Is commercial rooftop solar permitted development?

The confusion around this question has one source: England’s permitted development rules for solar live in two different classes, and nearly everything written online describes the wrong one. Class A of Part 14 covers houses and blocks of flats — the 0.2 m protrusion rules, the highest-part-of-roof test, the conservation-area wall restrictions. Class J covers everything else: offices, hotels, warehouses, schools, surgeries. If you are reading advice that mentions “the highest part of the roof excluding the chimney”, it is householder guidance.

What Class J actually says

On a non-domestic building, solar on the roof or walls is permitted development provided the equipment stays more than 1 m from the roof edge, rises no more than 1 m above a flat roof (0.2 m proud of a pitched slope), and the building is neither listed nor a scheduled monument. There has been no capacity cap since 21 December 2023 — the old 1 MW ceiling is gone.

The step most programmes underestimate: larger commercial arrays use the Class J(c) route, which keeps the PD right but requires a prior approval application to the borough — design, external appearance and glare, decided within 56 days with a 21-day site notice. It is not a planning application, but it is not nothing: it belongs at the front of the programme, next to the grid application. The full borough-by-borough picture — conservation areas, Article 4 directions, listed curtilage, car-park canopies under Class OA — is in our guide to commercial solar permitted development in London.

Where it goes wrong in London

Three patterns account for most refused or stalled schemes we see. A design drawn to the parapet edge, ignoring the 1 m setback. A listed building — or an unlisted building inside a listed curtilage — where Class J never applied and a full application was always the route. And Article 4 directions, which several boroughs use to switch off PD rights street by street in conservation areas; the direction map gets checked before the layout is drawn, not after. None of these kill a project by default, but each one moves it from a 56-day clock to a slower one — and the 2026 NPPF’s instruction to give substantial weight to renewable energy benefits now works in the applicant’s favour when they do.

Sequencing note: the prior approval clock and the UKPN G99 application run happily in parallel. Starting them together is the single cheapest programme saving available on a London commercial install.