A lantern on a conservatory and a lantern on an orangery are two different jobs that look similar from inside. A conservatory is mostly glazed and the lantern is often the whole roof. An orangery has a flat perimeter roof with a lantern set into the middle, so the lantern is a feature sitting in a built structure. The difference decides who carries the weight and where the water goes.
What the frame underneath has to do
Replacing a light polycarbonate conservatory roof with a glazed lantern adds real weight, and the frame and dwarf wall were designed for what was there originally. Any reputable installer will look at the existing structure before quoting, and on some older conservatories the honest answer is that the frame needs strengthening or replacing first. A quote that does not mention the existing structure at all has priced a product rather than a job.
The orangery lantern roof: a flat roof with a hole in it
An orangery roof is typically a flat perimeter deck with a kerbed opening carrying the lantern. That makes it a flat roofing job as much as a glazing one, because the perimeter has to drain, the kerb has to be weathered, and the insulation has to be continuous from the deck up the upstand. The common failure is a well made lantern sitting on a poorly detailed kerb, which leaks at the corners and is blamed on the glass.
Lantern roof conservatory cost: replacing a tired conservatory roof
Three options usually get quoted: a new glazed roof, a solid insulated roof with a lantern set into it, and a tiled roof with rooflights. The middle option is popular because it keeps the light over the centre of the room while giving the perimeter a real thermal performance. Converting a glazed conservatory roof to a solid one can change its status under the building regulations, so ask which route the installer is using and get the paperwork.
Condensation and ventilation
A conservatory that was always cold and draughty rarely had a condensation problem. Seal it up, insulate the perimeter and put a warm room under a glazed centre, and moisture has somewhere to condense. Trickle ventilation and a way of moving air matter more after the upgrade than before it, which is the part most quotes leave out.
Questions people ask about lantern roof conservatory
Can any conservatory take a glazed lantern?
No. The existing frame, dwarf wall and foundations were sized for the original roof, and glass is heavier than polycarbonate. A structural assessment before ordering is the difference between an upgrade and a repair bill.
Is a new conservatory roof a building regulations job?
It can be. A like for like glazed replacement on an exempt conservatory often is not, but replacing a glazed roof with a solid one, or changing how the room relates to the house, can bring it into control. Ask the installer to state the route in writing.
What is the difference between an orangery lantern and a conservatory lantern?
Mostly the structure around it. An orangery lantern sits in a kerbed opening in a flat insulated roof, so it is a flat roofing detail. A conservatory lantern is often the roof itself and is carried by the glazing frame.
Will a solid roof with a lantern make the room usable in winter?
It is the main reason people do it, because the perimeter stops being a single glazed sheet. Whether the room becomes genuinely comfortable also depends on the walls, the floor and whether there is any heating in there, so treat the roof as one part of it.
Who is responsible if the lantern leaks at the kerb?
Whoever built and weathered the kerb, which is often not the lantern supplier. That is exactly why a single contract covering deck, kerb, lantern and making good is easier to enforce than three separate ones.