Short answer: yes, in most cases. A new sealed unit does not have to copy the old one. It can carry a better coating, a warmer spacer, a safety inner pane or a different gas fill, as long as the frame can hold the new weight and thickness. What you can upgrade depends on the rooflight type, and we check that at the survey before anything is ordered.
What can be changed, and what is fixed by the frame
When a unit has failed, the glass is made again to the measured size, so its make-up is a free choice up to a point. The limit is the frame: the rebate that holds the glass has a set depth, and the sash or kerb has a set capacity for weight. A thicker unit that does not fit the rebate does not work, however good it looks on paper.
So the useful question is what the existing frame can take. A modern aluminium or timber frame often has room for a unit with a better coating and a warmer edge. An older frame may have been made for a thinner, plain double-glazed pane and have less room to give.
Better skylight glass in practice
Four things can be improved on a new unit.
The coating
A low-emissivity coating on one of the inner faces reflects heat back into the room. The glass looks near enough the same, and the pane loses less warmth through a cold Sheffield night. Older units may carry a basic coating or none at all.
The spacer
The bar round the edge of a unit is where heat slips through fastest. A warm-edge spacer in composite or plastic reduces that, and it also lowers the chance of condensation forming along the rim of the room-side glass.
The gas fill
Argon or a similar gas between the panes slows heat transfer better than plain air. It is a small gain on its own and a larger one with the coating and the spacer.
The glass type
Laminated glass has a plastic interlayer that holds the pane together if it breaks. Toughened glass is heat-treated so that it breaks into small blunt pieces. Over a bed, a landing or a stair, an inner laminated pane is worth discussing, and we put it forward where it makes sense for the room.
| Choice | What it does | Worth asking about when |
|---|---|---|
| Low-emissivity coating | Keeps warmth in the room | The room below is a bedroom or loft conversion |
| Warm-edge spacer | Cuts heat loss and rim condensation at the edge | The old unit misted along its rim |
| Gas fill | Slows heat flow through the gap | The coating is already being improved |
| Laminated inner pane | Holds together if struck or cracked | The glass is over a landing, a stair or a bed |
| Solar control coating | Reduces heat gain on bright days | The rooflight faces south over a kitchen or a sunroom |
What the regulations say about the new unit
Table 4.2 of Approved Document L (2021) sets the bar for existing houses. A roof window needs 1.4 W/m²K or a WER of Band B. A rooflight, flat or lantern, is allowed 2.2 W/m²K. The figures are for the finished unit in its frame.
A replacement unit is therefore a good moment to bring an old rooflight up to the current standard where that is reasonable. We read the figures off the manufacturer's data for the unit we propose, and we say in the written quote which limit applies. Changing only the sealed unit in a sound frame is not normally notifiable. If the job grows into a new sash or a whole new rooflight, it becomes controlled work, and the notification goes to Building Control from us.
When the upgrade needs a new sash or a new rooflight
Sometimes the frame cannot take a better unit. Typical signs are a rebate too shallow for the thicker glass, a sash that has warped, or timber that has rotted at the lower rail. In that case the sensible answer is a new sash or a whole new rooflight, and the upgrade comes with it.
We do not push a whole replacement when the frame is sound. We tell you which route we recommend and why, and the page on swapping only the glass sets out how we decide.
What an upgrade does to the cost
We give no figures without seeing the opening, but the factors are simple. A coated, gas-filled unit with a warm-edge spacer costs more to make than a plain one. Laminated glass adds again. A larger pane, or one that needs a lift to reach, adds access time.
Against that, a better unit keeps more heat in the room and reduces the chance of condensation on the inner glass. The fixed written quote lists each choice, so you can see what you are paying for. The life plan sets out how the new unit would be replaced again in future, and whether that would disturb the roof.
Does the glass type change the look?
Sometimes slightly. A solar control or low-emissivity coating can give the glass a faint tint, easiest to see when you stand at an angle to a pane next to an uncoated one. Reflections may look a touch different from outside. We can show you a sample before you decide, if you want to compare. The interlayer in laminated glass is clear, and you will not see it from the room.
What to expect from us
The survey is free, and so is the written quote that follows. The quote names the glass make-up, the size, the frame work (if any), and the life plan for the unit. Two related pages on the same hub cover the time a swap takes and why a unit mists in the first place.
Our work reaches from Sheffield to Rotherham, Barnsley and north Derbyshire. Send a message on WhatsApp with the make and size code of your rooflight, or ring, and we will talk through what a better skylight unit could be for your frame.