Velux and Fakro Roof Windows for London Loft Conversions: Specification, Planning, and Flashing Guide

VELUX IS THE MARKET-DOMINANT BRAND FOR ROOF WINDOWS IN THE UK AND THE DEFAULT SPECIFICATION FOR LONDON LOFT CONVERSIONS. THE MAIN VELUX PRODUCT LINES FOR RESIDENTIAL LOFT CONVERSIONS ARE AS FOLLOWS.

VELUX INTEGRA ELECTRIC (GGU / GGL INTEGRA): THE ELECTRICALLY OPERATED VERSION OF THE STANDARD VELUX ROOF WINDOW, WITH A BUILT-IN ELECTRIC MOTOR FOR REMOTE OPERATION (VELUX REMOTE CONTROL, APP, OR COMPATIBLE SMART HOME SYSTEMS). GGU = POLYURETHANE OUTER FRAME AND SASH (WHITE, HIGHLY WEATHER-RESISTANT, SUITABLE FOR ALL CLIMATES — RECOMMENDED FOR LONDON'S MIXED WET CLIMATE). GGL = PINE TIMBER SASH WITH POLYURETHANE OUTER FRAME (TIMBER INNER, MORE TRADITIONAL APPEARANCE). THE INTEGRA RANGE ALSO INCLUDES AN INTEGRATED RAIN SENSOR THAT AUTOMATICALLY CLOSES THE WINDOW IN RAIN. FOR LOFT CONVERSIONS WHERE ROOF WINDOWS ARE AWKWARD TO REACH (ABOVE A STAIRCASE OR AT HIGH LEVEL IN A DORMER CHEEK), INTEGRA ELECTRIC IS STRONGLY RECOMMENDED.

COMMON VELUX SIZES FOR LONDON LOFT CONVERSIONS: SK08 (1140MM WIDE X 1400MM HIGH): THE MOST COMMONLY SPECIFIED VELUX FOR LONDON FRONT-SLOPE LOFT WINDOWS — PROVIDES GOOD GLAZED AREA AND HEAD HEIGHT COMFORT. FK08 (660MM X 1400MM): NARROWER FORMAT FOR TIGHTER SPACING. CK04 (550MM X 980MM): SMALLER WINDOW FOR LOWER-SLOPE APPLICATIONS.

VELUX FCM (FIXED CURB MOUNT): A FIXED (NON-OPENING) VELUX UNIT FOR FLAT OR VERY LOW PITCH ROOF APPLICATIONS. THE FCM IS TYPICALLY USED ON FLAT ROOF EXTENSIONS AS A ROOFLIGHT — INSTALLED IN A TIMBER OR STEEL KERB UPSTAND RATHER THAN INTO A PITCHED ROOF. THE FCM IS NOT A CONTROLLED VENTILATION UNIT — IT PROVIDES DAYLIGHT ONLY.

VELUX CVU / CFU (PIVOT FLAT ROOF WINDOW): A VELUX SPECIFICALLY DESIGNED FOR LOW-PITCH APPLICATIONS (BETWEEN 15° AND 90°) — THE CVU HAS A DOUBLE SKIN DOME OVER A PIVOT SASH. FOR LONDON LOFT CONVERSIONS WITH VERY LOW PITCH FRONT SLOPES (COMMON IN SOME LONDON VICTORIAN DESIGNS), THE CVU IS SPECIFIED WHERE THE SLOPE IS BETWEEN 15° AND 20°.

VELUX SOLAR (VSE / VCE): SOLAR-POWERED ELECTRIC VERSION — NO MAINS CABLE REQUIRED. THE SOLAR PANEL IS INTEGRATED INTO THE WINDOW FLASHING SYSTEM. APPROPRIATE FOR CONVERSIONS WHERE RUNNING AN ELECTRIC CABLE TO THE WINDOW IS DIFFICULT.

FAKRO IS THE SECOND-LARGEST ROOF WINDOW MANUFACTURER IN THE WORLD (POLISH COMPANY, FOUNDED 1991) AND IS A GENUINE ALTERNATIVE TO VELUX IN THE UK RESIDENTIAL MARKET. FAKRO PRODUCTS ARE TYPICALLY 5 TO 15% LOWER IN COST THAN EQUIVALENT VELUX PRODUCTS.

FAKRO FTP-V THERMO (PINE SASH, TOP-HUNG, TRIPLE GLAZED): THE FTP-V THERMO IS FAKRO'S PREMIUM RESIDENTIAL ROOF WINDOW AND OFFERS TRIPLE GLAZING AS STANDARD — CENTRE-PANE U-VALUE 0.5 W/M'K, WHOLE-UNIT U-VALUE 1.0 TO 1.1 W/M'K. THIS IS SIGNIFICANTLY BETTER THERMAL PERFORMANCE THAN STANDARD VELUX DOUBLE GLAZING (CENTRE-PANE U-VALUE APPROXIMATELY 1.0 W/M'K). FOR LOFT CONVERSIONS TARGETING VERY LOW HEAT LOSS (SAP ENERGY CALCULATIONS FOR PART L), THE FAKRO FTP-V THERMO'S IMPROVED U-VALUE CAN HELP ACHIEVE COMPLIANCE WITHOUT OTHER COMPENSATING MEASURES.

FAKRO FPP-V PRESELECT (ELECTRIC OPERATION WITH PRESELECT OPENING SETTINGS): EQUIVALENT TO VELUX INTEGRA — ELECTRIC OPERATION WITH RAIN SENSOR AND REMOTE CONTROL. THE PRESELECT FUNCTION ALLOWS THE WINDOW TO BE PROGRAMMED TO STOP AT 10°, 25°, OR 50° OF OPENING — USEFUL WHERE THE WINDOW IS ABOVE A BED SPACE AND FULL OPENING IN HIGH WINDS WOULD BE UNDESIRABLE.

FAKRO FLASHING: FAKRO ROOF WINDOWS HAVE THEIR OWN PROPRIETARY FLASHING SYSTEMS — VELUX FLASHINGS ARE NOT INTERCHANGEABLE WITH FAKRO WINDOWS (DIFFERENT FRAME REBATE AND KERB DIMENSIONS). SPECIFY FLASHINGS AND WINDOWS FROM THE SAME MANUFACTURER.

THE FLASHING KIT IS AS IMPORTANT AS THE WINDOW ITSELF — AN INCORRECTLY SPECIFIED OR POORLY INSTALLED FLASHING IS THE MOST COMMON CAUSE OF ROOF WINDOW WATER INGRESS IN LONDON LOFT CONVERSIONS.

VELUX FLASHING SYSTEMS: VELUX SUPPLY A RANGE OF FLASHING KITS SPECIFIC TO THE ROOF TILE OR SLATE TYPE AND PITCH. THE MAIN SYSTEMS ARE:

EDW (RECESSED INSTALLATION FOR PLAIN CLAY AND CONCRETE TILES): FOR LONDON VICTORIAN TERRACES WITH ORIGINAL PLAIN CLAY TILES (68MM OR 65MM COURSING), THE EDW FLASHING CREATES A RECESSED INSTALLATION WHERE THE WINDOW SITS LOWER IN THE ROOF PLANE, REDUCING THE VISUAL IMPACT OF THE WINDOW ASSEMBLY.

EDC (CLAY/CONCRETE UNIVERSAL FLASHING — THE MOST COMMONLY INSTALLED): THE STANDARD VELUX FLASHING FOR MOST CONCRETE AND CLAY PLAIN TILE APPLICATIONS. INCLUDES APRON FLASHING, SIDE FLASHINGS, AND HEAD FLASHING IN POWDER-COATED ALUMINIUM. FOR LONDON PROPERTIES WITH EXISTING SLATE ROOFS (NATURAL WELSH SLATE OR FIBRE CEMENT SLATE), THE EDJ FLASHING (THIN TILE/SLATE APPLICATION) IS REQUIRED.

BDX (UNDERFELT COLLAR — NOT A TILE FLASHING): THE BDX UNDERFELT COLLAR IS A SEPARATE PRODUCT FROM THE TILE FLASHING — IT CONNECTS THE VELUX WINDOW FRAME TO THE SARKING FELT OR BREATHER MEMBRANE IN THE ROOF, FORMING THE WEATHERTIGHT SEAL BETWEEN THE WINDOW AND THE ROOF STRUCTURE. THE BDX IS INSTALLED OVER THE WINDOW FRAME AND UNDER THE TILE FLASHING AND IS ESSENTIAL FOR PREVENTING WIND-DRIVEN RAIN FROM TRACKING UNDER THE TILE FLASHING INTO THE ROOF STRUCTURE. IN MANY INSTALLATIONS, THE BDX IS OMITTED (INCORRECTLY) — THIS IS A COMMON CAUSE OF WATER INGRESS AROUND VELUX WINDOWS IN LONDON LOFT CONVERSIONS.

MOSSE RESISTANT WRAP-AROUND COPPER TAPE: WHERE CONCRETE TILES WITH ROUGH SURFACE TEXTURE ARE INSTALLED, ALGAE AND MOSS GROWTH AROUND THE WINDOW FLASHING CAN ACCELERATE. A COPPER TAPE STRIP INSTALLED IMMEDIATELY ABOVE THE WINDOW FLASHING (UNDER THE TILES ABOVE, PROJECTING SLIGHTLY) RELEASES COPPER IONS IN RAIN, INHIBITING ALGAE AND MOSS GROWTH FOR UP TO 5 YEARS.

VELUX ROOF WINDOWS IN LONDON LOFT CONVERSIONS ARE GENERALLY PERMITTED DEVELOPMENT — NO PLANNING PERMISSION IS REQUIRED. HOWEVER, SPECIFIC CONDITIONS MUST BE MET.

PERMITTED DEVELOPMENT CONDITIONS FOR ROOF WINDOWS (GPDO 2015, SCHEDULE 2, CLASS C): THE WINDOW MUST NOT PROJECT BEYOND THE PLANE OF THE EXISTING ROOF SLOPE (IT MUST BE FLUSH WITH OR RECESSED INTO THE ROOF SURFACE — STANDARD VELUX INSTALLATION). THE WINDOW MUST NOT BE INSTALLED ON THE PRINCIPAL ELEVATION (THE FRONT ROOF SLOPE FACING A HIGHWAY) OF THE HOUSE WHERE THE ROOF SLOPE IS WITHIN 15M OF THE HIGHWAY BOUNDARY — THIS RESTRICTION AFFECTS MANY LONDON TERRACES WHERE THE FRONT ROOF SLOPE IS CLOSE TO THE PAVEMENT. NOTE: THIS IS THE FREQUENTLY MISUNDERSTOOD 15M RULE. IN MOST LONDON TERRACES, THE FRONT SLOPE IS WITHIN 15M OF THE PAVEMENT — IN THESE CASES, VELUX WINDOWS ON THE FRONT SLOPE REQUIRE PLANNING PERMISSION OR MUST BE ASSESSED UNDER THE LPA'S SPECIFIC POLICY.

IN PRACTICE: MANY LONDON LPAS HAVE A WELL-ESTABLISHED POLICY OF APPROVING FRONT-SLOPE VELUX WINDOWS IN LOFT CONVERSIONS AS HOUSEHOLDER PLANNING APPLICATIONS, PROVIDED THE WINDOWS ARE CENTRE-HUNG, FLUSH WITH THE ROOF SLOPE, AND APPROPRIATELY SIZED RELATIVE TO THE ROOF PANEL. THE PLANNING APPLICATION FEE FOR A SINGLE HOUSEHOLDER APPLICATION INCLUDING FRONT-SLOPE VELUX WINDOWS IS £258.

CONSERVATION AREAS AND ARTICLE 4 DIRECTIONS: IN LONDON CONSERVATION AREAS, PD RIGHTS FOR ROOF WINDOWS ON FRONT SLOPES ARE REMOVED BY ARTICLE 4 DIRECTIONS IN MANY BOROUGHS. PLANNING PERMISSION IS REQUIRED FOR ANY ROOF WINDOW ON THE STREET-FACING SLOPE IN A CONSERVATION AREA PROPERTY. THE LPA'S CONSERVATION OFFICER TYPICALLY REQUIRES THAT WINDOWS ARE NO WIDER THAN THE WIDTH OF THE RAFTER PANEL AND THAT THE EXTERNAL FRAME IS FLUSH WITH THE SLATES/TILES RATHER THAN PROUD OF THE SURFACE.

ROOF WINDOWS MUST COMPLY WITH BUILDING REGULATIONS PART L AND PART E (ACOUSTIC) WHERE APPLICABLE.

PART L THERMAL COMPLIANCE: REPLACEMENT ROOF WINDOWS MUST ACHIEVE A MINIMUM WHOLE-UNIT U-VALUE OF 1.6 W/M'K FOR ROOFLIGHTS (THE SAME AS THE LIMIT FOR REPLACEMENT WINDOWS AND DOORS). NEW ROOF WINDOWS IN AN EXTENSION OR LOFT CONVERSION ARE ASSESSED AS PART OF THE OVERALL SAP CALCULATION FOR THE NEW DWELLING. VELUX STANDARD DOUBLE-GLAZED UNITS (GGU SK08 THERMO) ACHIEVE A WHOLE-UNIT U-VALUE OF APPROXIMATELY 1.2 TO 1.4 W/M'K — COMFORTABLY MEETING THE 1.6 W/M'K LIMIT. FAKRO FTP-V THERMO (TRIPLE GLAZED) ACHIEVES 1.0 TO 1.1 W/M'K.

ACOUSTIC PERFORMANCE: FOR LOFT CONVERSIONS IN LONDON WHERE AIRCRAFT NOISE (HEATHROW APPROACH CORRIDORS, GATWICK APPROACH PATHS OVER SOUTH LONDON) IS A SIGNIFICANT ISSUE, ACOUSTIC GLAZING IN ROOF WINDOWS IS WORTH CONSIDERING. VELUX OFFERS AN ACOUSTIC GLAZING UPGRADE ON SELECTED SIZES (TYPICALLY AN ASYMMETRIC DGU WITH 6.8MM ACOUSTIC LAMINATED GLASS ON THE OUTSIDE) PROVIDING ADDITIONAL SOUND REDUCTION COMPARED TO STANDARD DOUBLE GLAZING. THE IMPROVEMENT IS APPROXIMATELY 4 TO 6 DB REDUCTION IN AIRCRAFT AND TRAFFIC NOISE TRANSMISSION.

COSTS FOR ROOF WINDOW SUPPLY AND INSTALLATION IN LONDON LOFT CONVERSIONS ARE AS FOLLOWS.

VELUX GGU SK08 INTEGRA ELECTRIC (SUPPLY ONLY, INCLUDING FLASHING KIT): £800 TO £1,200 DEPENDING ON RETAILER AND FLASHING TYPE.

FAKRO FTP-V THERMO SK08 EQUIVALENT (SUPPLY ONLY, TRIPLE GLAZED, INCLUDING FLASHING): £600 TO £900.

INSTALLATION (PER WINDOW, INCLUDING SARKING FELT INTEGRATION, UNDERFELT COLLAR, FLASHING, AND MAKING GOOD): £350 TO £600 PER WINDOW WHEN DONE AS PART OF LOFT CONVERSION CONSTRUCTION. WHERE ROOFERS ARE RETURNING TO AN EXISTING ROOF FOR VELUX INSTALLATION ONLY (AFTER ORIGINAL LOFT CONVERSION CONSTRUCTION): £500 TO £900 PER WINDOW PLUS SCAFFOLD OR CHERRY PICKER ACCESS (£400 TO £1,200 DEPENDING ON PROPERTY).

PLANNING APPLICATION FOR FRONT-SLOPE VELUX WINDOWS (WHERE REQUIRED — 15M RULE OR CONSERVATION AREA): £258 PLANNING APPLICATION FEE + ARCHITECT DRAWING FEE £200 TO £600.

TYPICAL FRONT-SLOPE INSTALLATION FOR A LONDON LOFT CONVERSION (3 X VELUX GGU SK08 INTEGRA, INCLUDING FLASHINGS, UNDERFELT COLLARS, INSTALLATION, AND MAKING GOOD): £3,500 TO £6,000 SUPPLIED AND INSTALLED AS PART OF THE LOFT CONVERSION PACKAGE.