How To Install A Flat Rooflight
Flat rooflights are one of the most stylish and effective ways to bring more natural light into a space with a flat or low-pitch roof. Whether you’re working on a modern kitchen extension, a garden room, or a new build, a rooflight can transform a room by adding brightness, height, and that wow factor. But what we want to know – how to install a flat rooflight. If you’re considering a self-build, managing a project, or simply curious about the process, in this blog we will walk you through the key steps to installing a flat rooflight safely and effectively.
What Is a Flat Rooflight?
A flat rooflight or skylight is a fixed glazed unit installed into a flat roof to allow daylight to penetrate into the space below. Unlike pitched roof windows or lanterns, flat rooflights sit flush or slightly raised and have a sleek, contemporary appearance.
They’re typically made from aluminium frames with double or triple-glazed glass and often come with low-E glass, argon-filled units, and thermal breaks to improve energy efficiency.
What You’ll Need
Materials & Tools:
- Flat rooflight (pre-assembled)
- Fully supported timber upstand
- Drill and fixing screws
- Cover caps & horse shoe packers
- Silicone or sealant
- Spirit level and measuring tape
- PPE (gloves, eye protection, etc)
Building Control:
In the UK, most rooflight installations require compliance with Building Regulations, especially concerning:
- Structural safety
- Thermal performance
- Fire safety always check with your local authority or building inspector before beginning
If you are unsure whether or not you require planning permission for your installation, you should check with your local authority. Although, typically you will not require it for a small flat rooflight installation.
Installing Flat Rooflights
Every rooflight can differ, so it’s important to explore the technical details provided to you by your manufacturer. It’s also important that you have checked your local building regulations before installation, to ensure the glass unit is allowed on your property. However, most rooflights or roof windows have a smooth installation process using the following steps of how to fit a flat roof light.
1. Check the Opening
Check that your upstand has been installed securely, tightening any screws and inspecting the sealant to ensure there are no gaps. There should also be a minimum pitch of 5 degrees, which ensures efficient water-run off and avoid water pooling on the glass. Also, refer to your manufacturer’s guidelines to ensure the measurements of the upstand meet the required criteria.
2. Apply the Silicone
When you are happy with the quality and measurement of the upstand, apply a thick bead of compatible silicone sealant all the way round the top of the timber kerb/upstand. It is important during this step to apply the silicone evenly as this creates a waterproof membrane for the roof light, to ensure longevity and water resistance. Seal corners using low modulus silicone sealant.
3. Position the Rooflight
The next step is to place the roof light onto the upstand onto the prepared opening. Carefully ensure that the skylight is positioned correctly with a slight angle of the upstand to allow rainwater to easily run off. For larger rooflights, this may require two people, as the materials and the glass can be heavy as you lower it into position.
4. Pre-drill for screws
Pre-drill fixing holes through the aluminium and kerb/upstand. These should be 100mm from each corner, then at regular intervals. You should then use suitable fixing screws, with cover caps and horse shoe packers all the way around to secure the frame in place.
5. Fix Screws
For the final step, use suitable screws, with cover caps and horse shoe packers all the way around to secure the frame in place.
Final Checks
Once your successful installation is complete, inspect the roof light for any gaps, leaks or loose fittings. Test it under different weather conditions to ensure it is properly sealed. Regular maintenance, including cleaning and checking for sealant wear, will prolong the lifespan of your flat roof light.
What’s the Overhang on a Rooflight?
The overhang is the part of the rooflight that extends past the upstand. It may only stick out 20–50mm, but it plays a big role in helping to shed water, improve thermal performance, and give a clean, finished look. Always check the specs, as overhangs vary between models and manufacturers.
Common Mistakes to Avoid
- Poor sealing: Any gaps in the waterproofing can lead to leaks, so double-check all corners and edges
- Incorrect upstand height: Too low and water may pool; too high and it may look bulky
- Not checking structural requirements: Cutting joists without installing trimmers can compromise roof integrity
- Forgetting ventilation: Fixed rooflights don’t allow airflow, so in kitchens or bathrooms, consider combining with a vented option
Should You DIY or Hire a Pro?
Installing a flat rooflight is possible for confident DIYers, especially if you’re replacing an existing unit. However, because it involves structural work, roofing, and waterproofing, many people choose to hire a professional installer or a experienced roofer, especially for large or high-spec installations.
Flat Roof Light Installations
Installing a flat rooflight is a smart way to brighten up your home, improve energy efficiency, and add real architectural flair. While the process involves a few technical steps, careful planning, accurate measurements, and proper waterproofing can ensure a clean, leak-free skylight installation that will last for years.
Whether you’re adding one to a kitchen extension or bringing light into a dark hallway, a flat rooflight, or even a roof lantern is a stunning upgrade that’s worth every bit of the effort.
At UK Rooflights we offer a range of different types of roof lights and roof lanterns. Our rooflights are available in a variety of sizes, making them suitable for any space. Our wide range of stock sizes can be ordered in sizes up to 2000mm x 1000mm, but if you are looking for something more specific, our made-to-measure design options can reach impressive sizes of up to 3200mm x 1200mm. For expert advice contact our team on info@ukrooflights.co.uk or use our portal below.
