Rooflights for London Victorian Terraces: Flat Roof, Pitched Roof, and Lantern Specifications

ROOFLIGHTS FOR LONDON VICTORIAN TERRACE PROPERTIES FALL INTO THREE MAIN CATEGORIES — EACH WITH DIFFERENT PRODUCT TYPES, SPECIFICATION CONSIDERATIONS, AND PLANNING IMPLICATIONS.

CATEGORY 1 — PITCHED ROOF ROOFLIGHTS (INSTALLED IN THE SLOPING ROOF PLANE OF A PITCHED ROOF — FLUSH OR NEAR-FLUSH WITH THE ROOF SURFACE): USED IN LOFT CONVERSIONS (VELUX OR FAKRO ROOF WINDOWS IN THE REAR ROOF SLOPE) AND IN THE REAR ADDITION PITCHED ROOF OF A VICTORIAN TERRACE (WHERE THE REAR ADDITION HAS A LEAN-TO ROOF AT APPROXIMATELY 10-20° PITCH). INSTALLATION: THE ROOFLIGHT IS SEATED BETWEEN RAFTERS — RAFTERS MAY NEED TO BE TRIMMED (CUT AND RE-SUPPORTED WITH A DOUBLE TRIMMER RAFTER ON EACH SIDE OF THE OPENING) IF THE ROOFLIGHT WIDTH EXCEEDS ONE RAFTER SPACING. THE ROOFLIGHT FRAME SITS IN THE TRIMMED OPENING AND IS FIXED TO THE TRIMMER RAFTERS. FLASHING: THE JUNCTION BETWEEN THE ROOFLIGHT FRAME AND THE SURROUNDING ROOF COVERING MUST BE WEATHERPROOFED — VELUX AND FAKRO SUPPLY INTEGRATED FLASHING KITS FOR THEIR ROOFLIGHTS (SPECIFIC TO EACH ROOF COVERING TYPE — TILES, SLATES, FLAT ROOF — AND EACH PITCH RANGE).

CATEGORY 2 — FLAT ROOF ROOFLIGHTS (INSTALLED IN A FLAT OR LOW-PITCH ROOF — 0-15° — INCLUDING THE FLAT ROOF OF A NEW KITCHEN OR REAR EXTENSION): TWO MAIN TYPES: FIXED FLAT ROOFLIGHTS (SINGLE-UNIT UPSTAND-MOUNTED FIXED GLAZING — THE MOST COST-EFFECTIVE FLAT ROOF ROOFLIGHT — INSTALLED ON A UPSTAND OF 150MM MINIMUM HEIGHT TO ALLOW WATER TO RUN OFF THE ROOF COVERING AND AWAY FROM THE GLAZING UNIT BELOW THE FRAME) AND ROOFLIGHT LANTERNS (A RIDGE-AND-RAFTER STRUCTURAL GLAZING FRAMEWORK — EITHER ALUMINIUM OR TIMBER — FORMING AN UPSTAND ABOVE THE FLAT ROOF — THE MOST ARCHITECTURALLY IMPRESSIVE OPTION FOR A FLAT ROOF ABOVE A KITCHEN REAR EXTENSION).

CATEGORY 3 — STRUCTURAL GLASS ROOFLIGHTS AND WALK-ON ROOFLIGHTS (INSTALLED AT FLOOR LEVEL — TYPICALLY IN A LOWER-GROUND-FLOOR OR BASEMENT EXTENSION CONTEXT — OR AS A WALK-ON ELEMENT IN AN EXTERNAL TERRACE ABOVE A BASEMENT ROOM): NOT COVERED IN DETAIL IN THIS GUIDE — THESE ARE BESPOKE STRUCTURAL GLASS PRODUCTS (SKY-FRAME GLASS — CANTILEVERED STRUCTURAL GLASS PANEL — OR BOLTED CAST GLASS BLOCK SYSTEMS) AND REQUIRE STRUCTURAL ENGINEERING INPUT.

PITCHED ROOF ROOFLIGHTS FOR LONDON VICTORIAN TERRACE LOFT CONVERSIONS AND REAR ADDITION ROOFS.

VELUX GGU SK08 (VELUX A/S — DENMARK — THE MOST WIDELY SPECIFIED ROOF WINDOW IN UK RESIDENTIAL LOFT CONVERSIONS): THE VELUX GGU RANGE IS THE POLYURETHANE (PU) CLAD VARIANT OF THE VELUX PRODUCT RANGE — SUITABLE FOR WET ROOM OR BATHROOM APPLICATIONS (MOISTURE-RESISTANT CLADDING) AS WELL AS STANDARD DRY ROOM USE. SK08 = SIZE CODE: S = STANDARD (55MM FROM TOP OF BOTTOM SASH TO BOTTOM OF FRAME) — K = KILO (WIDER FRAME PROFILE) — 08 = SIZE CODE DESIGNATING 114MM WIDE X 140MM HIGH (ROUGH OPENING 970MM X 1600MM — EXCLUDING FRAME). THE GGU SK08 IS THE MOST COMMONLY SPECIFIED SINGLE UNIT FOR A LOFT CONVERSION EN-SUITE WET ROOM WHERE THE ROOF SLOPE AREA IS LIMITED. GLAZING: VELUX INTEGRA (ELECTRIC OPERATION VIA REMOTE CONTROL — USEFUL IN LOFT CONVERSIONS WHERE THE ROOFLIGHT IS HIGH ON THE ROOF AND DIFFICULT TO REACH) OR VELUX SOLAR INTEGRA (SOLAR-POWERED ELECTRIC OPERATION — NO MAINS WIRING REQUIRED TO THE ROOFLIGHT). GLAZING U-VALUE: VELUX TRIPLE GLAZED (THE CURRENT STANDARD FOR NEW VELUX INSTALLATIONS — CENTRE-GLASS U-VALUE 0.5 W/M²K — WHOLE-WINDOW U-VALUE APPROXIMATELY 1.0-1.2 W/M²K — MEETING PART L 2021 REQUIREMENT OF 1.8 W/M²K FOR ROOFLIGHTS). SUPPLY PRICE (GGU SK08 INTEGRA — ELECTRIC — TRIPLE GLAZED): APPROXIMATELY £700-1,100 (2025 UK BUILDERS MERCHANT). ADDITIONAL FLASHING KIT: £80-200 (SPECIFIC TO ROOF COVERING TYPE).

FAKRO FTP-V (FAKRO PP — POLAND — THE MAIN ALTERNATIVE TO VELUX IN THE UK MARKET — COMPARABLE SPECIFICATION AND PRICE): THE FAKRO FTP-V IS THE FLAT ROOF WINDOW (DIFFERENT FROM THE PITCHED ROOF MODELS — THE FTP-V IS A LOW-PITCH FIXED ROOFLIGHT FOR PITCHES 2-15°) — MOST COMMONLY USED ON THE LEAN-TO REAR ADDITION ROOF OF A LONDON VICTORIAN TERRACE WHERE THE PITCH IS TOO LOW FOR STANDARD PITCHED ROOF VELUX INSTALLATION (STANDARD VELUX MINIMUM PITCH IS 15° — SOME MODELS ACCEPT DOWN TO 10° WITH A TILE COVERING CONVERSION KIT). FAKRO FTP-V ALSO SUPPLIES A QUADRANT PROFILE FLASHING FOR THE LOW PITCH TRANSITION BETWEEN THE ROOFLIGHT AND THE ROOF COVERING (EPDM RUBBER OR MINERAL FELT). PRICE: SIMILAR TO VELUX EQUIVALENT (WITHIN 10-15%).

CONSERVATION ROOFLIGHTS (THE CORRECT PRODUCT FOR A CONSERVATION AREA PROPERTY OR LISTED BUILDING LOFT CONVERSION — WHERE FLUSH INSTALLATION IS REQUIRED RATHER THAN THE RAISED FRAME OF A STANDARD VELUX): FINELINE GLAZING (THE MOST WIDELY SPECIFIED UK CONSERVATION ROOFLIGHT MANUFACTURER — BASED IN WORCESTERSHIRE): THE FINELINE CONSERVATION ROOFLIGHT IS DESIGNED TO LIE AS NEARLY FLUSH WITH THE ROOF PLANE AS POSSIBLE (MAXIMUM PROJECTION OF 15-25MM FROM THE ROOF SURFACE — VS 50-75MM FOR A STANDARD VELUX FRAME) — ALUMINIUM FRAME — AVAILABLE IN STANDARD SIZES AND BESPOKE. PRICE: £350-800 PER UNIT (FIXED) — SIGNIFICANTLY MORE EXPENSIVE THAN VELUX FOR EQUIVALENT GLAZED AREA.

FOR A FLAT ROOF REAR EXTENSION (THE MOST COMMON TYPE OF NEW KITCHEN OR DINING ROOM REAR EXTENSION IN LONDON VICTORIAN TERRACE RENOVATION — EITHER WITH A FLAT EPDM RUBBER ROOF OR A WARM DECK FELT ROOF), THE MAIN ROOFLIGHT OPTIONS ARE FIXED FLATGLASS ROOFLIGHTS AND ROOFLIGHT LANTERNS.

FIXED FLATGLASS ROOFLIGHTS (SINGLE-UNIT ALUMINIUM-FRAMED FIXED GLAZING MOUNTED ON A 150MM MINIMUM UPSTAND ABOVE THE FLAT ROOF SURFACE): THE MOST COST-EFFECTIVE FLAT ROOF ROOFLIGHT SOLUTION. LEADING PRODUCTS: BRETT MARTIN SKY-FRAME FIXED (BRETT MARTIN LTD — COVENTRY — THE LARGEST UK MANUFACTURER OF FIXED FLAT ROOF ROOFLIGHTS FOR RESIDENTIAL USE — AVAILABLE IN SIZES FROM 600X600MM TO 3000X3000MM IN STANDARD SIZES). THERMALLY BROKEN ALUMINIUM FRAME (POLYAMIDE THERMAL BREAK — PREVENTS CONDENSATION ON INTERNAL FACE OF FRAME AT PERIMETER). TRIPLE GLAZED UNIT (28MM TOTAL DGU — 4MM OUTER GLASS + 16MM ARGON-FILLED CAVITY + 4MM INNER GLASS + ADDITIONAL GLASS = TRIPLE 4/12/4 — CENTRE-GLASS U-VALUE 0.8 W/M²K — WHOLE-UNIT U-VALUE APPROXIMATELY 1.5-1.8 W/M²K MEETING PART L 2021). AVAILABLE IN WHITE, ANTHRACITE GREY (RAL 7016), OR SILVER POWDER COAT. PRICE (SUPPLY ONLY): 1000X1500MM: APPROXIMATELY £450-700. 1500X2000MM: £700-1,100. 2000X3000MM: £1,200-1,800.

KORNICHE ALUMINIUM LANTERN (KORNICHE — THE MOST WIDELY SPECIFIED ALUMINIUM ROOFLIGHT LANTERN IN UK RESIDENTIAL EXTENSIONS 2022-2025): THE KORNICHE IS A PRE-ASSEMBLED RIDGE-AND-RAFTER ALUMINIUM STRUCTURAL GLAZING FRAME — SUPPLIED FLAT-PACKED AND ASSEMBLED ON SITE IN APPROXIMATELY 2-3 HOURS BY ONE OR TWO FITTERS (SIGNIFICANTLY FASTER THAN TRADITIONAL TIMBER OR STEEL FRAME LANTERNS). SLIM SIGHTLINES: THE KORNICHE HAS THE SLIMMEST ALUMINIUM SIGHTLINES OF ANY UK RESIDENTIAL ALUMINIUM LANTERN (37MM INTERNAL SIGHTLINE VS 60-80MM FOR TRADITIONAL ALUMINIUM LANTERNS) — MAXIMISING THE GLAZED AREA RELATIVE TO THE OVERALL LANTERN SIZE. THERMAL BREAK: THERMALLY BROKEN ALUMINIUM THROUGHOUT — CONDENSATION-FREE INTERNAL FACE. GLAZING: 36.4MM TRIPLE GLAZED UNIT (4MM TOUGHENED + 12MM ARGON + 4MM + 12MM ARGON + 4.2MM TOUGHENED — OR SIMILAR CONFIGURATION — U-VALUE CENTRE-OF-GLASS 0.6 W/M²K — WHOLE UNIT 1.4-1.6 W/M²K). COLOURS: ANY RAL COLOUR POWDER COAT + DUAL COLOUR (DIFFERENT INTERNAL AND EXTERNAL COLOUR — ANTHRACITE GREY EXTERNAL / WHITE INTERNAL IS THE MOST COMMONLY SPECIFIED COMBINATION FOR A LONDON REAR EXTENSION). STANDARD SIZES (L X W): 1000X1000MM TO 4000X2000MM — IN 250MM INCREMENTS. PRICE (SUPPLY ONLY): 1500X1500MM SQUARE LANTERN: APPROXIMATELY £1,200-1,800. 2000X1000MM RECTANGULAR: £1,000-1,400. 3000X1500MM: £2,000-2,800. LEAD TIME: TYPICALLY 4-8 WEEKS FROM ORDER TO DELIVERY.

ROOFLIGHTS IN LONDON PROPERTIES ARE SUBJECT TO SPECIFIC PLANNING RULES — AND THE POSITION AND VISIBILITY OF THE ROOFLIGHT FROM THE STREET IS THE KEY DETERMINANT OF WHETHER PLANNING PERMISSION IS REQUIRED.

PERMITTED DEVELOPMENT FOR ROOFLIGHTS (SCHEDULE 2, PART 1, CLASS A AND CLASS C OF THE GPDO 2015): ROOFLIGHTS ON THE REAR ROOF SLOPE (NOT VISIBLE FROM THE HIGHWAY — THE PRINCIPAL ELEVATION FACING THE STREET): PERMITTED DEVELOPMENT — NO PLANNING PERMISSION REQUIRED — IF THE ROOFLIGHT DOES NOT PROJECT MORE THAN 150MM FROM THE EXISTING ROOF PLANE. ROOFLIGHTS ON THE FRONT ROOF SLOPE (FACING THE STREET): (1) IN A CONSERVATION AREA: NOT PERMITTED DEVELOPMENT — PLANNING PERMISSION REQUIRED — CONSERVATION AREAS HAVE ARTICLE 4 DIRECTIONS RESTRICTING ALTERATIONS TO THE FRONT ELEVATION; (2) OUTSIDE A CONSERVATION AREA: PERMITTED DEVELOPMENT IF THE ROOFLIGHT DOES NOT PROJECT MORE THAN 150MM FROM THE EXISTING ROOF PLANE. ROOFLIGHTS IN A FLAT ROOF EXTENSION (REAR EXTENSION — NOT VISIBLE FROM HIGHWAY): PERMITTED DEVELOPMENT AS PART OF THE PERMITTED DEVELOPMENT RIGHTS FOR A SINGLE-STOREY REAR EXTENSION (WHICH ALSO COVERS THE FLAT ROOF OF THE EXTENSION AND ANY ROOFLIGHTS IN IT) — SUBJECT TO THE EXTENSION MEETING THE RELEVANT PERMITTED DEVELOPMENT SIZE LIMITS.

CONSERVATION AREA AND LISTED BUILDING SPECIFIC RULES: IN A CONSERVATION AREA: ROOFLIGHTS ON THE FRONT SLOPE — PLANNING PERMISSION REQUIRED. IN PRACTICE: CONSERVATION OFFICERS IN MOST LONDON BOROUGHS PREFER CONSERVATION ROOFLIGHTS (FINELINE TYPE — FLUSH OR NEAR-FLUSH WITH THE ROOF PLANE — MAXIMUM 25MM PROJECTION) OVER STANDARD VELUX-TYPE (50-75MM PROJECTION) ON THE FRONT SLOPE. ON THE REAR SLOPE — STILL PERMITTED DEVELOPMENT IN A CONSERVATION AREA (CONSERVATION AREA RESTRICTIONS ONLY APPLY TO ELEVATIONS VISIBLE FROM THE HIGHWAY). IN A LISTED BUILDING: LISTED BUILDING CONSENT IS REQUIRED FOR ANY NEW ROOFLIGHT — INCLUDING ON THE REAR SLOPE — BECAUSE THE ROOF STRUCTURE IS PART OF THE LISTED BUILDING. LBC IS APPLIED BY THE LOCAL PLANNING AUTHORITY — APPROVED IN MANY CASES BUT REQUIRES APPLICATION AND CONSENT.

ROOFLIGHTS IN AN EXISTING DWELLING (INCLUDING A REAR EXTENSION THAT IS BUILDING REGULATIONS-NOTIFIABLE) MUST MEET THE FOLLOWING U-VALUE REQUIREMENTS UNDER APPROVED DOCUMENT L 2021.

PART L 2021 U-VALUE TARGET FOR ROOFLIGHTS: NEW ROOFLIGHTS IN A NEW EXTENSION: MAXIMUM WHOLE-WINDOW (OR WHOLE-ROOFLIGHT) U-VALUE 1.8 W/M²K (LESS STRINGENT THAN THE WINDOW U-VALUE TARGET OF 1.6 W/M²K — BECAUSE ROOFLIGHTS ARE ALWAYS IN A HORIZONTAL OR NEAR-HORIZONTAL PLANE WHERE INTERNAL CONVECTION MEANS HEAT LOSS IS INHERENTLY HIGHER THAN FOR A VERTICAL WINDOW). MAXIMUM TOTAL AREA OF ROOFLIGHTS AND ROOF WINDOWS IN A DWELLING: THE TOTAL AREA OF GLAZED ELEMENTS (WINDOWS + ROOFLIGHTS) IN ANY EXTENSION SHOULD NOT EXCEED 25% OF THE FLOOR AREA OF THE EXTENSION UNDER THE NOTIONAL BUILDING CALCULATION — BUILDING CONTROL WILL ASSESS THIS AS PART OF THE PART L SAP/SBEM CALCULATION FOR THE EXTENSION.

PRODUCT U-VALUES (WHOLE-UNIT — APPROXIMATE — AS DECLARED BY MANUFACTURER FOR STANDARD SIZES): VELUX TRIPLE GLAZED GGU: APPROXIMATELY 1.0-1.2 W/M²K (WELL WITHIN 1.8 W/M²K LIMIT). FAKRO FTP-V TRIPLE GLAZED: APPROXIMATELY 1.1-1.3 W/M²K. BRETT MARTIN SKY-FRAME TRIPLE GLAZED: APPROXIMATELY 1.5-1.8 W/M²K (AT THE UPPER END OF COMPLIANCE — THE TRIPLE GLAZED SPECIFICATION IS REQUIRED). KORNICHE LANTERN TRIPLE GLAZED: APPROXIMATELY 1.4-1.6 W/M²K (COMPLIANT — THE SLIM SIGHTLINES REDUCE THE FRAME THERMAL BRIDGE CONTRIBUTION TO THE WHOLE-UNIT U-VALUE VS LARGER FRAME LANTERNS). NOTE: DOUBLE GLAZED ROOFLIGHTS (OLDER PRODUCTS OR BUDGET PRODUCTS — CENTRE-GLASS U-VALUE APPROXIMATELY 1.4-1.6 W/M²K — WHOLE-UNIT U-VALUE 2.0-2.5 W/M²K): DO NOT COMPLY WITH PART L 2021 1.8 W/M²K WHOLE-UNIT REQUIREMENT — ONLY TRIPLE GLAZED OR VACUUM GLAZED ROOFLIGHTS SHOULD BE SPECIFIED FOR NEW BUILDING REGULATIONS-NOTIFIABLE WORK.

ROOFLIGHT INSTALLATION COSTS IN LONDON (2025) — SUPPLY AND FIT — INCLUDING ROOFLIGHT UNIT, STRUCTURAL TRIMMING WORK TO THE ROOF STRUCTURE, FLASHING, AND INTERNAL LINING.

PITCHED ROOF ROOFLIGHT (VELUX GGU SK08 TRIPLE GLAZED INTEGRA — ELECTRIC — WITH FLASHING KIT — LOFT CONVERSION CONTEXT): VELUX GGU SK08 INTEGRA SUPPLY: £700-1,100. FLASHING KIT (ROOF COVERING-SPECIFIC): £80-200. STRUCTURAL TRIMMING (TRIMMER RAFTERS EACH SIDE OF OPENING — WHERE RAFTER MUST BE CUT): £150-300 (CARPENTER LABOUR). INSTALLATION (ROOFING CONTRACTOR — CUTTING HOLE IN ROOF COVERING, INSTALLING ROOFLIGHT AND FLASHING, RESTORING ROOF COVERING): £300-500. INTERNAL LINING (REVEAL LINING — PLASTERBOARD OR TIMBER — AROUND THE ROOFLIGHT OPENING INSIDE THE LOFT): £150-300. TOTAL (SUPPLY AND FIT — SINGLE VELUX SK08 INTEGRA — PITCHED ROOF LOFT): £1,380-2,400. CONSERVATION ROOFLIGHT (FINELINE TYPE — SAME SIZE AS VELUX SK08 — CONSERVATION AREA PROPERTY): SUPPLY: £350-800 (DEPENDING ON SIZE AND BESPOKE VS STANDARD). INSTALLATION: £400-700 (MORE COMPLEX FITTING THAN STANDARD VELUX — FLUSH INSTALLATION REQUIRES MORE CAREFUL ROOFING WORK). TOTAL: £750-1,500.

FLAT ROOF FIXED ROOFLIGHT (BRETT MARTIN SKY-FRAME OR EQUIVALENT — 1000X1500MM — INSTALLED IN A FLAT ROOF REAR EXTENSION): ROOFLIGHT SUPPLY: £450-700. UPSTAND CONSTRUCTION (TIMBER UPSTAND FRAME AT 150MM HEIGHT — BUILT FROM THE FLAT ROOF STRUCTURE — FLAT ROOF CONTRACTOR): £200-400. ROOFLIGHT INSTALLATION (FIT ROOFLIGHT TO UPSTAND, SEAL AND FLASH JUNCTION WITH FLAT ROOF MEMBRANE): £200-350. INTERNAL LINING (REVEALS AROUND ROOFLIGHT INSIDE THE EXTENSION — PLASTERBOARD): £150-250. TOTAL (SUPPLY AND FIT — 1000X1500MM FLAT FIXED ROOFLIGHT): £1,000-1,700.

KORNICHE LANTERN (2000X1000MM — RECTANGULAR — REAR EXTENSION FLAT ROOF): KORNICHE SUPPLY: £1,000-1,400. UPSTAND CONSTRUCTION: £300-500. KORNICHE INSTALLATION (2-3 HOURS FOR TWO FITTERS): £250-400. INTERNAL LINING: £200-350. TOTAL: £1,750-2,650. LARGER KORNICHE LANTERN (3000X1500MM): SUPPLY £2,000-2,800 + INSTALLATION £1,200-1,800 = TOTAL £3,200-4,600.