The route depends on the lawful use, size, height, boundaries and site restrictions. A proposal outside those limits may still be considered through a planning application. [1][2]
Shops, offices and other qualifying Class E premises
Part 7 Class A of the General Permitted Development Order covers qualifying commercial, business and service establishments. That is a permitted-development class, separate from planning use Class E, which describes the business activities. [1]
On a site outside article 2(3) land and a Site of Special Scientific Interest, the floorspace increase is limited to the lesser of 50% of the original building or 100 m². On those protected sites, the limit is the lesser of 25% or 50 m². These are not fresh allowances that reset each time an owner carries out an extension. [1]
The height of the building as extended must not exceed 4 metres. Development cannot extend beyond the front of an existing building under this route. Listed-building curtilages are excluded, and the provision does not authorise a new or altered shopfront or a shopfront security shutter. [1]
There is a two-metre boundary restriction where the relevant land adjoins premises in the specified residential or institutional use classes, or is article 2(3) land or a Site of Special Scientific Interest. It should not be rewritten as a universal two-metre separation rule for every commercial site. Other conditions also apply, including the permitted purpose of the extension. [1]
Industrial buildings and warehouses
Part 7 Class H has a different set of limits for industrial and warehouse development. For an extension on an ordinary site, the floorspace increase must not exceed the lesser of 50% of the original building or 1,000 m². Lower limits apply on article 2(3) land and separate limits on Sites of Special Scientific Interest. [1]
Development within five metres of the curtilage boundary is excluded. Where it is within ten metres of a boundary, the height limit is five metres; elsewhere the extended building must not exceed the existing building's height. The other conditions include protecting the space available for parking and vehicle turning. [1]
Class H also deals with some new buildings, but its separate limits for a new building should not be substituted for the extension limits. Establish exactly which operation is proposed before measuring the allowance. [1]
Measure against the right baseline
The legislation uses the original building and contains aggregation rules where original buildings in the same curtilage serve the same undertaking. A survey of today's building is not enough unless previous development and the correct baseline have been established. [1]
Check Article 4 directions and conditions that may restrict the route. Prepare an eligibility assessment against every applicable provision; the headline dimensions above are not a complete site-specific checklist. A lawful development certificate can provide a formal decision on a sufficiently defined proposal. [2]
Building regulations still apply
Planning permitted development does not remove building regulations requirements. Coordinate structure, fire safety, access and the relevant energy provisions with the extension design. A BREEAM requirement, where imposed through the planning route, is another separate matter. [3][4][5][6]
The published Future Homes and Buildings Standards changes generally commence on 24 March 2027, with separate provisions for specified higher-risk-building work. Check the applicable non-domestic guidance and transitional arrangements rather than assuming all commercial work uses new-home standards. [7]