You only need a new flat roof as well when the covering around the rooflight is close to the end of its life, is holding water, or has failed in more places than the rooflight. If the roof is sound and only the rooflight has failed, replacing the rooflight alone is the better value and the neater job. We decide which by looking at the roof, not the light, at the free survey.
The question behind the question
When a flat roof skylight starts to leak or mist, owners often assume the whole roof is finished. Sometimes it is. Often it is not. A flat roof and its rooflight age at different rates, and they are made of different things. The glass unit and seals wear on their own timetable, while the covering wears on another.
The aim is to replace the rooflight when it needs it and the roof when it needs it, ideally together only if both are due.
Signs the roof can stay
Look at the roof surface away from the rooflight. If the covering is flat and even, free of blistering, splits or soft spots, with no standing water days after rain, the roof is likely doing its job. The same goes for the ceiling beneath: no stains away from the rooflight, and no sagging. In that case the fault sits in the light or its kerb joint, and a replacement rooflight with a properly dressed upstand will do.
Fitting a rooflight to a roof that still has life in it is a sensible choice. It avoids stripping a good covering, and it means you are not paying for a roof you do not need.
Signs the roof should go too
- The covering is cracked, blistered or split across the main area, not just near the rooflight.
- Water stands on the surface for days, or the deck feels soft underfoot.
- There are stains or damp on the ceiling in places away from the rooflight.
- Earlier patches cover much of the roof.
In those cases, fitting a new light into a failing covering puts new work into something that will be disturbed again within a few years. The sensible order is covering and rooflight together, so the new upstand is built into new work and the joint is made once.
The cost of choosing wrongly
If you replace the rooflight alone on a roof that is about to fail, you may pay for access twice. If you replace the whole roof when only the rooflight had failed, you spend on a covering you did not need. We do not give figures without seeing the site, but the difference between the two comes down to the area of covering, the number of rooflights, the deck condition and the access.
| What we find | Replace the rooflight only | Renew the roof as well |
|---|---|---|
| Covering in sound condition | Yes | Not needed |
| Covering failing across the area | No | Yes |
| Deck soft or ponding | No | Yes, with deck work |
| Fault only at the kerb joint | Yes, rebuild the upstand | Not needed |
Timing a replacement
For flat roof skylight replacement timing, the best moment is when the unit or seals have shown clear signs: misting between the panes, a cracked pane or water at the frame. Waiting too long risks damage to the structure below. Acting before there is any sign of trouble is rarely needed, though a check at around year 5 and again later tells you how things are ageing. If the roof covering is due for renewal in the next few years, bring the two jobs together so that access, scaffold and disruption are shared.
What we check at survey
We walk the roof, look at the covering type and its age, check the falls and whether water drains freely, and examine the kerb joint and the deck near the opening. We then look inside at the ceiling and the structure around the opening. If a new or larger opening is wanted, we also cover the structure, since cutting into rafters or joists is structural work that needs approval. The covering decides the kerb, and our guide to roof coverings around a rooflight shows how each type is joined.
Garages, extensions and older kitchens
Sheffield has plenty of flat-roofed rear extensions on 1930s to 1960s semis, flat garage roofs and terrace kitchen extensions. Their coverings were laid at different times and by different hands, so two roofs of the same age can be in very different shape. A rooflight added later to one of these often shows up a covering that was already tired. Put the age of the covering and any earlier patches on the table at survey, and we will walk the roof with you.
Planning ahead for the rooflight itself
Whichever route you take, the new skylight or rooflight should be chosen with its replacement in mind. Our life plan names the parts that wear and says how each is replaced. On many modern units a sealed glass unit can be lifted out from above and changed without touching the covering, so a future glass replacement need not mean a new roof. We note this in every quote. Fitting a replacement rooflight to a house is controlled work, and we deal with the Building Control notice, which can go to the council or to a registered building control approver.
If your current light is leaking and you are unsure why, read our page on where flat rooflights leak first. If you are deciding between a fixed or an opening unit for the new one, see fixed or opening flat rooflight, and the main flat roof rooflights page covers the full process, from survey to fitting day.