Concrete Roof Tiles on London Victorian Terraces: Replacement, Repair, and Re-Roofing Advice

HOW TO IDENTIFY CONCRETE INTERLOCKING TILES ON A LONDON VICTORIAN TERRACE: - PROFILE: CONCRETE INTERLOCKING TILES ARE LARGER THAN TRADITIONAL CLAY PLAIN TILES (TYPICALLY 420MM × 330MM — ABOUT 12-16 TILES/M² VERSUS 60 PLAIN TILES/M²). THEY HAVE AN INTERLOCKING PROFILE (S-CURVE OR FLAT DOUBLE-LAP INTERLOCK) AT THE SIDES AND TOP. - COLOUR: ORIGINAL CONCRETE TILES WERE OFTEN A DARK GREY (MARLEY LUDLOW MAJOR GREY — THE MOST COMMON COLOUR ON 1960S-1980S RE-ROOFED LONDON TERRACES) OR A TERRACOTTA-EFFECT COLOUR FADED BY UV EXPOSURE. CONCRETE TILES THAT HAVE LOST THEIR SURFACE PIGMENT AND APPEAR GREY-WHITE OR MOTTLE-BLEACHED ARE LIKELY LATE IN THEIR LIFE. - WEIGHT: CONCRETE TILES ARE SIGNIFICANTLY HEAVIER THAN CLAY PLAIN TILES — APPROXIMATELY 45-55KG/M² FOR STANDARD CONCRETE INTERLOCKING (VERSUS 28-38KG/M² FOR CLAY PLAIN TILE AND 20-25KG/M² FOR FIBRE CEMENT SLATE). ON A LONDON VICTORIAN TERRACE, A CONCRETE TILE RE-ROOFING FROM THE 1970S MEANS THE ROOF STRUCTURE HAS BEEN CARRYING AN ELEVATED LOAD FOR 40-50 YEARS — INSPECT THE PURLINS AND RAFTER FEET CAREFULLY WHEN REMOVING CONCRETE TILES.

COMMON DEFECTS IN CONCRETE TILES NEAR END OF LIFE: 1. SURFACE EROSION AND LOSS OF GRANULE LAYER: THE SURFACE FINISH OF A CONCRETE TILE (A CEMENT SLURRY WITH MINERAL PIGMENT) WEATHERS AND ERODES OVER TIME — PARTICULARLY ON SOUTH-FACING SLOPES WITH HIGH UV EXPOSURE. THE SURFACE BECOMES ROUGH AND POROUS, WATER ABSORPTION INCREASES, AND FREEZE-THAW CYCLING IN LONDON WINTERS BEGINS TO SPALL AND DELAMINATE THE TILE FACE. VISUAL INDICATOR: WHITE OR LIGHT-GREY PATCHES ON TILES WHERE THE SURFACE GRANULE HAS GONE; ROUGH TEXTURE ON TILE FACE. 2. BREAKAGE: CONCRETE TILES BECOME MORE BRITTLE WITH AGE. FOOT TRAFFIC ON THE ROOF (FOR AERIAL WORKS, CHIMNEY MAINTENANCE, ETC.) CRACKS TILES THAT A NEWER TILE WOULD RESIST. THE NIBS (FIXING POINTS MOULDED INTO THE TOP OF THE TILE) CAN BREAK — THE TILE THEN RELIES ENTIRELY ON THE DOWNSLOPE INTERLOCK TO PREVENT WIND UPLIFT. 3. ORGANIC GROWTH: CONCRETE TILE SURFACES SUPPORT LICHEN, ALGAE, AND MOSS GROWTH MORE READILY THAN CLAY OR SLATE AFTER THEIR SURFACE SEAL IS LOST. MOSS RETAINS MOISTURE AGAINST THE TILE AND ACCELERATES FREEZE-THAW SPALLING. TREATMENT: BIOCIDE WASH (NEVER HIGH-PRESSURE WASH — THIS ACCELERATES SURFACE EROSION); ALLOW 2-3 MONTHS FOR DIE-BACK. 4. MORTAR RIDGE AND HIP BEDDING FAILURE: CONCRETE TILES USE MORTAR-BEDDED RIDGE AND HIP TILES SIMILAR TO CLAY TILES — THE MORTAR FAILS AFTER 15-25 YEARS AND MUST BE RE-BEDDED (OR CONVERTED TO FLEXIBLE COMPOUND MECHANICAL FIX SYSTEM — SEE RIDGE TILE GUIDE). RE-BEDDING THE MORTAR ON A CONCRETE TILE ROOF TYPICALLY COSTS £500-1,500 FOR A LONDON VICTORIAN TERRACE AND BUYS 10-15 YEARS MORE LIFE IF THE TILES THEMSELVES ARE STILL SOUND.

REPAIR VS REPLACEMENT DECISION: - REPLACE LESS THAN 10-15% OF TILES + SOUND SURFACE: REPAIR (INDIVIDUAL TILE REPLACEMENT — £50-100/TILE SUPPLY AND FIT) - 20-30%+ TILES DEFECTIVE OR SURFACE HEAVILY ERODED: RE-ROOF

RE-ROOFING FROM CONCRETE TILES — MATERIAL CHOICES: WHEN CONCRETE TILES ON A LONDON VICTORIAN TERRACE REACH END OF LIFE, THE RE-ROOFING IS AN OPPORTUNITY TO CHANGE BACK TO A PERIOD-APPROPRIATE MATERIAL: 1. CLAY PLAIN TILES (THE ORIGINAL VICTORIAN SPECIFICATION): - HANDMADE CLAY PLAIN TILES (265MM × 165MM): THE ORIGINAL VICTORIAN TERRACE SPECIFICATION. MANUFACTURERS: KEYMER, DREADNOUGHT, SANDTOFT HATHERSAGE, LIFESTILES. COLOUR: RED, MULTI-BLUE, BRINDLE (MARBLED RED/BLUE). COST: £70-140/M² SUPPLY ONLY (HANDMADE) — 3-5× MORE EXPENSIVE THAN CONCRETE TILES. - MACHINE-MADE CLAY PLAIN TILES (265MM × 165MM): CHEAPER THAN HANDMADE BUT MORE UNIFORM IN APPEARANCE. SANDTOFT SHIRE PLAIN, REDLAND PLAIN TILE, MARLEY ACME. COST: £30-60/M² SUPPLY ONLY. - WEIGHT: CLAY PLAIN TILES AT 28-38KG/M² ARE LIGHTER THAN CONCRETE INTERLOCKING (45-55KG/M²) BUT REQUIRE A CLOSER RAFTER SPACING AND MORE BATTENS (60 TILES/M² VERSUS 12-16 FOR CONCRETE INTERLOCKING) — THE BATTEN COUNT INCREASES SIGNIFICANTLY. - CONSERVATION AREA: CLAY PLAIN TILES ARE THE PREFERRED SPECIFICATION FOR RE-ROOFING A LONDON VICTORIAN TERRACE IN A CONSERVATION AREA. CONSERVATION OFFICERS OFTEN REQUIRE LIKE-FOR-LIKE (CLAY PLAIN TILE) REPLACEMENT WHEN RE-ROOFING IN A CONSERVATION AREA — EVEN IF THE PREVIOUS COVERING WAS CONCRETE.

2. FIBRE CEMENT SLATE: - FIBRE CEMENT SLATE IS A FACTORY-PRODUCED SLATE-FORMAT TILE (TYPICALLY 600MM × 300MM OR 500MM × 250MM, 5-7MM THICK) THAT REPLICATES THE APPEARANCE OF NATURAL WELSH SLATE AT LOWER COST. MANUFACTURERS: ETERNIT CEDRAL (FORMERLY SLATEX), MARLEY CEDRAL FIBRE CEMENT, BORAL. - WEIGHT: 20-25KG/M² — LIGHTER THAN BOTH CONCRETE AND CLAY PLAIN TILE. IMPORTANT FOR VICTORIAN ROOF STRUCTURES WHERE THE PURLIN AND RAFTER SIZES WERE CALCULATED FOR NATURAL SLATE (THE ORIGINAL SPECIFICATION ON MANY LONDON VICTORIAN TERRACES). - CONSERVATION AREA: FIBRE CEMENT SLATE IS GENERALLY NOT ACCEPTED AS A LIKE-FOR-LIKE REPLACEMENT IN CONSERVATION AREAS (WHERE CLAY PLAIN TILE OR NATURAL SLATE IS EXPECTED) BUT MAY BE ACCEPTABLE IN NON-CONSERVATION AREA APPLICATIONS.

3. CONCRETE INTERLOCKING TILES (LIKE-FOR-LIKE): - NEW CONCRETE TILES (MARLEY LUDLOW MAJOR, REDLAND 49, SANDTOFT CONTINENTAL) OFFER A LOWER-COST RE-ROOF OPTION. LIFESPAN: 50-60 YEARS. WEIGHT: 42-50KG/M². CHECK THE ROOF STRUCTURE CAN CARRY THE LOAD BEFORE SPECIFYING — ESPECIALLY IF THE EXISTING PURLINS OR RAFTER FEET HAVE BEEN WEAKENED BY AGE.

COSTS (SUPPLY AND FIT, LONDON 2025-2026): INDIVIDUAL CONCRETE TILE REPLACEMENT (SUPPLY AND FIT PER TILE): £50-100 RIDGE RE-BED (MORTAR, PER LONDON VICTORIAN TERRACE): £500-1,500 FULL RE-ROOF IN CLAY PLAIN TILE (HANDMADE — PER M², SUPPLY AND FIT): £150-250 FULL RE-ROOF IN MACHINE-MADE CLAY PLAIN TILE (PER M², SUPPLY AND FIT): £80-150 FULL RE-ROOF IN FIBRE CEMENT SLATE (PER M², SUPPLY AND FIT): £60-120 FULL RE-ROOF IN CONCRETE INTERLOCKING (PER M², SUPPLY AND FIT): £60-100 TYPICAL LONDON VICTORIAN TERRACE REAR SLOPE RE-ROOF (35-45M²): £3,000-11,000 DEPENDING ON MATERIAL