Lead Flashing for London Victorian Terraces: Types, Installation, and Repair

LEAD SPECIFICATIONS: LEAD FOR FLASHING IS SPECIFIED BY BS EN 12588 (ROLLED LEAD SHEET — UK) IN CODES BASED ON WEIGHT PER M²: - CODE 3 (1.32MM THICK, 14.97KG/M²): USED FOR SOAKERS (SMALL INDIVIDUAL FLASHINGS BETWEEN EACH COURSE OF SLATES OR TILES AT A SIDE ABUTMENT). - CODE 4 (1.80MM, 20.41KG/M²): THE MOST WIDELY USED CODE FOR DOMESTIC FLASHING — CHIMNEY BACK GUTTERS, VALLEY GUTTERS, COVER FLASHINGS, PARAPET FLASHINGS. - CODE 5 (2.24MM, 25.40KG/M²): FOR HEAVIER DUTY APPLICATIONS — LARGE BACK GUTTERS, BOX GUTTERS, FLAT ROOFS WHERE LEAD SHEETING IS THE WATERPROOF MEMBRANE.

MAIN FLASHING TYPES IN A LONDON VICTORIAN TERRACE:

1. CHIMNEY FLASHING SYSTEM (FRONT APRON + SOAKERS + STEP FLASHING + BACK GUTTER): A CHIMNEY STACK PENETRATING A SLATED OR TILED PITCHED ROOF REQUIRES A COMPLETE FLASHING SYSTEM: - FRONT APRON: THE LEAD FLASHING AT THE FRONT FACE OF THE CHIMNEY (UPSLOPE SIDE, LOWER EDGE). CODE 4. WEDGE-FIXED INTO THE HORIZONTAL MORTAR JOINT OF THE CHIMNEY STACK; DRESSED DOWN OVER THE TILES/SLATES IN FRONT OF THE CHIMNEY. MINIMUM UPSTAND 75MM INTO JOINT; MINIMUM OVERLAP ON ROOF COVERING 150MM. - SOAKERS: INDIVIDUAL SMALL LEAD PIECES (CODE 3) LACED BETWEEN EACH COURSE OF SLATES OR TILES AT THE SIDE ABUTMENTS OF THE CHIMNEY (LEFT AND RIGHT CHEEKS). SIZED: WIDTH = GAUGE (BATTEN SPACING) + LAP (MINIMUM 65MM FOR PLAIN TILES, 100MM FOR SLATES) + 25MM UPSTAND. SOAKERS ARE HIDDEN BY THE COVER FLASHING ABOVE. - STEP COVER FLASHING: A SINGLE CONTINUOUS LEAD COVER FLASHING OVER THE SOAKERS ON EACH SIDE — STEPPED UPWARD FOLLOWING THE SLOPE OF THE ROOF (ONE STEP PER COURSE OF TILES OR SLATES). CODE 4. WEDGE-FIXED INTO THE MORTAR JOINTS OF THE CHIMNEY CHEEK AT EACH STEP. - BACK GUTTER: THE MOST COMPLEX ELEMENT — A LEAD GUTTER FORMED AT THE BACK (DOWNSLOPE) FACE OF THE CHIMNEY STACK TO COLLECT RAINWATER RUNNING DOWN THE ROOF SLOPE BEHIND THE CHIMNEY. THE BACK GUTTER COLLECTS WATER AND DISCHARGES IT VIA LEAD SOAKERS UNDER THE TILES/SLATES AT THE SIDE OF THE CHIMNEY. CODE 4 OR CODE 5. MUST BE DESIGNED WITH ADEQUATE DEPTH (MINIMUM 75MM AT THE CHIMNEY FACE) AND CORRECT FALL TO DISCHARGE.

2. SIDE ABUTMENT FLASHING (WALL AND PITCHED ROOF — EXTERNAL WALL ABUTMENT): WHERE A PITCHED ROOF MEETS A WALL RUNNING PARALLEL TO THE RIDGE (E.G., A LEAN-TO ROOF AGAINST THE SIDE WALL OF A VICTORIAN TERRACE, OR A DORMER CHEEK): - SOAKERS + STEP COVER FLASHING (AS ABOVE): THE STANDARD APPROACH WHERE THE ROOF TILES/SLATES ARE INDIVIDUAL UNITS. - SECRET GUTTER (INTERNAL GUTTER): USED WHERE A VERY CLOSE ABUTMENT BETWEEN THE ROOF AND THE WALL MAKES A SURFACE FLASHING IMPRACTICAL — A LEAD OR GRP INTERNAL GUTTER IS FORMED IN THE ANGLE BETWEEN THE ROOF AND THE WALL.

3. VALLEY FLASHING: VALLEYS (THE INTERNAL ANGLE BETWEEN TWO ROOF SLOPES — AT AN L-SHAPED PLAN OR AT A HIP TO RIDGE JUNCTION) IN VICTORIAN TERRACES ARE SOMETIMES FORMED WITH LEAD CODE 4 VALLEY GUTTERS (A V-SHAPED OR TAPERED LEAD CHANNEL FITTED INTO THE VALLEY STRUCTURE BELOW THE TILES): - CLOSED VALLEY (TILES LAP OVER THE VALLEY): TILES OVER-SAIL AND THE VALLEY FLASHING IS NOT VISIBLE. REQUIRES CAREFUL DETAILING TO PREVENT WIND-DRIVEN RAIN FROM TRACKING UNDER THE TILE EDGE. - OPEN VALLEY (LEAD CHANNEL EXPOSED BETWEEN TILES CUT TO A MARGIN): MORE COMMON ON SLATE ROOFS. LEAD CODE 4, MINIMUM 300MM WIDE (150MM ON EACH SIDE). EXPANSION DRIPS AT MAXIMUM 1.5M INTERVALS.

4. PARAPET WALL BASE FLASHING: COVERED IN THE PARAPET WALL GUIDE — A CODE 4 COVER FLASHING DRESSED OVER THE FLAT ROOF COVERING AND WEDGE-FIXED INTO THE PARAPET WALL HORIZONTAL JOINT.

COMMON LEAD FLASHING FAILURES AND REPAIR METHODS:

1. LEAD PULLED OUT OF RAKED JOINT (THERMAL MOVEMENT): LEAD EXPANDS AND CONTRACTS SIGNIFICANTLY WITH TEMPERATURE CHANGES (LINEAR THERMAL EXPANSION COEFFICIENT ~ 28.9 × 10⁻⁶ /°C — MUCH HIGHER THAN BRICK OR TILE). IF A LEAD COVER FLASHING IS FIXED IN A RUN LONGER THAN 1.5M WITHOUT AN EXPANSION JOINT (A FREE LAP JOINT — ONE LEAD PIECE OVERLAPPING THE NEXT BY 100MM, NOT WEDGE-FIXED AT THE OVERLAP END), THE LEAD WILL PULL ITSELF OUT OF THE RAKED JOINT OVER A FEW SEASONS. REPAIR: RAKE OUT THE JOINT (15-20MM DEEP); RE-WEDGE THE LEAD BACK IN (NEW LEAD WEDGES EVERY 450MM); SEAL THE TOP OF THE JOINT WITH SIKAFLEX 11FC+ OR LEAD MASTIC. RE-DIVIDE THE LEAD INTO 1.5M BAYS IF THE ORIGINAL INSTALLATION WAS IN A SINGLE OVERLONG RUN.

2. CRACKED OR HOLED LEAD (FATIGUE CRACKING): LEAD CRACKS ALONG FOLD LINES (SUCH AS THE UPTURN AT A BACK GUTTER OR THE FOLD AT A DRIP EDGE) DUE TO THERMAL FATIGUE — REPEATED EXPANSION AND CONTRACTION EVENTUALLY FATIGUES THE LEAD AT THE SHARPEST FOLD. REPAIR: CLEAN THE AREA; CUT A PATCH FROM THE SAME LEAD CODE; APPLY LEAD SOLDER (PLUMBER\'S LEAD-TIN SOLDER 50:50 — FLUX: PLUMBER\'S FLUX PASTE; SOLDERING IRON OR PROPANE BLOWTORCH); OR USE LEADAX LEAD SUBSTITUTE SELF-ADHESIVE SHEET PATCH.

3. FAILED MORTAR SEAL ABOVE WEDGE-FIXED FLASHING: WHERE THE MORTAR IN THE JOINT ABOVE THE LEAD (ABOVE THE WEDGE-FIXED TOP EDGE) HAS CRACKED OR FALLEN OUT, WATER TRACKS BEHIND THE LEAD AND BYPASSES THE FLASHING. REPAIR: RAKE OUT THE JOINT ABOVE THE LEAD TO 15MM; REPOINT WITH A FLEXIBLE POINTING SEALANT (SIKAFLEX 11FC+ GREY — MORE DURABLE THAN MORTAR IN THIS EXPOSED POSITION AND MOVES WITH THE THERMAL MOVEMENT OF THE LEAD AND THE MASONRY).

LEADAX LEAD SUBSTITUTE: FOR SMALL PATCH REPAIRS WHERE WORKING WITH SHEET LEAD IS IMPRACTICAL, LEADAX (LEADAX BV — DUTCH PRODUCT, WIDELY STOCKED IN THE UK BY LEADAX UK) IS A FLEXIBLE SELF-ADHESIVE LEAD-FREE SHEET (ALUMINIUM/POLYMER COMPOSITE) THAT CAN BE DRESSED AND SHAPED LIKE LEAD AND IS ACCEPTED BY MOST BUILDING CONTROL BODIES FOR DOMESTIC FLASHING REPAIR WORK. NOT RECOMMENDED FOR FULL REPLACEMENTS — USE GENUINE BS EN 12588 LEAD FOR NEW INSTALLATIONS.

COSTS (SUPPLY AND FIT, LONDON 2025-2026): CHIMNEY FLASHING REPLACEMENT (COMPLETE SYSTEM — SOAKERS, STEP FLASHING, BACK GUTTER, FRONT APRON — SUPPLY AND FIT): £600-1,500 (DEPENDING ON CHIMNEY SIZE AND STACK HEIGHT) CHIMNEY FRONT APRON ONLY (SUPPLY AND FIT): £200-400 STEP FLASHING REPLACEMENT (PER M RUN — SUPPLY AND FIT): £80-180/M PARAPET BASE FLASHING (PER M RUN — CODE 4 — SUPPLY AND FIT): £80-180/M VALLEY FLASHING REPLACEMENT (PER M RUN — SUPPLY AND FIT): £120-250/M SMALL LEAD PATCH REPAIR (SUPPLY AND FIT): £100-250