Lead Flashing for London Victorian Terraces: Specification, Repair, and Replacement

LEAD SHEET FOR ROOFING AND FLASHING IN THE UK IS SPECIFIED BY CODE NUMBER — EACH CODE CORRESPONDING TO A NOMINAL WEIGHT (KG/M²) AND THICKNESS (MM). THE RELEVANT UK STANDARD IS BS EN 12588 (LEAD AND LEAD ALLOYS — ROLLED LEAD SHEET FOR BUILDING PURPOSES). THE CODES USED IN RESIDENTIAL ROOFING APPLICATIONS IN LONDON:

CODE 3 (1.25MM THICK — 14.18 KG/M²): THE MINIMUM WEIGHT FOR MOST RESIDENTIAL FLASHING APPLICATIONS. USED FOR: SOAKERS (THE INDIVIDUAL TRIANGULAR PIECES OF LEAD INTERLAID WITH PLAIN TILES OR SLATES AT STEP FLASHINGS — MINIMUM SIZE: 175MM X GAUGE + LAP, TYPICALLY 175MM X 175MM FOR A STANDARD 38MM GAUGE SLATE), SMALL DETAIL FLASHINGS (PIPE FLASHINGS, SMALL APRON FLASHINGS). CODE 3 IS TOO LIGHT FOR LONG UNSUPPORTED LENGTHS — MAXIMUM RECOMMENDED CONTINUOUS LENGTH WITHOUT EXPANSION JOINT IS 1500MM.

CODE 4 (1.80MM THICK — 20.41 KG/M²): THE STANDARD CODE FOR MOST RESIDENTIAL LEAD FLASHING APPLICATIONS IN LONDON. USED FOR: COVER FLASHINGS (THE VISIBLE LEAD FLASHING THAT IS TUCKED INTO THE MORTAR JOINT AND LAPS OVER THE SOAKERS OR THE ROOF SURFACE — MINIMUM 150MM LAP TO SURFACE AND 25MM CHASE DEPTH), CHIMNEY ABUTMENT STEP AND COVER FLASHINGS, APRON FLASHINGS BELOW ROOFLIGHTS, WINDOW AND DOOR HEAD FLASHINGS ON SOLID-WALL LONDON VICTORIAN TERRACE CONSTRUCTION. MAXIMUM CONTINUOUS LENGTH: 1500MM (JOINTS REQUIRED — WELTED AND CLIPPED EVERY 1500MM).

CODE 5 (2.24MM THICK — 25.40 KG/M²): USED FOR: BACK GUTTERS TO CHIMNEY STACKS (THE HORIZONTAL LEAD GUTTER AT THE UPSLOPE FACE OF THE CHIMNEY STACK — SUSCEPTIBLE TO PONDING AND REQUIRES THE HEAVIER GAUGE FOR DURABILITY), PARAPET WALL CAPPINGS, VALLEY GUTTERS (SECRET VALLEYS IN PLAIN TILE ROOFS), GUTTER LININGS WHERE LEAD IS SPECIFIED INSTEAD OF GRP. MAXIMUM CONTINUOUS LENGTH: 1500MM.

CODE 6 (2.65MM THICK — 30.05 KG/M²): HEAVY FLASHING APPLICATIONS — PARAPET GUTTER LININGS, LEAD ROOFING OVER FLAT SECTIONS WHERE SPECIFIED. MAXIMUM CONTINUOUS LENGTH: 1500MM.

WORK LEAD STANDARD: ALL LEAD SHEET USED IN LONDON RESIDENTIAL ROOFING SHOULD BE TO BS EN 12588 GRADE. THE LEAD SHEET ASSOCIATION (LSA) APPROVED STOCKISTS SUPPLY BS EN 12588 GRADE LEAD IN COIL OR SHEET FORM — CALDER INDUSTRIAL MATERIALS (CALDER LEAD) AND MIDLAND LEAD ARE THE UK'S PRIMARY MANUFACTURERS OF BS EN 12588 ROLLED LEAD SHEET.

LONDON VICTORIAN TERRACES HAVE SEVERAL DISTINCT TYPES OF LEAD FLASHING — EACH SERVING A DIFFERENT WATERPROOFING FUNCTION AT A DIFFERENT ROOF-TO-WALL OR ROOF-TO-ROOF JUNCTION.

STEP AND COVER FLASHING (CHIMNEY ABUTMENT — MOST COMMON FLASHING TYPE ON LONDON VICTORIAN TERRACES): AT A CHIMNEY STACK ABUTMENT ON A SLATED OR PLAIN-TILED ROOF, THE WATERPROOFING CONSISTS OF: SOAKERS (CODE 3 LEAD — INDIVIDUAL PIECES INTERLAID WITH EACH COURSE OF SLATES OR TILES, STEPPED UP THE SLOPE): SOAKER SIZE FOR WELSH SLATE (300X200MM SLATES): 175MM X (GAUGE + 25MM LAP) = TYPICALLY 175X175MM. COVER FLASHING (CODE 4 LEAD — A CONTINUOUS LEAD FLASHING TUCKED INTO A RAKED MORTAR JOINT IN THE CHIMNEY STACK BRICKWORK, STEPPED TO FOLLOW THE ROOF SLOPE, LAPPING OVER THE SOAKERS): DRESSED DOWN MINIMUM 150MM OVER THE SOAKERS. THE MORTAR JOINT CHASE IS TYPICALLY 25MM DEEP AND 25MM WIDE — RAKED OUT WITH A COLD CHISEL AND CLUB HAMMER (MUST NOT BE CHASED INTO THE MAIN BRICK BED JOINT — PERPEND JOINT RAKING ONLY).

BACK GUTTER (CHIMNEY STACK — AT THE UPSLOPE FACE): A HORIZONTAL LEAD GUTTER (CODE 5 MINIMUM) AT THE BASE OF THE UPSLOPE FACE OF THE CHIMNEY STACK — THE MOST VULNERABLE FLASHING ON A LONDON VICTORIAN TERRACE CHIMNEY BECAUSE IT RECEIVES THE MAXIMUM RAINWATER FLOW FROM THE ROOF SLOPE ABOVE. THE BACK GUTTER MUST HAVE: ADEQUATE CROSS-SECTION (MINIMUM 75MM CLEAR WIDTH BEHIND THE STACK — WIDER WHERE THE ROOF SLOPE AREA ABOVE IS LARGE). ADEQUATE FALL TO THE SIDE STEP FLASHINGS (MINIMUM 1:60 — PREFERABLY 1:40). GUTTER BOARDS FIXED FIRMLY — LEAD LAID OVER GUTTER BOARDS ON 3MM POLYESTER FLEECE UNDERLINER (PREVENTS BITUMEN CONTAMINATION FROM FELT UNDERLAYS).

APRON FLASHING (DOWNSLOPE FACE OF CHIMNEY STACK — AND BELOW ROOFLIGHTS): CODE 4 LEAD — TUCKED INTO HORIZONTAL MORTAR JOINT AT TOP, DRESSED DOWN OVER THE ROOF SURFACE MINIMUM 150MM. FOR ROOFLIGHTS (VELUX, FAKRO) — THE MANUFACTURER'S OWN LEAD APRON FLASHING KIT IS THE CORRECT PRODUCT (VELUX EDW FLASHING FOR SLATE ROOFS OR EDL FOR PLAIN TILES).

PARAT COPING AND FLASHING (FLAT-ROOF REAR EXTENSIONS — VERY COMMON ON LONDON VICTORIAN TERRACES): A PARAPET WALL ON A FLAT-ROOF REAR EXTENSION REQUIRES: PARAPET CAPPING (CODE 5 OR 6 LEAD, MINIMUM 600MM WIDE — FOLDED TO FORM THE TOP CAPPING WITH DRIP DETAIL EACH SIDE), VERTICAL UPSTAND BEHIND THE CAPPING (TUCKED INTO MORTAR JOINT, MINIMUM 150MM HIGH), DRESSED DOWN INTO GUTTER OR FLAT ROOF.

BEFORE DECIDING BETWEEN LEAD FLASHING REPAIR AND FULL REPLACEMENT ON A LONDON VICTORIAN TERRACE, A PROPER CONDITION ASSESSMENT IS REQUIRED — PREFERABLY ON THE ROOF (SAFELY, WITH APPROPRIATE LADDERS, PLATFORMS, OR SCAFFOLDING) RATHER THAN JUST FROM GROUND LEVEL.

SIGNS THAT EXISTING LEAD FLASHING CAN BE REPAIRED (RATHER THAN REPLACED): LEAD IS SOUND BUT HAS PULLED OUT OF THE MORTAR JOINT (MOST COMMON FAILURE MODE — THE LEAD CONTRACTS OVER TIME AND THE TAIL PULLS FREE FROM THE RAKED MORTAR JOINT): REPAIR: RE-CHASE THE MORTAR JOINT (RAKE TO 25MM DEPTH AND 25MM WIDTH), RE-INSERT THE LEAD TAIL, AND POINT WITH SULPHATE-RESISTANT MORTAR (1:4 CEMENT:SHARP SAND WITH SIKA 1 ADMIXTURE) — DO NOT USE UNDILUTED CEMENT MORTAR (TOO RIGID — WILL CRACK WITH THERMAL MOVEMENT). ALTERNATIVELY, A LEADFIX WEDGE SYSTEM (PLASTIC WEDGE-AND-SEALANT — VIBAC OR LEADFIX) CAN SECURE A PULLED-OUT FLASHING WITHOUT RE-MORTARING — SUITABLE WHERE REPEATED RE-MORTARING HAS WEAKENED THE MORTAR JOINT. LEAD IS INTACT BUT HAS A SMALL CRACK OR PINHOLE (TYPICALLY AT A BEND OR AT A NAIL HOLE): REPAIR: CLEAN SURFACE (WIRE BRUSH — REMOVE OXIDATION), APPLY BOSTIK FLASHBAND PLUS (50MM WIDE SELF-ADHESIVE FLASHING STRIP — BITUMINOUS) OVER THE CRACK — OVERLAP MINIMUM 50MM EITHER SIDE. THIS IS AN ACCEPTABLE TEMPORARY REPAIR BUT NOT A PERMANENT SOLUTION.

SIGNS THAT FULL LEAD FLASHING REPLACEMENT IS REQUIRED (NOT REPARABLE): LEAD HAS WIDESPREAD CRACKING, CORROSION, OR PINHOLES (TYPICALLY MORE THAN 2-3 CRACK/PINHOLE LOCATIONS PER FLASHING SECTION — FLASHBAND REPAIR BECOMES IMPRACTICAL). LEAD HAS BEEN PREVIOUSLY BADLY REPAIRED WITH CEMENT RENDER OVER THE TOP (A VERY COMMON BAD PRACTICE — THE CEMENT PREVENTS THE LEAD FROM THERMAL MOVEMENT AND ACCELERATES CRACKING BENEATH). LEAD IS PAPER-THIN (ORIGINAL CODE 3 OR LIGHTER — HEAVILY OXIDISED AND REDUCED IN THICKNESS THROUGH DECADES OF SURFACE LOSS). THE MORTAR JOINT IS SO DETERIORATED THAT THE CHASE CANNOT BE REFORMED WITHOUT STRUCTURAL BRICK REPAIR.

THE CORRECT TECHNIQUES FOR LEAD FLASHING REPAIR AND REPLACEMENT ON A LONDON VICTORIAN TERRACE FOLLOW THE LEAD SHEET ASSOCIATION (LSA) GOOD PRACTICE GUIDES — THE AUTHORITATIVE REFERENCE FOR LEAD ROOFING AND FLASHING WORK IN THE UK.

FULL LEAD FLASHING REPLACEMENT — STEP-BY-STEP: STEP 1 — STRIP EXISTING FLASHING (REMOVE THE OLD LEAD, RAKE OUT ALL OLD MORTAR POINTING FROM JOINT, CLEAN ALL REMAINING MORTAR FROM THE BRICKWORK FACE AND FROM THE ROOF SURFACE). STEP 2 — CHECK SOAKERS (IF REPLACING COVER FLASHINGS, CHECK THE CONDITION OF THE SOAKERS — IF CODE 3 AND THIN, REPLACE WITH NEW CODE 3 SOAKERS AT THIS STAGE WHILE THE ROOF IS ACCESSIBLE). STEP 3 — CUT NEW LEAD TO SIZE (FROM BS EN 12588 COIL — CUT WITH LEAD SNIPS OR GUILLOTINE, MARK WITH CHALK LINE — DO NOT USE GRINDER ON LEAD). STEP 4 — DRESS AND FORM LEAD (LEAD WORKERS BOSSING MALLET AND WOOD DRESSER TO FORM ANGLES, UPSTANDS, AND LAPS WITHOUT CREASING). STEP 5 — FIX LEAD: DRESS THE TOP EDGE INTO THE RAKED MORTAR JOINT (25MM DEEP), INSERT COPPER OR STAINLESS FLASHING CLIP AT 500MM CENTRES (LR17 LEAD CLIP — LSA SPECIFICATION — COPPER PINS PREVENT BIMETALLIC CORROSION WITH LEAD), WEDGE TIGHTLY WITH LEAD OR COPPER WEDGE. STEP 6 — POINT: FILL THE CHASED JOINT WITH SULPHATE-RESISTANT MORTAR (1:3 CEMENT:SHARP SAND — OR 1:4 NHL 3.5 LIME MORTAR FOR CONSERVATION AREAS WHERE HARD CEMENT IS NOT APPROPRIATE — TUCK POINT TO FLUSH OR SLIGHTLY RECESSED FINISH).

LEAD PATINATION: NEW LEAD SHEET HAS A BRIGHT SHINY SURFACE (LEAD OXIDE LAYER FORMS GRADUALLY OVER 6-12 MONTHS TO PRODUCE THE CHARACTERISTIC GREY-WHITE PATINA). PATINATION OIL (LSA APPROVED — LANTHANUM ACETATE-BASED LIQUID APPLIED WITH A CLOTH TO NEW LEAD SURFACES IMMEDIATELY AFTER FIXING): PREVENTS LIME RUN-OFF STAINING OF TILES BELOW AND ACCELERATES UNIFORM PATINA FORMATION — A PROFESSIONAL REQUIREMENT ON ALL NEW LEAD WORK.

WHILE LEAD IS THE TRADITIONAL AND HIGHEST-DURABILITY OPTION FOR FLASHING ON LONDON VICTORIAN TERRACES, SEVERAL ALTERNATIVE MATERIALS ARE USED IN RESIDENTIAL ROOFING — EACH WITH DIFFERENT PERFORMANCE AND COST CHARACTERISTICS.

ZINC FLASHING (CODE 14 — 0.65MM THICKNESS): ZINC IS INCREASINGLY USED AS AN ALTERNATIVE TO LEAD ON LONDON VICTORIAN TERRACE ROOF REPAIRS — PARTICULARLY WHERE LEAD THEFT IS A CONCERN (LEAD IS A TARGET FOR METAL THIEVES, PARTICULARLY FROM ACCESSIBLE FLAT-ROOF SECTIONS AND VALLEY GUTTERS IN LONDON). RHEINZINK (GERMAN — NATURAL, PREWEATHED, OR GRAPHITE-GREY ZINC) AND VM ZINC (FRENCH — QUARTZ-ZINC OR ANTHRA-ZINC): BOTH ARE BS EN 988 GRADE ZINC USED FOR FLASHINGS AND CLADDING. ZINC FLASHING IS LIGHTER THAN LEAD (DENSITY 7.13 KG/L VS LEAD 11.34 KG/L), SIMILAR DURABILITY (50-70 YEAR LIFESPAN), AND HARDER TO WORK (LESS MALLEABLE THAN LEAD — CANNOT BE BOSSED AS EASILY, MORE PRONE TO CRACKING AT BENDS IN COLD WEATHER). NOT APPROPRIATE IN CONSERVATION AREAS WHERE LEAD IS THE HISTORICALLY CORRECT MATERIAL.

COPPER FLASHING: CODE 0.6MM COPPER (BS EN 1172): THE MOST DURABLE NON-LEAD METAL FLASHING (100+ YEAR LIFESPAN). USED ON HERITAGE BUILDINGS AND COMMERCIAL PROJECTS — RARELY USED IN STANDARD LONDON VICTORIAN TERRACE REPAIR BECAUSE OF COST (APPROXIMATELY 3-4X THE COST OF EQUIVALENT LEAD THICKNESS). GREEN PATINA (VERDIGRIS) FORMS OVER 10-20 YEARS. CANNOT BE COMBINED WITH LEAD OR ZINC (BIMETALLIC CORROSION — COPPER CORRODES ZINC AND LEAD ON CONTACT IN THE PRESENCE OF RAINWATER).

GRP (GLASS-REINFORCED PLASTIC) LEAD ALTERNATIVE SYSTEMS: UBIFLEX (SIKA — FLEXIBLE GLASS-FIBRE-REINFORCED POLYMER ROLL — GREY COLOUR — SOLD AS A LEAD ALTERNATIVE): MECHANICALLY FIXED OR ADHERED, NOT TUCKED INTO MORTAR JOINTS — LESS DURABLE THAN LEAD AT MOVEMENT JOINTS AND LESS APPROPRIATE FOR COMPLEX CHIMNEY ABUTMENT FLASHINGS. SUITABLE FOR SIMPLE STEP AND COVER FLASHING SITUATIONS — NOT FOR BACK GUTTERS, PARAPET CAPPINGS, OR VALLEY GUTTERS.

FLASHBAND PLUS (BOSTIK): SELF-ADHESIVE BITUMINOUS FLASHING TAPE — ACCEPTABLE FOR EMERGENCY REPAIRS BUT NOT A LONG-TERM REPLACEMENT FOR LEAD FLASHING ON A LONDON VICTORIAN TERRACE CHIMNEY OR PARAPET.

LEAD FLASHING REPLACEMENT AND REPAIR COSTS IN LONDON VARY SIGNIFICANTLY BY JOB TYPE — FROM A SMALL APRON FLASHING REPAIR (UNDER £200) TO A FULL CHIMNEY STACK RE-FLASHING WITH BACK GUTTER AND SCAFFOLDING (£1,500 TO £3,000+).

SMALL REPAIR (PULL-OUT FLASHING — RE-CHASE AND RE-POINT): £80 TO £180 LABOUR (1 ROOFER — HALF DAY) + £10 TO £30 MATERIALS (MORTAR, WEDGES). ACCESS DEPENDENT ON EXISTING SCAFFOLDING OR LADDER ONLY: FOR LADDER ACCESS: ADD £0 (INCLUDED IN LABOUR RATE). FOR LOW-LEVEL SCAFFOLD (UP TO 6M): ADD £300 TO £600. FOR HIGH CHIMNEY OR DIFFICULT ACCESS: MOBILE TOWER OR SCAFFOLDING: ADD £500 TO £1,200.

APRON FLASHING REPLACEMENT (BELOW ROOFLIGHT — E.G. VELUX GGU 78CM X 118CM): VELUX EDW LEAD FLASHING KIT SUPPLY: £80 TO £150. LABOUR (ROOFER — 2-3 HOURS): £150 TO £300. TOTAL (LADDER ACCESS): £230 TO £450.

FULL CHIMNEY STACK RE-FLASHING (STEP AND COVER FLASHINGS, APRON FLASHING, BACK GUTTER — NEW CODE 4/5 LEAD THROUGHOUT — LONDON VICTORIAN TERRACE): LEAD MATERIALS (CODE 4 AND 5 — APPROXIMATELY 2-4M² FOR A TYPICAL VICTORIAN TERRACE STACK): £180 TO £400. LABOUR (SKILLED LEADWORKER — 1-2 DAYS): £400 TO £900. ACCESS SCAFFOLDING (TYPICALLY REQUIRED FOR CHIMNEY ACCESS — TUBE AND FIT SCAFFOLD OR MOBILE TOWER): £500 TO £1,200. TOTAL CHIMNEY RE-FLASHING: £1,080 TO £2,500 (DEPENDENT ON ACCESS AND STACK HEIGHT).

PARAET CAPPING RE-LEAD (REAR EXTENSION — 3M LENGTH — CODE 5): LEAD MATERIALS (CODE 5 — 3 X 0.6M = 1.8M²): £120 TO £250. LABOUR (LEADWORKER — 1 DAY): £300 TO £500. ACCESS (USUALLY FROM INSIDE FLAT ROOF — MINIMAL): £0 TO £200. TOTAL PARAPET RE-LEAD (3M): £420 TO £950.