How to choose a flat rooflight for your extension - without blowing your budget

A rooflight is a window designed specifically for flat or low-pitch roofs (0° to 15°). It draws daylight deep into home extensions and other spaces below, whether single-storey or multi-storey, as long as the roof above is flat. If you're searching for rooflights for flat roofs, here's what matters most. 

Many home extensions end up with rooms that don't get enough natural light, whether it's a ground floor space with limited windows, or an upper storey tucked under the roofline. A flat rooflight solves this by delivering daylight from directly overhead, right where it's needed most. 

The difference is significant. A flat rooflight delivers up to three times more daylight than a façade window1 of the same size. That means brighter rooms, fewer dark corners, and less reliance on electric lighting during the day. 

Research shows daylight can improve productivity by up to 15% and boost learning by up to 18%.² It supports circadian rhythm, lifts mood, and makes spaces feel more spacious and welcoming. 

Whether it's a kitchen, living room, home office or kids' playroom, a flat rooflight isn't a luxury. It's a practical necessity for comfortable everyday living. 

"Skylight" is the general term most people use for any roof-mounted window. "Rooflight" refers specifically to windows engineered for flat or low-pitch roofs, typically between 0° and 15°. 

The Skylight vs Rooflight distinction matters when you're shopping. VELUX rooflights are purpose-designed for flat roofs, with drainage, insulation, and weatherproofing built for horizontal installations. 

If your extension has a flat roof, you need a rooflight, or another type of flat roof window.

Yes. A rooflight is one of the smartest investments you can make in a home extension. Here's why: 

• More daylight: Up to 3× more than vertical windows of the same size. 
• Energy savings: Less artificial lighting needed during the day. 
• Better comfort: Fresh air ventilation reduces CO₂ and humidity, while night cooling helps release built-up heat for a more comfortable indoor climate. 
• Modern appearance: Glass rooflights enhance your property's design. 
• Long-term durability: Glass doesn't yellow or degrade like plastic. 

Unlike plastic dome solutions, a glass flat rooflight maintains its clarity and thermal performance for decades. VELUX backs this with a 10-year guarantee on flat roof windows. Electrical components and blinds carry a 3 to 5-year guarantee, depending on the type. Learn more here.  

You're not just buying a window. You're investing in brighter, healthier living, and a home that looks and feels more valuable. 

The right rooflight size depends on several factors: 

• Room size: Your flat rooflight should cover at least 10% of the room's floor area. 
• Room purpose: Habitable rooms need more daylight than utility spaces. 
• Other light sources: Sun tunnels or adjacent windows reduce the size needed. 
• Shadows and obstructions: If nearby buildings or trees block light, increase to 15–20%. 

This 10% guideline comes from the European Standard EN 17037. It recommends 300 lux for 50% of the year over 50% of the room area. ³ It is a reliable starting point for most home extensions. 

Not sure which size you need? Standard glass rooflight comes in 8 standard sizes suited to most residential needs. For larger spaces or maximum daylight, the Flat Glass Rooflight, as well as Curved glass rooflight offer 13 sizes up to 200×100 cm. 

Don’t forget that you can take advantage of our free design service with tailored daylight analysis for your specific room.  

Get free design advice — Book a free consultation with a VELUX Design Advisor 

Four factors determine how long your flat rooflight lasts and how well it performs. These are material quality, glazing type, installation method, and brand engineering. 

Glass is inherently more durable than plastic. It won't yellow, scratch, or lose clarity over time. A proven base unit, like the one the VELUX Standard glass rooflight is built on, ensures watertight integrity for decades. 

Regular maintenance and cleaning of the window helps, too. Keep your flat rooflight clean, clear drainage paths of debris, and inspect seals periodically. With proper care, you can expect multiple years of reliable performance.

In short: choose your flat rooflight based on four factors: exterior surface design, glazing and insulation (U-value), operation type, and budget tier. For most UK renovations, the mid-range VELUX Standard glass rooflight offers the best balance of modern design and thermal performance without stretching to premium pricing. 

Choosing the right flat rooflight for your home comes down to what matters most to you. Think about the surface design that suits your extension, the insulation you need to stay comfortable all year, and whether you'd like a fixed, electric, or solar-powered rooflight.  

Consider how much daylight you want to bring in, plus any accessories or security features, like burglary protection, that give you extra peace of mind. With VELUX, you'll find a rooflight designed to fit your home and your budget, so you don't have to compromise on quality or comfort. 

If you're looking for a balance of style, performance, and value, consider the VELUX Standard glass rooflight. Sitting in the mid-range, it offers a modern glass finish and solid thermal performance without the premium price tag, making it a cost-efficient upgrade from traditional domes if you want contemporary design at a realistic budget. 

The cost of your home extension can vary significantly. Size, materials, design complexity, and your location all play a role. 

Don't forget these indirect costs: 

• Architect and design fees 
• Building control and planning applications 
• Structural engineering reports 
• Landscaping and “making good” after the build 
• Allow a safety margin of about 20% for unforeseen expenses. Renovation projects rarely go exactly to plan, and a buffer prevents stressful compromises later. 

Most importantly, plan for your flat rooflight from the start. Specifying it during the design phase avoids costly retrofitting and lets your builder integrate it seamlessly into the roof structure. 

The exterior surface of your rooflight affects both appearance and long-term performance. You have four main options: 

• Dome with glazing: The most affordable and functional choice. Curved, raised appearance. Best suited to garages and utility spaces. 
• Curved glass rooflight: Subtly curved glass-top for effortless rainwater drainage. Slim frame and glass-to-edge design for more daylight and modern appearance. 
• Standard glass rooflight: A modern framed flat glass-top design with a low profile rooflight aesthetic. Clean lines and a contemporary look at a mid-range price. Ideal for any modern house where a sleek roofline matters. 
• Flat glass rooflight: Glass-to-edge design with a slim frame. Premium aesthetics and top-tier performance for design-led and new build projects. 

The Standard glass rooflight delivers a clear upgrade from domes without stretching into premium territory. It's a sweet spot for renovations and extensions.

The Standard glass rooflight uses two layers of glass. For most homes in the UK, this is more than enough to keep rooms warm and quiet. 

If you live in a particularly cold or noisy location, near an airport or railway line, for example, triple glazing is worth considering. In that case, take a look at the VELUX Curved glass rooflight or Flat glass rooflight, both of which are available with triple glazing. 

The Standard glass rooflight also includes: 

• Inner laminated safety glass for impact resistance. 
• Burglary-resistant design (RC2 Q-variant available). 
• Sound insulation of up to 37 dB 
• U-value of 0.75 to 0.82

Every flat rooflight is available in at least two variants: fixed and electric. 

Fixed rooflights provide daylight only. They're the simplest, most affordable option, ideal for rooms where ventilation isn't a priority. 

Electric rooflights add ventilation, rain sensors, and smart control. This is particularly valuable in kitchens, where cooking creates smells and humidity, as well as in "wet rooms" like bathrooms and utility rooms, where steam and moisture build up quickly. An electric rooflight lets you clear the air at the touch of a button, helping to prevent condensation and keep your space fresh and comfortable. 

They're just as beneficial in bedrooms, where frequent, effortless ventilation helps maintain a fresh, healthy indoor climate for better sleep. In fact, studies show that people with electric or solar-powered windows ventilate their homes twice as often as those with manual windows. Find more tips for healthy sleep here.  

Even better, the integrated rain sensor closes the window automatically if the weather turns, so you can ventilate with total peace of mind. The Standard glass rooflight's electric variant comes with: 

• A pre-paired wall switch for immediate operation. 
• An integrated rain sensor that closes automatically when it rains. 
• VELUX App Control compatibility for smartphone operation. 
• VELUX ACTIVE integration for automated climate management. 

Choose electric rooflights if: 

• You're planning a kitchen, living space, wet room, bathroom, or utility room. 
• You want regular ventilation without effort. 
• You value smart home integration. 

The Standard glass rooflight represents a cost-efficient step into modern glass, without premium pricing. Over time, better insulation also means reduced heating costs and lower artificial lighting needs. Understanding rooflight cost upfront helps you budget accurately. 

*A U-value (Urc,ref300) is a score for how well your flat rooflight keeps warmth inside your home. The lower the number, the less heat escapes, and the lower your energy bills. The VELUX Standard glass rooflight has a U-value of 0.75-0.82. It does a solid job of insulating most homes without stretching your budget. The premium Flat Glass Rooflight scores between 0.55 and 0.75. The exact value depends on operation method and glazing. It's worth considering if your home is already highly insulated and you want peak efficiency. Both are tested to European standards (EN 1873:2014+A1:2016), so you can trust the numbers are accurate and comparable.

Flat rooflight installation involves six steps: preparing the roof opening, fitting a kerb or upstand, sealing the insulated base unit, mounting the glass top unit, applying waterproof flashing, and finishing interior reveals.  

Professional installation by a VELUX Certified Installer ensures watertight performance, proper insulation, and full warranty protection. 

Here's a high-level overview of what you can expect during the installation: 

1. Opening prepared: Your builder creates the roof opening to match your chosen size. 
2. Kerb/upstand in place: A raised kerb or upstand around the opening provides the foundation for the rooflight and helps with drainage. 
3. Base unit installed: The pre-made, insulated VELUX base unit is positioned and sealed onto the kerb. 
4. Top unit fitted: The VELUX glass top unit is mounted onto the base unit, completing the rooflight. 
5. Flashing and waterproofing: Membranes and flashings are added to ensure a fully watertight seal. 
6. Interior finishing: Plasterboard reveals are fitted for a clean, finished look inside. 

You should use VELUX Certified Installers for guaranteed results. The Find an Installer service is free and non-binding, and you'll hear back from flat-roof specialists. 

Rooflight blinds control heat, glare, and privacy while fitting discreetly inside the rooflight's frame. VELUX offers three main types: solar anti-heat blinds that reduce heat and glare, blackout energy pleated blinds which create total darkness and add insulation, and translucent pleated blinds that diffuse light while maintaining brightness. 

Purpose-designed rooflight blinds will help you control the temperature at home, provide blackout when needed, and offer soft light control. They blend effortlessly with your rooflights, allowing maximum daylight to enter when not in use.   

VELUX solar-powered and electric blinds are very easy and convenient to use. They can be operated with a wireless wall switch, or your smartphone via VELUX App Control. It means that you can open and close the blinds from anywhere, whether you’re home or away. 

If you are looking for the blinds suitable for flat roof windows, such as VELUX Standard glass rooflight, please see the list below. 

The VELUX Anti-Heat Blind reduces heat and glare while allowing soft daylight through. That means that you will be able to work from home or watch TV comfortably, while you are hanging out in your home extension.  

The VELUX Anti-Heat Blind is fitted within the roof window, keeping it protected from wind and weather. Because it sits inside the window, it doesn't alter the appearance of your flat rooflight, which retains its sleek, clean glass-top design. What's more, these blinds are solar-powered — harnessing energy from the sun and continuing to work reliably, even on cloudy days. 

The VELUX blackout energy pleated blind provides total darkness and enhanced insulation through its double-pleated design. Its thermal insulation properties also improve your indoor comfort during the cold season. 

VELUX blackout energy pleated blinds are ideal for bedrooms and spaces requiring complete light control. You can choose solar-powered or electric operation. 

VELUX Translucent Pleated Blind offers soft, diffused light with a decorative folded design. It gently dims incoming light while maintaining privacy and a pleasant indoor atmosphere. 

The VELUX Translucent Pleated Blind is available with electric operation. It is a perfect choice for living areas where you want ambience without glare. 

SHOP NOW — Find the best blinds for your rooflight 

You now have everything you need to select the right flat rooflight for your home extension. Here are your next steps: 

1. Compare options. Use the comparison table above to shortlist the rooflight that fits your renovation budget and design goals. 
2. Get expert sizing advice. Book a free VELUX Design consultation for a tailored daylight analysis of your room. 
3. Find a Certified Installer. Use the free Find an Installer service to connect with a local professional for reliable rooflight installation. 
4. Complete your setup with blinds. Browse flat roof window blinds to manage heat, glare, and privacy across every season. 
5. Plan early and save. Specify your flat rooflight during the design phase to avoid retrofit costs and stay within your renovation budget.

Rooflights transform your home extension into a bright, comfortable, and energy-efficient living space. Start today and enjoy more natural light for decades to come.