External Render & Cladding for London Homes: Materials, Costs & Rules

BEFORE SELECTING A RENDER OR CLADDING SYSTEM, EVERY LONDON HOMEOWNER MUST ESTABLISH THEIR PLANNING POSITION.

CONSERVATION AREAS: IF YOUR PROPERTY IS IN A CONSERVATION AREA (WHICH APPLIES TO OVER 1,000 DESIGNATED AREAS ACROSS THE 32 LONDON BOROUGHS), RENDERING OR CLADDING THE EXTERNAL WALLS IS SPECIFICALLY NOT PERMITTED DEVELOPMENT. PLANNING PERMISSION IS REQUIRED. YOUR LOCAL PLANNING AUTHORITY WILL ASSESS THE APPLICATION AGAINST THE CONSERVATION AREA APPRAISAL — AND IN MANY CONSERVATION AREAS DOMINATED BY EXPOSED LONDON STOCK BRICK OR PAINTED RENDER, APPLICATIONS TO APPLY SILICONE RENDER OR ARTIFICIAL CLADDING WILL BE REFUSED ON CHARACTER GROUNDS.

COMPLIANT OPTIONS IN CONSERVATION AREAS: — LIKE-FOR-LIKE REPOINTING: MATCHING THE ORIGINAL MORTAR TYPE AND COLOUR — NHL 3.5 LIME MORTAR (NOT PORTLAND CEMENT) ON LONDON STOCK BRICK — PAINTED RENDER REPLACEMENT: WHERE THE BUILDING WAS ALREADY RENDERED, REPLACING LIKE-FOR-LIKE WITH A BREATHABLE LIME OR SILICONE RENDER IN THE SAME COLOUR IS GENERALLY ACCEPTABLE — LIMEWASH OR MASONRY PAINT ON EXISTING RENDERED SURFACES

ARTICLE 4 DIRECTIONS: MANY LONDON BOROUGHS HAVE ARTICLE 4 DIRECTIONS IN CONSERVATION AREAS SPECIFICALLY REMOVING THE PERMITTED DEVELOPMENT RIGHT TO CLAD OR RENDER EXTERNAL WALLS. EVEN WHERE AN AREA APPEARS OUTSIDE A CONSERVATION AREA, CHECK FOR ARTICLE 4 COVERAGE.

NON-CONSERVATION AREAS: FOR PROPERTIES NOT IN CONSERVATION AREAS, APPLYING RENDER OR CLADDING TO SIDE AND REAR ELEVATIONS IS GENERALLY PERMITTED DEVELOPMENT. FRONT ELEVATIONS IN NON-CONSERVATION AREAS ARE ALSO GENERALLY PD — BUT SOME BOROUGHS APPLY LOCAL POLICY PREFERENCES THROUGH DESIGN GUIDES THAT DISCOURAGE RENDER ON VICTORIAN BRICK TERRACES.

LISTED BUILDINGS: LISTED BUILDING CONSENT (FREE APPLICATION) IS ALWAYS REQUIRED FOR ANY MATERIAL CHANGE TO THE EXTERNAL APPEARANCE, INCLUDING RENDER OR CLADDING ON ANY ELEVATION.

MODERN SILICONE RENDERS ARE THE MOST WIDELY SPECIFIED EXTERNAL RENDER SYSTEM FOR LONDON HOME RENOVATIONS IN NON-CONSERVATION AREAS. THEY OFFER EXCELLENT WEATHER RESISTANCE, BREATHABILITY, SELF-CLEANING PROPERTIES, AND A WIDE RANGE OF COLOURS.

SYSTEM COMPONENTS (TYPICAL THREE-COAT SYSTEM): 1. POLYMER BASECOAT OR SAND-AND-CEMENT SCRATCH COAT: APPLIED TO CLEAN, PREPARED MASONRY. K-REND BASE COAT TC15 (15KG BAGS) OR WEBER.REND RB (ROUGHCAST BASE) — APPLIED 10-15MM THICK, KEY FOR THE TOPCOAT. 2. REINFORCEMENT: ALKALINE-RESISTANT (AR) FIBREGLASS MESH (100G/M2 MINIMUM) EMBEDDED IN A POLYMER BASECOAT (K-REND K1 BASECOAT OR WEBER.REND LAY) TO PREVENT CRACK PROPAGATION. 3. SILICONE TOPCOAT: K-REND SILICONE TC15 (1.5MM TEXTURE); WEBER.REND SILICONE ONE COAT (1.0MM OR 1.5MM TEXTURE); PAREX MONOREX GM (ROUGHCAST TEXTURE). ALL ARE FACTORY-MIXED WITH COLOUR PIGMENT — ORDER EXTRA FROM THE SAME BATCH AS COLOUR-MATCHING ACROSS BATCHES IS IMPERFECT.

COLOUR AND TEXTURE: SILICONE RENDERS ARE AVAILABLE IN HUNDREDS OF RAL AND BS COLOURS. POPULAR LONDON CHOICES: WHITE (RAL 9010), LIGHT GREY (RAL 7035), ANTHRACITE (RAL 7016), CREAM (BS 08B15). TEXTURE OPTIONS: FINE SCRAPED (1.5MM GRAIN — SMOOTHEST, MOST MODERN), MEDIUM SCRAPED (2.0MM GRAIN), ROUGHCAST (COARSER, MORE TRADITIONAL).

KEY PERFORMANCE PROPERTIES: — U-VALUE: RENDER ALONE ADDS MINIMAL THERMAL IMPROVEMENT (U≈0.04 W/M2K). FOR THERMAL IMPROVEMENT, EWI SYSTEM IS NEEDED. — BREATHABILITY: SILICONE RENDERS ARE SD (VAPOUR DIFFUSION RESISTANCE) <0.1M — MUCH MORE BREATHABLE THAN CEMENT RENDER. CRITICAL FOR OLDER SOLID-WALL PROPERTIES THAT MUST BREATHE. — SERVICE LIFE: 20-30 YEARS ON A CORRECTLY PREPARED AND PRIMED SURFACE.

COST: £35-£65/M2 INSTALLED FOR A THREE-COAT SILICONE RENDER SYSTEM ON PREPARED SOUND MASONRY (EXCLUDING SCAFFOLD, PRELIMINARY REPAIRS TO MASONRY OR RENDER REMOVAL).

EXTERNAL WALL INSULATION (EWI) SYSTEMS — ALSO CALLED EXTERNAL SOLID WALL INSULATION OR EWI — COMBINE THERMAL INSULATION WITH AN EXTERNAL RENDER OR FINISH. FOR LONDON'S LARGE STOCK OF SOLID-WALL VICTORIAN AND EDWARDIAN PROPERTIES (WHICH TYPICALLY HAVE U-VALUES OF 1.8-2.1 W/M2K), EWI IS THE MOST EFFECTIVE EXTERNAL FABRIC UPGRADE AVAILABLE.

HOW EWI WORKS: — INSULATION BOARDS (TYPICALLY 70-100MM EPS, 60-80MM PIR, OR 60MM MINERAL WOOL) ARE MECHANICALLY FIXED AND ADHESIVE-BONDED TO THE EXISTING EXTERNAL WALL. — BASE COAT WITH FIBREGLASS MESH REINFORCEMENT IS APPLIED OVER THE BOARDS. — TOPCOAT (SILICONE RENDER, MINERAL RENDER, OR BRICK SLIP CLADDING) IS APPLIED AS FINISH.

INSULATION TYPES: — EPS (EXPANDED POLYSTYRENE): WETHERBY EWI PRO 50; PERMAROCK EWI; KNAUF INSULATION EWI. LAMBDA VALUE 0.038 W/MK. 100MM EPS ACHIEVES U≈0.30 W/M2K ON A SOLID BRICK WALL. COST: £5-£8/M2 FOR BOARD. MOST AFFORDABLE OPTION. — MINERAL WOOL BOARD: ROCKWOOL FRONTROCK MAX E; KNAUF INSULATION SUPAFIL EARTHWOOL. LAMBDA 0.035-0.037 W/MK. ADVANTAGE: NON-COMBUSTIBLE (A2 FIRE REACTION CLASSIFICATION — CRITICAL FOR BUILDINGS OVER 11M). — PIR BOARD: KINGSPAN KOOLTHERM K5 (LAMBDA 0.020 W/MK) — THINNER SYSTEM, USEFUL WHERE CAVITY AT WINDOW REVEALS IS TIGHT. 60MM PIR ACHIEVES SIMILAR U-VALUE TO 100MM EPS. — AEROGEL RENDER SYSTEM: THERMACTIVE AEROGEL RENDER (LIME-AEROGEL COMPOSITE) — BREATHABLE, THIN (15-20MM), SUITABLE FOR HISTORIC BUILDINGS AND CONSERVATION AREAS. EXPENSIVE: £80-£140/M2 INSTALLED.

U-VALUE IMPROVEMENTS: — PRE-EWI SOLID BRICK WALL: ~1.8 W/M2K — AFTER 60MM EPS EWI: ~0.45 W/M2K — AFTER 100MM EPS EWI: ~0.30 W/M2K — AFTER 60MM PIR EWI: ~0.28 W/M2K

COST: £80-£130/M2 INSTALLED (INCLUDING BOARDS, BASECOAT, MESH, PRIMER, AND SILICONE RENDER TOPCOAT). SCAFFOLD ADDITIONAL (£1,500-£4,000 FOR A TYPICAL LONDON TERRACE).

ECO GRANT: FREE EWI IS AVAILABLE UNDER THE GREAT BRITISH INSULATION SCHEME (GBIS) AND ECO4 SCHEME FOR LOW-INCOME HOUSEHOLDS AND PROPERTIES WITH AN EPC RATING OF D OR BELOW. CHECK ELIGIBILITY AT OFGEM'S ECO4 PORTAL.

BRICK SLIP CLADDING APPLIES THIN SLICES OF REAL OR MANUFACTURED BRICK FACE TO AN EXTERNAL SURFACE, CREATING THE APPEARANCE OF NEW BRICKWORK WITHOUT THE WEIGHT OR COST OF FULL MASONRY CONSTRUCTION. INCREASINGLY POPULAR FOR EXTENSIONS, GARAGE CONVERSIONS, AND EWI TOPCOATS WHERE BRICK CHARACTER IS DESIRED.

SYSTEM OPTIONS:

GLUE-AND-GROUT BRICK SLIPS ON TILE BACKER: BRICK SLIPS (20-30MM THICK) ADHERED TO CEMENT BOARD (HARDIE BACKER, KNAUF AQUAPANEL) USING POLYMER-MODIFIED ADHESIVE (WEBER WEBERSET RAPID FLEX S1 C2F). GROUTED WITH COLOURED GROUT (MAPEI ULTRACOLOR PLUS FA) TO REPLICATE MORTAR JOINTS. SUITABLE FOR EXTENSIONS WHERE TIMBER FRAME IS USED (CEMENT BOARD OVER SHEATHING PLY).

CLIP-SYSTEM BRICK SLIPS (MOEDING, VANDERSANDEN): BRICK SLIPS WITH FACTORY-FORMED CLIPS THAT LOCK ONTO AN ALUMINIUM RAIL SYSTEM. FASTER INSTALLATION, EASIER REPLACEMENT OF INDIVIDUAL SLIPS. FIRE PERFORMANCE TYPICALLY A1 OR A2 CLASS (NON-COMBUSTIBLE REAL CLAY BRICK). SUPPLIERS: MOEDING BRICK SLIPS (GERMAN ORIGIN); VANDERSANDEN THIN BRICK; EUROBRICK K-SYSTEM.

COMPOSITE CLADDING PANELS: FOR MORE CONTEMPORARY PROJECTS: ROCKPANEL WOODS (BASALT FIBRE PANELS WITH WOOD EFFECT, A2-S1,D0 FIRE CLASS); TRESPA METEON HPL (HIGH-PRESSURE LAMINATE, EXCELLENT DURABILITY AND COLOUR RANGE); HARDIE ARCHITECTURAL PANEL (FIBRE CEMENT).

LIMITATIONS IN LONDON: BRICK SLIP CLADDING ON A HOUSE IN A NON-CONSERVATION AREA IS GENERALLY PD (FACING MATERIALS MUST CLOSELY MATCH THE EXISTING PROPERTY UNDER GPDO CLASS A — A DIFFERENT MATERIAL SUCH AS BRICK SLIPS ON A RENDERED BUILDING OR VICE VERSA IS POTENTIALLY OUTSIDE PD). IN CONSERVATION AREAS, PLANNING CONSENT IS REQUIRED.

COST: £60-£100/M2 INSTALLED FOR GLUE-AND-GROUT BRICK SLIP ON CEMENT BOARD; £90-£140/M2 FOR CLIP-SYSTEM BRICK SLIPS. COMPOSITE PANELS £80-£160/M2.

FOR LONDON'S LARGE STOCK OF GEORGIAN, VICTORIAN, AND EDWARDIAN SOLID-BRICK PROPERTIES — PARTICULARLY THOSE IN CONSERVATION AREAS OR LISTED BUILDINGS — LIME RENDER IS THE ONLY APPROPRIATE EXTERNAL WALL FINISH. CEMENT-BASED RENDERS ON PRE-1919 SOLID BRICK PROPERTIES TRAP MOISTURE AND CAUSE SALT DAMAGE, SPALLING, AND STRUCTURAL DETERIORATION. LIME ALLOWS THE WALL TO BREATHE.

LIME RENDER SYSTEM (THREE-COAT ON SOLID BRICK): 1. SCRATCH COAT (SPATTERDASH BOND COAT): ST ASTIER NHL 5 FEATHER FINISH + SHARP SAND 1:2.5. ACTS AS A BONDING LAYER. 2. FLOAT COAT (FLOATING COAT): ST ASTIER NHL 3.5 (FOR EXPOSED FACADES — SLIGHTLY STRONGER) OR NHL 2 (FOR SHELTERED ASPECTS) + SHARP SAND 1:2.5-1:3. APPLIED 10-12MM, SCRATCHED TO RECEIVE FINISH. 3. FINISH COAT: ST ASTIER NHL 3.5 + SILVER SAND 1:2.5. APPLIED 6-8MM, WORKED TO DESIRED TEXTURE — SMOOTH STEEL TROWEL (MOST PERIOD-APPROPRIATE), ROUGHCAST, OR PEBBLE DASH.

KEY PRODUCTS: — ST ASTIER NHL 3.5 (NATURAL HYDRAULIC LIME): THE BENCHMARK PRODUCT FOR EXTERNAL LIME RENDER IN LONDON. 25KG BAGS FROM LIME TECHNOLOGY, LIMETEC, OR BUILD WITH NATURE. — TARMAC LIMELITE RENOVATING PLASTER: PREMIXED LIME-BASED RENDER FOR INTERNAL AND SHELTERED EXTERNAL USE.

IMPORTANT: LIME RENDER MUST NOT BE APPLIED WHEN TEMPERATURES ARE BELOW 5°C OR ARE LIKELY TO FALL BELOW 5°C WITHIN 24 HOURS OF APPLICATION. THE CURING PROCESS REQUIRES SUFFICIENT MOISTURE — SPRAY WITH WATER DURING HOT DRY WEATHER TO PREVENT RAPID DRYING AND CRACKING. EACH COAT MUST BE ALLOWED TO SUFFICIENTLY CURE (TYPICALLY 2-4 WEEKS) BEFORE THE NEXT IS APPLIED. LIME RENDER PROGRAMMES TAKE 6-12 WEEKS FOR THREE COATS.

COST: £50-£80/M2 INSTALLED FOR THREE-COAT LIME RENDER ON SOLID BRICK (MORE EXPENSIVE THAN CEMENT-BASED RENDER DUE TO LONGER PROGRAMME, SKILLED TRADES REQUIRED, AND MATERIAL COSTS).