More homeowners across the UK are choosing to install an aluminium roof lantern and take advantage of the benefits they offer:
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Better ventilation
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Adding a feeling of space to smaller rooms
To install an aluminium roof lantern on a flat roof, you build a timber kerb, fix the insulated upstand, assemble the hip and ridge bars, fit and seal the glass, then weatherproof the upstand with your roof membrane. This guide covers a standard four-pane configuration. Unless you're fitting triple glazing, this applies to sizes up to 3000mm x 1500mm.
What Should You Check Before Installing a Roof Lantern?
Before fitting a roof lantern, check that the flat roof can be safely opened up (joists usually need cutting and trimming), that building control has been notified, whether planning permission is needed, and that you have at least two people to lift the glass. Confirm the size of roof lantern you need before any structural work begins.
Before deciding on your aluminium roof lantern installation, consider the following:
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Do you have the confidence and experience to DIY, or would you benefit from a builder?
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The roof structure will usually need structural alterations — cutting joists or rafters and fitting trimmers to carry the weight of the aluminium roof lantern.
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Adjacent joists may need strengthening to maintain roof support.
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Any aluminium roof lantern must comply with UK building regulations. Installation on an existing roof must be inspected and approved by building control.
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Fire performance needs consideration if the aluminium roof lantern is near a boundary.
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If roof work could affect bats, a survey may be required.
If you're confident installing an aluminium roof lantern yourself, follow the steps below.
How Do You Install an Aluminium Roof Lantern on a Flat Roof?
Build a level timber kerb around the opening, fix the insulated upstand to it with sealant and screws, attach the hip and ridge bars, lower in the glass, seal and cap the bars, then dress the roof membrane up the upstand and under the drip lip. The ten steps below cover each stage for a standard four-pane lantern.
Step 1: Check All Parts Against the Inventory
Check all parts against the inventory before assembling your aluminium roof lantern. The number and type of parts vary by size — all outlined in the inventory list.
Step 2: Measure the Opening
Before buying an aluminium roof lantern, measure the structural opening. The actual size should reflect the aluminium roof lantern you ordered.
For example, a 2,000mm x 1,000mm aluminium roof lantern needs a matching opening. The kerb opening should match the internal dimensions of the lantern's built-in upstand. The upstand kerb should have a minimum height of 70mm (increasable if necessary).
Step 3: Prepare the Roof
In most cases, you'll have installed your roof membrane over the ply deck of a flat roof. If so, leave enough extra material around the timber kerb and upstand to weatherproof your aluminium roof lantern when fitted. Fold this material to one side until installation.
We recommend applying the roof membrane after installing the aluminium roof lantern to prevent damage or punctures during fitting.
Step 4: Assemble the Aluminium Roof Lantern Frame
For most aluminium roof lantern sizes, the built-in insulated upstand comes assembled. If your aluminium roof lantern is larger than 3000mm x 1500mm, you may need to assemble the aluminium frame yourself.
Take two corner cleats and slide them into the slots of the aluminium frame. Insert the other end into the matching piece. Ensure nuts and bolts are in pre-drilled holes before sliding the two aluminium frame sections together. Use provided screws to fasten through the top of the upstand. Repeat for all corners, then turn the upstand over and repeat.
Step 5: Connect the Upstand to the Timber Kerb
The upstand is now ready to be fixed to your timber kerb. Apply a thick bead of professional-quality silicone sealant adhesive around the kerb, about 20mm from the inner edge.
Place the assembled upstand onto the kerb, ensuring it sits flush. Insert screws into the groove on the bottom edge of the upstand, 100mm from each corner. Pre-drill holes into the aluminium frame using a standard metal drill bit. Use 12 screws minimum 50mm long — two at each corner, plus one in the middle of each side.
Step 6: Attach the Bars to the Upstand
Attach the four hip bars to the upstand. Place each hip over the upstand and slide the bolt head into the slot. Pull the hip body forward while tightening to keep the internal nut in place. Repeat for each corner.
Ensure the hip body doesn't touch the timber kerb — cut slots in the hip bars if needed.
Now fit the ridge bar. Blocks at either end hold bolts that connect to the hip bars. Slot the grooved end of the hip bars over the screws in the ridge edge block. Position to align with the centre of the ridge bar. Repeat for the other end.
Remove protective film from both sides of the ridge and hip profile. Fit a packer to each corner of the kerb with silicone to prevent sliding.
Step 7: Install the Glass
Insert the glass panels — the heaviest components of your aluminium roof lantern. Peel back a small tab of protective glazing film from the ridge and hip bars.
Lift each glass panel onto the inside groove of the packers, then carefully lower into the aluminium frame, ensuring flush fit. Repeat for all four panels.
Step 8: Install the Carriers and Caps
Once glass is positioned correctly, apply generous silicone sealant into the top and bottom grooves of each hip bar. Run silicone between panels and frames on either side of the hip and ridge bars.
Tap hip carriers and top caps onto the hip bars by hand or with a rubber mallet. Slide hip carriers up so angled cutouts line up, centred to the ridge bar. Arrange so 100mm protrudes at the top — you can't slide hip caps in until the ridge carrier and top cap are fitted.
Run a thick bead of silicone between the glass and ridge bar on both sides. Tap the ridge carrier into place and check it's perfectly centred. Slide the ridge top cap in from one end.
Slide the top caps into place to meet equally at the top centre. Attach the four hip caps to the bottom ends of the hip bars using a screw gun on low gear — don't overtighten. Repeat for all corners.
Install the two ridge end caps. Fill the gap between hip caps and the end of the ridge cover with silicone, then attach.
Step 9: Install the Roof Membrane
Seal the underside of the bottom edge of the glass with silicone. From inside the aluminium roof lantern, gently peel off the remaining glazing film from the hip and ridge bars.
Weatherproof your upstand with your chosen roof membrane. Ensure it's tucked under the drip lip below the glass — this is the final weatherproofing stage to prevent water ingress.
Step 10: Check the Finished Installation
Once correctly installed, your aluminium roof lantern will give years of trouble-free pleasure, bringing more light into your home. The room below will enjoy a wealth of natural light, though suitable ventilation is still needed — sometimes through background venting where the product allows.
You'll also benefit from energy efficiency and weatherproofing with low maintenance requirements, thanks to the durable aluminium construction.
Which Doors and Windows Pair Best With a Roof Lantern?
Roof lanterns pair best with large glazed doors such as aluminium bifold doors or aluminium sliding doors, which together flood an extension with light from above and from the side. Matching the frame colour of the lantern, doors and windows gives a consistent finish. Our bifold door cost guide will help you budget for both.
The benefits of natural light have made aluminium roof lanterns, aluminium windows and aluminium doors ever-popular solutions. More homeowners are choosing aluminium bifold doors to take advantage of energy efficiency and ventilation benefits. They also free up space in smaller rooms and create a more aesthetically pleasing home.
With aluminium doors and aluminium windows like ours, you can achieve just that.
Once installed, follow our guide to sealing and maintaining aluminium doors and windows.
Roof Lantern Installation FAQs
Do I need planning permission to install an aluminium roof lantern?
Not always. Under permitted development, rooflights must not project more than 150mm above the existing roof plane, so a roof lantern added to an existing flat roof often needs planning permission, while one built as part of a new extension is usually covered by that extension's permission or permitted development rights. Permitted development also requires that:
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The aluminium roof lantern sits no more than 150mm from the existing roof plane
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It cannot be higher than the highest part of the roof
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Side-facing windows may need obscure glazing if overlooking boundaries
Minor repairs affecting less than 25% of the roof area generally don't need building regulations approval, unlike creating a new opening for an aluminium roof lantern.
What should the U-value of an aluminium roof lantern be?
To comply with building regulations, an aluminium roof lantern must achieve a maximum U-value of 2.2 W/m²K. This is set out in Approved Document L (2021 edition), which applies a limiting U-value of 2.2 W/m²K to new and replacement rooflights. During significant renovations, thermal insulation should be upgraded to reasonable standards to minimise heat loss through the aluminium roof lantern glazing.
How long does it take to install an aluminium roof lantern?
Set aside 3–4 hours to install your aluminium roof lantern, depending on size and whether the opening is already prepared. You'll need a minimum of two people, especially when lifting the glass into the aluminium frame.
Can you put a roof lantern on a pitched roof?
Roof lanterns are designed for flat roofs, or roofs with a very shallow fall, because they need a level kerb to sit on and shed water. On a pitched roof, an in-plane rooflight or roof window is the usual alternative. A lantern can sometimes be used where a pitched roof meets a flat-roofed section, such as an orangery.
What height should a roof lantern upstand be?
Most manufacturers recommend that the top of the kerb and upstand sits at least 150mm above the finished roof surface, so rainwater and snow can't back up over the edge. The lantern's built-in upstand is often around 70mm, with the timber kerb making up the rest. Our roof lantern measuring guide explains how to allow for the kerb in your order size.
Do you need building regulations approval for a roof lantern?
Yes. Cutting a new opening in a roof is a structural alteration, so building control must be notified and the work inspected. The lantern must meet the 2.2 W/m²K rooflight U-value limit and the room needs adequate ventilation. Our roof lantern cost guide covers these costs alongside the lantern itself.
Which type of roof lantern should I install?
Rectangular lanterns suit most kitchens and extensions, square lanterns suit square rooms, and pyramid or octagonal designs create a stronger focal point. Compare the options in our guide to the different types of roof lanterns.
