Guide
Class Q size limits: 150 sq m per home, 10 homes, 1,000 sq m
Updated
The size rules look simple until you have a unit with a history. Cumulative counting, not the individual barn, is what usually decides a scheme.
Question 1
Where is the building?
Class Q is a permitted development right in England only. Wales, Scotland and Northern Ireland have separate regimes.
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The three numbers
- 150 square metres
- The maximum floor space of any single dwellinghouse developed under Class Q.
- 10 dwellinghouses
- The cumulative maximum within the original limits of an established agricultural unit, counting all previous Class Q development.
- 1,000 square metres
- The cumulative floor space maximum across those dwellinghouses within the same unit.
Cumulative counting catches people out
The limits attach to the original limits of the established agricultural unit: all the land in the unit when it came into existence. Paragraph W also requires the application to state any previous Class Q development in the unit, with the number of homes and cumulative floor space.
An anti-avoidance rule counts previous development even where the converted part later left the unit, or the site was developed before leaving it. Splitting a holding does not reset the count.
The rear extension, precisely
- One extension only, and it must have no more than one storey.
- It must be sited to the rear of the existing building, and must not extend beyond a wall forming a side or principal elevation.
- It must not extend more than 4 metres beyond the rear wall.
- Its eaves must not exceed the height of the existing eaves, and it must not be higher than the lower of the existing roof height or 4 metres above the ground.
- It must sit on land already covered by a hard surface, which was either provided on or before 24 July 2023, or has been there for at least 10 years before the extension begins.
The Class Q curtilage
The space standard cuts the other way
Class Q has a lower limit too. Under Class Q.1(o), the existing building (excluding any extension, including building operations) must be able to meet the nationally described space standard. That is the March 2015 standard, read with the 2016 notes (gov.uk). A very small building can fail for being too small.
Measuring matters. Floor space here is the total floor space of the dwellinghouse, and the prior approval application has to state it per home on a floor plan. Get it measured properly before submission.