Planning Permission for Extensions in the New Forest

Extending a house inside the New Forest National Park is a different game to extending one in Poole or Southampton. The National Park Authority is its own planning authority, permitted development rights are stripped back, and there's a floorspace cap that catches owners out after they've already paid for drawings. We build across the Forest, from Brockenhurst and Sway up to Cadnam, and in our experience planning is where these projects are won or lost. Here's what actually applies in 2026.

None of this should put you off. Forest homes take some of the best extensions we build, timber-framed garden rooms and oak additions that suit the setting far better than anything on a modern estate. You just need the planning side handled properly, and early.

Why the Forest plays by different rules

The whole National Park sits on what planners call Article 2(3) land, which strips back the permitted development rights most homeowners take for granted. The larger home extension scheme that allows six or eight metre rear additions under prior approval elsewhere in England doesn't apply here. Side extensions aren't permitted development either, nor is recladding the outside of the house, and outbuildings positioned to the side of a dwelling need consent too.

In practice, most Forest extensions need a full householder application, including modest single-storey additions that a Bournemouth homeowner could build without asking anyone. That's not a reason to shelve the project. It just means the design needs to be right before anything goes in, because the Authority looks hard at scale, materials and the impact on the landscape. Listed cottages and homes in conservation villages carry extra consents on top, which we flag during the survey.

The 30% rule, explained properly

The one policy every Forest homeowner should know about is the extension cap in the Authority's local plan. As a general rule you can increase your home's habitable floorspace by up to 30%, measured against the dwelling as it stood on 1 July 1982, not as it stands today. That baseline matters. If a previous owner added a conservatory in the nineties, part of your allowance is already spent. We've surveyed properties around Burley where the whole allowance was gone and the owners had no idea until we pulled the planning history. The rule exists to stop the Forest's smaller cottages disappearing into oversized rebuilds, and the Authority applies it consistently.

There are exceptions worth knowing about:

• Homes in the four defined villages of Ashurst, Brockenhurst, Lyndhurst and Sway can extend beyond 30%, subject to the usual tests on scale and neighbour impact.

• Small dwellings of 80 square metres or less at the 1982 baseline can normally grow to around 100 square metres.

• Outbuildings and replacement dwellings fall under separate policies, so a garden office or detached garage is judged differently to the main house.

Fees and timescales for 2026

Application fees went up again in April 2026, so figures on older blogs are out of date. As things stand:

• A householder planning application costs £548 in England.

• A lawful development certificate, which confirms in writing that a project doesn't need permission, is £274.

• Prior approval, on the limited jobs where it still applies inside the Park, is £249.

Those are the council's fees rather than ours, and they sit alongside drawings and any tree or ecology reports a scheme needs. Determination normally takes around eight weeks from validation, though Forest applications can run longer when consultees weigh in. As for the build itself, we'll be straight with you: the same extension usually costs more in the Forest than in town. Materials the Authority will accept, access down narrow lanes and protected trees all add labour and lead time, which is why we price from a site survey rather than a rate card.

How we run planning on Forest jobs

We survey and measure before quoting, and on Park properties that includes pulling the planning history so the 30% arithmetic is done on day one, not after you've fallen for a design you can't build. From there we design to the Authority's own guidance on scale and materials, prepare the drawings, submit the application and handle the case officer's questions ourselves. Once consent lands, the same team that managed the paperwork delivers the extension and structural work, so nothing gets lost between architect and builder.

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Thinking about extending in the Forest?

If you're weighing up an extension in Lyndhurst, Brockenhurst, Sway or anywhere else in the Park, send us the address and a rough idea of what you want. We'll tell you where you stand on the 30% rule before you spend a penny on drawings. Book a site survey through completebuilds.com and we'll take it from there.