Patio and Hard Landscaping for London Gardens: York Stone, Porcelain, Indian Sandstone, and SuDS Guide

THE CHOICE OF PAVING MATERIAL IS THE MOST SIGNIFICANT AESTHETIC DECISION IN A PATIO PROJECT. THE THREE MAIN CATEGORIES FOR LONDON RESIDENTIAL GARDENS ARE NATURAL STONE (YORKSHIRE SANDSTONE, INDIAN SANDSTONE), PORCELAIN, AND CONCRETE BLOCK PAVING.

YORK STONE (RECLAIMED): YORKSHIRE SANDSTONE — COLLOQUIALLY "YORK STONE" — IS A FINE-GRAINED BUFF-TO-GREY CARBONIFEROUS SANDSTONE QUARRIED IN YORKSHIRE. RECLAIMED YORK STONE (SALVAGED FROM VICTORIAN PAVEMENTS) IS THE PREMIUM PAVING MATERIAL FOR PERIOD LONDON PROPERTIES — ITS COLOUR, TEXTURE, AND WEATHERED CHARACTER ARE UNIQUELY APPROPRIATE FOR VICTORIAN TERRACES. RECLAIMED YORK STONE SLABS ARE TYPICALLY 75MM TO 100MM THICK, IRREGULAR IN SIZE (RANDOM SETTS OR RECTANGULAR CUT FLAGS), AND ARE SOLD BY M'. SUPPLIERS IN LONDON: MILES STONE (HARLOW), ANTIQUE STONEWORKS (HORSHAM), LONDON STONE (SURREY/LONDON SHOWROOM). RECLAIMED YORK STONE: £60 TO £130 PER M' (MATERIAL ONLY) DEPENDING ON QUALITY, SIZE, AND WEATHERING GRADE.

INDIAN SANDSTONE (SAWN/TUMBLED): IMPORTED NATURAL SANDSTONE FROM RAJASTHAN, INDIA IS THE HIGHEST-VOLUME NATURAL STONE PAVING IN THE UK MARKET. THE MAIN TYPES USED IN LONDON RESIDENTIAL GARDENS ARE: BRETT BALMORAL (RIVEN-FACED MULTI-BUFF, 22MM THICK, 600X600/600X900MM), GLOBAL STONE COUNTY (SAWN KANDLA GREY, 22MM, LARGE FORMAT 900X600MM), AND STONEMASTER NATURA (MINT FOSSIL, 20MM, HIGHLY POLISHED — LESS APPROPRIATE FOR EXTERNAL USE IN LONDON'S CLAY GARDEN CONDITIONS WHERE SLIP RESISTANCE MATTERS). INDIAN SANDSTONE: £25 TO £65 PER M' (MATERIAL) DEPENDING ON QUALITY, FINISH, AND SUPPLIER.

PORCELAIN (LARGE-FORMAT, 20MM OUTDOOR): PORCELAIN PAVING HAS GROWN DRAMATICALLY IN POPULARITY FOR LONDON RESIDENTIAL GARDENS OVER THE PAST 10 YEARS. FULLY VITRIFIED PORCELAIN (VERY LOW WATER ABSORPTION — TYPICALLY BELOW 0.1%) IS HIGHLY STAIN-RESISTANT, FROST-PROOF, DOES NOT REQUIRE SEALING, AND WILL NOT SUPPORT ALGAE GROWTH AS READILY AS NATURAL SANDSTONE IN SHADED LONDON GARDENS. THICKNESS FOR OUTDOOR PEDESTRIAN USE: 20MM MINIMUM. POPULAR PRODUCTS: STONEMASTER MANHATTAN ANTHRACITE (600X900MM, 20MM, TEXTURED FINISH, R11 SLIP RATING), GLOBAL STONE PATIO-SMOOTH LUNAR GREY (600X600MM, 20MM), MARSHALLS SYMPHONY PORCELAIN (600X900MM AND 900X450MM MIXED PACKS). PORCELAIN: £30 TO £80 PER M' (MATERIAL) DEPENDING ON FORMAT, BRAND, AND FINISH.

THE LONG-TERM PERFORMANCE OF A PATIO IN LONDON DEPENDS AS MUCH ON THE UNSEEN SUB-BASE CONSTRUCTION AS ON THE QUALITY OF THE PAVING MATERIAL ABOVE. LONDON'S PREDOMINANTLY CLAY SOIL IS PARTICULARLY PRONE TO SEASONAL MOVEMENT (EXPANSION IN WET WEATHER, SHRINKAGE IN DRY SUMMER — PARTICULARLY SEVERE DURING THE LONDON CLAY SHRINKAGE INCIDENTS OF 2022). A CORRECTLY ENGINEERED SUB-BASE MITIGATES DIFFERENTIAL SETTLEMENT OF THE PAVING.

THE STANDARD SUB-BASE SPECIFICATION FOR A LONDON RESIDENTIAL PATIO IS AS FOLLOWS.

EXCAVATION: EXCAVATE TO A MINIMUM DEPTH OF 150MM BELOW THE PROPOSED FINISHED PAVING LEVEL FOR A PURELY PEDESTRIAN PATIO. WHERE LIGHT VEHICLE ACCESS IS REQUIRED (MOTORBIKE, WHEELBARROW ACCESS FROM SIDE GATE), EXCAVATE TO 200MM MINIMUM AND INCREASE SUB-BASE THICKNESS.

TYPE 1 SUB-BASE: LAY 100MM (MINIMUM) COMPACTED MOT TYPE 1 GRANULAR FILL (CRUSHED LIMESTONE OR RECYCLED CONCRETE AGGREGATE GRADED 0 TO 63MM, BS EN 13242 GRADE A). COMPACT WITH A VIBRATING PLATE COMPACTOR IN TWO OR MORE PASSES. LONDON CLAY GARDENS WITH KNOWN TREE ROOT INFLUENCE: INCREASE TO 150MM COMPACTED TYPE 1 AND CONSIDER A GEOTEXTILE SEPARATION MEMBRANE (TERRAM T1000 OR EQUIVALENT) BETWEEN THE SUBGRADE AND TYPE 1 TO PREVENT FINES MIGRATION.

BEDDING LAYER: FOR NATURAL STONE (YORK STONE, INDIAN SANDSTONE): 25MM TO 40MM SEMI-DRY MORTAR BED (3:1 SHARP SAND:CEMENT, DRY CONSISTENCY — DOES NOT SLUMP), LEVELLED AND SCREEDED TO THE CORRECT FALLS. THE STONE SLABS ARE TAPPED DOWN INTO THE SEMI-DRY BED AND THE JOINTS ARE FILLED WITH POINTING MORTAR (1:4 OR 1:5 CEMENT:SHARP SAND) AFTER ALLOWING THE BED TO CURE.

FOR PORCELAIN (WHICH REQUIRES A DIFFERENT APPROACH DUE TO ITS LOW ABSORPTION AND SMOOTH BACK FACE): FULL-BED FLEXIBLE ADHESIVE MORTAR (SBR-MODIFIED POLYMER TILE ADHESIVE) OR SEMI-DRY MORTAR BED WITH A PRIMED PORCELAIN BACK (BAL PRIME APD PRIMER OR MAPEI PRIMER SG) TO IMPROVE ADHESION. THE BACK OF THE PORCELAIN TILE MUST BE FULLY COVERED (95%+ COVERAGE) — BRIDGING OR SPOT FIXING WILL ALLOW WATER INGRESS AND FROST CRACKING.

SINCE OCTOBER 2008, PERMITTED DEVELOPMENT RIGHTS FOR FRONT DRIVEWAYS IN ENGLAND WERE CHANGED UNDER THE TOWN AND COUNTRY PLANNING (GENERAL PERMITTED DEVELOPMENT) (AMENDMENT) (NO. 2) (ENGLAND) ORDER 2008 TO REQUIRE THAT NEW HARD SURFACES OVER 5M' IN FRONT GARDENS ARE PERMEABLE OR DRAIN TO A PERMEABLE SURFACE, OR THAT PLANNING PERMISSION IS OBTAINED.

SUDS (SUSTAINABLE URBAN DRAINAGE SYSTEMS) PRINCIPLES: SuDS DESIGN AIMS TO MANAGE SURFACE WATER RUNOFF AS CLOSE TO THE SOURCE AS POSSIBLE — SLOWING THE RATE OF RUNOFF, REDUCING THE PEAK FLOW TO DRAINS AND WATERCOURSES, AND WHERE POSSIBLE PROMOTING INFILTRATION INTO THE GROUND. IN DENSE LONDON CLAY AREAS, INFILTRATION IS LIMITED, AND THE PRIMARY SuDS MEASURE IS PERMEABLE PAVING.

PERMEABLE PAVING OPTIONS FOR LONDON: BLOCK PAVING WITH 3MM TO 6MM GAPS (FILLED WITH SINGLE-SIZE GRAVEL RATHER THAN MORTAR): STANDARD 60MM CONCRETE BLOCK PAVING (MARSHALLS DRIVESETT TEGULA, BRETT OMEGA) WITH OPEN JOINTS ALLOWS WATER TO DRAIN BETWEEN THE BLOCKS INTO A FREE-DRAINING SINGLE-SIZE GRANULAR SUB-BASE (50MM TYPE 3 OPEN-GRADED AGGREGATE OVER 200MM TYPE 4 OR SuDS-SPECIFIC PERMEABLE SUB-BASE). PERMEABLE CONCRETE BLOCK PAVING (PCBP) SYSTEMS: SPECIALLY DESIGNED INTERLOCKING BLOCKS WITH INTEGRAL GAPS (E.G., MARSHALLS PRIORA, BRETT AQUAFLOW) HAVE LARGER AND MORE CONSISTENT OPENINGS THAN STANDARD BLOCK PAVING AND PROVIDE HIGHER INFILTRATION RATES.

PORCELAIN AND NATURAL STONE ON A LONDON REAR PATIO: THE SuDS REQUIREMENT FOR FRONT DRIVEWAYS DOES NOT APPLY TO REAR GARDENS (WHICH DO NOT ACCESS THE PUBLIC HIGHWAY). HOWEVER, ALL SURFACE WATER FROM A REAR PATIO MUST BE MANAGED — IT CANNOT BE DIRECTED TO THE FOUL SEWER (WHICH IN LONDON COMBINED SEWER AREAS OVERFLOWS DURING HEAVY RAINFALL). PATIO DRAINAGE DESIGN FOR LONDON REAR GARDENS: CREATE A CONSISTENT FALL OF 1:80 TO 1:40 (1.25% TO 2.5%) AWAY FROM THE HOUSE; COLLECT WATER IN A CHANNEL DRAIN (ACO CLASSIC OR MARSHALLS ALBANY LINEAR DRAIN) AT THE GARDEN END OF THE PATIO; DISCHARGE INTO A SOAKAWAY CRATE (POLYPIPE STORMCELL, WAVIN AQUACELL) EXCAVATED INTO THE GARDEN LAWN AREA WHERE CLAY CONDITIONS PERMIT, OR INTO THE SURFACE WATER DRAIN (NOT THE FOUL DRAIN).

SURFACE WATER DRAINAGE IS ONE OF THE MOST OVERLOOKED ASPECTS OF PATIO CONSTRUCTION IN LONDON — INADEQUATE DRAINAGE LEADS TO STANDING WATER, ALGAE GROWTH, FROST DAMAGE, AND WATER INGRESS TO THE HOUSE AT THE THRESHOLD.

GRADIENT FALLS: THE MINIMUM GRADIENT FOR SURFACE WATER TO DRAIN EFFECTIVELY FROM A PATIO IS 1:80 (1.25%). IN PRACTICE, 1:60 (1.67%) IS PREFERABLE FOR NATURAL STONE TO ACCOUNT FOR SLIGHT IRREGULARITIES IN LAYING. FALLS MUST BE DIRECTED AWAY FROM THE HOUSE — ALWAYS SLOPING FROM THE HOUSE OUTWARD TO THE GARDEN. FALLS TOWARDS AN ADJOINING NEIGHBOUR'S BOUNDARY MUST BE AVOIDED.

CHANNEL DRAIN AT THRESHOLD: WHERE A PATIO ABUTS EXTERNAL SLIDING DOORS OR BIFOLD DOORS, A CHANNEL DRAIN DIRECTLY AT THE THRESHOLD PREVENTS SURFACE WATER FROM BEING BLOWN INTO THE HOUSE IN HEAVY RAIN. ACO THRESHOLD DRAINS (ACO Q-DRAIN SLIM 60MM, 80MM, OR 125MM CHANNEL WIDTH) IN STAINLESS STEEL OR POLYMER CONCRETE BODY WITH STAINLESS MESH OR SLOTTED COVER ARE THE STANDARD PRODUCT — CONNECTED TO THE SURFACE WATER DRAIN OR SOAKAWAY.

SECONDARY CHANNEL DRAIN AT GARDEN EDGE: A LINEAR CHANNEL DRAIN (ACO CLASSIC C200 OR MARSHALLS ALBANY 120MM CHANNEL) AT THE FAR EDGE OF THE PATIO BEFORE THE LAWN AREA COLLECTS THE PRIMARY SURFACE WATER RUNOFF AND DISCHARGES TO THE DRAINAGE SYSTEM OR SOAKAWAY.

SOAKAWAY DESIGN: LONDON CLAY HAS VERY LOW PERMEABILITY (TYPICALLY 10-9 TO 10-8 M/S) — TRADITIONAL RUBBLE-FILL SOAKAWAYS IN LONDON CLAY DO NOT WORK AND WILL FILL WITH WATER AND OVERFLOW. POLYPIPE STORMCELL MODULAR GEOCELLULAR SOAKAWAY CRATES (INSTALLED IN THE LAWN AREA, AWAY FROM THE HOUSE AND FOUNDATIONS, WITH A GEOTEXTILE WRAP) CAN PROVIDE TEMPORARY SURFACE WATER ATTENUATION (BUFFERING PEAK FLOWS DURING STORMS) BEFORE SLOWER DISCHARGE IN CLAY — BUT PERFORM BEST WHEN COMBINED WITH AN OVERFLOW TO THE SURFACE WATER SEWER. IN AREAS OF LONDON WITH GOOD SANDY OR GRAVELLY SUB-SOILS BENEATH THE CLAY TOPSOIL, A DEEPER SOAKAWAY CAN SOMETIMES REACH THE PERMEABLE LAYER.

CONCRETE BLOCK PAVING (CBP) REMAINS THE MOST POPULAR SURFACE FOR LONDON FRONT DRIVEWAYS, COMBINING GOOD LOAD-BEARING PERFORMANCE, AESTHETIC OPTIONS, AND KERB EDGING CONTAINMENT.

BLOCK PAVING SPECIFICATION FOR LONDON DRIVEWAYS: MARSHALLS DRIVESETT TEGULA (60MM THICKNESS FOR PEDESTRIAN/CAR USE, 80MM FOR LIGHT COMMERCIAL) IN TUMBLED BUFF, CHARCOAL, BRINDLE, OR BIRCH FINISH. BRETT OMEGA (60MM, SIMILAR RANGE). TOBERMORE TEGULA (PREMIUM NORTHERN IRELAND MANUFACTURER — EXCELLENT QUALITY, STRONG COLOUR OPTIONS IN BRINDLE, SLATE, HEATHER).

SUB-BASE FOR DRIVEWAY: 150MM COMPACTED MOT TYPE 1 (FOR PRIVATE CARS); INCREASE TO 200MM FOR HEAVIER LOADS. 25MM SHARP SAND LAYING COURSE (NOT MORTAR — BLOCK PAVING REQUIRES A LOOSE SAND BED FOR INTERLOCK TO FUNCTION CORRECTLY).

EDGING: BLOCK PAVING REQUIRES RESTRAINED EDGING TO PREVENT THE BLOCKS SPREADING LATERALLY UNDER LOAD. MARSHALLS DRIVESETT KERB (MATCHING THE BLOCK COLOUR) HAUNCHED IN CONCRETE ON BOTH SIDES (100MM CONCRETE HAUNCH) IS THE STANDARD DETAIL. ALTERNATIVELY, 50X200MM IN-SITU CONCRETE EDGING BEAM.

JOINTING SAND: AFTER COMPACTION AND SPREADING OF BLOCKS, FINE KILN-DRIED JOINTING SAND (MARSHALLS BASECOAT OR ROMPOX EASY) IS SWEPT INTO THE JOINTS AND THE SURFACE VIBRATED WITH A PLATE COMPACTOR WITH A RUBBER PAD (TO AVOID MARKING BLOCKS). POLYMERIC JOINTING SAND (ROMPOX EASY DRAIN, EASY JOINT PRO) SETS HARD WITH WATER APPLICATION, PREVENTING WEED GROWTH AND ANT INGRESS — NOW STRONGLY PREFERRED OVER CONVENTIONAL KILN-DRIED SAND FOR LONDON DRIVEWAYS.

HARD LANDSCAPING COSTS IN LONDON DEPEND ON THE AREA, MATERIAL, DRAINAGE COMPLEXITY, AND ACCESS CONDITIONS. THE FOLLOWING ARE INDICATIVE RANGES FOR SUPPLY AND INSTALLATION.

INDIAN SANDSTONE PATIO (BRETT BALMORAL OR EQUIVALENT, 600X600MM MIXED, 25MM SEMI-DRY MORTAR BED, 100MM TYPE 1 SUB-BASE, INCLUDES POINTING, EXCLUDES DRAINAGE): £80 TO £130 PER M' INSTALLED. FOR A 20M' REAR PATIO: £1,600 TO £2,600.

PORCELAIN PATIO (GLOBAL STONE STONEMASTER 600X900MM 20MM, FULL-BED ADHESIVE MORTAR, 100MM TYPE 1, INCLUDES CHANNEL DRAIN AT THRESHOLD): £100 TO £175 PER M' INSTALLED. FOR A 20M' REAR PATIO: £2,000 TO £3,500.

RECLAIMED YORK STONE PATIO (SALVAGE GRADE B, VARIED SIZES, SEMI-DRY MORTAR BED, INCLUDES CUTTING TO FIT, NARROW POINTING): £150 TO £250 PER M' INSTALLED. PREMIUM GRADE A, CONSISTENT THICKNESS: £200 TO £350 PER M'.

CONCRETE BLOCK PAVING DRIVEWAY (MARSHALLS DRIVESETT TEGULA 60MM, 150MM TYPE 1 SUB-BASE, KERB EDGING, POLYMERIC SAND JOINTING, STANDARD LONDON TERRACE FRONT DRIVE 25-40M'): £60 TO £100 PER M' INSTALLED.

SEPARATE DRAINAGE ADDITIONS: ACO CLASSIC CHANNEL DRAIN (3M LENGTH, CONNECTED TO SURFACE WATER DRAIN): £300 TO £700 INSTALLED. SOAKAWAY CRATE (1M3 POLYPIPE STORMCELL, GEOTEXTILE WRAP, EXCAVATION): £600 TO £1,200 DEPENDING ON DEPTH AND ACCESS.