When it comes to roof lanterns, getting the sizing right the first time is essential. A roof lantern that fits perfectly not only looks better but performs better – offering optimal light, insulation, and watertight protection. For trade professionals and installers, the right measurements can be the difference between a seamless installation and a costly return visit.
At The Rooflight Centre, we work closely with builders, architects, and homeowners to ensure every roof lantern fits exactly as intended. Our precision-engineered products, expert guidance, and clear sizing information make the process simple and stress-free.
Explore our range of Flat Roof Windows to find the perfect size and style for your next project.
Why Roof Lantern Size Matters
Choosing the correct size for a roof lantern isn’t just about how it looks – it has a direct impact on your project’s functionality and performance.
A roof lantern that’s too large can overpower a space, add unnecessary weight to the structure, or cause heat gain in summer. On the other hand, a lantern that’s too small may not deliver enough daylight to justify the investment.
From an installer’s perspective, accurate sizing ensures:
– A watertight fit between the lantern and the upstand
– Compliance with building regulations
– Reduced installation time and waste
– Fewer costly call-backs or on-site adjustments
A correctly sized lantern helps balance aesthetics, natural light, and structural integrity, ensuring the best outcome for both you and your client.
Measuring the Opening vs External Size
One of the most common causes of installation errors comes down to confusion between the structural opening size and the roof lantern size.
Here’s the difference:
– Structural opening size is the size of the hole in your roof.
– External size refers to the full footprint of the roof lantern, including its frame and fixings. – Internal daylight size is the visible glass area inside the frame.
For example, a lantern listed as 1000mm x 2000mm typically refers to the external upstand size, not the opening in your roof. The upstand itself may add 75mm or more on each side, meaning your roof opening should be smaller to accommodate it.
At The Rooflight Centre, we provide clear technical drawings for every product so installers know exactly what measurements to use. By double-checking your opening vs external dimensions, you can avoid unnecessary adjustments on-site.
Factors That Affect Roof Lantern Sizing
A number of variables influence how your roof lantern fits and performs, and these should all be considered before finalising your order.
Pitch angle – Most roof lanterns have a fixed pitch, typically around 25-30 degrees. The higher the pitch, the taller the lantern will be, which may affect how it integrates with your roof structure.
Upstand height – Building regulations require the top of the upstand to sit at least 150mm above the finished roof level. This spacing affects how much room you have for insulation and flashing.
Insulation and roof build-up – The thickness of your insulation and waterproofing layers can impact your final measurements, particularly if you’re working with warm roof systems.
Surrounding structure – Always allow enough tolerance around the opening for roof build-up, trims, and sealing materials.
Failing to consider these details can lead to costly resizing or rework – something every trade professional wants to avoid.
Common Roof Lantern Sizes and Applications
At The Rooflight Centre, we supply roof lanterns in a wide range of standard and bespoke sizes, making it easy to find the perfect fit for any project.
Here are some of the most popular sizes and their typical applications:
– 1000mm x 1000mm – Ideal for small rooms, hallways, or bathrooms where natural light is needed but space is limited.
– 1000mm x 2000mm – A popular choice for kitchen extensions or dining areas, offering a good balance between light and proportion.
– 1500mm x 3000mm – Perfect for large open-plan living spaces where a statement feature and maximum light are desired.
– 2000mm x 4000mm and above – Used for expansive spaces, commercial projects, or modern homes with dramatic architectural designs.
If your project requires something unique, we can provide custom-sized roof lanterns tailored to your exact dimensions. This flexibility ensures that your installation fits perfectly without compromising on aesthetics or performance.
Tips for Getting It Right First Time
When it comes to sizing and installing roof lanterns, a few simple steps can prevent expensive mistakes:
1. Double-check your measurements – Measure twice before ordering. Confirm both structural opening and external sizes.
2. Order the upstand and roof lantern together – This ensures perfect compatibility and simplifies installation. 3. Confirm your roof build-up – Account for insulation, membrane thickness, and roof fall before cutting the
opening.
4. Check internal clearance – Ensure the lantern won’t interfere with joists, rafters, or ceiling features. 5. Use the manufacturer’s guidance – Always refer to the technical documentation provided for your specific model.
Following these steps helps you avoid unnecessary adjustments and ensures your roof lantern fits perfectly the first time.
Why Choose The Rooflight Centre?
When investing in a skylight or roof window, choosing the right supplier is just as important as the product itself. At The Rooflight Centre (RLC), we’re more than just an online retailer – we’re the e-commerce division of Lonsdale Metal Company (LMC), a fourth-generation family business founded in 1954. With decades of experience behind us, we’ve built a reputation for craftsmanship, reliability, and outstanding service.
Our rooflights have been trusted on some of the UK’s most iconic buildings, including Buckingham Palace, The British Museum, and 10 Downing Street. We’ve also supplied household names like Rod Stewart, Lord Alan Sugar, and Tracey Emin – proof that our products are chosen by both leading architects and discerning homeowners alike.
But our focus isn’t just on prestige projects. Since 2020, we’ve worked hard to make the same exceptional quality available to homeowners and tradespeople alike. Every rooflight in our range is handpicked to meet exacting standards for performance, design, and durability.
When you choose The Rooflight Centre, here’s what you can expect:
– Beautiful, high-performance rooflights that enhance your projects
– Fair pricing without compromising on quality
– Fast delivery and easy ordering from our online store
– Dedicated support from a team that genuinely cares about your success
This combination of heritage, craftsmanship, and personal service makes us a trusted choice for trade professionals who want rooflights that deliver on both performance and value.
Ready to Order Your Roof Lantern with Confidence?
Getting your roof lantern size right the first time saves time, money, and stress. With precision-engineered products, clear sizing guides, and expert support, The Rooflight Centre makes it simple for tradespeople and homeowners alike.
Explore our full range of Flat Roof Windows here and get expert advice to ensure your next installation fits perfectly.
By choosing The Rooflight Centre, you’re not just buying a rooflight – you’re investing in accuracy, reliability, and quality that stands the test of time.
