Wet Room Design and Installation for London Homes: Tanking, Drainage, Tiling, and Specification Guide

THE SPECIFICATION FOR A WET ROOM DIFFERS SIGNIFICANTLY DEPENDING ON WHETHER THE FLOOR IS CONCRETE (SOLID SLAB — COMMON IN GROUND-FLOOR BATHROOMS IN LONDON EXTENSIONS AND CONVERSIONS) OR TIMBER (SUSPENDED TIMBER FLOOR CONSTRUCTION — UNIVERSAL IN UPPER FLOORS OF LONDON VICTORIAN TERRACES).

WET ROOMS ON CONCRETE FLOORS (SIMPLER — INHERENTLY RIGID SUBSTRATE): FOR WET ROOMS ON GROUND-FLOOR CONCRETE SLABS OR UPPER-FLOOR CONCRETE DECKS (COMMON IN POST-WAR LONDON FLATS AND CONCRETE-FRAME BUILDINGS), THE CONCRETE PROVIDES A RIGID, NON-DEFLECTING SUBSTRATE THAT IS IDEAL FOR TILE ADHESIVE AND TANKING SYSTEMS. THE WATERPROOFING CAN BE APPLIED DIRECTLY TO THE CONCRETE SLAB (AFTER PRIMING) WITHOUT THE NEED FOR A STRUCTURAL BACKER BOARD LAYER. PREPARATION: GRIND DOWN ANY PROTRUSIONS, FILL CRACKS OR HOLLOWS WITH MAPEI MAPEGROUT SUPERFINE OR SIMILAR FLOWABLE GROUT, APPLY PRIMER (MAPEI PRIMER L) BEFORE APPLYING TANKING MEMBRANE.

WET ROOMS ON TIMBER FLOORS (MORE COMPLEX — REQUIRES RIGID SUBSTRATE LAYER): FOR UPPER-FLOOR BATHROOMS IN LONDON VICTORIAN TERRACES (TYPICALLY 38MM TONGUE AND GROOVE SOFTWOOD BOARDS ON 200MM X 50MM JOISTS AT 400MM CENTRES), THE EXISTING TIMBER FLOOR STRUCTURE MUST BE UPGRADED BEFORE A WET ROOM CAN BE INSTALLED. TIMBER FLOORS DEFLECT UNDER LOAD — EVEN SMALL DEFLECTIONS (1 TO 2MM) IN A TILED WET ROOM FLOOR WILL CAUSE GROUT AND TILE ADHESIVE CRACKING, EVENTUALLY DEFEATING THE WATERPROOFING. MINIMUM UPGRADE FOR TIMBER FLOOR WET ROOM: ADDITIONAL NOGGINGS (TIMBER BLOCKING) BETWEEN JOISTS AT 400MM MAXIMUM CENTRES. 18MM OR 22MM MOISTURE-RESISTANT PLYWOOD (WBPA B-BOND MARINE PLYWOOD OR KRONOSPAN OPTIFORM WR) SCREWED TO JOISTS AT 150MM CENTRES. TOTAL UPGRADED FLOOR RIGIDITY SHOULD TARGET L/360 DEFLECTION UNDER DESIGN LOAD — STRUCTURAL ENGINEER TO CONFIRM FOR HEAVIER TILE SPECIFICATIONS.

THE WATERPROOFING SYSTEM IS THE CRITICAL TECHNICAL ELEMENT OF A WET ROOM INSTALLATION — FAILURE OF THE WATERPROOFING IS CATASTROPHIC AND THE DEFECT MAY NOT BE VISIBLE UNTIL SIGNIFICANT STRUCTURAL DAMAGE HAS OCCURRED.

WEDI BOARD SYSTEM (CEMENTITIOUS FOAM SUBSTRATE BOARDS — INTEGRATED WATERPROOFING): WEDI BOARD IS A RIGID CEMENTITIOUS FOAM PANEL (EXTRUDED POLYSTYRENE CORE WITH GLASS-FIBRE REINFORCED CEMENT SKIN) DESIGNED AS AN INTEGRATED SUBSTRATE AND WATERPROOFING SYSTEM FOR WET AREAS. WEDI BOARD IS FULLY WATERPROOF — THE PANEL ITSELF IS IMPERMEABLE, AND JOINTS AND PENETRATIONS ARE SEALED WITH WEDI FIXING COMPOUND AND WEDI SEALING BAND. WEDI BOARD ADVANTAGES: NO SEPARATE TANKING MEMBRANE REQUIRED (THE BOARD IS THE WATERPROOFING). RIGID, STABLE SUBSTRATE FOR TILES. LIGHTWEIGHT (COMPARED TO TILE BACKER BOARD + SEPARATE TANKING). CAN BE USED ON WALLS AND FLOOR. WEDI BOARD IS THE PREMIUM WET ROOM SUBSTRATE CHOICE FOR LONDON BATHROOMS.

MAPEI MAPELASTIC SMART (FLEXIBLE CEMENTITIOUS TANKING MEMBRANE — THE MOST WIDELY SPECIFIED WET ROOM TANKING IN LONDON): MAPEI MAPELASTIC SMART IS A RAPID-SETTING FLEXIBLE TWO-COMPONENT CEMENTITIOUS WATERPROOF COATING. COMPONENT A (POWDER — CEMENT, AGGREGATES, POLYMERS) AND COMPONENT B (POLYMER DISPERSION) ARE MIXED AND APPLIED BY BRUSH OR ROLLER IN TWO COATS TO THE PRIMED SUBSTRATE (CONCRETE, PLASTERBOARD TILE BACKER, OR HARDIE BACKER). MAPELASTIC TAPE IS BEDDED INTO THE FIRST COAT AT ALL WALL/FLOOR JUNCTIONS AND AT PIPE PENETRATIONS — THESE ARE THE CRITICAL DETAILS WHERE MOST TANKING FAILURES OCCUR. MINIMUM COVERAGE: 2.0 KG/M² (TWO COATS) — FOLLOW MAPEI DATA SHEETS. ONCE SET (TYPICALLY 4 HOURS TO TACK-FREE, 24 HOURS TO FULL SET), THE MAPELASTIC COATING IS FULLY WATERPROOF AND TILES CAN BE APPLIED OVER IT WITH MAPEI KERAFLEX MAXI S1 (FLEXIBLE S1 ADHESIVE) OR MAPEI GRANIRAPID (TWO-COMPONENT RAPID SET ADHESIVE FOR LARGE-FORMAT TILES).

BAL TANKING SLURRY (ALTERNATIVE CEMENTITIOUS WATERPROOFING): BAL TANKING SLURRY IS A SINGLE-COMPONENT CEMENTITIOUS WATERPROOFING PRODUCT — MIXED WITH WATER AND APPLIED IN TWO COATS BY BRUSH. SLIGHTLY LOWER PERFORMANCE THAN MAPEI MAPELASTIC IN TERMS OF FLEXIBILITY (LESS CRACK-BRIDGING ABILITY) BUT WIDELY USED AND COST-EFFECTIVE. BAL WATERSEAL FLEECE TAPE MUST BE USED AT ALL JUNCTIONS FOR BEST PRACTICE.

GETTING THE WET ROOM DRAINAGE SYSTEM RIGHT IS AS IMPORTANT AS THE WATERPROOFING — A POORLY DRAINING WET ROOM CREATES STANDING WATER, UNHYGIENIC CONDITIONS, AND ACCELERATED GROUT FAILURE.

POINT DRAIN (FLOOR WASTE, CENTRED IN FLOOR): THE SIMPLEST DRAINAGE APPROACH — A SINGLE POINT DRAIN IN THE CENTRE (OR LOWEST POINT) OF THE SHOWER AREA. TILES ARE GRADED FROM ALL FOUR SIDES TO THE CENTRAL POINT. IMPEY AQUA-DEC LINEAR EVO POINT DRAIN (80MM GRATING, 40MM TRAP DEPTH, 40MM WATER SEAL) IS A POPULAR CHOICE FOR LONDON WET ROOMS — AVAILABLE IN STAINLESS STEEL, CHROME, AND BRUSHED GOLD. GRADIENT REQUIRED: MINIMUM 1:80 (12.5MM FALL PER METRE) FROM ALL SIDES TO THE DRAIN — THIS IS THE MINIMUM FOR SELF-DRAINING; STEEPER GRADIENT (1:60 — 16.7MM FALL PER METRE) IS PREFERRED WHERE POSSIBLE FOR FASTER DRAINAGE.

LINEAR DRAIN (CHANNEL DRAIN ALONG ONE WALL — THE MODERN SPECIFICATION FOR HIGH-END LONDON BATHROOMS): ACO SHOWERDRAIN AND IMPEY AQUA-DEC LINEAR EVO CHANNEL DRAINS ARE SPECIFIED FOR CONTEMPORARY LONDON MASTER BATHROOM WET ROOMS. A LINEAR DRAIN ALONG ONE WALL (TYPICALLY THE WALL OPPOSITE THE ENTRY) ALLOWS THE ENTIRE FLOOR TO BE GRADED IN ONE DIRECTION (TOWARDS THE LINEAR DRAIN) — THIS MEANS LARGE-FORMAT TILES (600MM X 600MM, 1200MM X 600MM) CAN BE USED WITHOUT MULTIPLE CUTS FOR GRADIENT CHANGES, PRODUCING A CLEANER AESTHETIC. ACO SHOWERDRAIN 585MM LENGTH STAINLESS STEEL GRATE: THE MOST COMMONLY SPECIFIED LONDON WET ROOM LINEAR DRAIN — CONNECTIONS TO 40MM WASTE PIPE, AVAILABLE WITH TILE-IN GRATE (TILE INSERT SET FLUSH WITH GRATE FOR INVISIBLE DRAIN EFFECT).

IMPEY AQUA-DEC LEVEL FLOOR SYSTEM: FOR ACCESSIBLE WET ROOMS TARGETING LEVEL ACCESS (PART M OF BUILDING REGULATIONS — REQUIRED IN NEW DWELLINGS, RECOMMENDED IN ACCESSIBLE RENOVATION), THE IMPEY AQUA-DEC LEVEL FLOOR SYSTEM (800MM X 1000MM OR 900MM X 900MM SHOWER TRAY AS A WETROOM FORMER) PROVIDES A PRE-FORMED SLOPED FLOOR ELEMENT WITH A BUILT-IN GRADIENT TO A CENTRAL OR LINEAR DRAIN — PRE-FORMED TO ACHIEVE THE CORRECT 1:60 FALL WITHOUT SAND-CEMENT SCREEDING.

TILE SELECTION FOR WET ROOM FLOORS IS SUBJECT TO ANTI-SLIP REQUIREMENTS THAT DO NOT APPLY IN DRY AREAS.

ANTI-SLIP RATING FOR WET ROOM FLOORS: THE EUROPEAN CLASSIFICATION FOR SLIP RESISTANCE IS RAMP TEST RATING (R-VALUE) — WET ROOM AND SHOWER FLOORS REQUIRE A MINIMUM R10 RATING (MEASURED BY DIN 51130 TEST ON DRY AND WET SURFACES AT GRADUATED RAMP INCLINES). FOR BAREFOOT WET AREAS (SHOWERS, WET ROOMS, SWIMMING POOLS), THE ADDITIONAL BAREFOOT RATING (A, B, C) IS RELEVANT — SHOWER FLOORS SHOULD HAVE A MINIMUM "B" BAREFOOT CLASSIFICATION. MOST PORCELAIN TILES MARKETED FOR WET ROOM FLOOR USE IN THE UK CARRY R10 MINIMUM RATING. NATURAL STONE (MARBLE, LIMESTONE) IN WET ROOMS REQUIRES HONING OR TUMBLING (NOT POLISHED FINISH) FOR ADEQUATE SLIP RESISTANCE.

POPULAR WET ROOM FLOOR TILES FOR LONDON BATHROOMS: PORCELAIN 300MM X 300MM R10 TILES (MANDARIN STONE, PORCELANOSA — COMPACT FORMAT AIDS GRADIENT CUTTING). PATTERNED ENCAUSTIC TILES (100MM X 100MM CEMENT TILES — POPULAR FOR LONDON VICTORIAN-STYLE BATHROOMS). LARGE FORMAT PORCELAIN SLABS (PORCELANOSA URBATEK 1200MM X 600MM WITH SPECIAL ANTI-SLIP SURFACE TREATMENT — FOR CONTEMPORARY MASTER BATHROOMS WITH LINEAR DRAIN).

WET ROOM WALL TILES: WALL TILES IN A WET ROOM DO NOT NEED ANTI-SLIP RATING. LARGE FORMAT TILES (600MM X 1200MM OR EVEN FULL-HEIGHT SLABS) WITH MINIMAL GROUT JOINTS ARE POPULAR FOR LONDON HIGH-SPECIFICATION BATHROOMS — REDUCING CLEANING AND PROVIDING A SEAMLESS APPEARANCE. MINIMUM ADHESIVE SPECIFICATION FOR WET ROOMS: S1 FLEXIBLE ADHESIVE (MAPEI KERAFLEX MAXI OR BAL RAPIDFLEX ALL-WEATHER FLEXIBLE) — NOT STANDARD CEMENT-BASED ADHESIVE. GROUT SPECIFICATION: MAPEI ULTRACOLOR PLUS FA (FLEXIBLE, ANTI-MOULD) OR BAL MICROMAX2 (FLEXIBLE ANTI-MOULD GROUT) — NEVER STANDARD UNSANDED GROUT IN A WET ROOM.

FOR LONDON HOME RENOVATIONS CREATING NEW BATHROOMS OR WET ROOMS, BUILDING REGULATIONS PART M (ACCESS TO AND USE OF BUILDINGS) MAY APPLY.

WHEN PART M APPLIES: FOR NEWLY BUILT DWELLINGS (NEW EXTENSIONS CREATING NEW DWELLING UNITS, NEW HOUSES): PART M CATEGORY 1 (VISITABLE DWELLINGS — MANDATORY FOR ALL NEW DWELLINGS) REQUIRES A MINIMUM 750MM WIDE DOOR OPENING TO AT LEAST ONE WC (OR BATHROOM) ON THE ENTRY LEVEL, AND A SHOWER OR BATH THAT IS ACCESSIBLE. PART M CATEGORY 2 (ACCESSIBLE AND ADAPTABLE DWELLINGS) REQUIRES A LEVEL-ACCESS SHOWER ON THE ENTRY LEVEL (NO STEP OVER A SHOWER TRAY). FOR EXISTING DWELLINGS BEING RENOVATED (THE MAJORITY OF LONDON EXTENSION AND REFURBISHMENT PROJECTS): PART M DOES NOT STRICTLY APPLY — BUT ITS PROVISIONS ARE ENCOURAGED AS GOOD DESIGN PRACTICE BY MANY LONDON BOROUGHS, AND THE ADOPTION OF LEVEL-ACCESS WET ROOMS IN LONDON RENOVATION ADDS ACCESSIBILITY AND FUTURE-PROOFS THE HOME FOR CHANGING NEEDS.

LEVEL ACCESS THRESHOLD DETAIL: FOR A PART M-COMPLIANT LEVEL-ACCESS WET ROOM, THE TRANSITION FROM THE BATHROOM FLOOR OUTSIDE THE SHOWER ZONE TO THE SHOWER ZONE FLOOR MUST BE EITHER FLUSH (LEVEL — PREFERRED) OR WITH A MAXIMUM 15MM TRANSITION STRIP. ACHIEVING A LEVEL THRESHOLD ACROSS THE ENTIRE FLOOR (RATHER THAN ONLY THE SHOWER ZONE) REQUIRES CAREFUL LEVEL MANAGEMENT FROM THE START OF THE STRUCTURAL FLOOR PREPARATION.

WET ROOM INSTALLATION COSTS IN LONDON VARY CONSIDERABLY BASED ON SUBSTRATE TYPE, SPECIFICATION LEVEL, AND TILE CHOICE.

WET ROOM ON CONCRETE FLOOR (INCLUDING MAPEI MAPELASTIC TANKING, POINT DRAIN, 300X300 R10 PORCELAIN TILE, ALL ADHESIVES AND GROUTS, SUPPLY AND INSTALL): £150 TO £250 PER M² FOR THE WETTED ZONE (FLOOR AREA + WALLS TO 1.5M HEIGHT WITHIN SHOWER ZONE). THIS EXCLUDES: PLUMBING CONNECTIONS, SHOWER VALVE, VANITY/SANITARYWARE, OR STRUCTURAL FLOOR MODIFICATIONS.

WET ROOM ON TIMBER FLOOR (INCLUDING STRUCTURAL UPGRADE PLYWOOD OVERLAY, WEDI BOARD SYSTEM OR TILE BACKER + MAPELASTIC, LINEAR ACO DRAIN, LARGE FORMAT PORCELAIN FLOOR + WALL TILES, SUPPLY AND INSTALL): £250 TO £450 PER M² FOR THE WETTED ZONE.

TYPICAL LONDON MASTER BATHROOM WET ROOM (3M² SHOWER ZONE — TIMBER FLOOR UPGRADE + WEDI BOARD + ACO LINEAR DRAIN + LARGE FORMAT PORCELAIN + FRAMELESS SCREEN): £2,500 TO £6,500 FOR THE WET ROOM ELEMENT ONLY. FULL BATHROOM INCLUDING SANITARYWARE, SHOWER VALVE, HEATED TOWEL RAIL, VANITY, AND WET ROOM: ADD £3,000 TO £8,000 DEPENDING ON SPECIFICATION.