Wrap around extension cost, and why the corner costs more than the two halves

How wrap around extension cost works

1. Settle whether it is permitted development. A great many wrap around extension are permitted development, which means no planning application, but the limits on depth, height, materials and how much of the plot is already built on are specific and a designer should read them against your own house before anybody prices anything.
2. Get drawings and a structural design. Existing and proposed drawings, then a structural engineer's calculations for whatever is being opened up or carried. On a wrap around extension this is a small share of the total and it is what turns an idea into something three builders can price identically.
3. Serve the party wall notices in time. Work on or near a shared wall, or excavation within three or six metres of a neighbour's foundations, engages the Party Wall etc. Act and the notice periods are set in months rather than weeks. Serving late is the commonest reason a start date slips.
4. Price it against a specification, not a sketch. Ask each builder to price the same written specification, with provisional sums shown as provisional sums. Two quotes that differ by a third almost always differ in what is included: the kitchen, the flooring, the decoration and the drainage diversion are the usual absentees.
5. Agree stages, retention and building control. A staged payment schedule against completed work, a small retention until sign-off, and a clear statement of who is notifying building control. The completion certificate is what a future buyer's solicitor will ask for.

Insurance and paperwork

Common questions

Does a wrap around need planning permission?

Usually. Permitted development treats a rear extension and a side extension under separate limits and a wrap around normally exceeds one or both, so an application is the normal route. A pre-application conversation with the council is often worth the fee.

What drives wraparound extension cost most? The corner

The corner. Two roofs meeting over a structure that carries two large openings needs a proper structural design and a proper drainage design, and skimping on either shows up as a leak or a sag within a few years.

Will the side return be dark?

It can be, which is why rooflights or a lantern are usually part of the design rather than an extra. Getting daylight into the middle of an L shaped plan is the whole point of the exercise.

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