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Conservatory Building Regulations: When a Conservatory Is Exempt, the Changes That End the Exemption, and the Planning Rules

Conservatory building regulations are simpler than most people expect, and easier to fall foul of later. A new conservatory in England is normally exempt from building regulations if it is single storey, at ground level, under 30 square metres, separated from the house by external quality doors or windows, and heated independently, provided the glazing and electrics meet the rules. The trouble starts afterwards, when owners take out the doors to the house, run the central heating into it or swap the glass roof for a solid one. Each of those ends the exemption. This page sets out the rules, the traps, and the separate planning test.

What counts as a conservatory

For building regulations, a conservatory is a mostly glazed room. The definition used in the energy efficiency guidance is a structure where at least three-quarters of the roof and at least half of the external walls are made of translucent material, glass or polycarbonate. A room with a solid roof and a few large windows is not a conservatory, whatever the brochure calls it: it is an extension, and extensions need building regulations approval.

The exemption, condition by condition

The Planning Portal says a conservatory is normally exempt from building regulations when all of these apply:

• It is single storey and built at ground level. A glazed room at first-floor level, or a balcony enclosure, is not exempt.
• The floor area is less than 30 square metres.
• It is separated from the house by external quality walls, doors or windows. In practice this usually means the original back door or patio doors stay in place, or new external-grade doors are fitted.
• It has an independent heating system with separate temperature and on/off controls, or no fixed heating at all.
• The glazing and any fixed electrical installation comply with the building regulations.

The last condition catches people out because it applies even to an exempt conservatory. Glazing in critical locations, such as doors and the panels beside them and low-level glass in walls, must be safety glass under Part K; our safety glass guide explains where. New circuits, sockets and outdoor lighting fall under Part P and must be done by a registered electrician or notified to building control; see our Part P guide.

Four changes that end the exemption

1. Removing the doors or wall to the house

Knocking through to make the conservatory part of the kitchen or living room is the most common breach. Once the separating doors go, the conservatory is no longer thermally separated from the house, so it must meet the energy efficiency standards for an extension, which a mostly glazed structure rarely does without changes. The Planning Portal is explicit that any new structural opening between the conservatory and the house needs building regulations approval, even if the conservatory itself is exempt. Widening an opening in a wall usually means a new lintel or beam, which needs structural calculations; our guide on removing a load-bearing wall covers that process.

2. Extending the central heating

A radiator on the house's heating circuit, controlled by the house thermostat, breaks the independent heating condition. Use a separate heater with its own controls, or treat the project as an extension and get approval. Our radiator regulations page covers the controls rules.

3. Replacing the glass roof with a solid one

Tiled and insulated replacement roofs are popular because old polycarbonate roofs make conservatories too hot in summer and too cold in winter. But once the roof is solid, the structure no longer meets the conservatory definition, and LABC's guidance is that you will need building regulations approval because the exemption no longer applies. Building control will want to know that the existing frames and base can carry a much heavier roof, and that the roof meets the thermal and ventilation requirements. Several roof systems hold LABC certification, which makes approval more straightforward, but the approval itself is still needed.

4. Building it 30 square metres or larger

Larger conservatories need full approval from the start. Measure internal floor area; a generous P-shaped or Edwardian design reaches 30 square metres faster than you might think.

What happens if you get it wrong

Unapproved work surfaces when you sell: the buyer's solicitor asks for completion certificates for any conservatory that has been knocked through or re-roofed. If you do not have one, the council can issue a regularisation certificate for work done since 11 November 1985, but it may require opening up parts of the structure for inspection. Our guide to regularisation certificates explains the process. Indemnity insurance is sometimes offered instead, but it does not make the work safe and is void once the council has been contacted.

Planning permission is a separate question

Being exempt from building regulations says nothing about planning permission. A conservatory is treated as a house extension for planning purposes, so it is permitted development, with no application needed, only if it stays within the limits for extensions. The main ones for a single-storey rear conservatory on a house in England:

Flats and maisonettes have no permitted development rights for extensions, so a conservatory always needs planning permission, and leaseholders also need the freeholder's consent. In conservation areas, side extensions are not permitted development, and listed buildings need listed building consent for almost any addition. See our pages on conservation area renovations and the Party Wall Act if the base will be close to a shared boundary.

Making a conservatory usable all year

Most conservatory complaints are about temperature, not regulations. Solar-control or low-emissivity glass, roof vents, blinds and a well-insulated floor make the biggest difference. If you are planning to knock through and use the space as part of a kitchen or living room, it is usually better to design and approve it as a glazed extension from the start, with a partly solid, insulated roof and rooflights, than to convert an exempt conservatory later. Our rooflight regulations and bifold door regulations pages cover the glazing side, and the Vertigo Interiors homepage has more on planning a renovation.

Sources: Planning Portal, conservatories: building regulations; LABC, conservatory roof guidance; MHCLG, permitted development rights for householders: technical guidance.