Single Storey Extensions in Olney | Building Control Handled

A single storey extension in Olney typically costs £2,400–£3,200 per m² finished ready for decoration — roughly £29,000–£38,500 for a 12m² rear extension, with any kitchen fit-out priced separately. An extension in Olney needs building regulations approval — Milton Keynes City Council’s 2026 scheme of charges lists a 10–40m² extension at £700 plus VAT (£840) on full plans, or £769 plus VAT as a building notice; up to 10m² is £555 plus VAT. It either fits within permitted development or needs householder planning permission, which costs £548 from April 2026 and is decided within eight weeks. In Olney’s conservation area the Article 4 direction removes permitted development for extensions, so you will need planning permission.

Typical cost: £2,400–£3,200 per m²
Council: Milton Keynes City Council
Planning: Needed in the conservation area (Article 4)
Building regulations: Needed
Ground: Limestone, mostly free-draining

Prices are our 2026 guide prices; your fixed price comes in writing after the free visit. Council fees checked October 2026.

Extensions in Olney

Extensions on Olney houses

Olney is a limestone market town with 119 listed buildings, a long conservation area through the centre and newer estates around the edge; the 2017 neighbourhood plan allocated around 300 more homes.

Most extensions we build here are single storey at the rear, matched to the existing brick or stone, with the drainage and any sewer nearby checked before the footings are dug.

We cover Olney (MK46) and the areas around it, including Emberton, Lavendon, Clifton Reynes, Weston Underwood, Warrington, Sherington, Newton Blossomville and Ravenstone. Travel does not change the price.

Olney specifically

Ground, drainage and conservation in Olney

Olney sits on Great Oolite limestone, which generally drains better than Milton Keynes clay — but clay bands and the Ouse flood plain change that locally, so we do a percolation test before designing a soakaway. Because the ground varies, the foundation depth is confirmed from the trial holes and agreed with building control on site.

Olney’s conservation area has an Article 4 direction for houses that removes permitted development for extensions, alterations, porches and painting outside walls. Front hard surfaces, outbuildings and boundary walls are not covered, so a permeable drive is still permitted development.

The Great Ouse valley runs along the south of the town, and Milton Keynes City Council’s flood risk assessment notes a cluster of sewer flooding records in Olney. You can check any address on the Environment Agency flood map.

Sources: Milton Keynes Article 4 directions (Olney) · Olney Conservation Area map.

Milton Keynes City Council

Planning, building regulations and fees in Olney

Step 1Check whether it fits permitted development, and if you want certainty apply for a lawful development certificate (£274). Planning Portal: extensions
Step 2In the Olney conservation area the Article 4 direction removes permitted development for extensions. Milton Keynes City Council: Article 4 directions
Step 3If permission is needed, apply for householder planning permission (£548 from April 2026), decided within eight weeks. Pre-application advice from Milton Keynes City Council costs £360 for a householder project (£180 for outbuildings), with a written reply within six weeks. Planning Portal: application fees
Step 4Apply for building regulations approval: Milton Keynes City Council’s 2026 scheme of charges lists a 10–40m² extension at £700 plus VAT (£840) on full plans, or £769 plus VAT as a building notice; up to 10m² is £555 plus VAT. Milton Keynes City Council: building regulation charges
Step 5If the extension is over or within 3m of a public sewer, check Anglian Water’s build-over criteria; a consultation costs £107. Anglian Water: building over or near our assets
Step 6We build to the approved drawings and work to the building control inspections at each stage.

Council fees and rules checked October 2026. Planning fees are the national fees from 1 April 2026.

What is included

Everything below is included in an extension

Drawings and the building control application
Foundations set from a trial hole, not a guess
Drainage diverted or rebuilt where it needs to be
Build-over and party wall matters flagged and handled
Roof and threshold junctions detailed properly
Electrics and plumbing by registered trades, with certificates
Building control sign-off at the end
A five year guarantee, in writing

Questions

Extensions in Olney: questions

How much does a single storey extension cost in Olney?

A single storey extension in Olney typically costs £2,400–£3,200 per m² finished ready for decoration — roughly £29,000–£38,500 for a 12m² rear extension, with any kitchen fit-out priced separately. Your fixed price comes in writing after the free visit.

How much does planning and building control cost for an extension in Olney?

Householder planning permission is £548 (from April 2026) if you need it, or £274 for a lawful development certificate. Milton Keynes City Council’s 2026 scheme of charges lists a 10–40m² extension at £700 plus VAT (£840) on full plans, or £769 plus VAT as a building notice; up to 10m² is £555 plus VAT.

Do I need planning permission for an extension in Olney?

Many single-storey rear extensions are permitted development within size limits. In Olney’s conservation area the Article 4 direction removes permitted development for extensions, so you will need planning permission.

Is Olney in a conservation area?