Skylight replacement on flat roofs
Old plastic rooflight domes go yellow, cloudy and brittle, and sooner or later they crack or leak. In most cases the upstand under the dome is still sound, so we take off the old dome and fit a new double-skin one in its place. The roof around it is not disturbed, and the room below gets its daylight back.
Also known as roof domes, rooflight domes or dome lights, these sit on flat roofs over kitchens, extensions and landings. Pitched-roof windows such as Velux are a different product; this page covers flat-roof domes.
Updated September 2026
Cracked dome letting water in? Ring 085 220 1422, or send a photo to WhatsApp with a rough size and we will tell you what it needs.
Signs the dome has had its day
The dome has turned yellow or milky and the room below is noticeably darker
Fine cracks or crazing in the plastic, often starting at the fixing holes
Drips under the rooflight after rain, or damp staining on the ceiling around it
A single-skin dome that runs with condensation every cold morning
Heat or scorch damage along the edge from earlier roofing work
The dome in this photo was scorched when the roof around it was torched on. The manufacturer’s fitting sheet says to keep a flame at least 150 mm from the dome, and we work to that on every roof.
Swapping the dome, step by step
Measure the upstand on the outside and order a dome made to fit it
Take off the old dome and its fixings and clean the top of the upstand
Check the upstand timber and the roof covering around it for rot or splits
Seat the new dome and screw it down through its fixing points, with caps clipped over every screw
Peel off the protective film and water test around the rooflight
If the upstand is soft or the roof covering around it has split, a new dome alone will not stop the leak. We show you what we find and price that repair before going further.
Double-skin domes from Skylux
We fit double-skin domes made by Skylux in Belgium. Two layers of clear plastic with an air gap between them keep more heat in than an old single-skin dome, cut down condensation and quieten the sound of rain.
Each dome is made to the size of the upstand it sits on. The one in these photos is 1000 x 1000 mm, but square and rectangular sizes are ordered to fit whatever is on your roof.
The dome carries the manufacturer’s guarantee, and our fitting comes with our own written guarantee, the same as all our work.
New dome or a whole new rooflight?
A new dome is enough when the upstand is solid and dry and the roof covering is still bonded to it all the way round. That is the case on most roofs we look at, and it is the quickest and cheapest way to fix a tired rooflight.
When the upstand timber has rotted, or the roof covering has pulled away from it, the whole rooflight needs rebuilding: a new upstand, the roof dressed back up it, and a new dome on top. If the rest of the flat roof is also near the end of its life, it makes sense to do both together. Our flat roofs and fibreglass GRP pages explain the options, and if water is coming in and you are not sure from where, start with leak detection.
Skylight replacement questions we get asked
Can you replace just the dome and keep the rest of the skylight?
Yes, as long as the upstand is sound. The new dome is made to the outside size of your existing upstand and screws onto it, so the roof covering does not need to be opened up. We check the upstand before we order anything.
Why is there sometimes condensation inside a new dome?
Plastic domes are not completely vapour-tight, so at certain times of the year a little condensation can form between the layers. The manufacturer notes that it clears again by itself and does not affect the dome or how long it lasts. A double-skin dome gets far less of it than an old single-skin one.
How long does it take?
Once the dome has arrived, swapping it on a sound upstand is usually done in a single visit. The wait is mostly for the dome itself, since it is made to your size.
How much does skylight replacement cost?
Most dome replacements on a sound upstand cost between €450 and €1,000 including fitting, depending on size: roughly €450–550 for a small 600 x 600 mm dome, €650–850 for a typical 1000 x 1000 mm dome and €850–1,000 for a large 1200 x 1200 mm one. If the upstand needs repair, that is priced separately. We give you a fixed price after a free survey across Kerry, Cork and Limerick.
Is this the same as replacing a Velux window?
No. Velux-type roof windows are glazed windows fitted into a sloped roof. This service is for the plastic domes on flat roofs, which sit on an upstand and are replaced from outside without opening up the roof.
Is it guaranteed?
Yes. The dome has the manufacturer’s guarantee, and our fitting is covered by our written guarantee.
Everything we do on a roof
We cover all three counties: roofers in Kerry, roofers in Cork and roofers in Limerick.
Flat roof systems and the rest
A rooflight is only as watertight as the roof around it. These pages cover the roof systems and materials we work with.
Get the daylight back in
Send us a photo of the rooflight and a rough size, or book a survey. We will tell you whether a new dome will do and what it costs. Free survey across Kerry, Cork and Limerick.