The short answer
Yes. A plastic dome can be replaced with a glass rooflight, and on most flat roofs the opening already suits it. What usually changes is the upstand: a dome often sits on a low, thin kerb, while glass needs a taller, insulated and stronger one. The gain is a clearer, longer-lasting pane, better thermal performance, and a room that sounds much calmer when it rains.
What you have now, and what replaces it
A plastic dome is a moulded acrylic or polycarbonate bubble, usually single or double skinned, sitting on a small kerb on a flat roof. The replacement is a flat or slightly raised glass unit on a purpose-made upstand.
Domes were the standard way to put daylight into a flat-roofed kitchen, hall or bathroom for a long time, and many post-war extensions around Crawley were fitted with them. They are light, cheap to make and easy to fit. They also yellow and craze in sunlight, scratch when cleaned, and often carry a thin kerb that was never insulated.
A glass rooflight swaps the bubble for a factory-sealed glazed unit, typically double glazed with a low-emissivity coating and a warm-edge spacer. The top pane is toughened or laminated, and the inner pane is laminated. It sits flat or at a slight rise on a kerb that is tall enough, dry enough and insulated enough to carry it. Our flat roof service page, flat roof rooflight installation, describes the finished result.
Dome and glass side by side
The two differ in almost every working respect, and the table shows the ones you will notice.
| Feature | Plastic dome | Glass rooflight |
|---|---|---|
| Clarity over time | Yellows, crazes | Stays clear |
| Heat retention | Modest | Coated, gas filled |
| Rain on the pane | Sharp tapping | Duller, damped |
| Weight on kerb | Very light | Much heavier |
The weight row is the one that shapes the job. Everything else about glass is an improvement, and the heavier unit simply has to be carried properly.
The upstand is the part to get right
The kerb is usually the real work. Glass asks more of it than plastic ever did.
Many old dome kerbs are made from thin timber, or a moulded plastic or GRP upstand, and were built to hold a few kilos of acrylic. They are often only a few centimetres high, with little or no insulation inside. A glass unit is many times heavier, and it needs a kerb of sound timber, firmly fixed to the deck, lined with insulation and finished with the roof membrane dressed up and over its outer face. As a general guide, the top of the upstand should stand around 150mm above the finished roof surface, so that water cannot be driven over it in heavy rain.
Before we quote, we look at what is under the old dome: the timber, any rot, how the deck is fixed and whether the opening is square. Sometimes the existing kerb can be rebuilt in place. Sometimes a new one goes on, and we check the deck beneath can take the extra load. The job does not change the size of the hole, so there is usually no new structural work, which is how it differs from putting in a bigger rooflight.
Why the room is quieter after the swap
Rain on a thin plastic bubble is sharp and close. Glass with a laminated inner pane changes the sound a great deal.
A dome is a thin, light shell held in a rigid frame, which is close to ideal for ringing. A raindrop makes a small tap, and heavy rain becomes a constant rattle. Our answer on whether skylights are noisy in the rain explains why thin skins behave like this.
The glass build works in the opposite direction. A thicker outer pane moves less. A laminated inner pane has a soft interlayer that damps the vibration. The cavity is chosen for sound and warmth together, and the kerb gives a dense, insulated base rather than a hollow shell. The room under it hears the weather as a soft wash rather than a tap. Our guide on reducing rain noise under a flat rooflight goes through the choices, and acoustic laminated glass explained covers the interlayer. We write the chosen build into the quiet spec with every quote.
The rules that apply to the change
Swapping a dome for glass is generally a replacement in an existing opening, and it has to meet current regulations.
The new unit has to meet the thermal standard in Part L, and glass overhead should be safe if it breaks, which is why the inner pane is laminated. Whether the work is notifiable is checked for the house, and where it is we handle the Building Control notification. The wider picture is in our explainer on Building Regulations for rooflights. Planning is rarely an issue for a like-for-like opening on a flat roof, although a conservation area or a flat has its own rules, and that is checked for the address.
Questions about moving from plastic to glass
Can I keep my existing dome kerb?
Sometimes. If the timber is sound, the height is enough and the insulation can be added, it can be rebuilt and reused. A survey decides. A kerb that has rotted or sits too low is replaced as part of the job.
Will the ceiling shaft need redoing?
The light shaft between the roof and the ceiling is usually kept. It is lined and finished, and often painted white, so the new unit sends more light down it. If the old lining is damaged we renew it.
Does glass let in more heat than a dome?
Glass with a solar control coating can reduce it. Our energy efficient rooflights page covers coatings, and how to choose a rooflight helps with the choice.
Is a glass unit safe to walk near or on?
A standard rooflight is not built to be walked on, and a walk-on unit is a different product with thicker laminated glass, as shown on our walk-on rooflight installation page. To have a dome swapped, get a quote or go back to skylight and rooflight installation.