External Wall Render for London Victorian Terraces: K-Rend, Weber, and Lime Render

APPLYING RENDER TO THE EXTERNAL BRICKWORK OF A LONDON VICTORIAN TERRACE IS A SIGNIFICANT EXTERNAL ALTERATION THAT HAS IMPORTANT PLANNING IMPLICATIONS — PARTICULARLY IN A CONSERVATION AREA OR ON A LISTED BUILDING WHERE THE ORIGINAL YELLOW LONDON STOCK BRICKWORK IS A CHARACTER-DEFINING FEATURE OF THE BUILDING AND THE AREA.

PERMITTED DEVELOPMENT (GPDO 2015 — SCHEDULE 2 PART 1): RENDERING THE EXTERNAL WALLS OF A DWELLING IS IN PRINCIPLE PERMITTED DEVELOPMENT UNDER GPDO 2015 (THE GENERAL PERMITTED DEVELOPMENT ORDER 2015) FOR A DWELLING HOUSE — MEANING THAT FOR A STANDARD (NON-LISTED, NON-CONSERVATION AREA) PROPERTY IN ENGLAND, APPLYING RENDER TO THE EXTERNAL WALLS DOES NOT REQUIRE EXPRESS PLANNING PERMISSION — IT CAN BE DONE WITHOUT A PLANNING APPLICATION. CONSERVATION AREA: IN A CONSERVATION AREA, HOWEVER, APPLYING A NEW RENDER TO A PREVIOUSLY UNRENDERED EXTERNAL WALL (PARTICULARLY THE FRONT ELEVATION OR ANY ELEVATION VISIBLE FROM A PUBLIC HIGHWAY OR OPEN SPACE) WILL TYPICALLY REQUIRE PLANNING PERMISSION BECAUSE: (1) MANY LONDON CONSERVATION AREA APPRAISALS SPECIFICALLY IDENTIFY THE ORIGINAL LONDON STOCK BRICKWORK AS A POSITIVE CHARACTER ELEMENT THAT SHOULD BE RETAINED — AND COVERING IT WITH RENDER WOULD HARM THE SPECIAL ARCHITECTURAL AND HISTORIC INTEREST OF THE CONSERVATION AREA; (2) LOCAL AUTHORITIES HAVE THE POWER TO REQUIRE PLANNING APPLICATIONS FOR EXTERNAL CLADDING OR RENDER IN A CONSERVATION AREA UNDER SECTION 211 OF THE TOWN AND COUNTRY PLANNING ACT 1990 (NOTIFICATION OF WORKS IN CONSERVATION AREAS). IN PRACTICE, MOST INNER LONDON CONSERVATION OFFICERS WOULD OBJECT TO THE APPLICATION OF A NEW THROUGH-COLOUR RENDER (K-REND, WEBER) TO THE FRONT ELEVATION OF A BRICK VICTORIAN TERRACE IN A CONSERVATION AREA — BECAUSE IT WOULD IRREVERSIBLY CONCEAL THE ORIGINAL BRICKWORK CHARACTER. EXCEPTION — REAR ELEVATION: APPLYING RENDER TO THE REAR ELEVATION OF A VICTORIAN TERRACE (NOT VISIBLE FROM THE PUBLIC HIGHWAY) IS GENERALLY MORE LIKELY TO BE ACCEPTED BY A CONSERVATION OFFICER — AND MAY BE PERMITTED DEVELOPMENT WHERE THE CONSERVATION AREA ARTICLE 4 DIRECTION DOES NOT SPECIFICALLY RESTRICT REAR ELEVATION CLADDING. LISTED BUILDING: ANY RENDER ON A LISTED BUILDING REQUIRES LISTED BUILDING CONSENT — REGARDLESS OF POSITION.

THROUGH-COLOURED SILICONE RENDER (ALSO CALLED COLOURED RENDER, ONE-COAT RENDER, OR MONOCOUCHE RENDER — FROM THE FRENCH MONOCOUCHE — SINGLE COAT) IS THE DOMINANT EXTERNAL RENDER PRODUCT FOR UK RESIDENTIAL RENOVATION IN THE 2020S — A FACTORY-MIXED, THROUGH-COLOURED RENDER CONTAINING SILICONE RESIN THAT IS MACHINE-APPLIED OR HAND-APPLIED IN A SINGLE COAT (OR SOMETIMES TWO COATS) TO PROVIDE A DURABLE, THROUGH-COLOURED, WEATHER-RESISTANT EXTERNAL COATING WITH A FINE-TEXTURED FINISH THAT DOES NOT REQUIRE PAINTING.

K-REND (K REND EXTERNAL RENDER — A BRAND OWNED BY KILWAUGHTER MINERALS LTD — LARNE, NORTHERN IRELAND — THE MOST WIDELY USED THROUGH-COLOUR SILICONE RENDER BRAND IN THE UK RESIDENTIAL RENOVATION MARKET): K-REND SILICONE TC15 (THE MOST WIDELY USED K-REND PRODUCT IN UK DOMESTIC RESIDENTIAL RENOVATION — A THROUGH-COLOURED SILICONE MONOCOUCHE RENDER — 15MM NOMINAL SINGLE-COAT THICKNESS — THE FIGURE 15 REFERS TO THE AGGREGATE MAXIMUM SIZE OF 1.5MM — THE RENDER IS MIXED WITH WATER ON SITE, APPLIED IN A SINGLE 15MM COAT, AND SCRAPED OR SCRATCHED WHEN GREEN TO PRODUCE A CLEAN, FLAT FINISH — AVAILABLE IN APPROXIMATELY 100 STANDARD COLOURS INCLUDING WHITE, BUFF, CREAM, LIGHT GREY, PEBBLE, AND A WIDE RANGE OF OTHER TONES — THE THROUGH-COLOUR MEANS THE COLOUR RUNS THROUGH THE FULL THICKNESS OF THE RENDER — MINOR SURFACE CHIPS OR SCRATCHES DO NOT REVEAL A DIFFERENT COLOUR UNDERNEATH); WEBER SILICONE ONE COAT (WEBER BUILDING SOLUTIONS — SAINT-GOBAIN — THE MAIN COMPETITOR TO K-REND IN THE UK THROUGH-COLOUR SILICONE RENDER MARKET): WEBER SILICONE ONE COAT IS THE EQUIVALENT PRODUCT TO K-REND TC15 — A THROUGH-COLOURED SILICONE MONOCOUCHE RENDER — ALSO APPLIED AT 15MM SINGLE COAT — SIMILAR COLOUR RANGE AND PERFORMANCE — AVAILABLE IN WHITE, LIGHT GREY, BUFF, AND MANY OTHER STANDARD COLOURS; PAREX MONOREX GM (PAREX — THE THIRD MAJOR THROUGH-COLOUR RENDER BRAND IN THE UK — PAREX MONOREX GM IS MACHINE-APPLIED THROUGH-COLOUR SILICONE RENDER — A 15MM SINGLE COAT PRODUCT — USED BY SPECIALIST RENDER CONTRACTORS WHO USE CONTINUOUS SCREW RENDERING MACHINES (RITMO M OR EQUIVALENT) FOR LARGE RENDERS). BASE COAT (REQUIRED UNDER K-REND TC15 OR WEBER SILICONE ONE COAT WHERE THE SUBSTRATE IS PARTICULARLY UNEVEN, VERY POROUS, OR NOT STRUCTURALLY SOUND): WEBER REND AID (A REINFORCED POLYMER PRIMER COAT) OR K-REND BASE COAT — APPLIED BEFORE THE MONOCOUCHE RENDER WHERE REQUIRED TO IMPROVE ADHESION AND REDUCE SUCTION — TYPICALLY 5-8MM THICKNESS.

LIME RENDER (A NATURAL HYDRAULIC LIME BASED RENDER USING ST ASTIER NHL LIME BINDER — THE TRADITIONAL AND CONSERVATION-APPROPRIATE EXTERNAL RENDER SYSTEM FOR LIME-BUILT MASONRY SUBSTRATES INCLUDING LONDON STOCK BRICK, STONE, AND EARTH-BONDED SUBSTRATES) IS THE CORRECT SPECIFICATION FOR RENDERING SOLID BRICK WALLS IN LONDON VICTORIAN TERRACES WHERE A BREATHABLE, VAPOUR-PERMEABLE EXTERNAL RENDER IS REQUIRED — AND IT IS THE RENDER SYSTEM MOST ACCEPTED BY CONSERVATION OFFICERS FOR LISTED BUILDINGS AND CONSERVATION AREA PROPERTIES WHERE RENDER IS PERMITTED OR ORIGINAL.

ST ASTIER NHL 3.5 LIME RENDER (THREE-COAT SYSTEM — THE STANDARD THREE-COAT LIME RENDER SYSTEM FOR A SOLID BRICK WALL IN A LONDON VICTORIAN TERRACE): SCRATCH COAT (ALSO CALLED THE DUBBING OUT OR RENDERING COAT — FIRST COAT — APPLIED DIRECTLY TO THE SUBSTRATE): ST ASTIER NHL 3.5 — 1 PART NHL 3.5 : 2.5-3 PARTS WASHED SHARP SAND (BY VOLUME) — THICKNESS: 10-15MM — SCRATCHED WHILE STILL GREEN TO PROVIDE A MECHANICAL KEY FOR THE NEXT COAT — FIBRES (GLASS FIBRE OR STEEL FIBRE) MAY BE ADDED TO THE SCRATCH COAT TO REDUCE CRACKING — WEBER RENDER PRIMER OR SBR BONDING AGENT MAY BE APPLIED TO THE SUBSTRATE BEFORE THE SCRATCH COAT WHERE THE SUBSTRATE IS VERY SMOOTH OR IMPERMEABLE; FLOAT COAT (SECOND COAT — APPLIED AFTER THE SCRATCH COAT HAS PARTIALLY CURED — TYPICALLY 24-48 HOURS FOR NHL 3.5 SCRATCH COAT — FORMS THE MAIN BODY OF THE RENDER): ST ASTIER NHL 3.5 — 1:2.5 SHARP SAND — THICKNESS: 8-12MM — FLOATED FLAT WITH A DEVIL FLOAT TO PRODUCE A LEVEL, KEY SURFACE; FINISH COAT (THIRD COAT — APPLIED AFTER THE FLOAT COAT HAS PARTIALLY CURED — TYPICALLY 24-48 HOURS — PROVIDES THE FINAL TEXTURE AND APPEARANCE): ST ASTIER NHL 2 — 1:3 SOFT SAND OR SHARP SAND — 5-8MM THICKNESS — CAN BE FINISHED: SMOOTH TROWELLED (TYPICAL FOR TRADITIONAL LIME RENDER ON A VICTORIAN TERRACE — THE SMOOTH SLURRY TEXTURE OF A WELL-WORKED LIME FINISH) OR ROUGHCAST/PEBBLE DASH (COARSER AGGREGATE THROWN AT THE WET FINISH COAT — MORE SUITABLE FOR EXPOSED POSITIONS). SAND-CEMENT RENDER (OPC:SAND — 1:4 OR 1:3 MIX — THE TRADITIONAL NON-LIME RENDER SYSTEM THAT HAS LARGELY BEEN SUPERSEDED BY K-REND AND WEBER MONOCOUCHE IN CONTEMPORARY UK RESIDENTIAL RENOVATION BUT IS STILL USED BY MANY GENERAL CONTRACTORS): COMPRESSIVE STRENGTH: 10-30 N/MM² — SIGNIFICANTLY HARDER AND LESS PERMEABLE THAN LIME RENDER — NOT RECOMMENDED FOR SOLID BRICK WALLS (TRAPS MOISTURE, BRIDGES WALL TIE CAVITIES, CAN CAUSE INTERNAL DAMP IF CRACKING ALLOWS WATER INGRESS) — MORE ACCEPTABLE FOR REINFORCED CONCRETE FRAME BUILDINGS, MODERN DENSE BLOCK CONSTRUCTION, AND BELOW-DPC APPLICATIONS.

EXTERNAL WALL INSULATION (EWI) RENDER SYSTEMS — ALSO CALLED INSULATED RENDER SYSTEMS, COMPOSITE WALL INSULATION SYSTEMS (CWIS), OR EXTERNAL INSULATION AND FINISH SYSTEMS (EIFS) — ARE COMPOSITE SYSTEMS WHERE A LAYER OF RIGID INSULATION BOARD IS FIXED TO THE EXTERNAL FACE OF THE EXISTING WALL AND THEN COVERED WITH A BASE COAT MESH RENDER AND A THROUGH-COLOUR FINISH COAT — PROVIDING BOTH THERMAL INSULATION AND A WEATHER-RESISTANT, DECORATIVE EXTERNAL FINISH IN ONE COMBINED SYSTEM.

WETHERBY BUILDING SYSTEMS (WETHERBY BUILDING SYSTEMS LTD — BRIGHOUSE, WEST YORKSHIRE — ONE OF THE LEADING UK EWI RENDER SYSTEM MANUFACTURERS): WETHERBY EWI SYSTEM (A COMPLETE EWI SYSTEM COMPRISING: WETHERBY ULTRA-S EXPANDED POLYSTYRENE (EPS) BOARD — 50MM/100MM/150MM THICKNESS — ADHESIVELY FIXED AND MECHANICALLY ANCHORED TO THE EXISTING MASONRY WALL — MECHANICAL ANCHORS: WETHERBY FIXMASTER — MINIMUM 6 FIXINGS PER M²; WETHERBY BASECOAT — A POLYMER-MODIFIED CEMENTITIOUS BASE COAT — REINFORCED WITH WETHERBY ALKALI-RESISTANT (AR) GLASS FIBRE MESH — 145 G/M² — EMBEDDED IN THE BASE COAT — THE MESH DISTRIBUTES THERMAL AND IMPACT STRESS ACROSS THE RENDER SURFACE TO PREVENT CRACKING; THROUGH-COLOUR SILICONE FINISH COAT — WETHERBY SILICONE THIN COAT RENDER — OR COMPATIBLE K-REND TC15 — SAME FAMILY OF SILICONE THROUGH-COLOUR RENDER AS DESCRIBED ABOVE). PERMAROCK (PERMAROCK PRODUCTS LTD — COVENTRY — AN ALTERNATIVE UK EWI SYSTEM MANUFACTURER): PERMAROCK EWI SYSTEM (SIMILAR SYSTEM TO WETHERBY — EPS BOARD + BASE COAT MESH + THROUGH-COLOUR FINISH — WIDELY SPECIFIED BY SOCIAL HOUSING AND WHOLE-HOUSE RENOVATION PROGRAMMES IN UK). THERMAL PERFORMANCE (WHY EWI MATTERS FOR A LONDON VICTORIAN TERRACE): A STANDARD 215MM SOLID BRICK WALL IN A LONDON VICTORIAN TERRACE (BUILT WITH LONDON STOCK BRICK AND LIME MORTAR) HAS A U-VALUE OF APPROXIMATELY 2.0-2.2 W/M²K (VERY POOR THERMAL PERFORMANCE — APPROXIMATELY 4-5X WORSE THAN THE CURRENT PART L 2021 REQUIREMENT FOR A NEW EXTENSION WALL OF 0.18-0.26 W/M²K); ADDING 100MM EPS EWI (LAMBDA 0.031-0.033 W/M·K — TYPICAL EPS BOARD LAMBDA): REDUCES THE WALL U-VALUE TO APPROXIMATELY 0.26-0.30 W/M²K — CLOSE TO PART L STANDARD — A DRAMATIC IMPROVEMENT; ADDING 150MM EPS: U-VALUE APPROXIMATELY 0.18-0.22 W/M²K — PART L COMPLIANT.

EXTERNAL WALL RENDER COSTS (LONDON 2025 — SPECIALIST RENDER CONTRACTOR — SUPPLY AND FIT — LABOUR AND MATERIALS — PER M² OF WALL AREA RENDERED).

K-REND SILICONE TC15 OR WEBER SILICONE ONE COAT (THROUGH-COLOUR MONOCOUCHE — BASE COAT + 15MM FINISH COAT — SUPPLY AND FIT — PER M² — LONDON): APPROXIMATELY £30-55/M² (INCLUDES SCAFFOLDING ON AREAS WHERE SCAFFOLDING IS INCLUDED IN THE CONTRACT — CHECK WHAT IS INCLUDED). NOTE: SCAFFOLDING IS A SIGNIFICANT ADDITIONAL COST FOR RENDER ON THE FRONT OR REAR ELEVATION OF A MULTI-STOREY VICTORIAN TERRACE — TYPICALLY £1,200-2,500 FOR A 4-WEEK HIRE ON A 3-STOREY FRONT ELEVATION. THREE-COAT LIME RENDER (ST ASTIER NHL 3.5 BASE + FLOAT + NHL 2 FINISH — SUPPLY AND FIT): APPROXIMATELY £40-70/M² (MORE EXPENSIVE THAN MONOCOUCHE DUE TO THREE-COAT APPLICATION AND SLOWER WORKING PACE OF LIME — CONSERVATION QUALITY — CONSERVATION AREA SPECIFICATION). EWI (EXTERNAL WALL INSULATION) RENDER SYSTEM (WETHERBY OR PERMAROCK — 100MM EPS BOARD + BASE COAT MESH + SILICONE FINISH COAT — SUPPLY AND FIT — INCLUDING MECHANICAL ANCHORS): APPROXIMATELY £80-130/M² (PER M² OF RENDERED WALL AREA — EWI SYSTEMS ARE SIGNIFICANTLY MORE EXPENSIVE PER M² THAN SURFACE RENDER BECAUSE THEY INCLUDE THE INSULATION BOARD, MECHANICAL FIXINGS, AND A MORE COMPLEX BUILD-UP — BUT THE ADDITIONAL THERMAL PERFORMANCE DELIVERED (U-VALUE IMPROVEMENT FROM ~2.0 TO ~0.26 W/M²K FOR 100MM EPS) MAY QUALIFY FOR ENERGY EFFICIENCY GRANTS SUCH AS THE GREAT BRITISH INSULATION SCHEME OR THE ENERGY COMPANY OBLIGATION (ECO4) — WHICH CAN SIGNIFICANTLY OFFSET THE EWI COST FOR ELIGIBLE HOUSEHOLDS). TYPICAL FULL REAR ELEVATION RENDER (LONDON VICTORIAN TERRACE — 3 STOREY — 30-40M² — K-REND TC15 WHITE — EXCLUDING SCAFFOLD): APPROXIMATELY £30-55 X 35M² = £1,050-1,925 PLUS SCAFFOLD £1,200-2,000 = TOTAL APPROXIMATELY £2,250-3,925. TYPICAL FULL REAR ELEVATION EWI RENDER (30-40M² — 100MM EPS — SILICONE FINISH): APPROXIMATELY £80-130 X 35M² = £2,800-4,550 PLUS SCAFFOLD APPROXIMATELY £4,000-7,050 TOTAL.