Skylights and Roof Windows Guide for London Homes

PITCHED ROOF WINDOWS (ALSO CALLED ROOF WINDOWS OR ROOFLIGHTS — TECHNICALLY A "ROOFLIGHT" IS FIXED AND A "ROOF WINDOW" IS OPENABLE, THOUGH THE TERMS ARE OFTEN USED INTERCHANGEABLY) ARE THE MOST WIDELY USED ROOF GLAZING SYSTEM FOR LONDON LOFT CONVERSIONS. THE DOMINANT BRANDS IN THE UK MARKET: (1) VELUX — THE GLOBAL MARKET LEADER WITH THE WIDEST PRODUCT RANGE AND BEST AVAILABILITY IN UK BUILDERS MERCHANTS. THE MAIN VELUX ROOF WINDOW SERIES FOR RESIDENTIAL USE IN LONDON: VELUX GGU (UPVC FRAME, CENTER-PIVOT OPENING) — THE STANDARD RESIDENTIAL ROOF WINDOW IN VELUX'S UK PRODUCT RANGE. AVAILABLE IN STANDARD SIZES FROM SK06 (114X118CM) DOWN TO S06 (114X118CM — NOTE: SIZES ARE COMPLEX — ALWAYS CHECK THE VELUX SIZE CODE). WHITE UPVC FRAME. GLAZING: STANDARD ENERGY (DOUBLE GLAZED, U=1.3 W/M2K) OR ENERGYSAVER (TRIPLE GLAZED, U=0.5 W/M2K — RECOMMENDED FOR LONDON LOFT CONVERSIONS WHERE PART L COMPLIANCE IS REQUIRED). VELUX GPL (PINE FRAME, TIMBER LINING) — PREMIUM TIMBER OPTION, STAINED, PAINTED, OR LACQUERED. MORE EXPENSIVE THAN GGU BUT WITH A WARMER AESTHETIC. U=1.1 W/M2K STANDARD GLAZING. VELUX INTEGRA GGU (ELECTRIC OPENING ROOF WINDOW) — SOLAR-POWERED OR MAINS-POWERED ELECTRIC ACTUATOR, OPERATED BY WALL SWITCH OR IO-HOMECONTROL APP. RAIN SENSOR AUTOMATICALLY CLOSES THE WINDOW IN RAIN (CRITICAL FOR LONDON WHERE UNEXPECTED RAIN IS COMMON). ADDITIONAL COST OVER STANDARD: £150-£250 PER WINDOW. (2) FAKRO — THE MAIN ALTERNATIVE TO VELUX IN THE UK MARKET. FAKRO FTP-V U3 (PINE FRAME, DOUBLE GLAZED, U=1.1 W/M2K) IS THE STANDARD RESIDENTIAL MODEL. FAKRO FTT U8 (TRIPLE GLAZED, VACUUM GLASS, U=0.5 W/M2K) IS THE PREMIUM ENERGY PERFORMANCE OPTION. FITTING: ROOF WINDOW INSTALLATION REQUIRES FORMATION OF A CURB OR WELLHEAD IN THE RAFTER STRUCTURE (SOLID BLOCKING BETWEEN RAFTERS AT HEAD AND SILL OF THE WINDOW APERTURE — TYPICALLY 47X150MM C16 TREATED TIMBER). THE WINDOW FLASHING KIT (VELUX EDW OR EDP FLASHING DEPENDING ON TILE TYPE AND PITCH) MUST BE USED — THE FLASHING KIT IS NOT INCLUDED WITH THE WINDOW AND IS ESSENTIAL TO PREVENT WATER INGRESS.

FOR FLAT-ROOF EXTENSIONS AND REAR ADDITIONS IN LONDON (VERY COMMON IN THE SINGLE-STOREY KITCHEN EXTENSION FORMAT), THE MAIN ROOF GLAZING OPTIONS ARE: (1) STRUCTURAL GLASS ROOFLIGHTS (ATLAS ROOFLIGHT, SUNSQUARE GLASS ROOFLIGHT, ELEMENT 4, KORNICHE) — DOUBLE OR TRIPLE GLAZED TOUGHENED LAMINATED SAFETY GLASS UNITS (TYPICALLY PLANITHERM ULTRA N OR GUARDIAN CLIMAGUARD A+ COATED GLASS, U=1.0-1.4 W/M2K FOR DOUBLE GLAZED; U=0.6-0.7 W/M2K FOR TRIPLE GLAZED) IN A THERMALLY BROKEN ALUMINIUM FRAME. THESE ARE THE PREMIUM OPTION FOR A CONTEMPORARY LONDON KITCHEN EXTENSION. KEY FEATURES: WALK-ON RATING (IF SPECIFIED) FOR ACCESSIBLE FLAT ROOFS; ANTI-CONDENSATION GLASS COATING (PILKINGTON ACTIV OR GUARDIAN CLIMATEGUARD FOR SELF-CLEANING SOLAR ACTIVE OUTER PANE — REDUCES CLEANING INTERVAL FROM MONTHLY TO EVERY 6 MONTHS); OPTIONAL ELECTRIC VENTING (OPENING VIA ELECTRIC ACTUATOR — ESSENTIAL FOR SUMMER VENTILATION IN A SOUTH-FACING EXTENSION). SIZES RANGE FROM SMALL FIXED UNITS (300X300MM) TO VERY LARGE BESPOKE WALK-ON STRUCTURAL GLAZING (UP TO 3M X 6M OR LARGER). COSTS: STANDARD FIXED GLASS ROOFLIGHT (800X800MM DOUBLE GLAZED): £250-£500 SUPPLY. VENTILATED GLASS ROOFLIGHT (1200X1200MM TRIPLE GLAZED, ELECTRIC OPENER): £1,200-£2,500 SUPPLY. (2) GRP (GLASS REINFORCED PLASTIC) DOME ROOFLIGHTS — THE BUDGET OPTION. POLYCARBONATE OR GRP DOME UNITS (BRITEX STANDARD DOME OR XTROLITE GRP DOME) ARE FACTORY-MOULDED, LIGHTWEIGHT, AND CHEAPER THAN GLASS (FROM £80-£200 SUPPLY). HOWEVER: OPAQUE APPEARANCE (DIFFUSE TRANSMISSION ONLY — NO CLEAR VIEW OF SKY); LOWER INSULATION PERFORMANCE (U=2.7 W/M2K SINGLE DOME; U=1.8 W/M2K DOUBLE DOME); YELLOWS WITH AGE AND UV EXPOSURE. NOT RECOMMENDED FOR PREMIUM LONDON EXTENSIONS. (3) POLYCARBONATE ROOFLIGHTS — SIMILAR PROFILE TO GRP DOMES BUT WITH BETTER TRANSLUCENCY. XTROLITE MULTIWALL POLYCARBONATE (25MM TRIPLE WALL, U=1.05 W/M2K) CAN BE AN ECONOMIC OPTION FOR UTILITARIAN SPACES (WORKSHOPS, GARDEN ROOMS) BUT NOT FOR HABITABLE ROOMS WHERE PLANNING AND BUILDING REGULATIONS REQUIRE PART L COMPLIANCE.

ROOF LANTERNS (ALSO CALLED LANTERN ROOFLIGHTS OR ROOF GLAZING LANTERNS) ARE PYRAMIDAL OR HIP-ROOFED GLASS STRUCTURES THAT SIT ABOVE A FLAT-ROOF EXTENSION — THE ARCHITECTURAL CENTREPIECE OF A PREMIUM LONDON KITCHEN EXTENSION. ROOF LANTERNS PROVIDE: MUCH MORE DAYLIGHT THAN A FLUSH FLAT ROOFLIGHT OF THE SAME BASE DIMENSION (THE VERTICAL SIDE GLAZING ADMITS ADDITIONAL LIGHT AT LOW SUN ANGLES WHILE THE SLOPED TOP GLAZING ADMITS DIRECT OVERHEAD LIGHT); A SENSE OF HEIGHT AND ARCHITECTURAL DRAMA IN A SINGLE-STOREY REAR EXTENSION; NATURAL VENTILATION IF THE LANTERN INCORPORATES OPENING RIDGE VENTS (CRITICAL IN A SOUTH-FACING KITCHEN EXTENSION IN SUMMER — A ROOF LANTERN WITHOUT VENTILATION IS A TRAP FOR HOT AIR). MAIN UK ROOF LANTERN MANUFACTURERS (2025): KORNICHE ROOF LANTERN (KORNICHE.COM) — THE MARKET LEADER BY VOLUME IN THE UK RESIDENTIAL SECTOR. THERMALLY BROKEN ALUMINIUM FRAME, DOUBLE GLAZED AS STANDARD (U=1.2 W/M2K CENTRE PANE; WHOLE UNIT U≈1.6 W/M2K), OPTIONAL TRIPLE GLAZED (U=0.7 W/M2K CENTRE PANE). STANDARD SIZES FROM 1.0M X 1.5M TO 4.0M X 4.0M. SLIMLINE 34MM ALUMINIUM RAFTERS GIVE A VERY MINIMAL APPEARANCE. COLOUR: POWDER COATED RAL 9010 (WHITE) OR RAL 7016 (ANTHRACITE GREY) AS STANDARD. COST: 2.5M X 1.5M KORNICHE: £1,800-£2,500 SUPPLY. ULTRASKY ROOF LANTERN (ULTRAFRAME GROUP) — POPULAR ALTERNATIVE TO KORNICHE. SIMILAR THERMAL PERFORMANCE AND SIZE RANGE. COST: 2.5M X 1.5M: £1,500-£2,200 SUPPLY. GLAZING VISION RIDGELINE (GLAZINGVISION.CO.UK) — PREMIUM ARCHITECTURAL GLAZING. WALK-ON GLASS OPTION. BESPOKE SIZES. COST: FROM £3,500 SUPPLY FOR STANDARD SIZES, SIGNIFICANTLY MORE FOR BESPOKE. RIDGE VENT SPECIFICATION: FOR NATURAL VENTILATION COMPLIANCE (BUILDING REGULATIONS PART F), THE RIDGE OF A ROOF LANTERN SHOULD INCORPORATE CONTINUOUS VENT OR MOTORISED OPENING RIDGE VENT (KORNICHE MOTORISED RIDGE VENT — COMES WITH RAIN SENSOR, CONTROLLED VIA REMOTE OR SMART HOME INTEGRATION). THE OPENING RIDGE VENT IS THE BEST VENTILATION SOLUTION FOR A LONDON KITCHEN EXTENSION.

IN CONSERVATION AREAS AND ON LISTED BUILDINGS, STANDARD VELUX UPVC ROOF WINDOWS AND MODERN FLAT GLASS ROOFLIGHTS ARE TYPICALLY NOT ACCEPTABLE TO PLANNING OFFICERS AND CONSERVATION TEAMS. THE CONSERVATION ROOFLIGHT WAS DEVELOPED SPECIFICALLY FOR THIS MARKET: SUNSQUARE CONSERVATION ROOFLIGHT (SUNSQUARE.CO.UK) — THE UK MARKET LEADER FOR CONSERVATION ROOFLIGHTS. THE SUNSQUARE IS A LOW-PROFILE ROOFLIGHT (MAXIMUM 16MM ABOVE THE PLANE OF THE ROOF TILES WHEN FITTED — COMPARED WITH 170-200MM PROTRUSION OF A STANDARD VELUX ROOF WINDOW) WITH A BLACK POWDER-COATED CAST ALUMINIUM FRAME. THE LOW PROFILE MEANS IT IS VIRTUALLY FLUSH WITH THE ROOF SLOPE AND IS ALMOST INVISIBLE FROM STREET LEVEL. PLANNING CONSIDERATION: SUNSQUARE AND SIMILAR CONSERVATION ROOFLIGHTS ARE ACCEPTED BY THE MAJORITY OF LONDON CONSERVATION OFFICERS WHERE STANDARD ROOF WINDOWS ARE NOT. CHECK WITH YOUR SPECIFIC LONDON BOROUGH LPA (E.G. CAMDEN, ISLINGTON, KENSINGTON AND CHELSEA — ALL VERY STRICT ON ROOF WINDOWS IN CONSERVATION AREAS). GLAZING: DOUBLE GLAZED TOUGHENED SAFETY GLASS (U=1.2 W/M2K) OR TRIPLE GLAZED (U=0.7 W/M2K). FIXED (NON-OPENING) AS STANDARD; ELECTRICALLY OPENING VERSIONS ARE AVAILABLE (SUNSQUARE MANUAL AND SUNSQUARE ELECTRIC). SIZES: FROM 60X90CM TO 120X180CM. VELUX CONSERVATION ROOFLIGHT (VELUX LOE, CONSERVATION PRODUCT) — VELUX ALSO PRODUCES A LOW-PROFILE CONSERVATION WINDOW IN THEIR PRODUCT RANGE. HOWEVER, THE SUNSQUARE IS WIDELY REGARDED AS THE SUPERIOR PRODUCT FOR CONSERVATION AREA USE DUE TO ITS LOWER PROFILE (16MM VS VELUX'S APPROXIMATELY 30MM ABOVE TILE PLANE). COST: SUNSQUARE 780X1340MM FIXED, DOUBLE GLAZED: £500-£700 SUPPLY; ELECTRIC OPENING: £900-£1,300 SUPPLY. INSTALLATION BY A SPECIALIST CONSERVATION ROOFER IS RECOMMENDED — THE FLASHING DETAIL IS CRITICAL TO WEATHER TIGHTNESS AND PLANNING COMPLIANCE.

ROOF WINDOWS AND SKYLIGHTS ARE SUBJECT TO THE FOLLOWING PLANNING RULES IN ENGLAND (GPDO 2015, SCHEDULE 2, PART 1): PITCHED ROOF WINDOWS (REAR AND SIDE SLOPES): PERMITTED DEVELOPMENT (NO PLANNING PERMISSION NEEDED) PROVIDED: (1) THE WINDOW DOES NOT PROTRUDE MORE THAN 150MM FROM THE ROOF PLANE; (2) THE WINDOW DOES NOT EXCEED THE HIGHEST POINT OF THE ORIGINAL ROOF; (3) THE WINDOW IS NOT ON THE FRONT ELEVATION (PRINCIPAL ELEVATION — THE SIDE OF THE HOUSE FACING THE HIGHWAY). FRONT SLOPE ROOF WINDOWS: NOT PERMITTED DEVELOPMENT IN ANY LOCATION — A PLANNING APPLICATION IS REQUIRED FOR ANY ROOF WINDOW ON THE FRONT SLOPE (HIGHWAY-FACING ELEVATION). IN CONSERVATION AREAS, THIS RULE IS PARTICULARLY STRICTLY ENFORCED. FLAT ROOF ROOFLIGHTS: FLAT ROOF ROOFLIGHTS ARE GENERALLY PERMITTED DEVELOPMENT ON REAR EXTENSIONS PROVIDED THEY DO NOT EXCEED 150MM ABOVE THE ROOF PLANE (DIFFICULT TO ACHIEVE FOR UPSTAND-MOUNTED ROOFLIGHTS) AND MEET THE OTHER CONDITIONS. IN PRACTICE, MOST FLAT ROOFLIGHTS ON REAR KITCHEN EXTENSIONS ARE PERMITTED DEVELOPMENT. CONSERVATION AREAS: FRONT SLOPE WINDOWS ARE ALMOST NEVER ACCEPTED IN CONSERVATION AREAS. REAR SLOPE WINDOWS IN CONSERVATION AREAS REQUIRE EITHER PLANNING PERMISSION (IF THE STANDARD PD CONDITIONS CANNOT BE MET WITH A CONSERVATION ROOFLIGHT) OR A CONSERVATION ROOFLIGHT (SUNSQUARE OR SIMILAR — LOW PROFILE WHICH TYPICALLY MEETS THE 150MM PD RULE). LISTED BUILDINGS: LISTED BUILDING CONSENT IS REQUIRED FOR ALL ROOF WINDOWS ON LISTED BUILDINGS — SUBMIT WITH A HERITAGE IMPACT STATEMENT ASSESSING THE IMPACT ON THE LISTED BUILDING'S SIGNIFICANCE.

VELUX GGU UPVC CENTRE-PIVOT SK06 (114X118CM) DOUBLE GLAZED, SUPPLY ONLY: £250-£350. VELUX GGU TRIPLE GLAZED ENERGYSAVER SK06: £450-£550. VELUX INTEGRA ELECTRIC GGU SK06 WITH SOLAR CHARGING: £550-£700. FAKRO FTP-V U3 DOUBLE GLAZED SK06: £200-£320. SUNSQUARE CONSERVATION ROOFLIGHT 780X1340MM FIXED DOUBLE GLAZED: £500-£700. SUNSQUARE ELECTRIC OPENING 780X1340MM: £900-£1,300. FLAT GLASS ROOFLIGHT 800X800MM DOUBLE GLAZED (ATLAS, KORNICHE): £300-£500. FLAT GLASS ROOFLIGHT 1200X1200MM TRIPLE GLAZED ELECTRIC VENT: £1,500-£2,500. KORNICHE ROOF LANTERN 2.5X1.5M DOUBLE GLAZED: £1,800-£2,500. KORNICHE ROOF LANTERN 4.0X2.0M TRIPLE GLAZED WITH MOTORISED RIDGE VENT: £5,000-£7,000. INSTALLATION COSTS (PER WINDOW, TYPICAL LONDON RATE INCLUDING FLASHING): STANDARD VELUX INSTALLATION (EXISTING LOFT STRUCTURE, ROOFER + LABOURER): £300-£500. CONSERVATION ROOFLIGHT INSTALLATION (SPECIALIST, LIME MORTAR FLASHING): £400-£700. FLAT ROOF LANTERN INSTALLATION (STRUCTURAL OPENING, UPSTAND, LANTERN FIT): £800-£2,000 DEPENDING ON SIZE AND SPECIFICATION.