Approved Document F gives guidance on the ventilation requirement of the Building Regulations for dwellings in England, and it contains specific paragraphs on adding a conservatory. Its 2021 edition took effect on 15 June 2022, and GOV.UK also lists a 2026 edition for buildings subject to the 2026 standards. This guide summarises the conservatory paragraphs of both, applies to England only, and is general information. Approved documents are guidance, not the only way to comply, and building control should confirm what applies to a particular project.

When Part F applies to a conservatory

Approved Document F, Volume 1 says that its guidance on a new conservatory applies to conservatories with a floor area that exceeds 30 square metres, and that conservatories with a floor area not exceeding 30 square metres are exempt from the Part F requirements. That matches the wider Building Regulations exemption explained in the guide to the Class 7 exemption, and the exemption depends on the conditions there, including the thermal separation discussed in the guide to removing the thermal separating wall. A conservatory that falls outside the exemption must meet the ventilation requirement F1(1), which is about providing adequate means of ventilation.

Background ventilators for the general ventilation rate

Paragraph 3.22 says the general ventilation rate for a new conservatory and, if necessary, the adjoining rooms could be achieved using background ventilators. The guidance in paragraphs 1.42 to 1.44 of the 2021 edition is to be followed regardless of the ventilation provisions in the existing room next to the conservatory. Those paragraphs deal with a habitable room ventilated through another room or a conservatory. They say the conservatory should have openings to the outside that provide purge ventilation, with a minimum total area based on the combined floor area of the room and the conservatory, and background ventilation of at least 10,000 square millimetres equivalent area. Between the two rooms there should be a permanent opening with a minimum area of one twentieth of the combined floor area.

The 2026 edition contains the same conservatory section and adds a note in the equivalent paragraph that conservatories should be thermally separated from the rest of the dwelling, and that its paragraph 1.40, on the permanent opening between the rooms, does not apply to conservatories. Which edition applies depends on the standards applicable to the building, as GOV.UK explains, so building control should be asked.

Purge ventilation

For purge ventilation in a new conservatory, paragraph 3.23 directs the reader to the general purge ventilation paragraphs. Those say a system for purge ventilation should be provided in each habitable room, capable of extracting at least four air changes an hour per room directly to the outside, and delivered through openings such as windows or doors or through mechanical extract. Where openings are used, Table 1.4 sets minimum opening areas: hinged or pivot windows opening 15 to 30 degrees need a total area of one tenth of the floor area of the room, and those opening 30 degrees or more need one twentieth. Hinged or pivot windows opening less than 15 degrees are not suitable for purge ventilation. The table is based on assumptions in BS 5925, including single-sided ventilation, an urban environment and a temperature difference of 3 degrees Celsius. Smaller openings might work in some designs or climates, but expert advice should then be sought.

Controls and testing

Paragraph 3.24 says performance testing follows the general paragraph on component and system performance, and controls follow the general ventilation control paragraphs. Those say ventilation should be controllable, manually by the occupant or automatically, and that background ventilators should be at least 1,700 mm above floor level to reduce cold draughts while still being easy to reach. They add that background ventilators are intended normally to be left open. For a conservatory with roof or high-level vents, the guide to conservatory roof vents explains the types and how they work.

How it fits with other requirements

Approved Document F says that in order to show compliance with Part O on overheating, higher purge ventilation rates than those in its own tables are likely to be needed, but the guide to Part O and conservatories explains why that does not apply to most new conservatories. The wider set of building regulation issues is in the guide to conservatory building regulations. The document also stresses that following an approved document does not guarantee compliance, since it cannot cover all circumstances, and an alternative approach should be agreed early with the building control body.

FAQs

Does a small conservatory need to meet Part F?

Approved Document F says conservatories with a floor area that does not exceed 30 square metres are exempt from the Part F requirements.

Can background ventilators provide the ventilation for a larger conservatory?

Paragraph 3.22 says the general ventilation rate for a new conservatory and adjoining rooms could be achieved using background ventilators, following the paragraphs on ventilating a room through a conservatory.

Is there a minimum opening size for purge ventilation?

Table 1.4 gives minimum total opening areas as a fraction of the room floor area, depending on window type and opening angle, such as one twentieth for hinged windows opening 30 degrees or more.

The bottom line

In England, Approved Document F exempts conservatories of 30 square metres or less from Part F, and gives guidance for larger ones: background ventilators for the general rate, purge ventilation openings sized by Table 1.4, and controllable ventilation. The 2026 edition adds a note about thermal separation and the permanent opening. This is general information, not legal or planning advice on any specific property.

Sources

This guide draws on the following primary sources, current as of 25 September 2026:

• GOV.UK, “Ventilation: Approved Document F” (Building Regulations guidance for England)
• MHCLG, “Approved Document F: Volume 1, Dwellings” (2021 edition, paragraphs 1.26 to 1.34, 1.42 to 1.44 and 3.21 to 3.24)
• MHCLG, “Approved Document F: Volume 1, Dwellings” (2026 edition)

Related guides

Compare Conservatories is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not legal or planning advice on any specific property — always confirm requirements directly with your local planning authority.