uPVC Window Replacement in London Victorian Terraces: A-Rated Double Glazing and Conservation Areas

UPVC (UNPLASTICISED POLYVINYL CHLORIDE) WINDOW FRAMES ARE THE DOMINANT MATERIAL FOR REPLACEMENT WINDOWS IN THE UK RESIDENTIAL MARKET — ESTIMATED TO ACCOUNT FOR APPROXIMATELY 75-80% OF ALL REPLACEMENT WINDOW INSTALLATIONS IN THE UK (2024) BY UNIT VOLUME. UPVC WINDOWS ARE MANUFACTURED FROM EXTRUDED PROFILES — THE PROFILES ARE PRODUCED BY A SMALL NUMBER OF LARGE EUROPEAN EXTRUSION MANUFACTURERS (REHAU, VEKA, DECEUNINCK, KOMMERLING — ALL OF WHICH SUPPLY PROFILES TO THE NETWORK OF UK FABRICATORS WHO WELD THE PROFILES INTO FINISHED WINDOW UNITS).

REHAU SYNEGO 86 (REHAU AG — REHAU, GERMANY — THE PREMIUM PROFILE SYSTEM FROM REHAU — THE WORLD'S LARGEST UPVC WINDOW PROFILE MANUFACTURER): 86MM SYSTEM DEPTH (THE FRAME DEPTH FROM INSIDE TO OUTSIDE — 86MM IS THE CURRENT PREMIUM DEPTH FOR UK TRIPLE GLAZED WINDOWS — COMPARED WITH THE EARLIER 70MM AND 60MM SYSTEMS WHICH ACCOMMODATE ONLY DOUBLE GLAZED UNITS). 7-CHAMBER INTERNAL GEOMETRY (THE INTERNAL PROFILE IS DIVIDED INTO 7 SEPARATE AIR CHAMBERS — EACH ADDITIONAL CHAMBER ADDS THERMAL RESISTANCE AND STRUCTURAL RIGIDITY TO THE FRAME). FRAME U-VALUE: 1.0 W/M²K (SIGNIFICANTLY BETTER THAN OLDER 60-70MM UPVC PROFILES AT 1.4-1.8 W/M²K). COMPATIBLE WITH TRIPLE GLAZED UNITS UP TO 44MM DGU THICKNESS. FULLY REINFORCED WITH HOT-DIPPED GALVANISED STEEL INSERTS FOR STRUCTURAL INTEGRITY. COLOUR OPTIONS: WHITE (STANDARD), GREY (RAL 7016 ANTHRACITE — THE MOST POPULAR NON-WHITE COLOUR IN LONDON RESIDENTIAL REPLACEMENT WINDOWS 2023-2025), CREAM, BLACK, AND FOIL-LAMINATED FINISHES (WOODGRAIN FOIL — GOLDEN OAK, ROSEWOOD — LESS POPULAR IN LONDON THAN IN THE MIDLANDS AND NORTH). PRICE RANGE FOR A FABRICATED WINDOW UNIT (SUPPLY ONLY): TYPICAL CASEMENT WINDOW 1200MM WIDE X 1000MM HIGH (A COMMON LONDON VICTORIAN TERRACE FIRST-FLOOR WINDOW SIZE): SINGLE CASEMENT WITH SIDELIGHT — REHAU SYNEGO 86 — WHITE — TRIPLE GLAZED (ARGON — LOW-E — WARM-EDGE SPACER): APPROXIMATELY £350-600 (FROM FABRICATOR).

DECEUNINCK 2800 (DECEUNINCK NV — HOOGLEDE-GITS, BELGIUM — THE SECOND LARGEST UPVC PROFILE MANUFACTURER IN EUROPE): 88MM SYSTEM DEPTH. 5-CHAMBER MAIN FRAME + INTEGRATED DRAINAGE CHANNELS. FRAME U-VALUE: 1.1 W/M²K. WHITE OR RAL COLOUR FOIL. WIDELY USED BY BUDGET AND MID-RANGE UK WINDOW FABRICATORS. COMPARABLE PERFORMANCE TO REHAU SYNEGO 86 AT A MARGINALLY LOWER COST.

VEKA SOFTLINE 82 (VEKA AG — SENDENHORST, GERMANY — THE THIRD LARGEST UPVC EXTRUSION MANUFACTURER): 82MM DEPTH. 5 CHAMBERS. FRAME U-VALUE: 1.2 W/M²K. SOFTER EXTERNAL SIGHTLINE RADII (THE EXTERNAL CORNERS ARE LESS SQUARE THAN REHAU OR DECEUNINCK — SOME SPECIFIERS CONSIDER THE SOFTER PROFILE MORE COMPATIBLE WITH THE CURVED ARCHITRAVES OF VICTORIAN TERRACE WINDOWS). PRICE: SIMILAR TO DECEUNINCK 2800.

THE GLAZING UNIT (THE INSULATING GLASS UNIT — IGU — COMPRISING THE GLASS PANES, SPACER BAR, AND GAS FILL) IS THE LARGEST CONTRIBUTOR TO THE WHOLE-WINDOW U-VALUE — THE FRAME ACCOUNTS FOR APPROXIMATELY 20-30% OF THE TOTAL WINDOW AREA AND THE GLAZED UNIT THE REMAINING 70-80% IN A TYPICAL WINDOW.

TRIPLE GLAZED IGU (THE CURRENT STANDARD FOR PREMIUM REPLACEMENT WINDOWS IN THE UK MARKET): THREE GLASS PANES (TYPICALLY 4MM TOUGHENED OUTER + 12MM GAS CAVITY + 4MM FLOAT + 12MM GAS CAVITY + 4MM INNER GLASS = 36MM TOTAL UNIT WIDTH — THE STANDARD TRIPLE GLAZED UNIT). GAS FILL: ARGON (THE MOST COMMON — CONDUCTIVITY APPROXIMATELY 0.0178 W/MK AT 50% ARGON CONCENTRATION — STANDARD IN MOST PREMIUM UK TRIPLE GLAZED UNITS) OR KRYPTON (HIGHER THERMAL PERFORMANCE — USED IN SLIMMER UNITS WHERE THE CAVITY SPACE IS LIMITED — CONDUCTIVITY APPROXIMATELY 0.0093 W/MK). LOW-E COATING: ALL PREMIUM DOUBLE AND TRIPLE GLAZED UNITS INCLUDE A LOW-EMISSIVITY (LOW-E) COATING ON THE INTERNAL GLASS SURFACE — PILKINGTON ENERGIKARE OR PILKINGTON OPTITHERM S3 PLUS (THE TWO MOST WIDELY USED LOW-E COATINGS IN UK REPLACEMENT WINDOWS) — THE COATING REFLECTS LONG-WAVE INFRARED RADIATION (HEAT) BACK INTO THE ROOM — REDUCING RADIANT HEAT LOSS THROUGH THE GLASS. WARM-EDGE SPACER (THE THERMALLY BROKEN SPACER BAR BETWEEN GLASS PANES — REPLACING THE TRADITIONAL ALUMINIUM SPACER WITH A POLYMER OR FOAM SPACER THAT DOES NOT CONDUCT HEAT BETWEEN THE GLASS PANES AT THE EDGE OF THE UNIT — REDUCING THE LINEAR THERMAL TRANSMITTANCE PSIS — AT THE PERIMETER OF THE GLASS): SWISSPACER V (THE PREMIUM WARM-EDGE SPACER — SWISSPACER AG, SWITZERLAND — EDGE-OF-GLASS CONDENSATION RESISTANCE APPROXIMATELY 40% BETTER THAN ALUMINIUM SPACER — USED BY ALL PREMIUM UK WINDOW FABRICATORS). TYPICAL CENTRE-OF-GLASS U-VALUE FOR A TRIPLE GLAZED 4/12/4/12/4 ARGON LOW-E UNIT: APPROXIMATELY 0.6-0.7 W/M²K. WHOLE-WINDOW U-VALUE (INCLUDING FRAME — REHAU SYNEGO 86 FRAME): APPROXIMATELY 0.8-1.0 W/M²K.

WINDOW ENERGY RATING (WER — THE BFRC WINDOW ENERGY RATING — THE BRITISH FENESTRATION RATING COUNCIL LABEL DISPLAYED ON REPLACEMENT WINDOWS IN THE UK — RATING A++ TO E): THE WER COMBINES THREE FACTORS: HEAT LOSS THROUGH THE WINDOW (U-VALUE), SOLAR HEAT GAIN (G-VALUE — HOW MUCH SOLAR ENERGY PASSES THROUGH THE GLAZING INTO THE ROOM), AND AIR LEAKAGE (L-VALUE). FOR A REPLACEMENT WINDOW TO COMPLY WITH PART L 2021 BUILDING REGULATIONS IN AN EXISTING DWELLING: THE WHOLE-WINDOW U-VALUE MUST BE A MAXIMUM OF 1.6 W/M²K (OR THE WINDOW MUST ACHIEVE A MINIMUM WER OF C-RATED UNDER THE BFRC SCHEME). TRIPLE GLAZED WINDOWS (REHAU SYNEGO 86 + 36MM TRIPLE GLAZED ARGON LOW-E UNIT): TYPICALLY RATED A OR A+ ON THE WER SCALE — EXCEEDING THE PART L 2021 MINIMUM. DOUBLE GLAZED WINDOWS (60-70MM UPVC FRAME + 24MM DOUBLE GLAZED LOW-E ARGON UNIT): TYPICALLY RATED B OR C — BORDERLINE COMPLIANCE WITH PART L 2021 1.6 W/M²K.

WINDOW REPLACEMENT IN A LONDON CONSERVATION AREA IS ONE OF THE MOST COMMON PLANNING ISSUES FACED BY VICTORIAN TERRACE HOMEOWNERS — BECAUSE THE ARTICLE 4 DIRECTION (A LOCAL AUTHORITY ORDER UNDER ARTICLE 4 OF THE TOWN AND COUNTRY PLANNING (GENERAL PERMITTED DEVELOPMENT) ORDER 2015) IN MANY LONDON CONSERVATION AREAS REMOVES THE PERMITTED DEVELOPMENT RIGHT TO REPLACE WINDOWS WITHOUT PLANNING PERMISSION.

ARTICLE 4 DIRECTIONS AND WINDOW REPLACEMENT IN CONSERVATION AREAS: WITHOUT AN ARTICLE 4 DIRECTION: WINDOW REPLACEMENT IS PERMITTED DEVELOPMENT (NO PLANNING PERMISSION REQUIRED) FOR HOUSES IN ENGLAND — UNDER SCHEDULE 2 PART 1 CLASS A OF THE GPDO 2015. WITH AN ARTICLE 4 DIRECTION (WHICH APPLIES TO MOST CONSERVATION AREAS IN INNER LONDON BOROUGHS — INCLUDING CAMDEN, ISLINGTON, HACKNEY, WANDSWORTH, SOUTHWARK, AND LAMBETH): WINDOW REPLACEMENT REQUIRES PLANNING PERMISSION — AND THE LOCAL AUTHORITY WILL TYPICALLY REQUIRE THAT REPLACEMENT WINDOWS MATCH THE ORIGINAL WINDOW STYLE (TYPICALLY VERTICAL SLIDING SASH STYLE FOR A VICTORIAN TERRACE) AND BE IN A MATERIAL THAT IS COMPATIBLE WITH THE CONSERVATION AREA CHARACTER — TYPICALLY TIMBER (NOT UPVC). UPVC IN CONSERVATION AREAS: UPVC WINDOWS ARE ALMOST ALWAYS REFUSED IN A CONSERVATION AREA WITH AN ARTICLE 4 DIRECTION WHERE THE ORIGINAL STYLE WAS TIMBER SASH — THE THICK FRAME PROFILES OF UPVC (TYPICALLY 65-80MM EXTERNAL SIGHTLINES) ARE VISUALLY INCOMPATIBLE WITH THE SLIM PROFILES OF ORIGINAL TIMBER SASH WINDOWS (TYPICALLY 15-25MM GLAZING BAR WIDTH AND 40-50MM FRAME SIGHT LINES).

TIMBER ALTERNATIVES ACCEPTED IN CONSERVATION AREAS (WHEN PLANNING PERMISSION FOR WINDOW REPLACEMENT IS REQUIRED IN A CONSERVATION AREA): ACCOYA (ACETYLATED RADIATA PINE — ACCOYA UK, HERTFORD — THE MOST DIMENSIONALLY STABLE MODIFIED TIMBER WINDOW FRAME MATERIAL AVAILABLE — MODIFIED BY ACETYLATION TO RESIST MOISTURE, ROT, AND DECAY — RATED FOR 50-YEAR ABOVE-GROUND DURABILITY WITHOUT BIOCIDES — THE PREFERRED MATERIAL FOR CONSERVATION AREA REPLACEMENT TIMBER SASH WINDOWS): AVAILABLE FROM BERECO (THE LEADING UK TIMBER SASH WINDOW MANUFACTURER — ABERDEENSHIRE — ACCOYA REPLACEMENT SASH WINDOW UNITS WITH SLIM DOUBLE GLAZED UNITS — BESPOKE AND STANDARD SIZES). PRICE: £1,500-3,000 PER WINDOW (SUPPLY ONLY — SIGNIFICANTLY MORE THAN UPVC). RATIONEL (DANISH — ALDAS AND FORMA RANGE — ACCOYA CLADDING ON PINE CORE — TRIPLE GLAZED — AVAILABLE FROM RATIONEL UK AND APPROVED RETAILERS): PREMIUM TIMBER WINDOW WITH EXCELLENT THERMAL PERFORMANCE (U-VALUE ~0.8 W/M²K WHOLE WINDOW — TRIPLE GLAZED). ALTERNATIVE FOR NON-CONSERVATION AREAS: COMPOSITE WINDOWS (ALUMINIUM-CLAD TIMBER — INTERNORM, VELFAC, RATIONEL VARIO — TIMBER INNER FACE + ALUMINIUM EXTERNAL CLADDING) PROVIDE THE LOOK OF TIMBER INTERNALLY AND REQUIRE MINIMAL EXTERNAL MAINTENANCE — POPULAR IN LONDON PREMIUM RENOVATION MARKET.

WINDOW REPLACEMENT IN A LONDON VICTORIAN TERRACE INVOLVES THREE MAIN INSTALLATION STAGES: REMOVAL OF THE EXISTING WINDOW, PREPARATION OF THE REVEAL (THE BRICK SURROUND OF THE WINDOW OPENING), AND FITTING OF THE NEW WINDOW UNIT.

REMOVAL OF THE EXISTING WINDOW: IN A VICTORIAN TERRACE WHERE THE EXISTING WINDOW IS A LATER UPVC REPLACEMENT (FITTED IN A STANDARD BRICK REVEAL WITHOUT SUBFRAME): THE UPVC WINDOW IS TYPICALLY REMOVED BY CUTTING THE FIXINGS (FRAME FIXINGS INTO THE REVEAL BRICKWORK — TYPICALLY RAWLBOLTS OR FRAME FIXINGS AT 600MM CENTRES THROUGH THE UPVC FRAME FLANGE INTO THE BRICK REVEAL) AND CUTTING THE MASTIC SEAL AT THE PERIMETER. THE EXISTING WINDOW IS THEN LIFTED OUT IN SASHES (REMOVE GLAZED SASHES FIRST TO REDUCE WEIGHT) AND THE FRAME PULLED CLEAR. IN A VICTORIAN TERRACE WHERE THE ORIGINAL TIMBER BOX FRAME IS STILL IN PLACE (EVEN IF THE SASHES HAVE BEEN REPLACED): THE ORIGINAL TIMBER BOX FRAME (THE CASED BOX FRAME WITH SASH WEIGHTS BEHIND) IS SUBSTANTIALLY DEEPER THAN A STANDARD UPVC REVEAL FRAME — REMOVING THE BOX FRAME REVEALS THE FULL MASONRY REVEAL BEHIND — THE NEW WINDOW FITS INTO THIS MASONRY REVEAL DIRECTLY (WITHOUT SUBFRAME). REVEAL PREPARATION: THE MASONRY REVEAL (BRICK JAMBS, HEAD, AND SILL) SHOULD BE CHECKED FOR: SOUND MORTAR JOINTS (REPOINT IN LIME OR CEMENT:LIME 4:1:3 MIX WHERE JOINTS ARE OPEN OR CRUMBLING); LEVEL SILL (THE STONE OR BRICK SILL ONTO WHICH THE WINDOW SITS SHOULD BE LEVEL AND UNDAMAGED — AN UNLEVEL SILL MUST BE BUILT UP WITH MORTAR BEFORE THE WINDOW IS FIXED); EXISTING LINTEL (THE LINTEL OVER THE WINDOW OPENING — IN A VICTORIAN TERRACE THIS IS TYPICALLY EITHER A BRICK JACK ARCH OR A CONCEALED STEEL LINTEL — MUST BE INTACT AND UNCRACKED BEFORE A NEW WINDOW IS FITTED).

FITTING THE NEW WINDOW: THE NEW WINDOW UNIT IS PLACED INTO THE REVEAL — PACKED OFF THE SILL WITH PLASTIC PACKERS TO ACHIEVE THE CORRECT SILL CLEARANCE (MINIMUM 10MM AIR GAP BELOW THE FRAME FOR VENTILATION AND DRAINAGE) — PLUMBED VERTICALLY AND LEVELLED — THEN FIXED THROUGH THE FRAME FLANGE INTO THE BRICK REVEAL WITH STAINLESS STEEL FRAME FIXINGS (MINIMUM 2 PER FRAME SIDE — AT 600MM MAXIMUM CENTRES). THE PERIMETER GAP BETWEEN THE WINDOW FRAME AND THE BRICK REVEAL IS SEALED WITH: EXPANDING FOAM (LOW-EXPANSION WINDOW AND DOOR FOAM — SOUDAL OR HILTI CF 812 — APPLIED AROUND THE FULL PERIMETER — ALLOWED TO CURE — TRIMMED FLUSH) AND EXTERNAL MASTIC SEALANT (SILICONE OR POLYURETHANE — APPLIED OVER THE CURED FOAM AT THE EXTERNAL FACE — TOOLED SMOOTH — ENSURES A CONTINUOUS WATERPROOF SEAL AT THE WEATHER FACE).

WINDOW REPLACEMENT IN AN EXISTING DWELLING (NOT A NEW BUILD OR EXTENSION) IS BUILDING REGULATIONS-NOTIFIABLE UNDER PART L (CONSERVATION OF FUEL AND POWER) IN THE FOLLOWING CIRCUMSTANCES.

WHEN IS WINDOW REPLACEMENT NOTIFIABLE: ALL WINDOW REPLACEMENTS (REMOVING AN EXISTING WINDOW AND FITTING A NEW UNIT IN THE SAME OPENING — REPLACEMENT WINDOWS) ARE NOTIFIABLE UNDER PART L BECAUSE THEY CONSTITUTE A RENOVATION TO A THERMAL ELEMENT (THE WINDOW IS A THERMAL ELEMENT OF THE BUILDING ENVELOPE). THE INSTALLER MUST EITHER: BE REGISTERED UNDER A COMPETENT PERSON SCHEME (FENSA — FENESTRATION SELF-ASSESSMENT SCHEME — OR CERTASS — THE TWO MAIN COMPETENT PERSON SCHEMES FOR WINDOW AND DOOR INSTALLERS IN ENGLAND — BOTH ALLOW REGISTERED INSTALLERS TO SELF-CERTIFY THEIR OWN WINDOW INSTALLATIONS WITHOUT BUILDING CONTROL INVOLVEMENT), OR NOTIFY BUILDING CONTROL BEFORE INSTALLATION AND OBTAIN A COMPLETION CERTIFICATE AFTER INSTALLATION (THE BUILDING CONTROL ROUTE — MORE EXPENSIVE AND SLOWER — NOT USED IN PRACTICE FOR STANDARD REPLACEMENT WINDOWS). VIRTUALLY ALL UK REPLACEMENT WINDOW INSTALLERS ARE FENSA OR CERTASS REGISTERED — THIS IS A STANDARD INDUSTRY REQUIREMENT. THE INSTALLER ISSUES A FENSA CERTIFICATE (OR CERTASS CERTIFICATE) AFTER INSTALLATION — THE CERTIFICATE IS REGISTERED WITH THE LOCAL AUTHORITY AND CAN BE SEARCHED BY SOLICITORS AS PART OF A HOUSE PURCHASE (FENSA CERTIFICATES ARE THE PRIMARY EVIDENCE THAT A REPLACEMENT WINDOW COMPLIES WITH BUILDING REGULATIONS — THE ABSENCE OF A CERTIFICATE FOR REPLACEMENT WINDOWS VISIBLE ON A HOUSE CAN CAUSE ISSUES ON CONVEYANCING).

PART L 2021 U-VALUE REQUIREMENT FOR REPLACEMENT WINDOWS: MAXIMUM WHOLE-WINDOW U-VALUE 1.6 W/M²K (OR MINIMUM BFRC WER OF C-RATING). IN PRACTICE: ALL CURRENT UPVC DOUBLE GLAZED WINDOWS (WITH LOW-E COATING AND ARGON FILL IN THE CAVITY) ACHIEVE APPROXIMATELY 1.4-1.6 W/M²K WHOLE-WINDOW U-VALUE — BORDERLINE COMPLIANCE. UPVC TRIPLE GLAZED WINDOWS (REHAU SYNEGO 86 OR EQUIVALENT): 0.8-1.1 W/M²K — WELL WITHIN PART L 2021. SINGLE GLAZED REPLACEMENT: WOULD NOT COMPLY WITH PART L 2021 AND SHOULD NOT BE SPECIFIED FOR NOTIFIABLE REPLACEMENT WINDOW WORK.

REPLACEMENT WINDOW COSTS IN LONDON (2025 — SUPPLY AND FIT — FENSA-REGISTERED INSTALLER — INCLUDING REMOVAL OF EXISTING WINDOW, FITTING OF NEW WINDOW, EXPANDING FOAM, MASTIC SEAL, AND FENSA CERTIFICATE REGISTRATION).

UPVC CASEMENT WINDOW (REHAU SYNEGO 86 OR EQUIVALENT — TRIPLE GLAZED — WHITE — STANDARD CASEMENT OPENING WITH FIXED SIDELIGHT — APPROXIMATELY 1200MM WIDE X 1050MM HIGH — THE STANDARD FIRST-FLOOR WINDOW SIZE IN A LONDON VICTORIAN TERRACE): SUPPLY: £350-600 PER WINDOW. INSTALLATION LABOUR: £150-250 PER WINDOW. TOTAL SUPPLY AND FIT: £500-850 PER WINDOW.

UPVC SASH REPLACEMENT WINDOW (A UPVC WINDOW DESIGNED TO REPLICATE THE APPEARANCE OF A TIMBER SASH WINDOW — VERTICAL SLIDING SASH MOVEMENT — DOUBLE HUNG — USED IN CONSERVATION AREAS WHERE UPVC IS PERMITTED OR FOR PROPERTIES OUTSIDE CONSERVATION AREAS WHERE THE OWNER WANTS A SASH APPEARANCE WITHOUT TIMBER MAINTENANCE): SUPPLY: £600-1,000 PER WINDOW (MORE EXPENSIVE THAN STANDARD CASEMENT — SASH-REPLACEMENT UPVC HAS A MORE COMPLEX PROFILE AND MECHANISM). TOTAL SUPPLY AND FIT: £750-1,250 PER WINDOW.

TIMBER SASH REPLACEMENT (ACCOYA — BERECO — CONSERVATION AREA): SUPPLY: £1,500-3,000 PER WINDOW. INSTALLATION: £250-500 PER WINDOW. TOTAL: £1,750-3,500 PER WINDOW.

FULL VICTORIAN TERRACE WINDOW REPLACEMENT (ALL WINDOWS — TYPICAL LONDON VICTORIAN TWO-STOREY TERRACE — 8-10 WINDOWS — UPVC CASEMENT TRIPLE GLAZED — WHITE): TOTAL SUPPLY AND FIT (INCLUDING BAY WINDOW IF APPLICABLE — BAY WINDOW MORE EXPENSIVE DUE TO ANGLED FRAME JOINS AND ACCESS REQUIREMENTS): £4,000-8,500. FOR TIMBER ACCOYA (CONSERVATION AREA — SAME QUANTITY): £14,000-35,000.

BAY WINDOW PREMIUM: IN A LONDON VICTORIAN TERRACE WITH A BAY WINDOW AT GROUND LEVEL (A VERY COMMON FEATURE — THREE-SIDED BAY AT 45° OR BOX BAY AT 90°), THE BAY WINDOW IS TYPICALLY 30-50% MORE EXPENSIVE THAN A FLAT WINDOW OF THE SAME SIZE — DUE TO THE ANGLED JOINERY AT THE BAY CORNERS, THE REQUIREMENT FOR A LEAD OR FELT-COVERED BAY ROOF, AND THE ADDITIONAL SCAFFOLDING OR ACCESS EQUIPMENT REQUIRED TO WORK ON THE EXTERNAL FACE.