Question · Energy Efficient Rooflights
Does Solar Control Glass Stop a Rooflight Overheating?
The short answer
Yes, it helps, but it is one part of the answer. Glazing with a solar control coating turns back some of the sun's heat at the surface, so a south or west facing rooflight gains less in summer. For a roof that still gets hot, pair it with an external blind and an opening sash that lets warm air leave.
How solar control glass works
Sunlight carries visible light and heat. Ordinary clear glass passes most of both. Solar control glass has a microscopically thin coating on one of its surfaces that reflects a portion of the heat while letting most of the visible light through, so the room stays bright but takes in less warmth.
The effect is measured by a figure called the g-value, which is the share of the sun's energy a pane lets through. A lower g-value means less summer heat entering. You do not need to memorise numbers: ask for a solar control unit and check the quote says so.
The coating usually sits on the face of the inner pane inside the sealed gap, so it is protected from dirt and cleaning. That also means it cannot wear off, and you clean the glass exactly as you would any other.
Where overheating comes from
A roof catches the sun for more hours than a wall does, and glass on a roof faces the sky when the sun is high. A loft room under a south or west facing slope can warm up in the late afternoon, and the heat then stays trapped under the roof into the evening. A flat-roofed kitchen extension with a large rooflight is the same story on a bigger scale.
North-facing slopes rarely overheat, and in a shaded Bristol terrace the issue may not arise at all. That is why we ask which way the roof faces before suggesting glass. Solar control on a north slope costs extra and gives little back, and it can lessen the free winter warmth that a sunny slope would collect. Our answer on whether skylights make a house colder covers the winter side of this balance.
Roof shape adds to it. A shallow pitch looks more directly at the high summer sun than a steep one, so a gentle slope over a loft conversion can collect more heat than the same window would on a vertical wall.
What glass alone cannot do
A coated pane reduces the heat that enters. It does not remove it. On a hot afternoon a room under a big sun-facing rooflight can still warm up, because some energy always gets through and the warm air has nowhere to go.
Solar control glass means the room can never get hot.
It cuts the heat gain. A shaded, ventilated roof does the rest, which is why blinds and opening sashes belong in the same plan.
Two additions do more than a better coating can. An external blind stops the sun before it reaches the glass, which works better than any blind inside the room. And an opening rooflight lets hot air rise out of the highest point of the room while cooler air comes in lower down. Our page on fresh air rooflights shows how that works in practice, and the roof lanterns service covers the larger flat-roof case.
Fixed units have the least room to cope, which is one reason we point to a sash that opens wherever the budget allows it. A vent bar for overnight air is the minimum worth considering on a south slope.
Matching the glass to the roof
| Roof | Sensible starting point |
|---|---|
| South or west loft slope | Solar control glass, outside blind, opening sash |
| North loft slope | Standard clear glass, triple glazing if the room is cold |
| Flat-roof extension | Solar control, vent bar or opening lantern |
| Shaded terrace | Clear glass, no extra coating needed |
Those are starting points, not rules. A tall tree, a neighbour's gable or a dormer can shade a slope that looks sunny on a map. During the survey we study the roof, note what blocks the sun and show the options on the written quote.
Solar control or clear, the unit still has to sit within the energy limits for an existing home, so the coating is one ingredient among several, alongside the warm edge and glazing choices described in our warm edge spacer answer.
Planning the whole summer setup
Treat overheating as a small system rather than a single product. Glass lowers the gain, a blind reduces it further, and an opening sash lets the heat leave. On a hot day you can close the blind, tilt the sash and leave a window below open so air moves up through the house. Electric and solar-powered options help when the rooflight is out of reach; see electric opening rooflights.
If your rooflight already overheats, glass can sometimes be changed on its own by replacing the sealed unit. A whole-unit swap is notifiable work that we take through Building Control. Our fitting carries a 10-year workmanship guarantee, and the costs page explains pricing. For the wider range, see the energy efficient rooflights hub.
It is easier to add the blind and the coating at the same visit than to come back to a finished room, so say at the survey if the room has ever been uncomfortable in summer.
A lantern on a south-facing extension is the usual place this glass is asked for. Our answer on roof lantern overheating looks at that case.
Hot roofs, coated glass and cooler rooms
Can solar control glass be fitted to the rooflight I already have?
Sometimes. If the frame is sound, the sealed glass unit can be swapped for a solar control one. If the frame is old or the unit is a non-standard size, replacing the whole window may suit better. The survey settles which.
Is solar control glass worth it on a north-facing roof?
Rarely. A north slope gets little direct sun, so the coating adds cost without much benefit. Clear glass with good insulation is the better match, and a blind is usually unnecessary.
Tell us about the room
A few details is all we need. We'll come out, advise and give you a written quote.
No pressure, no obligation.