House extension architects in Bath

Which Bath extensions can go ahead without an application?

Schedule 1 of the permitted development order names a World Heritage Site next to conservation areas as "article 2(3) land" (legislation.gov.uk), and the Planning Portal sets out what that removes (Planning Portal). Within Bath's designated areas, much of what a household might build at the back or side therefore needs a householder application. The table compares the two situations for an ordinary house, not a flat or a listed building.

Do not stop at the national table. A house can also lose rights through a planning condition on an earlier consent or an Article 4 direction. The council's planning check page says a proper check covers national rules, its constraints map and the property's planning history, and that it will certify the answer if you apply for a Certificate of Proposed Lawful Use. Flats, converted houses and listed buildings follow different routes; our national page on house extensions covers the general rules.

How should a Bath extension look next to its neighbours?

The council's city-wide appraisal, adopted on 31 August 2005, describes a limited palette of Bath stone, Welsh slate, painted iron and painted timber and notes that regular course heights of 14 or 12 inches are fundamental to how the stone is laid (character appraisal). It also records that some back and side walls are coursed rubble, much of it originally lime rendered. That matters at the rear of a terrace, where the new wall is often the one you will see most.

The same appraisal describes modern buildings with deep plans, large unbroken roof expanses and flat roofs as often out of character. Read that as a prompt to test any rear addition for depth and roof form. Ask your architect to show how the extension's stone coursing, window proportions and parapet or eaves line relate to the original, and how the join will look from the street if it can be seen.

What changes on a Bath slope or above a vault?

The appraisal says much of the city's 18th and early 19th century building stands on vaults, roughly four to five metres above the natural ground level, to avoid costly excavation. The council's guidance on historic vaults says they usually sit beneath the highway to the front, were never intended for habitation, and should not be regarded as potential habitable space (historic vaults guidance). A basement or lower-ground extension to a listed terrace is therefore a heritage question first and a construction question second.

Steep plots raise a drawing issue too. The council's drawing standards ask for sections showing how proposals relate to existing ground levels on sloping sites, and for a street scene or context plan where works will be visible from the road (drawing standards, June 2023).

What does the council expect in the application?

For a householder application the council's checklist says you may need a biodiversity and geological conservation assessment, a flood risk assessment, and parking and access arrangements set out in a design and access statement (householder checklist). If the house is listed, a heritage statement joins the list.

The drawing standards are strict about presentation:

• plans must be drawn to a stated metric scale such as 1:100 or 1:50, and drawings marked 'not to scale' or 'do not scale' are not accepted;
• existing and proposed drawings are best shown side by side at the same scale;
• each sheet needs a title box with address, proposal, drawing title, date, scale and number;
• files go in as PDFs under 10 megabytes each, with names that say what they show;
• drawings that lack detail make the application invalid, which delays registration.

Many of these points sound pedantic until a validation officer returns an application for a missing scale bar. A practice that prepares drawings to the council's published standard saves that round trip.

What does Bath building control charge for an extension?

B&NES Building Control publishes its table of charges (fees and charges). For extensions it lists £580 plus VAT up to 40m2 (£696 in total), £730 plus VAT from 40m2 to 60m2 (£876), and £820 plus VAT from 60m2 to 80m2 (£984). Floor area means the total internal floor area of all storeys, and larger extensions are quoted individually. If you apply for a loft conversion at the same time, the table reduces the loft charge by 25%.

These charges cover plan checking and inspection by the council's team. A private registered building control approver is another route, so compare what each quote includes before choosing. Terrace and semi-detached extensions will probably also need a party wall notice, which is separate from both planning and building control; see our guide to party wall agreements.

Is paying for pre-application advice worth it?

Level 1 of the council's pre-application service covers extensions to your own home. It costs £163, or £239 with a meeting, takes 20 working days and includes a site visit and a written report (pre-application advice). The council says the service gives a qualified opinion on whether a scheme is likely to be permitted, and flags issues early. It adds that pre-application advice does not guarantee approval and is not published on the planning register.

Treat it as a test of the design, not a formality. It is most useful where permitted development has gone, the plot is steep, a tree is close or the house is listed. For a listed building the council's schedule moves to higher levels, starting at £445 for a minor extension; see listed building work in Bath.

What if the council refuses?

The Planning Inspectorate's procedural guide gives 12 weeks from the date on the decision notice to appeal a refused householder application (procedural guide). That limit drops to 28 days if an enforcement notice has been served on the same or very similar development. Appeals on applications made from 1 April 2026 normally follow the Part 1 written procedure, where you cannot add evidence the council did not see unless circumstances have materially changed, so a missing report is better fixed in a fresh application. The council's guide to the decision process offers appeal or an amended resubmission, and recommends its pre-application service before resubmitting.

What should you ask a Bath extension architect?

1. Is my address inside the World Heritage Site, a conservation area or an Article 4 area, and how does that change the route?
2. Will you speak to the council before we apply, and who attends?
3. Which similar Bath stone or rendered-rubble extensions have you taken through the council?
4. Does your fee include drawings in the council's published standard and the heritage statement if one is needed?
5. Who coordinates building control, structural design and the party wall notice?

Check registration on the ARB register before you sign anything, and compare written quotes against one brief. The planning picture for the wider area is on the Bath hub page, and loft conversions in Bath cover the roof.