Glass answer
Do I need solar control glass in a rooflight?
Solar control glass is a coating that turns away part of the sun's heat before it reaches the room. Whether you need it comes down to which way the glass faces, how big it is and how the room is used.
The answer
It earns its place when the glass faces south or west, covers a big area, or lights a room you want cool in summer, like a loft bedroom or a kitchen extension. It trims the sun's heat at the glass. On a small north-facing rooflight over a landing, it adds little.
What does solar control glass actually do?
A thin coating on one pane turns back some of the sun's energy at the glass, leaving the room with less heat. Daylight still comes through, though a little less of it, and the glass can look slightly tinted.
Sunshine arrives as light and as heat. Ordinary clear glass lets nearly all of both through, which is why a sunlit conservatory can feel like an oven. Solar control glass is clear glass with a microscopically thin coating, put on one of the panes during manufacture, that sorts the energy before it enters.
The number that measures it
Datasheets give a g-value, sometimes called solar factor, which says what share of the sun's energy passes through the glass into the room. A lower g-value means less heat gets in. It is a separate figure from the U-value, which is about heat going out. A rooflight can score well on one and badly on the other, so ask for both.
What you give up
The coating also cuts some visible light, so the room is a touch dimmer and the glass may have a faint blue, green or grey cast when seen from outside. Manufacturers offer a range of coatings, from ones that barely alter the look to ones that are more strongly tinted. A bright, large rooflight rarely misses the light a coating removes, while a small one over a dim corridor might.
Which rooflights are worth specifying it for?
Those facing south, south-west or west, those with a large area of glass, and those above bedrooms, home offices and open-plan kitchens, where heat builds and stays.
The sun's path decides most of it. Glass that faces the midday or afternoon sun takes the full force of it, and a rooflight, being tilted or flat, sees the sky more directly than a wall window does.
Direction and size
A south-west facing lantern over a kitchen extension takes sun for much of the day. A small rooflight on a north-facing slope sees mostly sky light and little direct heat, so a coating there would trim comfort in winter for no summer gain. The larger the glass, the more energy it admits, and the greater the case for the coating.
The room underneath
A loft bedroom sits right under the roof with no floor of rooms above to soak up heat. A kitchen already makes its own warmth from the oven and hob. Both are rooms where extra sun is felt. A stairwell or landing, where people pass through, is a place that tolerates it. How a whole loft room behaves in summer is covered in our answer on overheating in a loft room.
Blinds as a partner
An external blind keeps heat out before it reaches the glass and works with a coating instead of replacing it. Internal blinds help with glare, but they stop the sun's heat only after it has entered the room.
| Where the rooflight faces | Room underneath | Coating |
|---|---|---|
| South or west | Loft bedroom or study | Strongly recommended |
| South or west | Open-plan kitchen | Worth having |
| East | Kitchen or bathroom | Optional |
| North | Landing or hall | Not needed |
Will it make the room colder in winter?
A little. The coating turns away some free winter sun as well as summer sun, so the room gains slightly less warmth on bright cold days. A good low-e unit still holds in the heat that is made indoors.
A coating cannot tell summer sun from winter sun. It reduces both. On a bright January day, a clear rooflight lets in a useful amount of free warmth, and a solar control one lets in a little less.
How big a trade is it
Winter sun is low and weak, and the days are short. The heat gain lost is small beside the summer heat the coating keeps out. Many solar control coatings also act as low-e coatings, so the glass keeps heat in as well as keeping some out. A well-made unit does not drop your heating performance in the way a tinted film might.
Choosing your trade
If the room has other windows facing the sun, a coated rooflight overhead costs you little. If the rooflight is your only glazing and the room is hard to warm, a lighter coating is the gentler choice. Our guide to the glazing build-up, double or triple glazed rooflights, shows how the panes and coatings combine.
How do I get it on a quote?
Say which way the rooflight faces and what the room is for. The coating is chosen at the survey, named in the fixed written quote, and fitted as part of the unit.
Solar control is a specification, not an add-on. It is built into the glass, so it has to be chosen before the unit is made.
What to tell us
Tell us the direction the roof faces, whether anything shades it, and how the room is used. Those details tell us whether a coating helps, and how strong it should be. The free survey puts us on the roof itself, so the choice follows the actual house.
What it adds to the quote
A coating adds a little to the glass cost, and the quote lists it by name in the specification. That figure is fixed unless the job changes. For the bigger picture, the costs page sets out what lifts or trims a quotation.
Ask for the numbers
Look for the g-value, the light transmission and the U-value on the unit's datasheet. If they are all there, you can compare one option with another fairly.
Sun and glass queries
Does solar control glass look different?
It can look slightly tinted from outside, in a faint blue, green or grey, and lighter coatings show almost nothing. Ask for a sample pane of the one proposed, so you can hold it against the sky.
Is solar control glass the same as tinted glass?
No. Tinted glass absorbs heat in the body of the glass and can get hot itself. Solar control glass carries a thin surface coating that reflects or filters energy, so the effect is cleaner and more precisely tuned.
Can I add it to a rooflight I already have?
Not to a sealed unit. The coating is applied during manufacture, inside the unit. Adding one means a new glazing unit or a new rooflight, and external shading is the option that suits an existing one.
Does it affect the planning rules?
No. Glass type is not something planners weigh. What counts is the projection from the roof, the position, and whether the home is owned as a house or as a flat. Our rooflight planning guide covers that side.