Heritage Renovation in London: Listed Buildings, Conservation Areas & Period Properties

A LISTED BUILDING IS A BUILDING OR STRUCTURE PLACED ON THE STATUTORY LIST OF BUILDINGS OF SPECIAL ARCHITECTURAL OR HISTORIC INTEREST UNDER THE PLANNING (LISTED BUILDINGS AND CONSERVATION AREAS) ACT 1990. IN ENGLAND, THE LIST IS MAINTAINED BY HISTORIC ENGLAND.

GRADES OF LISTING: — GRADE I: BUILDINGS OF EXCEPTIONAL INTEREST. ONLY 2% OF ALL LISTED BUILDINGS. IN LONDON: BUCKINGHAM PALACE, TOWER OF LONDON, THE NATURAL HISTORY MUSEUM, AND MANY OF INIGO JONES'S AND CHRISTOPHER WREN'S BUILDINGS. MOST STRINGENT CONTROLS. — GRADE II* (GRADE TWO STAR): PARTICULARLY IMPORTANT BUILDINGS OF MORE THAN SPECIAL INTEREST. AROUND 6% OF LISTED BUILDINGS. INCLUDES SIGNIFICANT VICTORIAN AND EDWARDIAN TERRACE STREETS IN LONDON AND GEORGIAN TOWNHOUSES. — GRADE II: NATIONALLY IMPORTANT AND OF SPECIAL INTEREST. APPROXIMATELY 92% OF ALL LISTED BUILDINGS. INCLUDES THE MAJORITY OF LONDON'S GEORGIAN, REGENCY, AND EARLY VICTORIAN HOUSING STOCK THAT IS LISTED.

LISTED BUILDING CONSENT: ANY WORKS TO A LISTED BUILDING THAT AFFECT ITS CHARACTER AS A BUILDING OF SPECIAL ARCHITECTURAL OR HISTORIC INTEREST REQUIRE LISTED BUILDING CONSENT (LBC) FROM THE LOCAL PLANNING AUTHORITY. THIS IS IN ADDITION TO ANY PLANNING PERMISSION REQUIRED. THERE IS NO FEE FOR AN LBC APPLICATION, BUT THE APPLICATION REQUIRES DETAILED HERITAGE IMPACT ASSESSMENT AND SUPPORTING DOCUMENTATION.

IMPORTANT: LISTED BUILDING STATUS APPLIES TO THE ENTIRE BUILDING, ALL FIXED ELEMENTS, AND ANY CURTILAGE BUILDINGS — NOT JUST THE FACADE. INTERNAL WORKS TO A LISTED BUILDING (REMOVING A FIREPLACE, REPLACING FLOORBOARDS, TAKING DOWN AN INTERNAL WALL) MAY ALL REQUIRE LISTED BUILDING CONSENT IF THEY AFFECT SIGNIFICANCE.

CONSEQUENCES OF UNLAWFUL WORKS: WORKS TO A LISTED BUILDING WITHOUT CONSENT IS A CRIMINAL OFFENCE UNDER S.7 OF THE PLANNING (LISTED BUILDINGS AND CONSERVATION AREAS) ACT 1990 — REGARDLESS OF WHETHER THE WORKS WOULD HAVE BEEN APPROVED. PENALTIES INCLUDE AN UNLIMITED FINE AND/OR UP TO 2 YEARS IMPRISONMENT FOR INDIVIDUALS, AND THE LPA MAY REQUIRE RESTORATION OF THE BUILDING AT THE OWNER'S EXPENSE.

CONSERVATION AREAS ARE AREAS OF SPECIAL ARCHITECTURAL OR HISTORIC INTEREST DESIGNATED BY LOCAL PLANNING AUTHORITIES UNDER S.69 OF THE PLANNING (LISTED BUILDINGS AND CONSERVATION AREAS) ACT 1990. LONDON HAS OVER 1,000 CONSERVATION AREAS — MANY BOROUGHS HAVE DOZENS (CAMDEN HAS 37; WESTMINSTER HAS 55; ISLINGTON HAS 28).

WORKS REQUIRING PERMISSION IN CONSERVATION AREAS: — DEMOLITION OF A BUILDING OVER 115M3 REQUIRES CONSERVATION AREA CONSENT (C.A. CONSENT APPLICATION) — EXTERNAL CHANGES VISIBLE FROM A PUBLIC PLACE THAT AFFECT THE CHARACTER OF THE AREA REQUIRE PLANNING PERMISSION — REPLACING WINDOWS: PERMITTED DEVELOPMENT FOR WINDOW REPLACEMENT IS REMOVED IN MOST CONSERVATION AREAS — PLANNING PERMISSION REQUIRED, AND REPLACEMENT WITH UPVC IS ALMOST ALWAYS REFUSED — INSTALLING SOLAR PANELS, SATELLITE DISHES, OR OTHER VISIBLE EXTERNAL ITEMS: OFTEN RESTRICTED IN CONSERVATION AREAS — EXTENSIONS ON FRONT ELEVATION: ALMOST ALWAYS REQUIRE PLANNING PERMISSION AND SCRUTINISED FOR CHARACTER IMPACT

ARTICLE 4 DIRECTIONS: BEYOND CONSERVATION AREAS, MANY LONDON BOROUGHS APPLY ARTICLE 4 DIRECTIONS TO SPECIFIC STREETS OR AREAS — REMOVING PERMITTED DEVELOPMENT RIGHTS AND REQUIRING PLANNING PERMISSION FOR WORKS THAT WOULD OTHERWISE BE PD. BEFORE CARRYING OUT ANY EXTERNAL WORKS, CHECK WITH THE BOROUGH WHETHER AN ARTICLE 4 DIRECTION APPLIES.

BORIOUGH CHARACTER APPRAISALS: EACH LONDON CONSERVATION AREA HAS (OR SHOULD HAVE) A PUBLISHED CHARACTER APPRAISAL AND MANAGEMENT PLAN FROM THE LPA — TYPICALLY AVAILABLE ON THE BOROUGH'S WEBSITE. THESE DOCUMENTS DESCRIBE THE SIGNIFICANCE OF THE AREA, THE ARCHITECTURAL FEATURES THAT DEFINE ITS CHARACTER, AND THE SPECIFIC DESIGN REQUIREMENTS FOR PROPOSALS. READING THE CHARACTER APPRAISAL BEFORE PREPARING AN APPLICATION IS ESSENTIAL — IT IDENTIFIES WHICH MATERIALS, PROPORTIONS, AND DETAILS ARE EXPECTED.

THE CORRECT SPECIFICATION OF MATERIALS IS THE MOST CRITICAL TECHNICAL ELEMENT OF HERITAGE RENOVATION IN LONDON. USING INCOMPATIBLE MODERN MATERIALS IN A HISTORIC BUILDING CAN CAUSE MORE DAMAGE THAN THE PROBLEM THEY WERE INTENDED TO SOLVE.

LIME MORTAR (THE FUNDAMENTAL RULE): PRE-1920 LONDON BUILDINGS WERE BUILT WITH LIME-BASED MORTARS — EITHER HOT LIME (QUICKLIME SLAKED ON SITE) OR HYDRAULIC LIME MORTARS. PORTLAND CEMENT MORTARS (WHICH BECAME STANDARD AFTER 1920) ARE INCOMPATIBLE WITH HISTORIC BRICKWORK AND STONEWORK BECAUSE: — CEMENT MORTAR IS MUCH STRONGER AND LESS PERMEABLE THAN THE HISTORIC BRICK — WHEN THERMAL CYCLING CREATES MOVEMENT, THE BRICK FACES SPALL RATHER THAN THE JOINT COMPRESSING (THE INTENDED "SACRIFICIAL JOINT" FUNCTION) — CEMENT MORTAR TRAPS MOISTURE WITHIN THE WALL RATHER THAN ALLOWING VAPOUR TO ESCAPE THROUGH THE PERMEABLE LIME JOINT

CORRECT LIME MORTAR SPECIFICATION FOR LONDON STOCK BRICK REPOINTING: — ST. ASTIER NHL 3.5 (NATURAL HYDRAULIC LIME) OR LIME PUTTY + SHARP SAND (1:2.5 OR 1:3 MIX) — AGGREGATE COLOUR AND TEXTURE: SHARP SILVER SAND OR WASHED BUILDING SAND MATCHING ORIGINAL MORTAR COLOUR — TYPICALLY WARM BUFF/PALE YELLOW FOR LONDON STOCK BRICK — JOINT PROFILE: FLUSH-STRUCK OR SLIGHTLY RECESSED — NEVER WEATHERSTRUCK (PROJECTING) POINTING WHICH CHANNELS RAINWATER ONTO BRICK FACES — AVOID: PREMIXED READY-MIXED CEMENT MORTARS FOR REPOINTING HISTORIC BRICKWORK

BRICK MATCHING: RECLAIMED LONDON STOCK BRICK (FROM LASSCO, BRIGHTON ARCHITECTURAL SALVAGE, HUTTON+ROSTRON) IS THE GOLD STANDARD FOR REPAIRS AND EXTENSIONS. NEW LONDON STOCK (IBSTOCK KB71, HANSON LONDON YELLOW STOCK, MICHELMERSH SURREY MULTI) IS ACCEPTABLE BUT NEVER AS WELL-MATCHED AS RECLAIMED.

TIMBER: OAK, ACCOYA, AND SOFTWOOD: For heritage timber repairs (window frames, sashes, doors, joinery), accoya is the modern preferred timber — rot-resistant class 1, dimensionally stable, accepts lime and oil-based paints. Oak for structural elements (beam repairs, floor joists). Scandinavian redwood for like-for-like sash window replacements.

ROOF MATERIALS: — WELSH SLATE (CWMORTHIN, PENRHYN SLATE): THE AUTHENTIC ROOF MATERIAL FOR MOST GEORGIAN AND VICTORIAN LONDON TERRACES. STILL AVAILABLE NEW FROM WELSH SLATE LTD AND RECLAIMED FROM SALVO. — CLAY PLAIN TILES (ACME CLAY OR KEYMER): FOR CLAY-TILED AREAS OF LONDON — LEAD (CODE 5 OR CODE 6 BS EN 12588): FOR FLAT ROOF SECTIONS, VALLEY GUTTERS, FLASHINGS, AND PARAPET LININGS IN HERITAGE CONTEXTS WHERE AUTHENTICITY IS REQUIRED

THE MOST TECHNICALLY DEMANDING ASPECT OF HERITAGE RENOVATION IN LONDON IS THE MANAGEMENT OF MOISTURE AND THE APPLICATION OF INSULATION IN A WAY THAT IS COMPATIBLE WITH HISTORIC FABRIC.

BREATHABLE CONSTRUCTION PRINCIPLE: HISTORIC SOLID-WALL BUILDINGS (LONDON GEORGIAN AND VICTORIAN TERRACES ARE TYPICALLY 215MM-340MM SOLID BRICK, NOT CAVITY CONSTRUCTION) WERE DESIGNED TO MANAGE MOISTURE BY ABSORPTION AND EVAPORATION — THE LIME MORTAR, LIME PLASTER, AND DISTEMPER PAINTS USED HISTORICALLY ALL PERMITTED VAPOUR TRANSMISSION. MODERN CEMENT-BASED RENDERS, GYPSUM PLASTERS, AND VINYL PAINTS REDUCE OR ELIMINATE THIS VAPOUR PERMEABILITY — TRAPPING MOISTURE IN THE WALL AND CAUSING INTERSTITIAL CONDENSATION, DAMP, MOULD, AND ACCELERATED DECAY OF HISTORIC MATERIALS.

INTERNAL WALL INSULATION FOR SOLID BRICK HERITAGE WALLS: EXTERNAL WALL INSULATION IS RARELY ACCEPTABLE ON HERITAGE BUILDINGS — IT ALTERS THE EXTERNAL APPEARANCE (OFTEN REFUSED IN CONSERVATION AREAS). INTERNAL WALL INSULATION IS TECHNICALLY FEASIBLE BUT MUST BE SPECIFIED CAREFULLY:

1. BREATHABLE INTERNAL INSULATION (PREFERRED FOR HERITAGE): — WOOD FIBRE BOARD (GUTEX THERMOWALL 60MM, PAVATEX ISOLAIR, OR DIFFUTHERM): VAPOUR-PERMEABLE THERMAL INSULATION FIXED DIRECTLY TO THE INTERNAL BRICK FACE, PLASTERED WITH LIME FINISH PLASTER. U-VALUE IMPROVEMENT: FROM ~2.0 W/M2K (215MM SOLID BRICK) TO 0.7-0.8 W/M2K. — HEMP LIME (HEMCRETE BY LIME TECHNOLOGY): CAST OR SPRAYED HEMP-LIME COMPOSITE — HIGHLY BREATHABLE, EXCELLENT HYGRIC BUFFERING, VERY GOOD MATCH TO HISTORIC MATERIALS.

2. PIR / CONVENTIONAL RIGID INSULATION (NOT RECOMMENDED FOR HERITAGE): CELOTEX OR KINGSPAN PIR RIGID FOAM WITH GYPSUM BOARD FACING — HIGH THERMAL RESISTANCE BUT VERY LOW VAPOUR PERMEABILITY. CREATES A VAPOUR CHECK WITHIN THE WALL THAT RISKS INTERSTITIAL CONDENSATION IN THE RESIDUAL VOID BETWEEN INSULATION AND HISTORIC BRICK. USE A FULL WUFI HYGROTHERMAL ANALYSIS (WUFI-PRO OR WUFI-2D) BEFORE SPECIFYING IN A HERITAGE CONTEXT.

FLOOR INSULATION IN HERITAGE BUILDINGS: ORIGINAL SUSPENDED TIMBER GROUND FLOORS IN LONDON TERRACES ARE TYPICALLY BREATHABLE — AIR CIRCULATES BELOW THE FLOOR THROUGH AIRBRICKS. INSULATING FROM BELOW (EARTHWOOL GLASSWOOL DRAPING BETWEEN JOISTS) IS MORE HERITAGE-COMPATIBLE THAN FROM ABOVE (WHICH RAISES FLOOR LEVEL AND AFFECTS DOOR AND ARCHITRAVE DETAILS).

PRESERVING AND RESTORING ORIGINAL FEATURES IS BOTH A REGULATORY REQUIREMENT IN LISTED BUILDINGS AND A POWERFUL WAY TO PRESERVE AND ENHANCE THE VALUE OF A LONDON PERIOD PROPERTY.

FIREPLACES AND CHIMNEY STACKS: VICTORIAN AND EDWARDIAN LONDON FIREPLACES WERE TYPICALLY CAST-IRON (CAST-IRON REGISTER GRATES WITH TILED SURROUND AND CAST-IRON FIRE SURROUND) IN BEDROOMS AND SIMPLE ROOMS, AND MARBLE SURROUNDS WITH CAST-IRON INSERTS IN RECEPTION ROOMS. RESTORED FIREPLACES: LASSCO, ARCHITECTURAL FORUM, NOSTALGIA IRONMONGERS, THORNHILL GALLERIES (ALL LONDON-BASED) STOCK PERIOD ORIGINAL AND REPRODUCTION ITEMS.

FLOORBOARDS: ORIGINAL WIDE VICTORIAN FLOORBOARDS (TYPICALLY 125-150MM WIDE SOFTWOOD — SCANDINAVIAN REDWOOD OR SCOTS PINE) SHOULD BE RESTORED WHERE POSSIBLE. GAP-FILLING (TRADITIONAL PAPER AND PASTE TECHNIQUE, OR MODERN FLEXIBLE GAP FILLER LIKE BOSTIK SEAL 'N' FLEX) BEFORE SANDING AND RE-FINISHING WITH HARDWAX OIL (OSMO POLYX-OIL 3054 CLEAR SATIN OR BONA HARDWAX OIL).

CORNICING AND CEILING ROSES: PLASTER CORNICES AND CEILING ROSES ARE SIGNIFICANT FEATURES IN GEORGIAN AND VICTORIAN LONDON ROOMS. WHERE ORIGINAL CORNICE IS MISSING: — FIBROUS PLASTER REPRODUCTION (PROPORTIONAL PLASTER, STEVENSONS OF NORWICH, HB FULLER FIBROUS PLASTER): CAST FROM ORIGINAL PROFILES OR PERIOD-MATCHED CATALOGUES — CAN BE NEARLY INDISTINGUISHABLE FROM ORIGINAL. — LIME PLASTER CORNICE RUN IN SITU: THE AUTHENTIC METHOD — A SKILLED PLASTERER RUNS LIME PUTTY PLASTER CORNICE IN SITU USING A PROFILE TEMPLATE. FEWER SKILLED PRACTITIONERS EXIST (LIME GREEN, TRADITIONAL LIME)

DOORS AND IRONMONGERY: PANELLED TIMBER DOORS (2-PANEL, 4-PANEL, OR 6-PANEL DEPENDING ON FLOOR AND PERIOD) IN RECLAIMED VICTORIAN SOFTWOOD (LASSCO) OR REPRODUCTION (LPD DOORS VICTORIAN 4-PANEL IN HEMLOCK). IRONMONGERY: RECLAIMED OR REPRODUCTION BRASS (BRASS "MORTICE KNOB" SETS FROM CHATSWORTH IRONMONGERY, BRITISH IRONMONGERY, RICHMOND DOOR KNOBS, OR THE CAST IRON SHOP).