Converting a conservatory into an orangery

You can turn most conservatories into an orangery without knocking them down. The pitched roof comes off and an insulated flat roof goes on around the edge, with a glazed roof lantern set into the middle. Many conversions also swap some glazed sections for insulated columns or walls. Guardian, which sells one of these systems, says existing structures are assessed and may need extra support, and that building regulations approval is usually required.

It is the most expensive and longest of the roof options, so it is worth being clear about what you get for the money.

What makes a room an orangery?

Which? describes an orangery as primarily a brick structure, usually with a flat roof and a central glazed lantern, where a conservatory is mostly glass. The Glass and Glazing Federation says orangeries have more brickwork and more in common with a traditional extension. Which? adds that orangeries generally cost more than conservatories but less than an extension, and can add more value than a conservatory.

A conversion gets you there in stages: the roof always changes, and the walls sometimes do.

Three ways to get the orangery look

A flat perimeter roof with a lantern

This is the full conversion. An insulated flat roof is built on joists or rafters around the edge, with an insulated upstand in the middle for the lantern, a waterproof membrane on top and a plastered ceiling underneath. Systems sold for converting existing conservatories include:

• SupaLite ILite: engineered timber I-beam joists with up to 200mm of insulation, U-values down to 0.1 W/m²K according to SupaLite, paired with the S1 lantern. 10 years on the product.
• LEKA Orangery Roof: GRP rafters with a structural upstand, PIR insulation and an EPDM rubber or fibreglass finish. U-values from 0.10 and a 40-year component warranty, both LEKA’s claims.
• Warmer Roof WarmerBeam: I-beam joists on a glulam eaves beam with an EPDM membrane, up to 5.5m projection as standard or 7m with an upgrade. 25-year manufacturing warranty.
• Icotherm IcoSpan: a structurally calculated flat roof supplied for the installer to cover in felt, rubber or GRP.
• CI Group SkyTherm: a flat roof with a lantern or flat rooflight, fitted by CI Group’s own teams.

A glass roof with an insulated pelmet

A cheaper route keeps a glazed roof and adds a plastered, insulated band around the inside edge. Ultraframe’s Ultrasky roof is a lantern-style glass roof whose bars run down to the eaves, with an insulated internal pelmet as standard, so from inside it looks like a flat ceiling with a lantern. Its Insulated Pelmet (formerly LivinRoom) is a steel frame 300mm to 1200mm deep, filled with mineral wool and finished in plasterboard, which also hides wiring for downlights and speakers. Most of the roof is still glass, so in winter it behaves more like a glass roof than a solid one. Ultraframe does not say whether the pelmet can be added to an existing roof.

Columns and walls

To get the solid corners of a true orangery, some conversions replace glazed sections with insulated structural columns or walls. Ultraframe’s Loggia columns replace brick piers, and Ultraframe says they are five times better insulated than a brick pier. Guardian’s Home Extension goes further, combining its warm roof with insulated wall panels to replace a conservatory with an insulated extension.

Choosing the lantern

Lanterns are sold by size, pitch and glass. Watch which U-value you are given: many makers publish the figure for the glass alone (the centre of the pane), not for the whole lantern with its frame.

In England a new rooflight in an existing home should not exceed a U-value of 2.2 W/m²K under Approved Document L. ExpertSure puts a fitted lantern at £1,800 to £3,500 for a standard unit, which is part of why these conversions cost more than a tiled roof.

What the survey and the rules decide

• Structure. The existing frames, base and house wall are checked just as for a tiled roof. Adding columns or walls can mean work to the base as well.
• Span. Flat roof systems have limits on how far they can reach from the house, such as WarmerBeam’s 5.5m standard projection, so check the system suits the size of your conservatory.
• Height. A flat roof with an upstand and lantern changes the profile. In England permitted development limits a single-storey extension to 4m high, and to 3m at the eaves within 2m of a boundary. On a lean-to, a flat section may need a higher wall plate on the house wall.
• Planning status. Listed buildings, conservation areas, Article 4 areas and flats have tighter rules. Our planning permission guide covers when you need to apply.

Who an orangery conversion suits, and who it does not

A conversion suits you if the conservatory is a main living space, such as a kitchen-diner or family room, and you want it to feel like part of the house without the cost and upheaval of demolishing it. The rectangle of an Edwardian suits the layout well, and on a Victorian the bay shape can be carried through in the perimeter ceiling.

It suits less well if budget is tight: a tiled roof gives most of the warmth for less, as our tiled roof vs orangery comparison shows. Gable fronted conservatories are converted less often because the upright front does not suit a lantern layout. And if the frames and base are failing, compare the cost with a new extension before committing.

Questions to ask before you sign

When you get quotes, ask each installer:

1. Which flat roof system and which lantern, and who makes each?
2. What is the roof membrane (EPDM, GRP or felt), and how long is its guarantee?
3. What is the whole-lantern U-value, not just the glass?
4. Will the new roof be taller than the old one, and have you checked planning?
5. Are columns or new walls included, and do they need new foundations?
6. Where does the flat roof drain to?
7. Who applies for building control, and will I get the completion certificate?

The orangery conversion cost guide shows typical prices by size and shape.