLD SURFACES (BY INSULATION OR HEATING) SO THAT THEY ARE ABOVE THE DEWPOINT OF THE INDOOR AIR.

(1) REDUCE MOISTURE GENERATION: USE KITCHEN EXTRACT FAN (DUCTED TO OUTSIDE — NOT RECIRCULATING — A RECIRCULATING EXTRACTOR HOOD REMOVES GREASE ODOURS BUT DOES NOT REMOVE MOISTURE FROM THE AIR) WHEN COOKING; ALWAYS USE BATHROOM EXTRACT FAN (VENTAXIA LO-CARBON TEMPRA OR TITON HRV1.5 — PART F 2021 MINIMUM 15 L/S EXTRACT RATE FOR BATHROOM — 30 L/S FOR UTILITY) WHEN SHOWERING OR BATHING AND FOR AT LEAST 30 MINUTES AFTER; DRY CLOTHES OUTSIDE WHERE POSSIBLE — OR IN A ROOM WITH THE DOOR CLOSED AND A WINDOW OPEN OR WITH A DEHUMIDIFIER; (2) INCREASE VENTILATION: BACKGROUND VENTILATION (TRICKLE VENTS IN WINDOW FRAMES — TITON TRIMVENT XCITE 4000 OR RAVEN AIRMASTER — SELF-CLOSING — PROVIDE BACKGROUND FRESH AIR SUPPLY EVEN WHEN WINDOWS ARE CLOSED — REQUIRED BY PART F 2021 FOR ALL NEW HABITABLE ROOMS); PURGE VENTILATION (OPENING WINDOWS FOR A SHORT PERIOD — 15-30 MINUTES — TO RAPIDLY REDUCE INDOOR HUMIDITY AFTER HIGH-MOISTURE ACTIVITY — PARTICULARLY AFTER SHOWERING, BATHING, AND COOKING — REFERRED TO AS PURGE VENTILATION IN PART F 2021); DEMAND-CONTROLLED VENTILATION (HUMIDITY-TRIGGERED EXTRACTOR FANS IN BATHROOMS AND KITCHENS — VENTAXIA LO-CARBON TEMPRA PLUS — THE FAN AUTOMATICALLY INCREASES SPEED WHEN INDOOR HUMIDITY EXCEEDS A SET POINT AND REDUCES WHEN HUMIDITY DROPS — ENSURES EXTRACT IS PROVIDED WHEN NEEDED WITHOUT CONSTANT RUNNING); FOR PROPERTIES WITH PERSISTENT CONDENSATION THAT CANNOT BE CONTROLLED BY BACKGROUND VENTILATION AND PURGE VENTILATION ALONE: POSITIVE INPUT VENTILATION (PIV — ENVIROVENT CYCLONE 7 OR NUAIRE DRIMASTER ECO — A UNIT INSTALLED IN THE LOFT THAT GENTLY PRESSURISES THE HOUSE WITH FILTERED OUTSIDE AIR — DILUTING AND DISPLACING MOIST INDOOR AIR — TYPICALLY£500-1,200 SUPPLY AND FIT — ONE OF THE MOST COST-EFFECTIVE WHOLE-HOUSE VENTILATION IMPROVEMENTS FOR A VICTORIAN TERRACE WITH PERSISTENT CONDENSATION); MECHANICAL VENTILATION HEAT RECOVERY (MVHR — ZEHNDER COMFOAIR Q350 OR VENT-AXIA SENTINEL KINETIC PLUS — SUPPLIES FRESH AIR AND EXTRACTS STALE MOIST AIR WITH HEAT RECOVERY UP TO 93% EFFICIENCY — THE HIGHEST SPECIFICATION VENTILATION SOLUTION — TYPICALLY £3,000-7,000 SUPPLY AND FIT INCLUDING DUCTWORK — BEST VALUE AS PART OF A DEEPER RETROFIT); (3) RAISE SURFACE TEMPERATURES — INSULATION: EXTERNAL WALL INSULATION (EWI — WETHERBY EWI OR PERMAROCK EWI — APPLIES AN INSULATION LAYER TO THE OUTSIDE OF THE SOLID BRICK EXTERNAL WALL — ELIMINATES THE THERMAL BRIDGE AT THE WALL SURFACE — RAISES INTERNAL WALL TEMPERATURE SIGNIFICANTLY — DRAMATICALLY REDUCES CONDENSATION ON WALLS — U-VALUE IMPROVEMENT FROM 2.0-2.3 W/M²K TO APPROXIMATELY 0.18-0.30 W/M²K DEPENDING ON INSULATION THICKNESS — THE MOST EFFECTIVE REMEDY FOR CONDENSATION ON SOLID BRICK EXTERNAL WALLS IN LONDON VICTORIAN TERRACES — BUT REQUIRES PLANNING PERMISSION IN CONSERVATION AREAS AND ALTERS EXTERNAL APPEARANCE); INTERNAL WALL INSULATION (IWI — KINGSPAN K18 INSULATED PLASTERBOARD OR KNAUF INSULATED PLASTERBOARD SYSTEM ADHERED OR DOT-AND-DABB ED TO THE INSIDE FACE OF THE EXTERNAL WALL — IMPROVES U-VALUE AND RAISES INTERNAL WALL SURFACE TEMPERATURE — LESS DISRUPTIVE AND LESS VISIBLE EXTERNALLY THAN EWI — BUT REDUCES INTERNAL ROOM DIMENSIONS AND CREATES THERMAL BRIDGE AT THE PERIMETER WHERE IWI MEETS FLOOR, CEILING, AND PARTITION WALLS — REQUIRES CAREFUL DETAILING TO AVOID NEW THERMAL BRIDGES AT JUNCTIONS); SECONDARY GLAZING (ADDS A SECOND PANE TO EXISTING SINGLE-GLAZED SASH WINDOWS — BESPOKE TIMBER OR ALUMINIUM SECONDARY GLAZING — RAISES THE TEMPERATURE OF THE WINDOW INNER SURFACE — ELIMINATES CONDENSATION ON WINDOWS — TYPICALLY £200-500 PER WINDOW SUPPLY AND FIT).