01Straight answer
It can help a little, and it will not decide your band
An Energy Performance Certificate looks at the whole house, and one rooflight is a small part of that picture.
An EPC rates how energy efficient a home is, from A (best) to G. The assessor looks at the walls, the roof, the heating system, the hot water, the lighting and the windows, and works out a score from all of it. A single rooflight is one entry among many.
So can a new rooflight improve your rooflight EPC rating? If the one you have is very poor, such as an old single glazed unit or a cracked plastic dome, replacing it with a modern sealed unit can add a small improvement to the calculation. If your current rooflight is already double glazed and in decent shape, the change will be tiny or not visible at all.
We will not promise that a new skylight moves you up a band. Nobody honestly can before the assessment is done. The bigger items, such as loft insulation, wall insulation and the boiler, usually matter far more. The rooflight is worth doing for comfort and daylight first, and the certificate is a possible small extra.
Think of it like changing one bulb in a house full of old ones. It is a step in the right direction, and you will notice it, but the total depends on everything else. The same holds for a skylight: it is a visible feature, yet a small share of the energy the house loses.
Likely to show up
Swapping a very old single glazed or twin-skin unit for a modern low-e double glazed rooflight, recorded correctly.
Unlikely to show up
Replacing an already decent double glazed unit with a similar one, or adding a rooflight where there was none.
02How it is judged
What an assessor actually looks at
The certificate runs on what the assessor can record, and some of that is guesswork if nothing is written down.
Assessors work from what they can see and what you can show them. If the rooflight is old and nothing proves its age or type, they will often enter a cautious default for the glazing. That means a newer, better unit can go unrecognised if the paperwork is missing.
Keep the guarantee, the specification sheet with the U-value (the measure of how fast heat passes through, where lower is warmer) and any Building Control sign-off. A complete new rooflight, frame and glass together, comes under Part L as a controlled fitting, so Building Control is told and we deal with that, which leaves a record. Our page on Building Regulations for rooflights explains it in full.
Ask for the whole-unit figure rather than the centre-pane figure, which always looks flattering. The EPC process cares about the glazing type and how well it is documented, so a clear specification beats a verbal promise. If your home is rented out or about to be sold, a current certificate matters, and a little preparation costs nothing.
- Choose a unit with a published, whole-window U-value
- Keep the specification sheet and your 10-year workmanship guarantee
- Keep the Building Control completion paperwork where the work is notifiable
- Show all three to the assessor on the day of the next EPC
03Bigger picture
Where a rooflight sits among the other upgrades
If the certificate is your goal, the glass is a small step on a longer staircase.
Loft and roof insulation, wall insulation, a modern boiler or heat pump, and draught proofing all carry more weight than one opening. A rooflight in an extension roof, though, can still be a good place to improve, since a poor unit there is a visible cold spot. The key is to do the well insulated build, not just the glass. Our warm specification shows what we fit, from the kerb up.
Daylight counts for something in a home too. A bright room needs fewer lights on, which is a real, if modest, benefit in the bills even though the EPC may not credit it much. For a sense of how glazing choices compare, see double and triple glazed rooflights.
One more thing to keep in mind is that a certificate is a snapshot for a home as a whole, not a verdict on any single window. Fit the rooflight for the room, and treat any certificate benefit as a bonus.
04Next step
How we can help
We will tell you whether a new unit is worth doing, and what it is worth.
A free survey and written quote from Radiant Skylights covers the glass, the frame and the kerb, and what each would do for the room. We will say honestly if your current rooflight is fine and the money is better spent elsewhere. If you want to know what a replacement involves, read replacing an old rooflight.
- A written specification you can hand to an assessor
- Warm-edge glazing as standard
- The Building Control notification handled for you
- A 10-year workmanship guarantee in writing
Will an assessor notice, and does the number move?
Will a new skylight take my home up an EPC band?
We cannot promise that. One rooflight is a small part of the whole assessment, and the result depends on everything else in the house. A very poor old unit gives the best chance of a small gain.
Does a bigger rooflight lower my EPC score?
More glass in the roof can mean more heat loss in the calculation, so a large new opening does not help the score. Daylight and appearance are the reasons to choose it, with a warm specification to keep the loss down.
Is triple glazing worth it for the EPC?
It lowers heat loss further, but the effect on the certificate from a single rooflight is likely to be small. Our page on whether triple glazing is worth it weighs it up.
Where can I read more about efficient rooflights?
Our energy efficient rooflights page is the best place to start.
