The short answer
Most single-storey ground-floor conservatories in 2026 are permitted development (PD) under Class E of Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 (the GPDO), and do not need a planning application. But the PD status is conditional on size, height, and the position of the conservatory relative to the boundary, and Building Regulations still apply in many cases where planning does not.
For the cost side of the project, see Conservatory Cost UK 2026: Price by Size, Style, and Region and Conservatory Prices UK 2026: What You Actually Get for Your Money.
When a conservatory is permitted development
A conservatory is PD under Class E if all of the following conditions are met:
- It is a single-storey ground-floor extension to the rear or side of the original house.
- The original house is a dwellinghouse (not a flat, maisonette, or other use class).
- The total floor area of the conservatory plus any previous extension, outbuilding, or other addition within the original curtilage of the house does not exceed 50% of the total curtilage area (excluding the original house footprint).
- The conservatory does not extend beyond the rear wall of the original house by more than 4 m for a terraced or semi-detached house, or more than the relevant Class A limit for a detached house.
- The maximum height is 4 m, with eaves no higher than the existing house eaves. If the conservatory is within 2 m of a boundary, the eaves height must not exceed 3 m.
- Materials used in any visible external work are similar in appearance to those used on the original house.
- No verandas, balconies, or raised platforms are included.
- No chimney, flue, or soil vent pipe is added to a side elevation facing a neighbour.
If all of the conditions are met, the conservatory is PD and no planning application is needed. There is no prior-approval process for a Class E conservatory (unlike a Class A larger-home extension), so you can go straight to construction once Building Regulations are satisfied.
When a conservatory always needs full planning
Six situations always force a full householder planning application, regardless of the size or height of the conservatory:
- The property is a flat or maisonette. Flats have no Part 1 PD rights, so any conservatory needs a full application.
- The property is in a conservation area, AONB, National Park, the Broads, or a World Heritage Site, and the local authority has an Article 4 Direction that removes PD for conservatories or roof extensions. This is increasingly common in conservation areas.
- The building is listed. Listed Building Consent is required in addition to any planning application.
- The design exceeds any of the Class E limits — typically the 50% curtilage coverage, the 4 m height, the 3 m eaves within 2 m of a boundary, or the materials condition.
- The conservatory is two-storey or includes a first-floor element. Class E is single-storey only.
- The conservatory sits forward of the principal elevation of the house (i.e. it is at the front rather than the rear or side). Front conservatories need a full application.
In practice, the most common Class E breach on a typical 3-bed semi is the 3 m eaves rule within 2 m of a boundary. Many terraced and semi-detached houses have a rear alley that is less than 2 m from the boundary, and a standard 2.4–2.7 m house eaves plus the new conservatory's roof structure can exceed the 3 m cap. The practical answer is to design the conservatory with a low-pitched or flat roof, with the eaves set 200 mm below the 3 m cap to allow for tolerance.
Building Regulations still apply
This is the part that catches most homeowners out. A conservatory can be PD for planning purposes and still need a full Building Regulations application. Building Regulations are a separate, parallel approval regime that runs to Approved Documents Part B (fire safety), Part F (ventilation), Part K (stairs and guards), Part L (conservation of fuel and power), and Part N (condensation).
A conservatory is exempt from Building Regulations if all of the following are true:
- It is a single-storey ground-floor extension.
- The floor area is less than 30 m².
- It is separated from the rest of the house by external-quality walls, doors, or windows (the standard uPVC or aluminium door set between the house and the conservatory is the usual way to satisfy this).
- It is not used as a kitchen or a sleeping room (sleeping rooms include bedrooms, but a one-off guest bed in a conservatory is treated as a sleeping room for these purposes).
- It has an independent heating system from the rest of the house (or none at all).
- Glazing and electrical work comply with the relevant Approved Documents.
If any one of these is breached, the conservatory becomes a standard extension for Building Regulations purposes, and a Full Plans or Building Notice application to Building Control (or an Approved Inspector) is required. The most common breaches in 2026 are:
- Floor area over 30 m² (a 5 m × 6 m conservatory is exactly 30 m², anything larger needs Building Regs).
- Open-plan layout into the kitchen (a wide opening, a kitchen island that flows into the conservatory, or a glazed roof over the kitchen-conservatory boundary removes the "separated from the house" exemption).
- A radiator connected to the central heating system (an "independent heating system" means a standalone electric heater, not a radiator on the boiler).
A 2026 fixed-fee conservatory quote from a national installer will usually note "PD — no planning required" on the front page. It is much rarer for the same quote to address Building Regulations exemption, and most installers leave it to the homeowner to decide. If the conservatory does not meet the exemption criteria, the homeowner needs a Building Notice or Full Plans application, with the same building control fees and inspections as a standard extension.
How much does a planning application cost?
If a full householder planning application is needed for a 2026 conservatory, the fee is £548 from 1 April 2026 (CPI-indexed from £528 in 2025). The statutory determination period is 8 weeks, with a 16-week planning guarantee longstop. The application is the same form as for any other householder extension, and is submitted via the Planning Portal for English and Welsh councils.
Most LPA planning officers do not object to a well-designed conservatory on a typical 3-bed semi. The two most common refusal grounds are overlooking of a neighbour's garden (where the conservatory is on a side return that overlooks a neighbour) and incongruous design in a conservation area (where the design does not match the host house or the area's character).
What if you build without permission?
If you build a conservatory that needed planning permission but you did not get it, the LPA can serve an enforcement notice requiring you to undo the work or apply retrospectively. Retrospective applications are routinely refused on the same grounds the original application would have been.
The enforcement immunity period in England is 10 years for all breaches of planning control from 25 April 2024 onwards, following amendments to section 171B of the Town and Country Planning Act 1990 by the Levelling-up and Regeneration Act 2023. A conservatory substantially completed before 25 April 2024 may still benefit from the old 4-year rule for operational development.
For Building Regulations breaches, the rules are different. The local authority can serve a regularisation application request at any time (no 10-year limit), and you must pay the building control fee and bring the conservatory up to current standards. Selling a property with an unregularised conservatory is a red flag for surveyors and conveyancers.
Where a measured building survey fits in
A conservatory needs the same baseline data as any other extension: a measured building survey of the existing house gives the architect the floor plans, elevations, and a section showing the existing floor levels and ceiling heights. A conservatory design that is 50 mm too tall for the 4 m height cap, or that extends 100 mm too far past the 50% curtilage coverage, can be caught at design stage if the architect has an accurate measured survey to work from.
A measured building survey for a typical 3-bed semi in 2026 costs in the region of £1,200–£2,000.
icelabz provides RICS-compliant measured building surveys across London and the South East, with deliverables in 2D CAD and (optionally) Revit BIM and point cloud. Contact us for a fixed-fee quote and a typical 10–15 working-day turnaround.