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.
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, which the Order defines by reference to all the land which comprised the unit at the time it came into existence. Paragraph W also requires the prior approval application to state whether previous Class Q development has taken place within the unit and, if so, the number of homes and cumulative floor space. There is an anti-avoidance provision too: previous development counts even where the converted part later ceased to be part of the unit, or where the site had already been developed before ceasing to be part of 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 space standard cuts the other way
As well as an upper limit, Class Q has a lower one. Class Q.1(o) prevents development where the existing building, excluding any proposed extension but including proposed building operations, would not be capable of complying with the nationally described space standard issued in March 2015 as read with the 2016 notes (gov.uk). A very small building can therefore fail Class Q for being too small, just as a large one fails for being too big.
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.