Garden Walls and Boundary Structures for London Homes: Brick, Flint, Stock Brick, and Retaining Wall Guide

LONDON STOCK BRICK IS THE TRADITIONAL HANDMADE BRICK OF THE LONDON REGION — YELLOW-CREAM IN COLOUR (RANGING FROM PALE YELLOW TO GOLDEN BUFF TO WARM GREY-GREEN) DUE TO THE CHALK AND GAULT CLAY CONTENT OF THE LONDON CLAY FROM WHICH THEY WERE MADE. LONDON STOCKS ARE ASSOCIATED WITH ALL LONDON BUILDINGS AND BOUNDARY WALLS CONSTRUCTED FROM APPROXIMATELY 1750 TO 1930 — THEY ARE THE PREDOMINANT BRICK VISIBLE IN GEORGIAN, REGENCY, VICTORIAN, AND EDWARDIAN LONDON ARCHITECTURE.

NEW LONDON STOCK BRICK: WHERE A NEW BOUNDARY WALL IS TO MATCH EXISTING LONDON STOCK BRICK GARDEN WALLS (AS REQUIRED IN CONSERVATION AREAS AND FOR EXTENSIONS MATCHING EXISTING BRICKWORK), THE FOLLOWING SOURCES PROVIDE LONDON STOCK MATCHING BRICKS: KENTISH STOCK (K.H.M. BRICKWORKS KENT — THE TRADITIONAL SOURCE). TOWNSEND YELLOW STOCK (IBSTOCK — THE MOST WIDELY USED NEW LONDON STOCK ALTERNATIVE FOR LONDON CONSERVATION AREA MATCHING). HANDMADE YELLOW STOCK (MICHELMERSH BRICKWORKS OR WIENERBERGER CONTINENTAL RANGE). THESE ARE ALL "WIRECUT" OR "HANDMADE" BRICKS WITH IRREGULAR TEXTURE THAT APPROACHES THE ORIGINAL HANDMADE QUALITY, THOUGH EXACT MATCHING TO WEATHERED ORIGINAL STOCK BRICK REQUIRES RECLAIMED STOCK (SEE BELOW).

RECLAIMED LONDON STOCK BRICK: FOR THE MOST ACCURATE VISUAL MATCH TO EXISTING VICTORIAN LONDON STOCK BRICKWORK IN CONSERVATION AREAS, RECLAIMED LONDON STOCK BRICKS (SALVAGED FROM DEMOLISHED LONDON BUILDINGS AND WALLS) ARE THE BEST OPTION. RECLAIMED LONDON STOCKS ARE AVAILABLE FROM LONDON ARCHITECTURAL SALVAGE COMPANIES (LONDON RECLAIMED BRICK, LASSCO, SALVO LONDON) AND TYPICALLY COST £1.20 TO £2.50 PER BRICK DEPENDING ON QUALITY AND AVAILABILITY. RECLAIMED BRICKS MUST BE CLEANED (MORTAR REMOVED BY HAMMER AND BOLSTER — NOT BY SANDBLASTING WHICH DAMAGES THE BRICK FACE) AND SORTED FOR QUALITY BEFORE LAYING.

MORTAR FOR LONDON STOCK BRICK WALLS: LONDON STOCK BRICK IS A RELATIVELY SOFT, LOW-STRENGTH BRICK (TYPICAL COMPRESSIVE STRENGTH 14-28 N/MM²). A CEMENT-RICH MORTAR USED WITH STOCK BRICK WILL BE STRONGER THAN THE BRICK ITSELF — CAUSING THE BRICK FACE TO SPALL RATHER THAN THE MORTAR JOINT TO ERODE NATURALLY WHEN SUBJECTED TO FREEZE-THAW CYCLES. THE CORRECT MORTAR FOR NEW LONDON STOCK BRICKWORK IS A LIME-RICH MIX: 1 PART OPC : 2 PARTS LIME : 9 PARTS SAND (BY VOLUME) FOR EXPOSED GARDEN WALL APPLICATIONS. FOR REPOINTING EXISTING STOCK BRICK WALLS, A LIME MORTAR WITHOUT OPC IS PREFERRED: NATURAL HYDRAULIC LIME (ST ASTIER NHL 3.5) : SHARP SAND AT 1:2.5 OR A PRE-MIXED CONSERVATION REPOINTING MORTAR (HIRST CONSERVATION, TARMAC LIMEREND).

GARDEN BOUNDARY WALLS IN LONDON ARE GENERALLY "FREE-STANDING WALLS" (NOT RETAINING EARTH ON BOTH SIDES) AND MUST BE DESIGNED TO RESIST LATERAL WIND LOADS AND ACCIDENTAL IMPACT WITHOUT OVERTURNING.

FREE-STANDING WALL STABILITY GUIDANCE (BS 5628-1 / EUROCODE 6): THE STABILITY OF A FREE-STANDING BRICK OR BLOCKWORK WALL AGAINST OVERTURNING UNDER WIND LOAD DEPENDS ON THE WALL HEIGHT, THICKNESS, AND THE SPACING OF PIERS (WHICH ACT AS BUTTRESSES). INDICATIVE RULES OF THUMB FOR LONDON RESIDENTIAL BOUNDARY WALLS: HALF-BRICK (102MM) SINGLE-LEAF WALL: MAXIMUM PRACTICAL HEIGHT APPROXIMATELY 600MM WITHOUT PIERS. ONE-BRICK (215MM) DOUBLE-LEAF WALL: MAXIMUM PRACTICAL HEIGHT APPROXIMATELY 1.2M WITHOUT PIERS OR 1.8M WITH PIERS AT MAXIMUM 3.0M CENTRES. ONE AND A HALF BRICK (327MM): MAXIMUM PRACTICAL HEIGHT APPROXIMATELY 1.8M WITHOUT PIERS OR 2.4M WITH PIERS AT 3.0M CENTRES.

FOUNDATIONS FOR FREE-STANDING GARDEN WALLS: FREE-STANDING GARDEN WALLS IN LONDON MUST HAVE ADEQUATE FOUNDATIONS TO PREVENT SETTLEMENT AND OVERTURNING. TYPICAL FOUNDATION: 600MM WIDE X 300MM DEEP MASS CONCRETE (C25/P READYMIX) FOOTING FOR A 215MM (ONE BRICK) WALL. MINIMUM DEPTH TO THE UNDERSIDE OF THE FOOTING: 600MM (TO AVOID FROST ACTION IN LONDON CLAY GROUND) — DEEPER IN AREAS WITH TREE ROOTS (MINIMUM 900MM TO 1200MM IN LONDON CLAY WITHIN 3.0M OF MATURE TREES). FOUNDATIONS MUST EXTEND BEYOND THE BOUNDARY ONTO THE CLIENT'S OWN LAND — A PARTY WALL FOUNDATION STRADDLES THE BOUNDARY AND REQUIRES PARTY WALL AGREEMENT UNDER SECTION 1 OF THE PARTY WALL ETC. ACT 1996.

COPING STONES: COPING STONES ON THE TOP OF BOUNDARY WALLS SHED WATER AND PROTECT THE BRICKWORK FROM FREEZE-THAW DAMAGE. TRADITIONAL LONDON WALL COPINGS: HALF-ROUND BLUE ENGINEERING BRICK COPING (FOR STOCK BRICK WALLS), SADDLE BACK PRECAST CONCRETE COPING (GREY — LESS APPROPRIATE FOR CONSERVATION AREAS), NATURAL STONE COPING (YORKSHIRE STONE OR PORTLAND STONE — PREMIUM OPTION FOR CONSERVATION AREA OR HERITAGE PROJECTS).

BOUNDARY WALL WORK IN LONDON FREQUENTLY ENGAGES THE PARTY WALL ETC. ACT 1996 — PARTICULARLY WHERE THE WALL IS ON OR NEAR THE LINE OF THE BOUNDARY WITH A NEIGHBOURING PROPERTY.

SECTION 1 (PARTY WALL ON THE LINE OF JUNCTION — NEW WALL ON BOUNDARY): IF A NEW WALL IS TO BE BUILT ASTRIDE THE LINE OF JUNCTION (BOUNDARY) BETWEEN PROPERTIES, SECTION 1 OF THE PARTY WALL ACT REQUIRES THE BUILDING OWNER TO GIVE ONE MONTH'S NOTICE TO THE ADJOINING OWNER. IF THE ADJOINING OWNER CONSENTS, THE WALL MAY BE BUILT ASTRIDE THE BOUNDARY WITH SHARED COSTS (THE NEIGHBOUR PAYS FOR HALF THE COST OF THE WALL). IF THE ADJOINING OWNER DOES NOT CONSENT, THE WALL MUST BE BUILT ENTIRELY WITHIN THE BUILDING OWNER'S OWN LAND.

SECTION 2 (PARTY FENCE WALL — WORK TO EXISTING SHARED BOUNDARY WALL): WHERE A WALL ON THE LINE OF JUNCTION (A "PARTY FENCE WALL" — A WALL NOT FORMING PART OF A BUILDING) IS TO BE REPAIRED, RAISED, OR REDUCED, SECTION 2 OF THE PARTY WALL ACT MAY APPLY. TWO MONTHS' NOTICE IS REQUIRED.

SECTION 6 (EXCAVATION NEAR ADJOINING PROPERTIES): WHERE EXCAVATION FOR WALL FOUNDATIONS WITHIN 3.0M (OR 6.0M IN SOME CIRCUMSTANCES) OF THE ADJOINING OWNER'S FOUNDATIONS IS REQUIRED, A SECTION 6 NOTICE IS REQUIRED IF THE EXCAVATION EXTENDS BELOW THE LEVEL OF THE NEIGHBOUR'S FOUNDATIONS. THIS IS PARTICULARLY RELEVANT FOR RETAINING WALLS IN LONDON GARDENS WHERE GROUND LEVELS CHANGE.

PRACTICAL ADVICE: BEFORE STARTING ANY BOUNDARY WALL WORK IN LONDON, CONFIRM THE BOUNDARY POSITION (TITLE DEEDS AND HM LAND REGISTRY PLAN) AND CHECK WHETHER PARTY WALL NOTICE IS REQUIRED. A PARTY WALL SURVEYOR (TYPICAL FEE £500 TO £1,500 PER PROPERTY) CAN ADVISE ON NOTICE REQUIREMENTS AND MANAGE THE PARTY WALL PROCESS.

MANY LONDON GARDENS — PARTICULARLY IN HILLY AREAS (NORTH LONDON HEIGHTS, GREENWICH HILL, HIGHGATE, UPPER NORWOOD) — HAVE SIGNIFICANT CHANGES IN LEVEL THAT REQUIRE RETAINING WALLS.

RETAINING WALL STRUCTURAL REQUIREMENTS: A RETAINING WALL MUST RESIST BOTH THE WEIGHT OF THE RETAINED EARTH (ACTIVE EARTH PRESSURE) AND ANY SURCHARGE LOADING (PEOPLE WALKING NEAR THE WALL, VEHICLES NEAR THE TOP, WATER PRESSURE). FOR WALLS RETAINING MORE THAN 1.0M OF EARTH, STRUCTURAL DESIGN BY A STRUCTURAL OR GEOTECHNICAL ENGINEER IS REQUIRED.

TYPICAL RETAINING WALL SPECIFICATIONS IN LONDON GARDENS: FOR WALLS UP TO 1.0M RETAINED HEIGHT: 215MM (ONE BRICK) CONCRETE BRICK RETAINING WALL ON 600MM WIDE X 450MM DEEP REINFORCED CONCRETE (RC) STRIP FOOTING (C25 CONCRETE WITH 2 X T12 BOTTOM BARS), WITH WEEPHOLES AT 1.0M CENTRES THROUGH THE BASE COURSE TO PREVENT HYDROSTATIC WATER BUILDUP. FOR WALLS OF 1.0M TO 1.5M RETAINED HEIGHT: RC BLOCKWORK WALL (215MM AGGREGATE CONCRETE BLOCKS GROUTED CORE WITH T10 VERTICAL BARS AT 450MM CENTRES) ON 1.0M WIDE X 600MM DEEP RC STRIP FOOTING (T12 @ 200MM EACH WAY). DESIGN BY STRUCTURAL ENGINEER REQUIRED. FOR WALLS OF 1.5M+ RETAINED HEIGHT: ENGINEER-DESIGNED REINFORCED CONCRETE OR GABION BASKET RETAINING WALL. GABION BASKETS (WOVEN STEEL WIRE MESH CAGES FILLED WITH LOCAL STONE — TYPICALLY GRANITE COBBLES OR FLINT) ARE AN ATTRACTIVE AND PERMEABLE ALTERNATIVE TO REINFORCED CONCRETE FOR LONDON GARDEN RETAINING WALLS OF UP TO 2.0M HEIGHT.

DRAINAGE BEHIND RETAINING WALLS: HYDROSTATIC WATER PRESSURE CAN DRAMATICALLY INCREASE THE LOAD ON A RETAINING WALL AND CAUSE FAILURE. MINIMUM DRAINAGE SPECIFICATION: GEOCOMPOSITE DRAINAGE LAYER (DELTA-DRAIN OR TERRAM DRAIN GEOCOMPOSITE — A DRAINAGE CORE WITH GEOTEXTILE FILTER LAYER) FIXED TO THE BACK FACE OF THE WALL, DRAINING TO A PERFORATED DRAIN PIPE (POLYPIPE 100MM PERFORATED LATERAL DRAIN IN GRAVEL BEDDING) AT THE BASE.

FLINT WALLS ARE A CHARACTERISTIC ELEMENT OF LONDON'S HISTORIC BOUNDARY AND GARDEN WALL STOCK — PARTICULARLY IN SOUTH LONDON (NORWOOD, SYDENHAM, DULWICH), NORTH LONDON (HIGHGATE, HAMPSTEAD), AND THE SUBURBAN FRINGE WHERE FLINT IS THE LOCAL VERNACULAR BUILDING MATERIAL. FLINT WALLS ARE ALSO COMMON IN THE HOME COUNTIES (KENT, SURREY, WEST SUSSEX) NEAR LONDON'S OUTER EDGES.

FLINT TYPES: UNKNAPPED FLINT (WHOLE FIELD FLINT — ROUNDED NODULES USED FULL-FACE): THE TRADITIONAL RURAL APPROACH — IRREGULAR ROUNDED FLINTS SET IN LIME MORTAR, GIVING A VERY ORGANIC AND TEXTURED APPEARANCE. KNAPPED FLINT (FLINT SPLIT TO EXPOSE THE BLACK GLASSY INTERIOR): FLINTS ARE STRUCK WITH A FLINT-KNAPPING HAMMER TO SPLIT THEM INTO APPROXIMATELY HALF-SPHERICAL PIECES WITH A SMOOTH, GLASSY BLACK FACE. THE SMOOTH BLACK FACE IS LAID OUTWARD, GIVING A MORE REFINED AND FORMAL APPEARANCE — THE CHARACTERISTIC APPEARANCE OF FLINT FLUSHWORK IN KENT, SUSSEX, AND LONDON'S FLINT BUILDINGS AND WALLS.

FLINT WALL MORTAR SPECIFICATION: LIKE LONDON STOCK BRICK WALLS, FLINT WALLS MUST NOT BE REPOINTED WITH HARD CEMENT MORTAR — POINTING THAT IS HARDER THAN THE FLINT NODULES WILL CAUSE FROST DAMAGE TO THE FLINT SURFACE AS FREEZE-THAW FORCES CANNOT HARMLESSLY FLEX THROUGH THE JOINTS. CORRECT MORTAR: ST ASTIER NHL 3.5 : 2.5 SHARP SAND (SIMILAR TO LIME MORTAR SPECIFICATION FOR STOCK BRICK). TUCK POINTING IS A TRADITIONAL FINISHING TECHNIQUE FOR FLINT WALLS WHERE THE LIME MORTAR JOINTS ARE FINISHED WITH A FINE RIBBON OF WHITE OR CREAM LIME PUTTY — GIVING A MORE REFINED APPEARANCE AND IMPROVED WEATHER PROTECTION.

FLINT WALL REPAIR: FAILED OR MISSING MORTAR IN FLINT WALLS SHOULD BE REPOINTED WITH MATCHING NHL MORTAR. STRUCTURAL FAILURE (WHERE THE WALL LEANS OR HAS SECTIONS COLLAPSED) REQUIRES CAREFUL DEMOLITION OF THE FAILED SECTION, RECONSTRUCTION USING RECLAIMED MATCHING FLINTS, AND REBUILDING WITH THE CORRECT LIME MORTAR. MATCHING FLINTS ARE AVAILABLE FROM FLINT WALL SUPPLIERS IN KENT AND EAST SUSSEX.

PLANNING REQUIREMENTS: FREE-STANDING GARDEN WALLS ARE PERMITTED DEVELOPMENT IN MOST LONDON RESIDENTIAL AREAS — BUT WITH HEIGHT LIMITS. WALLS WITHIN OR ON THE BOUNDARY OF THE CURTILAGE OF A LISTED BUILDING REQUIRE LISTED BUILDING CONSENT. WALLS ADJACENT TO THE HIGHWAY: MAXIMUM HEIGHT 1.0M WITHOUT PLANNING PERMISSION. WALLS NOT ADJACENT TO THE HIGHWAY (WITHIN THE REAR GARDEN OR ON THE REAR BOUNDARY): MAXIMUM HEIGHT 2.0M WITHOUT PLANNING PERMISSION. IN CONSERVATION AREAS, ARTICLE 4 DIRECTIONS MAY REMOVE PERMITTED DEVELOPMENT RIGHTS FOR GARDEN WALLS — MEANING PLANNING PERMISSION IS REQUIRED FOR ANY NEW WALL OR SUBSTANTIAL ALTERATION OF AN EXISTING WALL. CONSULT THE SPECIFIC LONDON BOROUGH LPA FOR CONSERVATION AREA GUIDANCE.

COSTS FOR LONDON BOUNDARY WALL PROJECTS: NEW HALF-BRICK (102MM) STOCK BRICK GARDEN WALL (UP TO 1.2M HEIGHT, INCLUDING FOOTING, BRICK, LIME MORTAR, COPING, POINTING): £250 TO £400 PER LINEAR METRE (USING NEW MATCHING STOCK BRICK). WITH RECLAIMED LONDON STOCK BRICK: ADD £40 TO £80 PER LINEAR METRE ADDITIONAL MATERIAL COST. NEW ONE-BRICK (215MM) STOCK BRICK GARDEN WALL (1.2M TO 1.8M HEIGHT, INCLUDING FOOTING, ENGINEERING BRICK COPING): £400 TO £700 PER LINEAR METRE. FLINT WALL REPAIR (REPOINTING ONLY): £80 TO £180 PER M² OF WALL FACE. FLINT WALL REBUILD (INCLUDING FOOTING, FLINT SUPPLY AND LAY, LIME MORTAR, COPING): £500 TO £900 PER LINEAR METRE DEPENDING ON HEIGHT AND SPECIFICATION. RETAINING WALL UP TO 1.0M RETAINED HEIGHT (ONE-BRICK CONCRETE BLOCKWORK, RC FOOTING, WEEPHOLES, GEOCOMPOSITE DRAINAGE): £450 TO £750 PER LINEAR METRE.