Velux Roof Windows vs Flat Rooflights: Which Is Better for a Flat Roof?
If you are planning overhead glazing for a flat roof and comparing your options, you have likely encountered both Velux roof windows and flat rooflights. The two products look similar at a glance but they are fundamentally different in design, application and performance. This guide gives you a clear comparison so you can identify the right product for your project.
What Is a Velux Roof Window?
Velux is a Danish brand primarily associated with pitched roof windows. Their core product range is designed for sloped roofs, typically at angles between 15 and 90 degrees. Velux windows open for ventilation, follow the pitch of the surrounding roof covering and are engineered specifically for pitched roof applications.
Velux does produce a separate flat roof range under product names including the CFP (flat glass fixed) and CVP (curved glass), but this is a distinct product line from their pitched roof windows. When most people refer to a Velux roof window, they are referring to the pitched roof product, which is not designed for flat roof installation.
What Is a Flat Rooflight?
A flat rooflight is a glazed unit engineered specifically for flat or very low-pitched roofs. It is positioned on an upstand above the roof surface and is designed to be completely weatherproof without relying on roof pitch for drainage. Flat rooflights are available in framed and frameless designs, in a wide range of sizes and with multiple glazing options to suit different project requirements. At Rooflights and Skylights UK, every flat rooflight is manufactured in Britain to UKCA certification standards, available in standard sizes from 500x500mm to 1000x3000mm, with custom dimensions for non-standard openings.
The Key Differences: Velux Roof Window vs Flat Rooflight
Design and Roof Type Compatibility
A standard Velux roof window is designed for pitched roofs and cannot be correctly installed on a flat roof. The product requires a minimum roof pitch to function correctly and drain rainwater effectively. Installing a pitched roof window on a flat roof would result in water pooling, leaks and unnecessary structural remediation.
A flat rooflight is engineered specifically for flat roofs. It is set on an upstand above the roof surface, allowing water to drain away from all sides. This is the correct product for any flat roof application, including kitchen extensions, rear extensions, loft conversions with flat sections and garden rooms.
Verdict: For a flat roof, a flat rooflight is the correct product. A standard Velux roof window is not suitable for flat roof installation.
Thermal Performance
Both products are available in double and triple glazed versions. Our double glazed flat rooflights achieve a U-value up to 1.0 W/m²K and triple glazed units achieve up to 0.5 W/m²K. Thermally broken aluminium frames minimise cold bridging and heat loss through the frame itself.
Verdict: For flat roof thermal performance, a purpose-built flat rooflight with triple glazing (U-value up to 0.5 W/m²K) and a thermally broken frame is the correct specification.
Find the Right Flat Rooflight for Your Roof
Discover the Perfect Flat Roof Skylight for Your Home
Explore Flat Roof Skylights→Sizing and Flexibility
Velux pitched roof windows come in standard sizes aligned to common rafter spacings. Their flat roof product range also comes in fixed standard dimensions, which means the roof opening must match those dimensions or be adapted to fit.
Our flat rooflights are available in standard sizes from 500x500mm to 1000x3000mm and in custom dimensions for any opening size. If the roof opening is non-standard, a custom flat rooflight can be manufactured to the exact dimensions required with no compromise to weatherproofing or thermal performance.
Verdict: Flat rooflights offer significantly more sizing flexibility, including bespoke dimensions for non-standard openings delivered within 7 to 10 working days.
Aesthetics
Velux pitched roof windows have a profile designed to integrate with the angle of a sloped roof. On a flat roof, that profile does not read correctly against a horizontal surface.
Our flat rooflights are designed specifically for flat roofs. Frameless designs are precision-fitted with minimal visible edging for a clean, contemporary appearance.
Framed designs have a defined aluminium edge that gives a structured, architectural finish. Both look proportionally correct on a flat surface in a way that a pitched roof product cannot.
Verdict: Flat rooflights are designed for flat roofs. The visual result is cleaner and more proportionate than a pitched roof product adapted to a flat surface.
Cost
Flat rooflights from Rooflights and Skylights UK start from £165 ex VAT for a 500x500mm frameless unit and £392 ex VAT for a framed unit. Pricing is displayed transparently on all product pages with no need to request a quote through a merchant. Velux flat roof products are typically priced through merchants and distributors, which can add a markup and reduce pricing transparency.
Verdict: Flat rooflights from a direct UK manufacturer offer transparent pricing from £165 ex VAT with no merchant markup.
Delivery
Standard size flat rooflights from Rooflights and Skylights UK are dispatched within 3 to 4 working days with free delivery to all UK mainland addresses. Custom sizes are delivered within 7 to 10 working days. Velux flat roof products are ordered through merchants and distributors and lead times depend on local stock availability and merchant processing times.
Verdict: Direct UK supply means faster, more predictable delivery, 3 to 4 working days for standard sizes, free to UK mainland.
Guarantee
Every flat rooflight from Rooflights and Skylights UK carries a 10-year guarantee as standard. Each unit is individually inspected before dispatch. We have been recognised with the Professional Builder Top Product Award in both 2024 and 2025, voted for by tradespeople and builders across the UK.
Verdict: A 10-year guarantee on every unit, with independent industry recognition from the professionals who specify and install these products daily.
Which Should You Choose for a Flat Roof?
For any flat roof application, a purpose-built flat rooflight is the correct product. A standard Velux roof window is not compatible with flat roof installation and should not be used in this context. When comparing the Velux flat roof product range with UK-made flat rooflights, the following considerations apply.
- If the roof opening does not match a standard Velux flat roof dimension, a UK flat roof specialist can manufacture to any custom size within 7 to 10 working days.
- If buying direct from a manufacturer rather than through a merchant is preferred, a UK manufacturer gives clearer pricing and faster access to the team behind the product.
- If the build programme requires delivery within one week, a UK manufacturer dispatching standard sizes in 3 to 4 working days provides greater certainty.
- If UK manufacturing and UKCA certification are required by the project specification, Rooflights and Skylights UK is a Made in Britain manufacturer with full UKCA certification on every unit.
- If a contemporary frameless profile is specified for a flat roof extension, a dedicated flat roof skylight manufacturer offers a wider choice of design and finish than the Velux flat roof range.
UK-made flat rooflights — framed and frameless, standard sizes from 500x500mm to 1000x3000mm, custom sizes available. Standard sizes dispatched in 3 to 4 working days with free UK mainland delivery and a 10-year guarantee. Browse the full range at rooflightsandskylightsuk.co.uk/collections/rooflights-skylights
Frequently Asked Questions
- Can a Velux roof window be used on a flat roof?
- What is the difference between a Velux window and a flat rooflight?
- Which is better for a flat roof, Velux or a flat rooflight?
- How much does a flat rooflight cost compared to Velux?
- Are flat rooflights more thermally efficient than Velux windows?
- Can I get a flat rooflight in a custom size?
- How quickly can a flat rooflight be delivered?
- Do flat rooflights come with a guarantee?
A standard Velux roof window is designed for pitched roofs and cannot be correctly installed on a flat roof. Velux does produce a separate flat roof range, but their pitched roof window product requires a minimum roof pitch to drain correctly. For flat roofs, a purpose-built flat rooflight is the correct product.
A Velux window is primarily a pitched roof product designed to sit within a sloped roof at the same angle as the surrounding covering. A flat rooflight is engineered specifically for flat or low-pitched roofs, positioned on an upstand above the roof surface with drainage designed for a horizontal installation. The two products are designed for different applications and are not interchangeable.
For a flat roof, a purpose-built flat rooflight is the appropriate choice. It is designed specifically for the application, delivers correct proportions and weatherproofing for a flat surface and is available in a wider range of sizes including custom dimensions. UK-made flat rooflights from Rooflights and Skylights UK are dispatched in 3 to 4 working days, start from £165 ex VAT and carry a 10-year guarantee as standard.
Flat rooflights from Rooflights and Skylights UK start from £165 ex VAT for a 500x500mm frameless unit and £392 ex VAT for a framed unit. Pricing is displayed transparently on all product pages. Velux flat roof products are priced through merchants, which can vary depending on the supplier and local stock levels.
Flat rooflights from Rooflights and Skylights UK are available in triple glazed versions achieving a U-value up to 0.5 W/m²K with thermally broken aluminium frames. This is the appropriate thermal specification for flat roof applications where superior insulation performance is the priority. Our team can advise on the right glazing specification for your specific project before any order is placed.
Yes. Rooflights and Skylights UK manufactures flat rooflights in custom dimensions for openings outside the standard 500x500mm to 1000x3000mm range. Custom orders are manufactured and delivered within 7 to 10 working days to all UK mainland addresses. Our team will confirm the right specification and pricing for your opening dimensions before any order is placed.
Standard size flat rooflights from Rooflights and Skylights UK are dispatched within 3 to 4 working days with free delivery to all UK mainland addresses. Custom sizes are delivered within 7 to 10 working days. Deliveries to Scottish Highlands, Northern Ireland and the Channel Islands carry a £250 surcharge.
Yes. Every flat rooflight from Rooflights and Skylights UK carries a 10-year guarantee as standard. Each unit is individually inspected before dispatch to confirm it matches the specification and meets our quality standards. We have been recognised with the Professional Builder Top Product Award in both 2024 and 2025, voted for by tradespeople and builders across the UK.