When a Conservatory Is Exempt From Building Regulations
A ground-level conservatory under 30 m², separated from the house and heated independently, is exempt under Schedule 2 Class 7 of the Building Regulations 2010. No application, no inspection, no fee. The exemption has five conditions and it is easier to lose than most installers explain.
Upgrading a conservatory into a heated envelope · when the exemption is lost
£1,200 to £2,900 plus the building control fee
Thin evidenceOne publisher, May 2026. Checked 20 August 2026.
When is a conservatory exempt from building regulations?
When it is at ground level, under 30 m², single storey, separated from the house by external-quality walls, doors or windows, and heated independently of the dwelling. Meet all of that and the work is exempt under Schedule 2 Class 7 of the Building Regulations 2010, read with regulation 21(4).
Exempt means there is no application, no inspection and no fee for the conservatory itself. It does not mean nothing applies: the glazing must still comply with Approved Document K, and any fixed electrical installation must still comply with Part P. Those two survive the exemption in every case. If you want the money side of the decision first, price your conservatory.
The five conditions in Approved Document L paragraph 0.14
All five have to hold at the same time. Fail one and the structure is no longer the thing Class 7 describes.
- 1. It is at ground level. A conservatory on a raised deck or at first floor is outside the class.
- 2. Its floor area does not exceed 30 m². Measured internally. A 6m × 5m conservatory is exactly at the line.
- 3. The glazing complies with Part K on glazing in critical locations, which in Wales is Approved Document N instead.
- 4. Any wall, door or window separating the conservatory from the dwelling is retained, or if removed, is replaced. This is the condition that knocks out most open-plan conversions.
- 5. The dwelling's heating system is not extended into the conservatory. A radiator run off the house boiler ends the exemption. An independent electric heater with its own controls does not.
One devolution detail worth having, because it is commonly stated as if it applied everywhere. In England, regulation 21(4) has two limbs: the separating wall, door or window being removed, and the heating system being extended in. The third limb people quote, that a fixed heating appliance has been provided, is Wales only. Retrieved from legislation.gov.uk and Approved Document L Volume 1, 2021 with the 2023 amendments, paragraph 0.14, on 20 August 2026.
The 75 per cent glazing rule was withdrawn in 2010
It is still quoted on most pages in this category, including by installers.
The rule people repeat is that a conservatory must have at least 75 per cent of its roof and 50 per cent of its walls in translucent material. That test came from editions of the Approved Documents that no longer exist, and the government withdrew it explicitly.
“the definition of conservatory in terms of percentage translucent material as set out in previous editions of the Approved Documents no longer applies”
What replaced it is a judgement rather than a percentage. The live test is whether a significant proportion of the walls and roof are glazed, and it is decided by building control bodies case by case. The 2013 circular puts it in those words.
“a significant proportion of the walls and roof are glazed”, decided “by building control bodies on a case by case basis”
This matters practically, not just pedantically. If you are told your planned roof keeps you inside a 75 per cent threshold, you are being reassured against a test nobody applies. The question your building control body will actually ask is whether what is left still reads as a conservatory.
The two commonest ways people lose the exemption
Knocking through
Removing the separating wall to open the conservatory into the kitchen fails condition 4. There is a second trap underneath it: forming a new structural opening between the conservatory and the house needs building regulations approval in its own right, even where the conservatory itself is still exempt. This is the single commonest exemption mistake we found, and it is usually discovered at sale.
Extending the heating
Adding a radiator on the house system fails condition 5. Installers do it as a matter of routine because it is the cheapest way to make the room usable, and because nobody asks them not to. It is also why the room can be perfectly warm and still be a problem on a solicitor's enquiry four years later.
There is one more line worth knowing that is not about the exemption at all: new floor space above 100 m² can attract the Community Infrastructure Levy. That is far above the 30 m² ceiling here, so it only bites if the conservatory is part of something larger.
What it costs when the exemption goes
While the exemption holds there is no fee at all, which is why the register has so little to say about the exempt case. The figures start when the exemption stops.
| Fee or cost | Low | High | Evidence | Source and date |
|---|---|---|---|---|
| Upgrading the conservatory into a heated envelope | £1,200 | £2,900 | Thin | One UK publisher, May 2026 |
| Building control approval, solid roof conversion | £200 | £800 | Reasonably | Two UK publishers, 2026 and March 2026 |
| Building control fee on a new conservatory base | no figure | no figure | Gap | Not separately published, and mostly moot under Class 7 |
| Planning application fee | no figure | no figure | Gap | Our register carries no planning fee row at all |
Sources: one UK publisher, May 2026, for the heated envelope upgrade, a single source, so Thin. Two UK publishers, 2026 and March 2026, for the building control fee, who disagree by 2.0x on the floor and 1.74x on the ceiling, so there is no defensible typical. All checked 20 August 2026. The two gap rows are absences we are publishing rather than numbers we could not find: an invented statutory fee is the figure a homeowner repeats to a council officer.
Read the ladder in order. Losing the exemption is not one fee, it is a fee plus a building specification: the roof becomes a regulated thermal element and has to perform to the standard for one, which is where the £1,200 to £2,900 goes. The Conservatory Cost Calculator puts that against what the rest of the job costs.
Put a number against your own conservatory
Six questions, roof condition first, phone number last. They live on the calculator, not on this page.
Or get quotes for your roof and ask each installer, before anything else, whether the work they are proposing keeps the conservatory exempt. The answer tells you more about them than the price does.
Check what your conservatory will cost. We pass your details to vetted installers so they can quote, and we are paid when they do. how we make money.
Roof replacements are a different test
Class 7 asks what the structure is. A roof job asks what you are doing to it, and those are separate questions with separate answers. Regulation 9(1)(b) keeps the exemption alive through further work only if, afterwards, the structure is still a building of the kind Schedule 2 describes. Take the glazing out of the roof and it is not.
At that point the work is a material alteration, it is notifiable, and it goes to Local Authority Building Control or a Registered Building Control Approver. No competent person scheme covers it. The whole route, with the primary sources quoted, is on conservatory roof replacement building regulations.
Planning permission is a third question again, and it usually has a shorter answer: a roof change on a house is normally permitted development under Class C of the GPDO 2015. Size limits for building a conservatory in the first place are a planning matter too, and they are England-only rules with separate regimes in Scotland, Wales and Northern Ireland that we do not publish because we hold no verified figures for them.
Questions people ask first
Do you need building regulations for a conservatory?
How big can a conservatory be before it needs approval?
Does a conservatory have to be 75 per cent glazed?
Can I knock through into my conservatory?
What does it cost if the exemption is lost?
Sources for this page
All retrieved and checked 20 August 2026.
The full list, with what each source is trusted for, is on the primary sources we use. Checked 20 August 2026, next check due 20 November 2026.
Find out what yours costs
Six questions, about sixty seconds, and an estimate built from published UK figures with every source shown. Then up to four local installers can quote you, if you want them to.