An orangery sits somewhere between a conservatory and an extension. It usually has solid brick or stone piers and a lot of glazing between them, but the feature that sets it apart is the roof: a flat or gently pitched perimeter roof running round the room, with a raised glazed lantern in the middle. The perimeter gives the room a ceiling you can fit lights to. The lantern floods the centre with daylight. Lantern-style roofs on ordinary conservatories borrow the same idea. The combination is attractive and it is also demanding, because the roof has two quite different parts that must be joined watertight: a flat roof covering at the edges and a glass structure rising out of it. This guide explains how each part is built, where they fail, and what replacing one involves. It is not a design guide for a new orangery. It is aimed at the owner of an existing room whose roof is leaking, tired or cold, and who wants to know what the options are before getting quotes.
What an orangery roof is made of
The roof has three layers of structure, and it helps to picture them from the inside upwards.
First, the timber or steel rafters run between the house wall and the outer walls, and they also frame the opening for the lantern. Where the roof is flat, joists do the same job, and the members round the opening carry the lantern. Second, the deck: boards or sheet material fixed on top of the timbers. On a warm roof, which is the usual modern build, insulation boards sit on top of the deck and the waterproof covering goes over them. On an older cold roof, insulation is between the joists with a ventilated gap above it. Third, the waterproof covering, which may be EPDM (a rubber membrane laid as a sheet), GRP (fibreglass resin laid wet and left to cure), lead, or in some cases felt or a single-ply membrane.
The lantern is a separate frame, usually aluminium, timber or a mix, that stands on an upstand (a raised kerb of timber or insulated panel around the opening). Glass or polycarbonate panels fit between its bars, and a ridge runs along the top. The lantern is closed at its base with a flashing or trim that laps over the roof covering.
Not every lantern-style roof is the same. A smaller conservatory may have a pitched glazed roof with a raised central section, or a lantern set on a plain glazed roof. The point to grasp is that the details are the same: a waterproof covering at the edges, a kerb or frame raising the glazed part, and a junction where they meet. It is also worth noting that the term orangery has no fixed legal definition, so the label on a brochure tells you little about the build. Look at the roof, not the name.
Why the perimeter roof fails
The flat part of the roof does the hard work, because it has to shed rain with very little slope. Most perimeter roof failures are drainage or detail failures, not the covering simply wearing out.
Flat roofs need a fall, a slope that lets water run to the gutter. BS 6229:2018, as quoted by manufacturers, recommends a minimum finished fall of 1:80, and designing to 1:40 allows for tolerances in the deck. A roof built too flat holds puddles, and standing water ages every covering faster. Many leaks that show up at the edges of an orangery trace back to ponding at a low point near the lantern.
Detailing is the other cause. Wherever the covering turns up a wall or the lantern upstand, it needs a firm edge, a good lap and a trim to protect it. On the house wall, a lead flashing is tucked into the brickwork. A badly glued corner on EPDM, a lifted GRP edge or a split lead upstand will let water in however good the flat area is.
Age matters as well. Typical UK sources give EPDM a life of about 20 to 30 years or more, GRP 25 to 40 years, and lead roofs and flashings well beyond a lifetime of ordinary use if properly laid, though these figures depend on exposure and workmanship, not promises. An orangery built a generation ago may be on its original covering, and a repair may be the sensible thing if the rest is sound.
Gutters are the last point. Orangery roofs often finish behind a parapet or fascia, with a concealed gutter, which is harder to reach and more likely to be neglected. A blocked outlet can overload the edge of the roof in a heavy shower.
The lantern: glass, bars and seals
The lantern has its own failure points, and they overlap with the faults described in our guide to conservatory roof repairs.
Seals and gaskets
Glass units are held in the bars by gaskets and caps. When the gaskets harden and shrink, rain gets in along the glass edge and trickles along the inside face of the bar. In a lantern, that water often collects on the ledge where the bar meets the kerb, then soaks into the timber below.
The base and the kerb
The kerb is the weak point most people never see. If the covering has lifted at its edge, water runs behind the lantern base and into the kerb, and the timber rots slowly out of sight. A lantern with a long history of drips should have its kerb checked before anything is put back on it.
Failed glass units
A misted double-glazed unit has lost its seal. Replacing a single unit is possible if the size and specification can be matched. If many panels have fogged, it is a sign that the whole lantern is ageing together.
Heat and light
A lantern brings daylight into the middle of a deep room. It also lets heat in and out, so solar-control coatings and openable vents matter. A fully glazed lantern over a south-facing room can overheat without them.
Where a lantern is in good shape but the surrounding roof has failed, the lantern can sometimes be lifted off, the roof renewed, and the lantern reset on a new kerb. That depends on the frame being sound enough to be moved.
Replacing an orangery roof
A replacement can mean renewing the covering, the whole perimeter roof, the lantern, or all three. The scope depends on what the survey finds.
If the structure is sound, the usual approach is to strip the old flat covering and insulation back to the deck, repair or replace the deck where it is damp or soft, and lay a new warm roof. Insulation boards go on first, then the waterproof layer. Falls are corrected with tapered boards where the old roof ponded, because laying a new covering over the same low point only repeats the problem. The kerb is rebuilt or renewed, the lantern is reset or replaced, and the flashings at the house wall are redone in lead.
Choosing the covering is a decision about detail as much as life. Typical UK costs per square metre from MyBuilder's flat roof cost guide (2026) are £90 to £130 for EPDM, £95 to £150 for GRP and £150 to £200 or more for lead, against £70 to £100 for bitumen felt. These are national ranges and not Empire prices. EPDM suits large, simple areas. GRP forms one continuous sheet and suits corners, curves and tall upstands. Lead is used for flashings, upstands and sometimes the whole roof where the look and long life justify the price.
If the roof is being altered rather than simply re-covered, for instance swapping a glazed roof for a solid one, a Building Regulations application is needed (Homebuilding and Renovating magazine, 2023). Our page on the conservatory roof replacement cost deals with the wider pricing, and the insulation question is covered by the same checks as other warm roofs.
Listed buildings and conservation areas are a separate matter. Where the house itself is listed, speak to B&NES Council before the look of the orangery changes.
Condensation, light and comfort
Owners often ask about orangery roofs because the room is cold, damp or too bright, and not because of a leak. The cause is usually in the build-up.
A well-built warm perimeter roof, with continuous insulation and a vapour control layer, keeps the ceiling surface warm, and condensation on it is rare. A poorly built or old cold roof can collect moisture in the joists if warm room air reaches the cold deck and there is not enough ventilation to carry it away. The symptoms are damp patches on the ceiling, mould spotting, and in time, rot in the timbers. Our answer on whether a solid roof will stop conservatory condensation explains how roof type and room use interact.
The lantern is the coldest surface in the room and so is where moisture shows first. Glass with a warm-edge spacer and a low-emissivity coating is less prone to it than basic units, and the aluminium bars should have a thermal break. Opening vents to let damp air out helps in daily use.
Light needs the same balance. A lantern that is too large for the room, or faces due south, makes the space hot and glary in summer. Solar-control glass, blinds that fit the lantern and a clear route for air all help. If you intend to use the room all year, it is worth thinking about the roof, walls and heating together, as our guide to using a conservatory as a year-round room describes.
None of these points is a reason to avoid an orangery. They are reasons to specify the roof properly and to keep the drainage working.
Surveying, pricing and what to ask
The best way to deal with an unfamiliar roof is to have someone look at it on site. An orangery roof hides a lot: the deck, the insulation, the kerb and the flashings are all under something.
On the survey, we check the deck and the covering for ponding and splits, the upstand and kerb around the lantern, the lantern seals and glass, the lead at the house wall, and the outlets and gutters. We photograph your own roof and send the pictures, so you can see what the findings are based on. The price that follows is fixed and written, itemised by scope, and the workmanship carries our 10-year written guarantee. Where repair does the job, we recommend it and price it that way.
Whoever you invite, put the same questions to each firm. What is the new covering, and who makes it? How will falls be corrected? Is the deck being renewed or only covered over? What happens to the kerb? Is the lantern being reset, repaired or replaced? What lead is being used at the house wall, and is the gutter included? Does the price cover Building Regulations where it applies?
An answer of "a bit of sealant" to a lantern that has leaked for years deserves a follow-up. A good roof starts with the details that are hidden, and a good quote names them.
If you are weighing up a more traditional change, our conservatory roof replacement service covers glass, polycarbonate, tiled and lightweight warm roofs, as well as lantern-style designs.