Plastic domes are everywhere on flat roofs: on extensions, garages, schools, shops and blocks of flats. Over the years the plastic yellows, goes brittle and cracks, and the seals at the kerb dry out and let water in. Replacing a dome is usually quick, because the kerb is already there. On a sound kerb a like-for-like swap takes a few hours, and on larger roofs several domes can often be replaced in a day.
The kerb decides how simple the job is. Many old domes sit on kerbs that are still sound but are an odd size or too low, so the new dome may need a kerb adaptor or packing. If you want to upgrade from plastic to glass, the kerb needs to suit a heavier unit and usually a set fall. We check all of this before quoting, supply a new multi-skin dome or glass unit, or fit one you have already bought.
What's included
- Old dome unscrewed, lifted off and taken away
- Kerb top cleaned of old sealant, fixings and loose felt
- Kerb checked for rot, size and height before the new unit goes on
- Adaptor or packing fitted where the old kerb needs it
- New multi-skin dome or glass unit fixed and sealed
- Membrane checked where it meets the kerb, with small repairs made
- Inside checked for drips and the trim refitted
Guide prices
Like-for-like dome
Old dome taken off, new multi-skin dome fixed to the sound existing kerb
Dome with kerb adaptor
New dome where the kerb needs an adaptor or packing
Upgrade to glass
Dome swapped for a double-glazed glass rooflight on the existing sound kerb, as in our replacement service
Guide ranges for supply & fit, per dome; building control notice fee extra on homes in England and Wales. Your price is fixed in a written quote after we have seen photos or surveyed. Scaffold, access towers or a crane are priced separately if the job needs them, and building control or building warrant fees, where a job needs them, are shown as their own line.
How we fit a dome rooflight
- Count and measureWe count the domes, measure each kerb and check its condition, so each one is matched to a new dome, adaptor or glass unit.
- Work safely around old domesOld domes are fragile and will not carry weight, so we work from boards or edge protection, never leaning on a dome to reach another.
- Take off the old domeFixings are released and the dome lifted off. The kerb top is cleaned so the new unit beds onto clean, sound timber.
- Adapt if neededWhere the kerb is an odd size or too low, an adaptor or packing is fitted, or the kerb is rebuilt if the timber has gone.
- Fit the new unitThe new dome or glass unit is bedded and fixed at the maker's spacings, then sealed so water cannot get under its edge.
- Check inside and clear upWe check each dome from inside, refit any trims and take the old domes away, so nothing is left on the roof.
Things we check before quoting
Is the kerb sound?
We check each kerb for rot and movement before quoting a dome swap. A new dome on a soft or split kerb will leak at the joint, so any kerb that has failed is priced for repair or rebuild rather than hidden under a new unit.
Kerb size and adaptors
We measure every kerb against the new dome's sizes. Old kerbs are not always a standard size today, and where the new unit does not match, an adaptor or packing can make up the difference without rebuilding the kerb.
Upgrading to glass
We check whether the kerb suits a glass unit before recommending one. Glass is heavier than a dome, usually needs a set fall, and some glass lids are made specifically for existing kerbs of around 150 mm, so the answer depends on what is on your roof.
Fragile dome safety
We treat old domes as fragile at all times. An old dome will not carry the weight of someone stepping or falling onto it, so we use boards, covers or edge protection around them during the work, whether it is one dome or forty.
Multi-skin domes and energy
We fit multi-skin domes rather than single-skin ones as replacements. More skins insulate better, and a replacement should be no worse than the unit it replaces, so we check the new dome's published performance against the rules for your building.
Bought replacement domes yourself?
Replacement domes are easy to buy online, and we fit them. Send the dome sizes and product details, plus photos of your kerbs, and we will check they match before booking. Check domes on arrival for cracks or scratches, and report any damage to the seller. On the day we check the kerbs again and fit to the maker's instructions. The product warranty stays with the maker or seller; our written guarantee covers our fitting.
Planning and building regulations
A new dome on an existing kerb is a replacement rooflight. In homes in England and Wales that makes it a controlled fitting, either self-certified through a competent person scheme or notified to building control. We are not registered with a scheme, so we notify replacements with a building notice and show the fee on the quote. The new unit should perform no worse than the old one. On commercial buildings, fire performance near a boundary may affect which dome or glass unit can be used.
| Nation | What usually applies |
|---|---|
| England | New openings usually need building regulations approval. Replacements are controlled fittings; we are not scheme-registered, so we notify them to building control and show the fee on the quote. Rooflights in existing homes must meet 2.2 W/m²K (roof windows 1.4 or WER Band B). Most house rooflights are permitted development if they project no more than 0.15 m; listed buildings need consent. |
| Wales | New openings generally need building regulations approval; replacements need a scheme installer's certificate or a building notice, and we use a building notice. Energy limits are 2.2 W/m²K for rooflights and 1.4 for roof windows. Rooflights aren't permitted development in conservation areas, National Parks, AONBs or World Heritage Sites. |
| Scotland | New rooflights need a building warrant. Replacing a rooflight complete with its frame doesn't, but must meet the standards, including 1.6 W/m²K. Householder permitted development rights don't apply in conservation areas; listed buildings need consent. |
| Northern Ireland | New openings alter the roof structure, so expect a building control application; confirm with your council. Rooflights in existing homes must meet WER Band C or 1.6 W/m²K. Permitted development (Class B) allows up to 15 cm on road-facing slopes, at least 0.5 m from ridge, eaves and verge; not in conservation areas or listed curtilage. |
A summary, not legal advice. We confirm what applies to your address before you commit. Read the full guide.
Questions about dome rooflight replacement
Why has my plastic dome gone yellow?
Plastic domes yellow and go brittle with age and sunlight, and the seals at the kerb dry out. A yellowed dome lets in less light and is more likely to crack. Once that happens, replacing it is usually better value than trying to repair it, and the kerb is often reusable.
Can a new dome go on my old kerb?
Usually, if the kerb is sound. Where its size does not match a current dome, an adaptor or packing can make up the difference. If the kerb is rotten or very low, it needs rebuilding first. We check each kerb before quoting, so you know which domes are a straight swap.
Can I swap a dome for a glass rooflight?
Often, yes. Glass units are clearer, quieter in rain and usually last longer than plastic. They are heavier, though, and usually need a set fall and a certain kerb height. Some glass units are made to fit common existing kerbs. We check yours and price both a new dome and a glass upgrade where it helps.
How many domes can you replace in a day?
It depends on the access, the kerbs and the size of the domes. On a roof where the kerbs are sound and access is easy, several domes can often be replaced in a day. Where kerbs need adapting or rebuilding, fewer get done. We give an expected duration with the quote.
Do you replace domes on commercial buildings?
Yes. Many schools, offices and blocks of flats have rows of old domes. For larger roofs we survey each dome and kerb, plan safe access and edge protection, and price per dome with site set-up shown separately. See our commercial rooflight page for how multi-unit jobs are run.
