The short answer
A conservatory under 30 m² at ground level with a mostly glazed roof and walls, separated from the main house by external-quality doors and walls, is generally exempt from Building Regulations Part L. All three conditions must be met. If the conservatory is permanently heated, has a solid roof, or the internal separation is removed, the exemption typically falls away. See planning permission for the separate planning question.
Building regulations and planning permission are two separate processes that often get confused. Planning permission is about land use and the impact of a structure on its surroundings. Building regulations are about the technical performance of the structure itself — structural safety, fire, energy efficiency and other standards. For conservatories, the key building regulation is Part L, which covers the conservation of fuel and power. The Part L exemption for conservatories was designed to allow homeowners to add a modest glazed space without the full energy compliance regime that applies to habitable extensions — but the exemption has conditions that are frequently misunderstood.
Building regulations at a glance
- Main regulation Part L (energy efficiency / fuel & power)
- Exemption condition 1 Built at ground level
- Exemption condition 2 Floor area less than 30 m²
- Exemption condition 3 Thermally separated from main house
- If heated permanently Exemption lost — Part L applies
- Solid roof Changes classification — check regs
The three conditions for the Part L exemption
Building Regulations Approved Document L sets out the conditions under which a conservatory is exempt from the energy-efficiency requirements that apply to extensions. All three conditions must be met simultaneously:
- Ground level: the conservatory must be built at ground level, not elevated above the main structure.
- Under 30 m²: the internal floor area must be less than 30 m². A conservatory of exactly or over 30 m² must comply fully with Part L as an extension.
- Thermally separated: the conservatory must be separated from the main dwelling by walls, doors or windows that have no less thermal performance than the original external walls, doors or windows of the house. In practical terms, this means the door and glazed wall between the conservatory and the existing house must be to at least the same standard as the external walls and windows.
Condition three is the most commonly breached. Homeowners who remove the dividing doors and open the conservatory into the kitchen to create an open-plan kitchen-diner effectively remove the thermal separation and, with it, the exemption. If this change is made without building regulations approval, the conservatory is technically non-compliant, which can surface during surveys and conveyancing.
| Condition | Met? | Result |
|---|---|---|
| Ground level + under 30 m² + thermally separated | All three | Part L exempt |
| Any one condition not met | No | Full Part L compliance required |
| Permanently heated | No | Full Part L compliance required |
| Solid/tiled roof | Depends on spec | Likely requires compliance |
Which other Building Regulations apply to conservatories?
Even where a conservatory is exempt from Part L, other building regulations still apply. Part N (glazing — safety in relation to impact) requires that all glazing in critical locations — typically within 800 mm of the floor or in doors — is toughened or laminated safety glass. This applies to all new glazing regardless of the Part L exemption. Part A (structural) applies if any structural work is involved — for instance, if an opening is made in the existing house wall to create the connection, or if any load-bearing element is affected. Most conservatory installers will be aware of these requirements, but you should confirm that the installer is handling compliance for any structural openings as part of the works.
When to make a building regulations application
If your conservatory does not meet the Part L exemption conditions — because it is over 30 m², is being permanently heated, or has a solid roof — you will need to make a building regulations application to your local authority building control (LABC) or to an approved inspector. There are two routes: a Full Plans application (submitted before work starts, best for larger or complex projects) or a Building Notice (submitted shortly before work begins, suitable for smaller projects where the specification is clear). A building regulations completion certificate is issued when the work has been inspected and approved. This certificate is important evidence when you sell the property — a buyer’s solicitor will ask for it.
Retrospective compliance and regularisation
If an existing conservatory was built without the required building regulations approval, LABC can issue a regularisation certificate after the fact. This involves an inspection of the existing structure to confirm it complies (or as-is, with any remediation required). It is not always straightforward — some elements may be concealed — but it is usually the right approach if missing documentation surfaces during a sale. Always check what documentation exists for any conservatory before completing a purchase. This page is general information, not building control or structural advice; consult your LABC or a qualified building inspector for your specific project.
Planning a new conservatory?
A FENSA-registered conservatory installer will handle glazing compliance and can advise on building regulations for your specific project. Compare quotes to understand the full cost.
Frequently asked questions
Does a new conservatory need building regulations approval?
A conservatory under 30 m² at ground level with thermal separation from the main house is generally exempt from Building Regulations Part L. Other regulations (Part N for safety glazing, Part A for any structural work) still apply.
What happens if my conservatory doesn't comply with building regulations?
Non-compliance can surface during surveys and cause delays or complications when you sell the property. LABC can issue a regularisation certificate retrospectively, but this involves an inspection and may require remediation work.
Does removing the conservatory doors from the main house affect building regulations?
Yes. Removing the thermal separation between the conservatory and the main house typically removes the Part L exemption. The conservatory then needs to comply with Part L energy-efficiency requirements, which may require retrospective work.
What is a building regulations completion certificate?
A completion certificate is issued by building control after inspecting the work and confirming it complies with the Building Regulations. It is important evidence of compliance and is often requested by solicitors and lenders when you sell or remortgage.
Sources & further reading
- GOV.UK — Building Regulations Approved Document L (conservation of fuel and power), conservatory exemption conditions
- LABC — Local Authority Building Control guidance on conservatory compliance, regularisation and completion certificates
- Planning Portal — the relationship between planning permission and building regulations for conservatories
- Glass & Glazing Federation — safety glazing requirements (Part N) and FENSA registration for conservatory glazing
This is general information about conservatories and orangeries in the UK, not planning, structural, legal or financial advice. Costs are typical illustrations only and are not quotes for any specific project; actual prices vary with size, site conditions and your chosen installer.