Under the glass, or over it?
Almost every veranda quote is for shading laid over the roof. It is the older answer and it is not a bad one — but it is a building job, and for most people it is not the one they need.
If you have asked anyone about shading a glass roof, you have been quoted for fabric laid across the outside of it. That is the trade's default, it has been for thirty years, and there is a good physical reason for it. There is also a reason it is the wrong purchase for most of the people who are offered it, and nobody selling it is likely to tell you what that is.
What each one actually does
Shading outside the glass stops sunlight before it reaches the glazing. Nothing fitted indoors can match that, because by the time light is inside, the energy is already in the room. On a south-facing, uninsulated glass roof in full sun all day, external shading keeps the structure itself cooler and there is no arguing with it.
Shading under the glass works on what you actually feel: the glare on a screen, the hot stripe across the table, the fact that the room is unusable from two in the afternoon. The glass above it still warms. For most verandas that distinction turns out to be academic, because the part people live with is the room, not the roof.
Where the difference stops being physics
Everything else about the two is a question of what you are buying into, and the gaps are not small.
| Under the glass | Over the glass |
|---|---|
| Two people and an afternoon | A crew, usually with scaffolding |
| Dusted when the room is | Cleaned from on top of the roof |
| Nothing reaches it | Retracts above a stated wind speed |
| Folds back along the rafter | Cassette and rails stay up there |
| Ages like an indoor blind | Outdoors every day of the year |
The weather row is the one that catches people out. An external system has a wind rating, and above it the fabric has to come in — which, on the kind of bright blustery day a Belgian summer specialises in, is exactly when you wanted the shade. An internal system has no such conversation.
What it costs you to be wrong
An over-roof system is quoted after a survey, with the system, the structural fixings and a crew's day inside one figure you see at the end. An under-roof system is a price on a screen before you order. That is not only a difference in money; it is a difference in how much you know before you commit.
The question is not which system is better. It is which problem you have.