Is a glass roof better than polycarbonate?

In every respect except price. It is quieter in rain, far better at keeping summer heat out and winter heat in, does not discolour, and does not creak as it expands. Polycarbonate is cheaper and lighter, which is why so many conservatories have it.

Does a glass roof need building regulations approval?

Replacing like with like on a glazed roof usually does not, where the conservatory remains thermally separated from the house and mostly glazed. That is the practical difference from a solid roof, which generally does. Your installer should confirm it for your specific case rather than assume.

Will it still be too hot in summer?

Cooler, and for most people the difference is the one that matters, but no glass roof will match a solid one on the hottest days. If the room is currently unusable rather than uncomfortable, be honest about that when you enquire so you get quoted for the right thing.

Conservatories

Replacing a conservatory roof with glass

Replacing a polycarbonate conservatory roof with modern glass typically costs between £9,450 and £18,225, with the spread driven mostly by the size of the conservatory. Solar-control and self-cleaning coatings cut the summer heat and the glare and make the room much quieter in rain, while keeping the daylight that a solid roof takes away.

Glass is the more expensive of the two roof replacements and the less insulating, which sounds like it should never be the answer. It is the right answer more often than that suggests, because the problem most conservatories have is not insulation.

Why glass costs more than tiles and insulates less

It is worth being plain about this, because it is counter-intuitive and the trade rarely volunteers it. Published cost guides put a glass replacement roof above a tiled one, and a glazed roof will never match an insulated solid one for heat retention in January.

What you are paying for is performance in the other direction. A modern glass roof unit is not the glass that was in a conservatory twenty years ago:

A solar-control coating reflects a large part of the infra-red before it enters the room, which is what makes a conservatory intolerable in July. This is the single biggest improvement over old glass or polycarbonate.
A low-emissivity coating on the inner pane keeps heat in during winter, so a modern glass roof is far better than the one it replaces even though it is worse than tiles.
Self-cleaning outer glass, which matters more on a roof than anywhere else in a house, because nobody wants to climb onto one.
Laminated inner panes, which is a safety requirement for overhead glazing and also cuts noise. Rain on a glass roof is dramatically quieter than rain on polycarbonate.

When glass is the right answer

Three situations where it beats a solid roof outright:

The conservatory is the main light source for a room behind it. A solid roof over a conservatory off a kitchen can leave the kitchen needing lights at midday, and that is not recoverable afterwards.
The problem is summer, not winter. If the room is pleasant most of the year and unusable in July, you have a solar gain problem, and solar-control glass addresses it directly.
The existing structure is light. A glass roof weighs less than tiles, so there is less likelihood of needing to reinforce the frames or the base.

Where a solid roof wins is a room you want to use as a room all year. See tiled conservatory roofs.

What to put in writing

Glass specifications are where quotes diverge most, and the words are easy to ask for:

The U-value of the roof glazing, as the whole unit rather than the glass centre pane.
The solar factor or g-value, which is the number that describes how much heat it lets through. This is the one that decides whether July is bearable, and it is the one most often left off a quote.
Whether the inner pane is laminated, which it should be for overhead glazing, and whether the outer is self-cleaning.
Whether the existing frames and base have been assessed, and whether the glazing bars are being replaced or reused.

For what U-values mean and why a glass-only figure flatters a window, see U-values explained.

Glass conservatory roof: common questions

Is a glass roof better than polycarbonate?: In every respect except price. It is quieter in rain, far better at keeping summer heat out and winter heat in, does not discolour, and does not creak as it expands. Polycarbonate is cheaper and lighter, which is why so many conservatories have it.
Does a glass roof need building regulations approval?: Replacing like with like on a glazed roof usually does not, where the conservatory remains thermally separated from the house and mostly glazed. That is the practical difference from a solid roof, which generally does. Your installer should confirm it for your specific case rather than assume.
Will it still be too hot in summer?: Cooler, and for most people the difference is the one that matters, but no glass roof will match a solid one on the hottest days. If the room is currently unusable rather than uncomfortable, be honest about that when you enquire so you get quoted for the right thing.

Other conservatories

TrustedGlazing does not make, supply or fit windows and doors, and the prices above are published industry guides rather than our own. We match your enquiry to one local installer, who quotes and contracts with you directly.