Loft Conversions3 min read

Velux and Fakro Roof Windows for London Victorian Terraces: Specification, Building Regulations, and Costs

Roof windows — the skylights installed within the pitch of a slated or tiled roof to provide natural light and ventilation to a converted loft space — are one of the defining elements of a London Victorian terrace loft conversion. The two dominant brands in the UK residential loft conversion market are Velux (VKR Group — Denmark) and Fakro (Fakro — Nowy Sącz, Poland). The choice of roof window model, size, and installation specification is determined by: the planning context (permitted development vs conservation area vs planning application requirements), the Building Regulations requirements (Part L thermal performance, Part B fire egress, Part F ventilation), and the structural and weatherproofing requirements of installation into a 100-150 year old slate or plain clay tile Victorian pitched roof. This guide covers the key roof window specifications, planning considerations, and Building Regulations requirements for London Victorian terrace loft conversions.

Key Takeaways

✓Planning permission for roof windows (GPDO 2015 Schedule 2 Part 1 Class C — additions to the roof of a dwelling house): permitted development conditions: (1) protrusion max 150mm beyond plane of existing roof slope (measured perpendicular to slope, from surrounding tile/slate surface to outer face of window glass); (2) highest point of roof window must not exceed highest point of existing roof ridge; rear slope (non-conservation area): generally permitted development — no planning permission required; front slope (non-conservation area): generally permitted development if within 150mm protrusion + ridge height limits — no planning permission required; CONSERVATION AREA (front slope — most inner London boroughs): planning permission typically required — most inner London conservation area Article 4 Directions restrict front-slope rooflights (alters uniform Victorian terrace roofline character) — conservation-type flush rooflight (Velux EDW, slim aluminium frame, minimal visual impact) may be accepted where standard projecting window refused; conservation area (rear slope): generally more likely acceptable — often permitted development — confirm with conservation officer; LISTED BUILDING: Listed Building Consent required for any new roof window regardless of slope or type; planning fee Householder Application: £258 (England 2024-2025)
✓Velux product range (VKR Group, most widely specified UK residential loft conversion brand, ~70% UK market share): GGU (polyurethane frame, white painted, moisture/humidity resistant, no repainting required — suitable for bathrooms): GGU SK08 (114cm H x 114cm W, 1.30m² glass, most popular UK loft conversion size — good light/ventilation bedroom up to ~20m²); GGU MK04 (98cm H x 78cm W — tight rafter spacing); GGU CK04 (98cm H x 55cm W — compact for standard 450mm rafter centres); GGU CK04/MK04/SK08 centre-pivot manually operated; Velux Integra GGU 0060 (GGU frame + integrated electric motor — wall switch/Velux remote KLI 310/Velux App — rain sensor KFX 110 auto-closes in rain — preferred specification for loft bedrooms with window above comfortable reach — ~£250-350 more than manual GGU — Integra Solar GGU 0066 = battery powered solar panel, no mains wiring required); GPL (lacquered pine timber inner frame — slightly less moisture resistant than GGU — requires repainting ~8-10yr); Cabrio Balcony GDL SD0W225 (pair of windows convert to balcony when open — lower sash folds to balcony floor, upper rises as railing — conservation area alternative to dormer — REQUIRES PLANNING PERMISSION as projecting structure)
✓Fakro (Fakro Sp z o.o., Nowy Sącz, Poland — second largest roof window manufacturer, ~15-20% UK market share): FTP-V U5 (PVC frame — direct competitor to Velux GGU — centre-pivot — U-value 0.97-1.1 W/m²K depending on size, triple glazed — typically 10-20% lower price than equivalent Velux — growing acceptance UK loft contractors); DEF-V (electric motorised — Fakro equivalent of Velux Integra — rain sensor + wind sensor — remote/smart home compatible); DSF Conservation Rooflight (flush/near-flush, slim aluminium frame — equivalent to Velux EDW Conservation — triple glazed, U-value ~1.0-1.2 W/m²K — appropriate for conservation area front slopes); U-value comparison: Fakro FTP-V U5: 0.97-1.1 W/m²K vs Velux GGU: 1.2-1.3 W/m²K — Fakro slightly better U-value in standard models; Part L 2021 backstop for roof windows in existing dwelling material alteration: 2.2 W/m²K — both brands comfortably exceed minimum
✓Building Regulations compliance for loft conversion roof windows: Part B (Fire Safety, Approved Document Part B Vol 1 Dwellings 2019+2020): habitable room in loft conversion = must provide emergency escape opening through roof window if only means of escape via staircase; requirements: clear opening (when open) ≥450mm wide AND ≥450mm high, minimum area 0.33m²; sill of clear opening ≤1,100mm above floor level (allows person to climb through); Velux GGU SK08 (114x114cm) fully open provides ~500mm H x 900mm W clear opening — meets Part B; Part F 2021 (Ventilation): loft bedroom minimum background ventilation: 5,000mm² EA trickle ventilator (fitted in roof window frame or surround); rapid ventilation: openable area ≥1/20 of room floor area (Velux GGU SK08 meets this for rooms up to ~20m²); Part L 2021 (Thermal): backstop U-value for new roof windows in material alteration existing dwelling: 2.2 W/m²K — Velux GGU and Fakro FTP-V both achieve 1.0-1.3 W/m²K — comfortably exceed minimum; rafter trimming: installing a roof window requires cutting intermediate rafters and installing trimmer rafters (doubled or sister rafters on each side of the opening) — this is structural work — typically included in loft conversion contractor's scope but requires Building Control inspection
✓Costs London 2025 (roofer/loft conversion contractor, supply+fit per window): Velux GGU SK08 (114x114cm, manual, centre-pivot, polyurethane): window ~£300-420 + Velux EW flashing kit ~£100-180 + install (rafter cut, trimmers, fit window+flashing, plasterboard reveals) ~£300-600 = total ~£700-1,200/window; Velux Integra GGU SK08 0060 (electric motorised, rain sensor): ~£950-1,500/window + electrician for mains connection; Fakro FTP-V U5 (78x118cm or 94x140cm): ~£580-1,070/window; conservation rooflight (Velux EDW or Fakro DSF, flush-fit, slim aluminium frame, front slope conservation area): ~£1,000-1,900/window; typical London loft conversion 2 x Velux Integra GGU SK08 rear slope (most common specification): ~£1,900-3,000 both windows supply+fit; roof window cost almost always included in loft conversion contractor's overall quote — above costs for standalone installation only

1. Planning Permission and Roof Windows
2. Velux Product Range for Loft Conversions
3. Fakro Roof Windows
4. Building Regulations Requirements for Roof Windows
5. Roof Window Costs in London
6. Frequently Asked Questions

Planning Permission and Roof Windows

INSTALLING ROOF WINDOWS (ROOFLIGHTS) IN A LONDON VICTORIAN TERRACE PITCHED ROOF IS SUBJECT TO SPECIFIC PERMITTED DEVELOPMENT RULES UNDER GPDO 2015 (THE GENERAL PERMITTED DEVELOPMENT ORDER 2015 — ENGLAND — SCHEDULE 2 PART 1 CLASS C — ADDITIONS ETC TO THE ROOF OF A DWELLING HOUSE).

PERMITTED DEVELOPMENT — CLASS C RULES FOR ROOF WINDOWS: (1) THE ROOF WINDOW MUST NOT PROTRUDE MORE THAN 150MM BEYOND THE PLANE OF THE EXISTING ROOF SLOPE — I.E., THE FINISHED OUTER SURFACE OF THE ROOF WINDOW GLASS (THE TOP SURFACE OF THE INSTALLED WINDOW) MUST NOT PROJECT MORE THAN 150MM ABOVE THE SURFACE OF THE SURROUNDING ROOF TILES OR SLATES MEASURED PERPENDICULAR TO THE ROOF SLOPE — THIS EFFECTIVELY LIMITS ROOF WINDOWS TO FLUSH-FIT OR LOW-PROFILE INSTALLATION; (2) THE HIGHEST POINT OF THE ROOF WINDOW MUST NOT EXCEED THE HIGHEST POINT OF THE EXISTING ROOF RIDGE; (3) ON THE PRINCIPAL ELEVATION (THE FRONT ROOF SLOPE — FACING THE HIGHWAY): ROOF WINDOWS ARE PERMITTED DEVELOPMENT ONLY WHERE THEY DO NOT PROTRUDE MORE THAN 150MM AND MEET THE HEIGHT LIMITATION; (4) CONSERVATION AREA: IN A CONSERVATION AREA, PERMITTED DEVELOPMENT FOR ROOF WINDOWS ON THE PRINCIPAL (FRONT) ELEVATION IS TYPICALLY REMOVED — MOST INNER LONDON CONSERVATION AREA APPRAISALS AND ARTICLE 4 DIRECTIONS SPECIFICALLY RESTRICT THE INSTALLATION OF ROOF WINDOWS (ROOFLIGHTS) ON THE FRONT ELEVATION — BECAUSE THEY ALTER THE APPEARANCE OF THE UNIFORM VICTORIAN TERRACE ROOFLINE THAT IS A CHARACTER-DEFINING FEATURE OF THE CONSERVATION AREA. REAR ROOF SLOPE: ROOF WINDOWS ON THE REAR ROOF SLOPE (NOT VISIBLE FROM THE HIGHWAY — TYPICALLY WITHIN PERMITTED DEVELOPMENT EVEN IN MOST LONDON CONSERVATION AREAS — PROVIDED THEY DO NOT PROTRUDE MORE THAN 150MM BEYOND THE ROOF PLANE). PLANNING APPLICATION: WHERE A ROOF WINDOW IS PROPOSED ON THE FRONT ELEVATION IN A CONSERVATION AREA, A FULL PLANNING APPLICATION (HOUSEHOLDER APPLICATION — FEE £258 IN ENGLAND 2024-2025) IS REQUIRED — AND MOST CONSERVATION OFFICERS WILL OBJECT UNLESS THE WINDOW IS OF A CONSERVATION ROOFLIGHT TYPE (FLUSH FITTING — NOT PROJECTING — WITH A SLIM ALUMINIUM FRAME THAT DOES NOT SIGNIFICANTLY CHANGE THE APPEARANCE OF THE ROOF SLOPE).

Velux Product Range for Loft Conversions

VELUX (VKR GROUP A/S — VILLENEUVE-D'ASCQ, FRANCE / HØRSHOLM, DENMARK — THE WORLD'S LARGEST ROOF WINDOW MANUFACTURER — APPROXIMATELY 70% MARKET SHARE IN THE UK ROOF WINDOW MARKET) IS THE DOMINANT BRAND FOR RESIDENTIAL LOFT CONVERSION ROOF WINDOWS IN THE UK.

VELUX GGU (POLYURETHANE FINISH — WHITE PAINTED POLYURETHANE FRAME — THE MOST WIDELY USED VELUX MODEL FOR UK RESIDENTIAL LOFT CONVERSIONS — MOISTURE AND HUMIDITY RESISTANT — SUITABLE FOR BATHROOMS AND HIGHLY HUMID SPACES — THE POLYURETHANE FINISH DOES NOT REQUIRE REPAINTING): VELUX GGU SK08 (SK08 = 114CM H X 114CM W — ONE OF THE MOST POPULAR VELUX SIZE CODES FOR UK LOFT CONVERSION BEDROOMS — PROVIDES GOOD NATURAL LIGHT AND VENTILATION IN A DORMER-LESS REAR SLOPE LOFT CONVERSION — CENTRE-PIVOT OPERATION — MANUALLY OPERATED); VELUX GGU CK04 (CK04 = 98CM H X 55CM W — COMPACT WIDTH — USED WHERE THE RAFTER SPACING LIMITS WINDOW WIDTH — TYPICALLY ON A STANDARD VICTORIAN TERRACE WITH 450MM RAFTER CENTRES); VELUX GGU MK04 (MK04 = 98CM H X 78CM W — MEDIUM SIZE — GOOD BALANCE OF LIGHT AREA AND STANDARD RAFTER SPACING COMPATIBILITY); VELUX INTEGRA (GGU 0060 — THE ELECTRIC MOTORISED VERSION OF THE GGU — OPERATED BY WALL SWITCH, VELUX REMOTE CONTROL, OR VELUX APP — WEATHER SENSOR AUTOMATICALLY CLOSES THE WINDOW WHEN RAIN IS DETECTED — THE PREFERRED SPECIFICATION FOR LOFT CONVERSION BEDROOMS WHERE THE WINDOW IS ABOVE REACH FROM THE FLOOR BELOW): VELUX INTEGRA GGU SK08 0060 (114CM X 114CM — ELECTRIC MOTORISED — RAIN SENSOR — WHITE POLYURETHANE FRAME — THE MOST FREQUENTLY SPECIFIED VELUX MODEL FOR LONDON LOFT CONVERSIONS IN THE 2020S). VELUX GPL (TIMBER FRAME EQUIVALENT OF THE GGU — LACQUERED PINE TIMBER INNER FRAME — SUITABLE WHERE A TIMBER INTERIOR FINISH IS PREFERRED — SLIGHTLY LESS MOISTURE RESISTANT THAN GGU — REQUIRES REPAINTING TYPICALLY EVERY 8-10 YEARS). VELUX CABRIO BALCONY WINDOW (GDL SD0W225 — THE VELUX CABRIO CONVERTS A PAIR OF STANDARD VELUX ROOF WINDOWS INTO A BALCONY WHEN FULLY OPENED — THE LOWER WINDOW SASH FOLDS DOWN TO FORM THE BALCONY FLOOR AND THE UPPER SASH RISES TO FORM THE BALCONY RAILING — THE VELUX CABRIO IS AN ALTERNATIVE TO A FULL DORMER CONVERSION IN CONSERVATION AREAS WHERE A DORMER IS NOT ACCEPTABLE — CREATES OUTDOOR SPACE WITHOUT A MAJOR STRUCTURAL CHANGE — BUT NOTE: THE VELUX CABRIO CREATES A PROJECTING STRUCTURE AND TYPICALLY REQUIRES PLANNING PERMISSION).

Fakro Roof Windows

FAKRO (FAKRO SP Z O.O. — NOWY SĄCZ, POLAND — THE SECOND LARGEST ROOF WINDOW MANUFACTURER IN THE WORLD AFTER VELUX — APPROXIMATELY 15-20% UK MARKET SHARE IN THE 2020S) IS THE MAIN COMPETITOR TO VELUX IN THE UK RESIDENTIAL LOFT CONVERSION MARKET.

FAKRO FTP-V U5 (FAKRO'S STANDARD MANUALLY OPERATED PVC ROOF WINDOW — THE DIRECT COMPETITOR TO THE VELUX GGU — PVC FRAME — CENTRE-PIVOT OPERATION — U-VALUE: 0.97-1.1 W/M²K DEPENDING ON SIZE AND GLAZING OPTION — TRIPLE GLAZED AVAILABLE — AVAILABLE IN EQUIVALENT SIZES TO VELUX SIZE CODES — TYPICAL SIZES USED IN UK LOFT CONVERSIONS: 78CM X 118CM / 78CM X 140CM / 94CM X 140CM): FAKRO FTP-V U5 OFFERS EQUIVALENT OR SUPERIOR U-VALUE PERFORMANCE TO VELUX GGU AT A LOWER PRICE POINT — FREQUENTLY PREFERRED BY COST-CONSCIOUS LOFT CONVERSION CONTRACTORS. FAKRO DEF-V — ELECTRIC MOTORISED (THE FAKRO EQUIVALENT OF THE VELUX INTEGRA — ELECTRICALLY OPERATED PVC ROOF WINDOW — RAIN SENSOR AND WIND SENSOR — REMOTE CONTROL OR SMART HOME COMPATIBLE — COMPARABLE SPEC TO VELUX INTEGRA GGU 0060 AT A TYPICALLY LOWER PRICE). FAKRO DSF CONSERVATION ROOFLIGHT (A FLAT, SLIM-PROFILE CONSERVATION ROOFLIGHT IN A SLIM ALUMINIUM FRAME — THE FAKRO EQUIVALENT OF THE VELUX EDW CONSERVATION ROOFLIGHT — FLUSH OR NEAR-FLUSH FITTING — APPROPRIATE FOR CONSERVATION AREA FRONT SLOPES WHERE A CONSERVATION-TYPE ROOFLIGHT IS ACCEPTABLE — SMALLER LIGHT-ADMITTING APERTURE THAN A STANDARD ROOF WINDOW — TRIPLE GLAZED — U-VALUE ~1.0-1.2 W/M²K). U-VALUE COMPARISON: VELUX GGU SK08 (114 X 114): U-VALUE 1.2-1.3 W/M²K (CENTRE PANE) — TRIPLE GLAZED VELUX UNITS ACHIEVE 1.0-1.1 W/M²K; FAKRO FTP-V U5: U-VALUE 0.97-1.1 W/M²K — PART L 2021 (APPROVED DOCUMENT PART L 2021 — ENGLAND): FOR AN EXISTING DWELLING (MATERIAL ALTERATIONS — LOFT CONVERSION), THE U-VALUE STANDARD FOR NEW ROOF WINDOWS IS 2.2 W/M²K OR BETTER (THE NOTIONAL DWELLING BACKSTOP VALUE FOR A ROOF LIGHT) — BOTH VELUX GGU AND FAKRO FTP-V COMFORTABLY MEET THIS MINIMUM.

Building Regulations Requirements for Roof Windows

ROOF WINDOWS IN A LOFT CONVERSION OF A LONDON VICTORIAN TERRACE MUST COMPLY WITH SEVERAL APPROVED DOCUMENTS — THE MOST CRITICAL ARE PART B (FIRE SAFETY), PART F (VENTILATION), AND PART L (THERMAL PERFORMANCE).

PART B — FIRE EGRESS (APPROVED DOCUMENT PART B — FIRE SAFETY — VOLUME 1 — DWELLINGS — ENGLAND — 2019 EDITION WITH 2020 AMENDMENTS): ANY HABITABLE ROOM (BEDROOM, STUDY, LIVING ROOM) IN A LOFT CONVERSION THAT IS ACCESSED BY A STAIRCASE THAT CONSTITUTES THE ONLY MEANS OF ESCAPE FROM THE LOFT LEVEL MUST BE PROVIDED WITH AN OPENING FOR EMERGENCY ESCAPE — THE ROOF WINDOW CAN SERVE AS THIS EMERGENCY ESCAPE OPENING — PROVIDED: (A) THE CLEAR OPENING WIDTH IS AT LEAST 450MM (NOT THE FRAME WIDTH — THE CLEAR OPENING WHEN THE WINDOW IS OPEN) AND THE CLEAR OPENING HEIGHT IS AT LEAST 450MM WITH A MINIMUM AREA OF 0.33M²; (B) THE SILL HEIGHT (THE BOTTOM OF THE CLEAR OPENING WHEN THE WINDOW IS OPEN) IS NOT MORE THAN 1,100MM ABOVE THE FLOOR LEVEL — TO ALLOW A PERSON TO CLIMB THROUGH; NOTE: A VELUX GGU SK08 (114CM X 114CM) CENTRE-PIVOT FULLY OPEN PROVIDES A CLEAR OPENING OF APPROXIMATELY 500MM HIGH X 900MM WIDE (HALF THE WINDOW OPENS) — MEETING PART B FIRE EGRESS REQUIREMENTS. PART F — VENTILATION (APPROVED DOCUMENT PART F 2021 — MEANS OF VENTILATION — ENGLAND): BEDROOMS IN A LOFT CONVERSION REQUIRE A MINIMUM BACKGROUND VENTILATION OF 5000MM² EQUIVALENT AREA (EA) (TRICKLE VENTILATOR — FITTED IN THE ROOF WINDOW FRAME OR SURROUNDING STRUCTURAL OPENING) AND A RAPID VENTILATION AREA OF 1/20 OF THE ROOM FLOOR AREA (THE OPENABLE AREA OF THE ROOF WINDOW MUST BE AT LEAST 1/20 OF THE ROOM FLOOR AREA — VELUX GGU SK08 MEETS THIS REQUIREMENT FOR A ROOM UP TO APPROXIMATELY 20M² FLOOR AREA). PART L — THERMAL PERFORMANCE: BACKSTOP U-VALUE FOR ROOF WINDOWS IN A MATERIAL ALTERATION OF AN EXISTING DWELLING: 2.2 W/M²K — BOTH VELUX GGU (1.2-1.3 W/M²K) AND FAKRO FTP-V U5 (0.97-1.1 W/M²K) COMFORTABLY EXCEED THIS MINIMUM — TRIPLE GLAZED OPTIONS MEET PART L 2021 NEW DWELLING STANDARD.

Roof Window Costs in London

ROOF WINDOW COSTS (LONDON 2025 — ROOFER/LOFT CONVERSION CONTRACTOR — SUPPLY AND FIT — LABOUR AND MATERIALS — PER WINDOW).

VELUX GGU SK08 (114 X 114CM — MANUALLY OPERATED — CENTRE PIVOT — WHITE POLYURETHANE — INCLUDING VELUX EW (STANDARD EXTERNAL FLASHING KIT FOR PLAIN TILE / SLATES — REQUIRED FOR WEATHERPROOF INSTALLATION — SPECIFIC FLASHING KIT FOR TILE TYPE — VELUX EW FLASHING KIT FOR SLATES OR VELUX EDW INSTALLATION PACKAGE): VELUX GGU SK08 WINDOW SUPPLY: APPROXIMATELY £300-420 (VELUX TRADE PRICE VIA TRAVIS PERKINS, JEWSON, BUILDPOINT — VELUX EW FLASHING KIT ADDITIONAL ~£100-180); INSTALLATION LABOUR (PER WINDOW — INCLUDING CUTTING RAFTER, FITTING TRIMMER RAFTERS, FITTING WINDOW + FLASHING, MAKING GOOD INTERIOR REVEALS IN PLASTERBOARD): APPROXIMATELY £300-600; TOTAL PER WINDOW: APPROXIMATELY £700-1,200. VELUX INTEGRA GGU SK08 0060 (114 X 114CM — ELECTRIC MOTORISED — RAIN SENSOR — THE PREMIUM SPECIFICATION FOR A LONDON LOFT CONVERSION BEDROOM): SUPPLY: APPROXIMATELY £550-750 (INTEGRA MOTORISED PREMIUM OVER MANUAL GGU) + FLASHING KIT + INSTALLATION = TOTAL APPROXIMATELY £950-1,500 PER WINDOW (PLUS ELECTRICIAN TO WIRE MOTOR IF NOT SELF-CONTAINED BATTERY UNIT). FAKRO FTP-V U5 (EQUIVALENT SIZE TO VELUX SK08 — 78X118CM OR 94X140CM): SUPPLY: APPROXIMATELY £200-320 (LOWER PRICE POINT THAN VELUX GGU) + FAKRO FLASHING KIT ~£80-150 + INSTALLATION £300-600 = TOTAL APPROXIMATELY £580-1,070 PER WINDOW. CONSERVATION ROOFLIGHT (VELUX EDW OR FAKRO DSF — FLUSH CONSERVATION ROOFLIGHT — FIXED OR OPENING — SLIM ALUMINIUM FRAME — FOR CONSERVATION AREA FRONT SLOPES — SMALLER OPENING): SUPPLY: APPROXIMATELY £600-1,200 (CONSERVATION ROOFLIGHTS ARE SIGNIFICANTLY MORE EXPENSIVE THAN STANDARD ROOF WINDOWS — SMALLER SERIES, FLUSH PROFILE MANUFACTURING PREMIUM) + INSTALLATION £400-700 = TOTAL APPROXIMATELY £1,000-1,900 PER CONSERVATION ROOFLIGHT. TYPICAL LONDON LOFT CONVERSION WITH 2 X VELUX GGU SK08 INTEGRA MOTORISED REAR SLOPE: APPROXIMATELY £1,900-3,000 FOR BOTH WINDOWS SUPPLY + FIT.

Frequently Asked Questions

Do I need planning permission for Velux windows in a London Victorian terrace?▼

Planning permission for Velux or other roof windows depends on location: non-conservation area property: roof windows on the rear slope are generally permitted development (GPDO 2015 Schedule 2 Part 1 Class C) provided the window does not protrude more than 150mm beyond the roof plane and does not exceed the ridge height — no planning permission required for most standard installations on the rear slope; front slope (non-conservation area): also generally permitted development if the 150mm protrusion limit and ridge height limit are met — no planning permission required; conservation area (front slope — most inner London boroughs): in a conservation area, installing a roof window on the principal (front) elevation typically requires planning permission — most inner London conservation area Article 4 Directions specifically restrict front-slope rooflights because they alter the uniform Victorian terrace roofline character — a conservation-type flush rooflight (Velux EDW Conservation Rooflight or equivalent, slim aluminium frame, flush-fit, minimal visual impact) may be accepted where a standard projecting roof window would be refused; conservation area (rear slope): rear slope roof windows are generally more likely to be accepted even in a conservation area — often permitted development — but confirm with the local authority conservation officer before proceeding; listed building: Listed Building Consent is required for any new roof window on a listed building — regardless of slope or type.

What size Velux window do I need for a loft conversion bedroom?▼

For a standard London Victorian terrace loft conversion bedroom (typically 8-12m² floor area), the recommended Velux sizes are: Velux GGU SK08 (114cm H x 114cm W — 1.30m² glass area — the most popular size for UK loft conversion bedrooms — provides excellent natural light and adequate ventilation for a bedroom up to ~20m²); Velux GGU MK04 (98cm H x 78cm W — suitable where rafter centres limit width to ~78cm — 0.76m² glass area — adequate for smaller bedrooms up to ~12-15m²); Velux GGU CK04 (98cm H x 55cm W — compact size for tight rafter spacings — 0.54m² glass area — adequate for small bedrooms/bathrooms); size is also constrained by rafter spacing: a standard Victorian terrace has rafters at 400-600mm centres — the roof window must fit between two adjacent rafters (with trimmer rafters installed — which requires cutting one or two intermediate rafters); a Velux SK08 (114cm wide) typically spans approximately 2-3 rafter bays with trimmers; Part B fire egress: the roof window must provide a clear opening of at least 450mm x 450mm with a minimum area of 0.33m² when open — Velux GGU SK08 fully open provides approximately 500mm x 900mm clear opening — meets Part B; Part F ventilation: the openable area must be at least 1/20 of the room floor area — Velux SK08 meets this requirement for rooms up to approximately 20m².

What is the difference between Velux GGU and Velux Integra?▼

Velux GGU is the manually operated version — Velux Integra GGU 0060 is the electrically motorised version: Velux GGU (manually operated, centre-pivot): the white polyurethane Velux roof window, manually operated by a pole hook or by reaching the handle on the sash — available in all standard size codes (SK08, MK04, CK04 etc) — the most widely used Velux model in UK residential loft conversions; Velux Integra GGU 0060 (electrically motorised, same polyurethane frame): the same white polyurethane GGU sash but with an integrated electric motor — operated by wall switch, Velux remote control (KLI 310), or Velux Active / Velux App (iOS/Android); includes a rain sensor (KFX 110 rain sensor) that automatically closes the window when rain is detected — even when no one is home; preferred for loft conversion bedrooms where the window is above comfortable reach from the floor (typically 2.0-2.3m sill height above floor level in a sloping ceiling loft conversion); costs more than the manually operated GGU: approximately £250-350 more for the motorised unit; requires electrical connection to 240V mains (a 5A fused connection unit or junction box above ceiling level) — or select the Velux Integra Solar (GGU 0066 — battery powered solar panel on outer frame — no mains wiring required); Velux GGU size codes used in UK loft conversions: SK08 (114x114cm, most popular), MK04 (98x78cm), CK04 (98x55cm), FK08 (140x114cm for larger openings).

What is the difference between Velux and Fakro roof windows?▼

Velux and Fakro are the two dominant roof window brands in the UK loft conversion market: Velux (VKR Group, Denmark): approximately 70% UK market share — the most widely specified and recognised roof window brand in the UK — well-established supply chain through Travis Perkins, Jewson, Buildpoint — wide range of accessories (flashing kits for every tile/slate type, blinds, remote controls) — Integra electric motorised version with rain sensor is industry standard for loft conversion bedrooms — more expensive than Fakro; Fakro (Fakro Sp z o.o., Nowy Sącz, Poland): approximately 15-20% UK market share — the main competitor to Velux — FTP-V U5 is the direct competitor to Velux GGU — similar performance and dimensions — often 10-20% lower supply price than equivalent Velux — growing acceptance among UK loft conversion contractors; thermal performance: Fakro FTP-V U5: U-value 0.97-1.1 W/m²K (triple glazed option 0.97) vs Velux GGU: U-value 1.2-1.3 W/m²K (triple glazed 1.0-1.1) — Fakro has a slight U-value advantage in standard models; both brands meet Part L 2021 backstop U-value of 2.2 W/m²K comfortably; product availability: Velux has a larger and more established UK network of flashing kits, blinds, and accessories — Fakro's accessory range is adequate but less extensive in UK merchants; for most standard London loft conversions: either brand is technically suitable — the choice is often driven by contractor preference and merchant availability.

How much do Velux windows cost to install in a London loft conversion?▼

Velux and roof window costs London 2025 (roofer/loft conversion contractor, supply+fit, per window): Velux GGU SK08 (114x114cm, manually operated, centre-pivot, white polyurethane): window supply ~£300-420 + Velux EW flashing kit ~£100-180 + installation (cut rafter, trimmer rafters, fit window + flashing, plasterboard reveals) ~£300-600 = total ~£700-1,200 per window; Velux Integra GGU SK08 0060 (114x114cm, electric motorised, rain sensor): window supply ~£550-750 + flashing kit + installation = total ~£950-1,500 per window (plus electrician for mains connection if not solar battery); Fakro FTP-V U5 (equivalent to SK08, 78x118cm or 94x140cm): supply ~£200-320 + Fakro flashing kit ~£80-150 + installation ~£300-600 = total ~£580-1,070 per window; conservation rooflight (Velux EDW or Fakro DSF, flush-fit, slim aluminium frame, front slope conservation area): supply ~£600-1,200 + installation ~£400-700 = total ~£1,000-1,900 per conservation rooflight; typical London loft conversion with 2 x Velux Integra GGU SK08 rear slope (most common specification): ~£1,900-3,000 for both windows supply+fit; note: roof window installation is almost always included in the overall loft conversion contractor's quote — the above costs are for a standalone roof window replacement or addition only.

Important Note

This guide is for general information only. Building regulations, planning rules, and legal requirements change regularly and vary by local authority. Always seek professional advice specific to your project and location. RCB Design & Build offers free initial consultations — book your free survey.

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