Orangery building regulations explained

Building regulations are separate from planning permission. Planning is about what a building looks like and how it affects the neighbours. The regulations are about whether it stands up, keeps heat in and is safe to use. An orangery can need neither, one or both.

When an orangery is exempt

Very rarely. The exemption people have heard of is the one for conservatories, and the Planning Portal sets out every condition a room must meet to use it:

• It is built at ground level and has a floor area under 30 m².
• At least three quarters of the roof and half of the new wall area are glazed or translucent.
• It is separated from the house by walls, windows and doors of external quality.
• Its heating is independent of the house system, with its own on/off and temperature controls.
• Its glazing meets the safety glazing rules and any fixed electrical work is done to the electrical safety rules.

The second condition is the one an orangery fails. A plastered deck with a lantern in the middle is mostly solid roof, so the room is treated as an extension even if it is small and closed off behind doors. A design with a very large lantern and almost no solid ceiling can occasionally qualify, but that is closer to a conservatory with brick corners. If someone tells you your orangery is exempt, ask your building control team to confirm it in writing.

When full approval is needed

In practice, for any room with a solid roof, and always when the room is open to the house, over 30 m², or heated from the house system without separate controls. From that point every relevant part of the regulations applies.

What the regulations ask for

Structure. Foundations suited to the ground, which near trees on clay can mean trenches well over a metre deep. A calculated beam where the house wall is opened up. Roof joists sized for the span and for the weight of the lantern.

Insulation. New elements have to meet maximum U-values: 0.18 W/m²K for walls and floors, 0.15 for the roof, 1.4 for windows and glazed doors, and 2.2 for rooflights, which is how a lantern is assessed.

Glazing area. The total area of windows, doors and rooflights should stay within 25% of the new floor area, with an allowance added for any existing openings the extension blocks. An orangery will normally be above that. It is still allowed, provided a calculation shows the whole room performs at least as well as one that met the limit. Better glass and extra insulation in the floor and deck are the usual way to do it.

Ventilation. Opening windows or vents equal to a set fraction of the floor area, and background ventilators. If the orangery covers the only window of an existing room, that room’s ventilation has to be considered too.

Electrics and drainage. New circuits must be installed and certified by a registered electrician or inspected by building control. Rainwater from the new roof needs somewhere to go, normally a soakaway or the existing surface water drain.

How approval works

You, or more often your builder, apply to the council’s building control service or to a private registered building control approver. There are two routes. With full plans, the drawings are approved before work starts. With a building notice, work starts sooner and is checked as it goes, which suits simple jobs and carries more risk on complicated ones.

Each council sets its own building control charges. For a single-storey extension of 10 to 40 m², expect about £700 to £1,100 including VAT across the plan check and the inspections.

An inspector visits at set stages: foundations, damp-proof course, drains, roof structure and completion. At the end you receive a completion certificate. Keep it with the house deeds. A missing certificate is one of the commonest causes of delay when a house with an orangery is sold.

Two things outside the regulations

If the foundations are within 3 m of a neighbour’s building and go deeper than theirs, or you build on the boundary line, the Party Wall Act requires you to give written notice before starting.

Building over or within 3 m of a public sewer needs the water company’s consent, usually as a build-over agreement. Building control will ask to see it.

Scotland

Scotland uses building warrants in place of building regulations approval. A warrant must be granted before work starts, and a completion certificate accepted at the end. The warrant fee is set nationally by the value of the work: from 1 April 2026 it is £1,035 for a job valued at £50,001 to £60,000, for example. Applying late costs more, because a late warrant is charged at 200% of the fee. Small conservatories can be exempt, but the limit is far lower than in England, so assume an orangery will need one.

For what all of this adds to the price, see our orangery cost guide.