Conservatory Building Regulations: When You Need Approval (2026 Guide)
Most conservatories are exempt. But the exemption has four conditions. Missing one means building regs apply - here is the full picture.
Updated April 2026.
The Four-Part Exemption Test
A conservatory is exempt from building regulations (under Regulation 9 of the Building Regulations 2010) only if it meets ALL four of the following conditions. Failing any one condition means building regulations approval is required.
Floor area under 30m2
The conservatory floor area (including the internal area within the frame) must be less than 30 square metres. A 5m x 6m conservatory is exactly at the limit. Always measure before ordering.
Key point: Most UK conservatories are well under this limit. A 5x4 (20m2) or smaller satisfies this condition.
External-quality door to house
There must be an external-quality door (same thermal and weathering standard as an external front door) separating the conservatory from the main house. An internal door, however well-insulated, does not satisfy this condition.
Key point: This is the most commonly missed condition. Using an internal door - even a solid one - removes the exemption.
Independent heating controls
Any heating in the conservatory must not be connected to the main house heating circuit. A separate thermostat controlling a separate circuit satisfies this. A radiator on the main house system does not.
Key point: Electric radiators or underfloor heating on a separate circuit satisfies this. A radiator fed from the boiler does not.
Safety glazing below 800mm
Any glazing below 800mm from the floor level must comply with Approved Document K (safety glass requirements). This is standard for modern conservatories but should be confirmed in the specification.
Key point: Most 2026-specification conservatories use toughened or laminated safety glass as standard. Confirm in the installer's specification.
When Building Regulations Always Apply
Orangeries
An orangery has a solid roof, meaning it functions as a room, not a glazed extension. The conservatory exemption does not apply. Building regulations approval is always required for orangeries.
Converted conservatories
If an existing exempt conservatory is converted to an 'additional room' by removing the internal door, connecting to main heating, or fitting insulated ceiling panels, building regulations apply retroactively to the conversion works.
Over 30 square metres
Any conservatory exceeding 30m2 floor area is not covered by the exemption and requires building regulations approval regardless of other conditions.
Structural work on host wall
If the conservatory installation requires structural work on the house wall - removing a load-bearing element, inserting a new lintel, or widening an existing opening - the structural works require building control inspection.
Attached to a commercial property
The conservatory exemption applies to dwellinghouses only. Conservatories attached to mixed-use properties or commercial buildings require building regulations approval.
Any work on main drainage
If the conservatory involves any connection to or diversion of main drainage, building regulations Part H applies.
Approved Document L: Thermal Standards (If BR Applies)
If building regulations apply to your conservatory or orangery, Approved Document L (Conservation of Fuel and Power) sets out the thermal performance requirements. The 2022 edition (in force for new applications as of June 2022) sets the following U-value targets for extensions:
| Building element | Target U-value (W/m2K) | Note |
|---|---|---|
| Roof | 0.15 | Effectively requires a tiled warm roof or equivalent insulated system |
| Walls | 0.18 | Solid brick walls can achieve this; glazed walls typically cannot |
| Windows and glazed walls | 1.4 | Standard double-glazed low-E achieves 1.0-1.4 - just passes |
| Floor | 0.18 | Requires insulation under the concrete slab or screed |
| External doors | 1.4 | Most modern double-glazed composite or aluminium doors achieve this |
These requirements explain why orangeries - which must comply with Part L - are substantially more expensive than exempt conservatories of the same footprint. The roof insulation alone (to reach 0.15 W/m2K) requires a full warm roof system rather than the standard glass or polycarbonate specification.
Part P: Electrical Work
Approved Document P (Electrical Safety in Dwellings) applies to all electrical installation work in a conservatory, regardless of whether the conservatory itself requires building regulations. Adding a new circuit from the consumer unit, installing sockets, or fitting fixed lighting all require Part P compliance.
The practical implication: your conservatory electrician must be registered with a competent persons scheme (NICEIC, NAPIT, Stroma CERTASS) and issue a Minor Electrical Works certificate or a Building Regulations Compliance Certificate for the installation. Keep this certificate permanently - it will be requested during conveyancing.
Completion Certificate: Why It Matters
When building regulations apply and work is completed satisfactorily, the local building control authority issues a Completion Certificate. This is a permanent record that the work was inspected and met the regulatory standards at the time.
Without a completion certificate where one was required, conveyancing solicitors will flag the property as having potential compliance issues. This can delay or jeopardise a sale, reduce the price, or require indemnity insurance. Indemnity insurance typically costs £200-£800 per policy but does not fix the underlying legal position.
Building Control Fees (2026)
| Route | Typical fee | What you get |
|---|---|---|
| Local authority (full plans) | £400 - £1,200 | Plan check + site inspections + Completion Certificate |
| Local authority (building notice) | £350 - £900 | No plan check; inspections only. Faster but higher risk |
| Approved inspector (private) | £350 - £1,000 | Same as LA but via a private company. Often faster turnaround |
| Regularisation (retrospective) | £500 - £1,500 | For work already done without approval. Involves inspection of completed work |