Valley Gutters in London Victorian Terraces: Lead, GRP, and Zinc Valley Repair

THREE MAIN VALLEY GUTTER TYPES IN LONDON VICTORIAN TERRACES:

1. OPEN VALLEY (LEAD CODE 4 VALLEY TROUGH — MOST RELIABLE): AN OPEN VALLEY IS A VISIBLE LEAD CHANNEL RUNNING DOWN THE VALLEY ANGLE — THE TILES OR SLATES ON EACH SIDE ARE CUT TO A MARGIN (100-150MM FROM THE VALLEY CENTRE LINE) AND THE LEAD IS EXPOSED BETWEEN THE TILE EDGES. - LEAD SPECIFICATION: CODE 4 (1.80MM) MINIMUM. CODE 5 FOR WIDE OR LONG VALLEYS WITH HIGH WATER VOLUME. - WIDTH: MINIMUM 300MM TOTAL (150MM ON EACH SIDE). WIDER VALLEYS (400MM+) ARE PREFERRED WHERE THE VALLEY COLLECTS WATER FROM A LARGE ROOF AREA. - DRIPS AND EXPANSION: A CONTINUOUS OPEN VALLEY MUST HAVE LEAD DRIPS (A FOLD IN THE LEAD FORMING A STEP THAT PREVENTS WATER FROM RUNNING UP UNDER THE JUNCTION) AT MAXIMUM 1.5M CENTRES — THE DRIP ALSO ACTS AS AN EXPANSION JOINT FOR THE LEAD. WITHOUT DRIPS, CAPILLARY ACTION DRAWS WATER UNDER THE TILES AND THE LEAD DEVELOPS FATIGUE CRACKING. - BEDDING AT TILE EDGES: THE CUT TILE EDGES ARE BEDDED ON MORTAR (TRADITIONALLY) OR ON A FLEXIBLE POINTING COMPOUND (MODERN — SIKAFLEX 11FC+ OR BOSTIK CEMENTONE) AGAINST THE LEAD VALLEY — PREVENTS WIND-DRIVEN RAIN FROM GETTING UNDER THE TILE EDGES. OVER-BEDDING (TOO MUCH MORTAR FORMING A RAISED HEEL AT THE TILE EDGE) RESTRICTS WATER FLOW IN THE VALLEY AND CAUSES BACKING UP BEHIND THE RAISED MORTAR BED.

2. SECRET (INTERNAL) GUTTER VALLEY: A SECRET GUTTER VALLEY IS A HIDDEN GUTTER FORMED INSIDE THE ROOF STRUCTURE — THE TILES ON EACH SIDE TILE OVER THE TOP OF THE GUTTER AND MEET WITH A MINIMUM GAP OR WITH A WOVEN SLATE FINISH (THE TILES INTERLEAVE). THE GUTTER IS NOT VISIBLE FROM OUTSIDE. - SECRET GUTTER CONSTRUCTION: A LEAD (CODE 4) OR GRP (GLASS FIBRE) TROUGH FORMED IN THE VALLEY ANGLE — BENEATH THE TILE COURSES. ADEQUATE WIDTH (MINIMUM 300MM) AND ADEQUATE UPSTAND HEIGHT (MINIMUM 75MM ON EACH SIDE) ARE ESSENTIAL — A COMMON PROBLEM WITH ORIGINAL VICTORIAN SECRET GUTTERS IS AN INADEQUATE UPSTAND THAT ALLOWS WATER TO OVERFLOW THE GUTTER SIDES IN HEAVY RAIN. - SECRET GUTTER DEFECTS: THE GUTTER IS NOT VISIBLE AND MAY BE BLOCKED WITH DEBRIS (MOSS, LICHEN, LEAVES FROM A NEARBY TREE — COMMON IN LONDON VICTORIAN TERRACES NEAR GARDEN TREES) WITHOUT THE HOMEOWNER BEING AWARE. BLOCKED SECRET GUTTERS BACK WATER UP AND OVERFLOW INTO THE ROOF STRUCTURE. PERIODIC INSPECTION (EVERY 2-3 YEARS — VIA A ROOF LADDER OR MIRROR AND TORCH INSPECTION OF THE VALLEY ABOVE THE SOFFIT) AND CLEARANCE IS ESSENTIAL.

3. SWEPT OR WOVEN VALLEY (SLATES INTERLACED — NO GUTTER): A TRADITIONAL APPROACH ON SLATE ROOFS (COMMON IN SOME LONDON VICTORIAN TERRACES WITH NATURAL WELSH SLATE) WHERE THE SLATES ON EACH SIDE ARE INTERLEAVED AT THE VALLEY ANGLE WITHOUT A SEPARATE GUTTER CHANNEL — THE OVERLAPPING SLATES DIVERT WATER DOWN EACH ROOF SLOPE. NOT SUITABLE FOR PLAIN CLAY TILES (TOO INFLEXIBLE TO INTERLEAVE WITHOUT CRACKING). REQUIRES EXPERT SLATING TO ACHIEVE A WATERTIGHT RESULT.

GRP (GLASS REINFORCED PLASTIC) VALLEY TROUGH: FOR REPLACING A FAILED LEAD VALLEY, GRP (FIBREGLASS) VALLEY TROUGHS ARE AN INCREASINGLY COMMON ALTERNATIVE: - PROFILE: GRP VALLEY TROUGHS ARE MOULDED TO A V OR L PROFILE TO FIT INTO THE VALLEY ANGLE. WIDTHS: 280MM, 330MM, 380MM (WIDER IS BETTER FOR HIGH-RAINFALL OR LARGE-CATCHMENT VALLEYS). - ADVANTAGES: LIGHTER THAN LEAD; RIGID (DOES NOT REQUIRE THERMAL EXPANSION JOINTS IN THE SAME WAY); LOWER COST; NO LEADWORK SKILL REQUIRED FOR FITTING. GRP VALLEY TROUGH INSTALLATION IS WITHIN THE CAPABILITY OF AN EXPERIENCED ROOFER WITHOUT SPECIALIST LEADWORK TRAINING. - DISADVANTAGES: NOT AS LONG-LIVED AS LEAD (30-50 YEAR LIFESPAN VERSUS 60-100 YEARS FOR LEAD); LESS THERMALLY ADAPTIVE THAN LEAD (CAN BECOME BRITTLE IN EXTREME COLD); NOT SUITABLE FOR CONSERVATION AREAS WHERE LEAD IS SPECIFIED.

COMMON VALLEY GUTTER DEFECTS: 1. BLOCKED VALLEY: LEAVES, MOSS, AND DEBRIS ACCUMULATE IN THE VALLEY (PARTICULARLY SECRET GUTTERS) AND RESTRICT OR BLOCK WATER FLOW — WATER BACKS UP AND OVERFLOWS INTERNALLY. ANNUAL INSPECTION AND CLEARANCE (AUTUMN — AFTER LEAF FALL) IS ESSENTIAL. 2. CRACKED OR HOLED LEAD: THERMAL FATIGUE CRACKING AT DRIP FOLDS AND ALONG FOLD LINES (CODE 4 LEAD IN AN OPEN VALLEY SHOULD LAST 60-80 YEARS IF CORRECTLY INSTALLED — BUT INCORRECTLY DETAILED LEAD [WRONG CODE, NO DRIPS, OVER-LONG BAYS, PINNED THROUGH THE BODY OF THE LEAD RATHER THAN CLIPPED] WILL CRACK WITHIN 10-20 YEARS). 3. INADEQUATE UPSTAND HEIGHT: WHERE THE SECRET GUTTER UPSTANDS ARE TOO LOW (< 75MM), WATER OVERFLOWS IN HEAVY RAIN — REBUILDING THE VALLEY WITH A DEEPER GUTTER TROUGH IS THE ONLY PERMANENT FIX. 4. MORTAR BED FAILURE AT TILE EDGES: THE BEDDING MORTAR AT THE TILE EDGES IN AN OPEN VALLEY CRACKS AND ALLOWS WIND-DRIVEN RAIN UNDER THE TILE EDGES AND INTO THE VALLEY STRUCTURE. REPLACE WITH FLEXIBLE SEALANT (SIKAFLEX, BOSTIK CEMENTONE). 5. GRP TROUGH JOINT FAILURE: GRP TROUGHS ARE TYPICALLY INSTALLED IN SECTIONS WITH OVERLAP JOINTS — A FAILED JOINT (DRY BUTT JOINT — NO SEALANT OR FIBREGLASS TAPE) LEAKS. REPAIR: CLEAN THE JOINT AREA; APPLY GRP REPAIR KIT (FIBREGLASS MAT + POLYESTER RESIN — AVAILABLE FROM DEKS INDUSTRIES, EASY-COMPOSITES) OR APPLY FLEXIBLE SEALANT (GEOCEL 2300 CRYSTAL CLEAR BUTYL SEALANT).

VALLEY INSPECTION CHECKLIST (ANNUAL — AUTUMN): - CLEAR ALL DEBRIS FROM VALLEY (BRUSH OUT FROM RIDGE TO EAVES WITH A SOFT BRISTLE BROOM — DO NOT USE A METAL RAKE) - CHECK FOR CRACKED OR HOLED LEAD SECTIONS - CHECK MORTAR BEDDING AT TILE EDGES FOR CRACKING - CHECK ALL LEAD DRIPS AND EXPANSION JOINTS ARE INTACT - CONFIRM VALLEY IS CLEAR AND FREE-FLOWING (TEST WITH A BUCKET OF WATER FROM RIDGE LEVEL) - CHECK INTERNAL CEILING BELOW VALLEY FOR WATER STAINING

COSTS (SUPPLY AND FIT, LONDON 2025-2026): LEAD VALLEY REPLACEMENT (CODE 4 — OPEN VALLEY — PER M RUN, SUPPLY AND FIT): £120-250/M GRP VALLEY TROUGH REPLACEMENT (PER M RUN — SUPPLY AND FIT): £80-150/M VALLEY CLEARANCE AND REPOINTING (PER M RUN — LABOUR ONLY): £60-120/M SECRET GUTTER REPLACEMENT (CODE 4 LEAD — PER M RUN, SUPPLY AND FIT): £150-300/M