Wraparound Extension: Why You Can’t Do It Under Permitted Development (And What It Actually Costs You)

The Client’s Plan

They wanted a wraparound extension on their detached house: a side extension and a rear extension, built together with no gap between them, creating one continuous space.

They’d done their homework on permitted development. Under prior approval, a detached house can extend to the rear by up to 6m in depth. A side extension can go up to 50% of the width of the house, and can also extend past the rear wall by up to 3m.

Their plan was:

Side extension:2.7m wide, extending 3m past the rear wall
Rear extension: 5m in depth

Both numbers sat comfortably under their respective PD limits. On paper, it looked straightforward.

Where It Falls Apart

Permitted development covers a side extension. It covers a rear extension. It does not cover the two joined together with no gap — a genuine wraparound is not something you can apply for under PD, no matter how compliant each individual piece is on its own.

This is the detail that catches people out, because nothing in the individual PD guidance for side or rear extensions tells you this. You can read both sets of rules end to end, be within every limit stated, and still not have a route to build what you’re picturing — because the combination itself is the problem, not either extension in isolation.

The Staged Workaround — And Why It’s Not a Good One

Once the client understood PD wouldn’t cover the wraparound, the alternative was a staged approach:

1. Apply for and build the shell of the rear extension under prior approval.
2. Once that’s constructed, apply separately for the side extension under a householder planning application, designed to attach onto the completed rear extension along the side of the house.

The catch: to complete the rear extension as a standalone structure first, you need to build its full side wall. Then, once the side extension is approved and built, that wall has to come down again to join the two spaces internally.

That’s a wall built purely to be demolished a few months later — added material cost, added labour, and a build programme stretched across two separate construction phases instead of one. For most clients, once they see the real time and cost impact of building and then demolishing a structural wall, the staged route stops looking like a workaround and starts looking like the expensive option.

What They Actually Did

Faced with the staged route’s added time, cost, and complication, the client opted for a single householder planning application covering the whole wraparound as one scheme.

The trade-off: householder applications are assessed against local council policy, not national PD limits. Their property falls under Runnymede Borough Council, where the policy limit for ground floor rear extensions is 3m in depth — not the 5-6m available under prior approval.

Going this route meant redesigning the rear extension down from 5m to 3m, a 2m reduction the client was understandably unhappy about. But it avoided the staged build’s wasted wall and split programme, and delivered the joined space they actually wanted in one build.

The Real Takeaway

There’s no route that preserves both a genuine wraparound and PD-level depth. Once you want the two extensions joined, you’re in householder application territory, and your council’s standard depth limit applies — whatever that happens to be locally. Prior approval is the only route to the larger PD depths, and prior approval cannot approve a wraparound.

If a wraparound extension is what you’re picturing, the useful question to ask early isn’t “am I within the PD limits” — it’s “what does my specific council allow for a rear extension under a full planning application,” because that number, not the national PD figure, is what you’ll actually be designing to.