When installing a roof light or roof lantern, one key component often goes unnoticed, yet it’s absolutely essential to the entire system’s performance. That component is the rooflight curb, also known as an upstand. A commonly asked question is what is a rooflight curb and how does it work?

A rooflight curb might look simple at first glance, but it plays a vital role in keeping your roof light secure, weatherproof, and compliant with building regulations. Without it, even the highest-quality roof light wouldn’t perform as intended.

What Is a Rooflight Curb?

A rooflight curb is the raised frame or structure that sits between the flat roof surface and the roof light or roof lantern itself.

It serves two main purposes:

1. To elevate the glazing above the roof surface, protecting it from standing water and debris.
2. To provide a secure, level base for fixing the roof light frame.

You can think of it as the foundation that your roof light sits on, just as a building needs strong foundations to perform properly, so does your roof glazing system.

Curbs can be made from a variety of materials, including:

• Timber (commonly used on-site for custom installations)
• PVC or GRP (Glass Reinforced Plastic) (popular for pre-formed, factory-made curbs)
• Aluminium (used for high-end or bespoke applications)

At Lantern Superstore, our roof lights and roof lanterns are available with precision-engineered, insulated upstands designed for perfect compatibility, long-term performance, and easy installation.

Why Do You Need a Rooflight Curb?

A rooflight curb isn’t just a support, it’s a functional component that impacts the weatherproofing, insulation, drainage, and stability of your roof glazing system.

Here’s why it’s so essential:

1. Weatherproofing
   The curb raises the roof light above the finished roof level, helping to keep water away from the glazing unit and seals. This prevents leaks and ensures effective drainage across the roof surface.
2. Thermal Performance
   Modern rooflight curbs are insulated to prevent cold bridging, a common cause of heat loss and condensation. An insulated upstand helps maintain your building’s energy efficiency and prevents moisture issues inside.
3. Structural Support
   The curb provides a stable, level surface for fixing the roof light. Without it, installation would be difficult, and the glazing might not sit evenly, compromising both appearance and performance.
4. Compliance with Building Regulations
   In the UK, Building Regulations Approved Document C requires roof glazing to be raised at least 150mm above the finished roof surface to prevent water ingress. The curb ensures your installation meets this essential standard.
5. Ease of Installation
   A well-designed curb makes installation faster, cleaner, and more accurate, reducing time on site and ensuring the perfect fit for your roof light or roof lantern.

How Does a Rooflight Curb Work?

A rooflight curb works as an interface between the structure of your roof and the roof light above.

Here’s a step-by-step look at how it functions in practice:

1. Base Fixing
   The curb is securely fixed to the structural roof deck. Depending on the roof type, this might involve mechanical fixings or adhesive bonding.
2. Weatherproof Integration
   Once in place, the roof’s waterproof membrane (such as EPDM, felt, or GRP) is dressed up and over the outside of the curb. This creates a continuous, watertight seal between the roof and the upstand.
3. Thermal Separation
   Insulated curbs contain a thermal break, usually rigid foam insulation, that prevents heat loss through the roof junction.
4. Rooflight Installation
   The roof light or lantern is then installed on top of the curb, with high-quality compression seals and fixings ensuring a weatherproof and airtight connection.
5. Drainage and Ventilation
   Because the curb raises the glazing above the roofline, rainwater naturally drains away, reducing standing water and protecting the seals from long-term damage.

In short, the rooflight curb ensures your roof light performs exactly as designed, structurally sound, watertight, and energy-efficient.

Different Types of Rooflight Curbs

Not all curbs are the same, the right choice depends on your roof construction, insulation requirements, and aesthetic preferences.

Here are the most common types:

1. Timber Curbs

A traditional option often built on-site. Timber curbs are affordable and easy to customise, but they must be correctly treated and insulated to prevent rot and heat loss.

2. Pre-Fabricated PVC or GRP Curbs

These factory-made units offer consistent quality and come ready to install. GRP curbs are particularly popular because they’re lightweight, durable, and completely waterproof.

At Lantern Superstore, our GRP upstands are precision moulded to ensure perfect fit and compatibility with our rooflight systems, saving installation time and ensuring long-term reliability.

3. Aluminium Curbs

Used mainly for commercial or architectural applications, aluminium curbs are strong, sleek, and long-lasting, but they require proper thermal breaks to prevent condensation.

Key Benefits of Using a Quality Rooflight Curb

• Improved Weather Resistance – Keeps your roof light dry and leak-free.
• Enhanced Energy Efficiency – Reduces heat loss through insulated design.
• Compliance – Meets the 150mm regulation height requirement.
• Faster Installation – Pre-fabricated curbs simplify fitting.
• Aesthetics – Provides a neat, professional finish.
• Longevity – Protects your roof light for decades of performance.

When you invest in a roof light, the curb isn’t just an accessory, it’s a crucial part of the system. Choosing a high-quality, purpose-built upstand ensures your installation is reliable from day one.

How to Choose the Right Rooflight Curb

When selecting a rooflight curb for your project, consider:

1. Compatibility – Make sure the curb is designed to fit your chosen rooflight model perfectly.
2. Insulation – Look for insulated upstands that prevent cold bridging.
3. Material – Choose GRP or PVC for durability and low maintenance.
4. Height – Confirm it meets the minimum 150mm requirement above the finished roof level.
5. Ease of Installation – Pre-formed curbs can save hours of site work.

At Lantern Superstore, we supply our roof lights and roof lanterns with or without integrated curbs, depending on your project needs. Each upstand is designed for precision, performance, and a perfect fit.

Rooflight Curbs and Flat Roof Design

Flat roofs present unique challenges when it comes to drainage and waterproofing. That’s why a rooflight curb is even more important on flat roof applications.

Without a raised upstand, water can pool around the glazing, leading to leaks, seal failure, or even structural damage over time. The curb elevates the roof light, allowing water to run off freely while maintaining a sleek, low-profile aesthetic.

Our flat rooflights and frameless roof systems are specifically designed to integrate seamlessly with insulated GRP curbs, combining modern design with maximum weather protection.

Why Choose Lantern Superstore?

We manufacture high-performance roof lights, roof lanterns, and rooflight curbs that meet the highest standards for quality, safety, and energy efficiency.

Our integrated curb systems are:

• Precision-engineered for a perfect fit
• Fully insulated for superior thermal performance
• Easy to install with clear, step-by-step guidance
• Compliant with all UK building regulations

From design to installation, we’re here to make your roof glazing project simple, secure, and stunning.

Final Thoughts

A rooflight curb may not be the most visible part of your roof glazing system, but it’s one of the most important. It provides the foundation for your roof light, ensuring it performs safely, efficiently, and beautifully for years to come.

Whether you’re planning a new extension, replacing an existing roof light, or upgrading to a modern roof lantern, never overlook the importance of a well-designed upstand.

At Lantern Superstore, we take care of every detail, from the glass to the curb, so you can enjoy the full benefits of natural light, energy efficiency, and long-lasting performance. Interested in getting a roof light with a good curb, that helps to improve your home’s curb appeal? Speak to our team on sales@lanternsuperstore.co.uk today!