A home extension cost in Petts Wood follows the same national per-square-metre figures that trail every suburb - and here they are broadly right, because this is a district of 1930s semis and detached houses with proper gardens and driveways. So the useful question is not whether you can extend, but how the borough's rules shape what you add, and one of those rules is unusual.
That is the Petts Wood twist. The suburb was built as a planned garden estate in the 1930s, laid out around the new railway station, and Bromley has placed Article 4 directions on the original estate to protect its uniform interwar character. Those directions remove some permitted development rights, so work that would be automatic elsewhere - a porch, a roof change, cladding - needs planning permission here. Away from the estate the usual permitted development rules apply, and most houses extend freely.
So an honest guide to Petts Wood answers two questions. What can you add - and whether an Article 4 direction changes the route - and what does it cost on a BR5 house. The national benchmarks are close to the mark here, because a Petts Wood build has room to work. The Federation of Master Builders puts a single-storey extension at £1,800 to £3,000 per square metre, and in BR5 the realistic figure sits a little above that, for the finish local buyers expect.
A home extension cost in Petts Wood starts around £45,000 in 2026 for a single-storey rear extension. A two-storey side or rear extension runs £90,000 to £165,000, a wrap-around or large kitchen extension runs £140,000 to £260,000, and a two-storey full-width extension or near-rebuild runs £230,000 to £430,000 and beyond. Per square metre that is roughly £2,300 to £3,300 for single-storey work and £2,200 to £3,000 for two-storey work. Those are Buildaway's own BR5 quoting ranges. National guidance sits at £1,800 to £3,000 per square metre, so Petts Wood is close to it. The bigger variables here are Bromley's Article 4 directions on the 1930s estate, the character of the suburb, and party walls on the semis.
What Does a Home Extension in Petts Wood Cost in 2026?
A home extension cost in Petts Wood falls into four bands in 2026. A single-storey rear extension runs £45,000 to £90,000. A two-storey side or rear extension runs £90,000 to £165,000. A wrap-around or large open-plan kitchen extension runs £140,000 to £260,000. A two-storey full-width extension or near-rebuild runs £230,000 to £430,000 and beyond. Each band covers design, structure, envelope, services, finishes and VAT.
Petts Wood Home Extension Cost, by Project Type
Buildaway BR5 quoting ranges, 2026 - bars scaled to the top of each range
Source: Buildaway 2026 quoting data for Petts Wood extension projects. Not drawn from any third-party cost index.
| Project type | What it includes | Petts Wood range | On site |
|---|---|---|---|
| Single-storey rear extension | 12–24 m² across the back of the house. New foundations, a steel beam through the rear wall, a flat or pitched roof, glazing and drainage. | £45,000 – £90,000 | 8 – 14 weeks |
| Two-storey side or rear extension | 20–40 m² over two floors. Foundations, structural openings, a roof tie-in and a bedroom or bathroom above. | £90,000 – £165,000 | 14 – 22 weeks |
| Wrap-around or large kitchen extension | 30–55 m² around the rear and side. A steel frame, structural glazing or a lantern, and an open-plan fit-out. | £140,000 – £260,000 | 16 – 26 weeks |
| Two-storey full-width extension or near-rebuild | 45–90 m² of new space, or a substantial remodel. A full structural frame, new roof sections, a re-planned house and a high-specification finish. | £230,000 – £430,000+ | 22 – 34 weeks |
Per square metre is the more useful comparison once you are weighing one option against another. The table below shows how the main project types price out per square metre of new floorspace in Petts Wood. As before, these are our own 2026 figures, not a published index.
| Work type | Petts Wood rate per m² | What drives the spread |
|---|---|---|
| Single-storey rear extension | £2,300 – £3,300 | Glazing, roof type, and the level of kitchen and finish specified |
| Two-storey extension | £2,200 – £3,000 | Cheaper per m² as roof and foundations are shared over two floors |
| Wrap-around with structural glazing | £2,700 – £3,800 | Steel frame, sliding doors and lantern rooflights carry the cost |
| Internal remodelling with structural openings | £1,600 – £2,600 | New structure and services with no new floorspace added |
It also helps to think in proportion. Land Registry figures put the average Bromley property at around £560,000 in May 2026, and Petts Wood's 1930s family houses trade around and above that. A fourth bedroom, a bigger kitchen or a home office is measured against what the next house up the road costs, which is why owners here so often extend rather than move once the stamp duty and moving costs on a larger BR5 house are set against a well-planned extension.
Why does a BR5 extension cost what it does?
A Petts Wood home extension sits close to the national average, a little above it for the quality local buyers expect. The reasons are the finish, the Article 4 and character rules that need careful design, and standard suburban London labour. Access, for once, works in your favour: there is usually a garden, a driveway and room for a crane.
- Article 4 directions. On the original 1930s estate, Bromley has removed some permitted development rights to protect the uniform character, so work that would normally be automatic - a porch, a roof alteration, cladding - needs planning permission. That redesign and application add time and fees.
- Matching the 1930s character. Even off the estate a scheme reads best when it respects the interwar detailing - the bay windows, the hipped roof, the render and brick - so materials are chosen to match rather than to be cheapest.
- Suburban access. There is usually a driveway to load from and room for a skip, and on the wider roads a crane can help with steel or a lantern, which keeps the programme moving.
- Party walls on the semis. Many Petts Wood houses are semi-detached, so a two-storey side extension, a rear extension near the boundary or a loft cutting into the party wall triggers notices.
- London clay and mature trees. Petts Wood's leafy roads sit on clay, and foundations near a protected tree may have to go deeper than a textbook depth.
- The finish local buyers expect. A Petts Wood extension is usually a bespoke kitchen, bi-fold or sliding doors, a rooflight and underfloor heating - where most of the money goes.
- Suburban London labour. Skilled BR5 trades charge London rates, without the central-London access premium but above the national average.
- Protected trees. Mature garden and street trees can carry Tree Preservation Orders, and foundations may have to be designed around their root protection areas.
For the wider comparison, our guide to single-storey rear extension costs in London sets out what the same work costs closer to the centre, where access and constraint push the numbers higher.
Where does the money end up?
On a typical Petts Wood extension, structure and enabling take about a quarter to a third of the budget, envelope and roof about a fifth, and fit-out and services a large share between them, because that is where the kitchen, the glazing and the underfloor heating live. Fees are lower here than in central London, because there is no estate to satisfy.
Where the Budget Goes on a Petts Wood Extension
Buildaway BR5 project data, 2026 - indicative split on a single-storey rear extension
Source: Buildaway 2026 project data for Petts Wood and surrounding BR5 extensions. Bars are scaled against the largest band, not against 100%.
On a 1930s house nobody has seen the original foundations, and the drains rarely match the record - so we hold a 6% to 9% contingency rather than the 5% a new-build would take. It is the difference between an honest fixed price and a running tally of variations.
How does cost change across Petts Wood?
- The original 1930s estate. The uniform garden-suburb streets under Article 4 control, where rear extensions and loft conversions dominate and front or roof changes need planning permission.
- The wider Petts Wood streets. Interwar and later houses beyond the Article 4 area, where the usual permitted development rules apply and side and rear extensions go ahead more freely.
- The Poverest and St Mary Cray fringe. A mix of interwar and post-war stock with fuller plots, where two-storey and wrap-around extensions do most of the work.
Can You Actually Extend a Property in Petts Wood?
For most Petts Wood houses, the answer is yes. This is a suburb of houses with gardens, not an estate-locked square. Most homes can extend, and many do so under permitted development - but on the original 1930s estate an Article 4 direction can pull work that is normally automatic back into the planning system, so the first step is to check exactly what applies to your address.
What permitted development allows
Schedule 2, Part 1 of the General Permitted Development Order grants houses a real set of rights: a single-storey rear extension up to 3 metres deep on a semi or 4 on a detached house, larger versions under the prior approval neighbour consultation route, two-storey rear extensions within limits, and a rear dormer loft within a volume allowance. But flats are excluded, and on the original Petts Wood estate an Article 4 direction removes some of those rights - typically for anything visible from the street - so a full application is needed where it would normally be automatic. A lawful development certificate is worth having to prove the position to a future buyer.
What Petts Wood owners build
So a Petts Wood home extension is usually one of five things. A single-storey rear extension for an open-plan kitchen. A two-storey side extension, the classic move on a 1930s semi. A loft conversion, usually a hip-to-gable with a rear dormer. A wrap-around combining rear and side. Or, for a flat, an internal remodelling that wins space without adding a square metre.
| Property type | Where you find it | What is realistically possible | Dominant constraint |
|---|---|---|---|
| 1930s semi-detached | The bulk of the estate and the wider suburb | Single-storey rear, two-storey side, hip-to-gable loft | Article 4 on the estate and the shared boundary |
| 1930s detached | The larger plots and the estate's principal roads | Rear, two-storey and wrap-around extensions | Front and roof changes controlled under Article 4 |
| Post-war house | The Poverest and St Mary Cray fringe | Rear extension, two-storey side, loft conversion | Standard permitted development limits |
| Bungalow | Scattered across BR5 | Rear extension, loft conversion, first-floor addition | Roofline and neighbour amenity |
| Larger house near the woodland | The older roads by Petts Wood and Hawkwood | Rear or side extension, loft conversion | Character and mature protected trees |
| Flat or maisonette | Purpose-built blocks and conversions | Internal remodelling in almost every case | No permitted development rights; the freeholder and lease |
If you own a flat and extension is closed to you, the money is usually better spent on the space you already have. Our guide to kitchen renovation costs in Petts Wood covers that route. Where the property is a house with roof space, a loft conversion in Petts Wood is often the cheapest way to the same bedroom.
What Consents Does a Petts Wood Home Extension Need?
A Petts Wood home extension either falls under permitted development or needs a full planning permission from Bromley. Building regulations approval is always required. On the original estate, an Article 4 direction can change which route you are on. A flat or maisonette needs the freeholder's consent, and party wall notices apply on the semis. There is no estate licence here.
Does an Article 4 direction apply to your house?
This is the first question in Petts Wood, because it decides whether your scheme is permitted development or needs a planning application. Bromley made the directions to protect the 1930s garden-suburb appearance, and they typically remove permitted development rights for changes visible from the street - porches, roof alterations, cladding, and front elevations. A rear extension hidden from public view is often less affected, but the safest first step is to ask Bromley exactly what your direction covers before you assume anything.
Conservation and the 1930s character
Whether or not an Article 4 direction bites, a Petts Wood scheme reads best when it respects the interwar character - the bay windows, hipped roofs, render and brick that give the suburb its look. Bromley expects new work to match rather than clash, and near Petts Wood and Hawkwood, the National Trust woodland on the southern edge, there may be additional controls and protected trees to design around.
Which statutory consents apply?
- Planning permission or a lawful development certificate. Where the work exceeds permitted development you need a full application; the householder fee in England is £548 from 1 April 2026. Where it is permitted development, a lawful development certificate proves the position to a future buyer.
- Article 4 directions. On the original Petts Wood estate, an Article 4 direction removes some permitted development rights - typically for changes visible from the street - so work that is automatic elsewhere needs a planning application. It is the biggest single variable in whether you need consent.
- Permitted development limits. Where they still apply, they cover a single-storey rear extension, a two-storey rear within limits and a rear dormer loft within a volume allowance - but never a flat, and reduced by any Article 4 direction.
- Listed building consent. Uncommon in a 1930s suburb but not impossible. Historic England is blunt: unauthorised work to a listed building is a criminal offence under section 9 of the Planning (Listed Buildings and Conservation Areas) Act 1990, carrying up to two years in prison or an unlimited fine.
- Party Wall etc. Act 1996. A party structure notice needs two months' notice, and an excavation notice one month. On a semi-detached house you serve the attached neighbour; a side extension near the far boundary may need the other neighbour too.
- Building Regulations. Part A covers the structure, Part B fire and escape - which matters on a loft, where a protected staircase is required - Part C ground moisture, Parts F, K and L ventilation, safety and thermal elements, and Part P the new circuits. Since April 2024 the private route is a Registered Building Control Approver.
- Community Infrastructure Levy. A scheme comes into charge at 100 m² of new floorspace, or where it creates a dwelling. Bromley charges its own CIL, and the Mayoral CIL applies on top. An extension to your own home can claim the residential exemption, but only if it is claimed and granted, and a commencement notice served, before work starts.
- Protected trees. Petts Wood's leafy roads and woodland edge mean mature trees often carry Tree Preservation Orders, and work near one needs the council's consent and, usually, an arboricultural report.
How Long Does a Petts Wood Home Extension Take?
Allow four to nine months from first call to handover for most Petts Wood extensions. On site a single-storey rear extension takes eight to fourteen weeks, a two-storey extension fourteen to twenty-two weeks, and a wrap-around with structural glazing sixteen to twenty-six weeks. The build is predictable here, because access and space are on your side. Planning and lead times, not construction, set the pace.
What Are the Hidden Costs of a Petts Wood Home Extension?
The costs that catch BR5 owners out are the design and consent layer, any Article 4 application, and the finish. Below are the twelve that turn up most often, with the impact we typically see.
| Line item | Why it applies in Petts Wood | Typical impact |
|---|---|---|
| Planning and design fees | Designer, structural engineer, and any Article 4 or heritage statement | £4,000 – £12,000 across the design team |
| Article 4 planning application | Where the estate direction pulls otherwise-permitted work into planning | £548 fee plus design time |
| Party wall surveyors | The attached neighbour on a semi, sometimes both | £2,000 – £5,000 per adjoining owner |
| Arboricultural report and tree protection | Where a protected tree sits near the works | £600 – £2,000 plus protective measures |
| Community Infrastructure Levy | Bromley CIL plus Mayoral CIL over 100 m² unless the exemption is claimed first | Avoidable in most cases, painful when the claim is missed |
| Structural glazing and rooflights | Sliding doors and lanterns are a big share of a rear extension | £6,000 – £22,000 depending on spec |
| Loft fire and escape works | A protected staircase, fire doors and mains-linked alarms on a loft | £3,000 – £8,000 |
| Ground and foundation upgrades | London clay near mature trees can mean deeper footings | £2,000 – £12,000 depending on ground |
| Kitchen and joinery | Usually a client provisional sum, and often larger than expected | £12,000 – £45,000+ as specified |
| Skip and scaffold | Skip hire, scaffold for a loft and site power across the build | Recurring across the programme |
| Making good and redecoration | Blending the new opening back into the existing house | Often underestimated |
| VAT | Standard-rated at 20%; 5% where a home has been empty two years or more | 20% of everything above |
How Do You Choose a Petts Wood Extension Contractor?
Judge a Petts Wood home extension contractor on planning fluency before you judge them on price. The contractors who finish on programme here can tell you, on the first visit, whether an Article 4 direction applies to your address, whether the rest of the scheme is permitted development, and which party wall notices your neighbour will receive. Seven questions worth asking before you compare a single number:
- Does an Article 4 direction apply to this address, and how does it change what I can build?
- Is the rest of the scheme permitted development, and will you obtain a lawful development certificate?
- How should the extension match the 1930s character - the bay windows, the roof, the render?
- If we are converting the loft, how do the fire and escape rules shape the staircase?
- Which party wall notices will my neighbour receive, and who pays for their surveyor?
- Does the quote include design fees, building control, any CIL and an arboricultural report, or are those excluded?
- Will you price against an approved scheme, or a drawing that has not been consented yet?
The last one counts. A price given before consent is a guess wearing a spreadsheet.
You can see how we work locally on our page for home extension specialists in Petts Wood, which sets out how we run a Petts Wood home extension from feasibility to handover. Our home extensions service explains the design and build stages in more detail.
Planning an extension in BR5? Buildaway handles the feasibility, the Article 4 and permitted development check, the planning application and the build as one team, with one fixed quote - conservation areas and listed buildings included.
Request a free quote →Frequently Asked Questions
How much does a home extension cost in Petts Wood in 2026?
A single-storey rear extension on a Petts Wood house costs £45,000 to £90,000. A two-storey side or rear extension costs £90,000 to £165,000. A wrap-around or large open-plan kitchen extension costs £140,000 to £260,000. A two-storey full-width extension or near-rebuild costs £230,000 to £430,000 and beyond. Per square metre, Buildaway's 2026 BR5 rates run £2,300 to £3,300 for single-storey work, £2,200 to £3,000 for two-storey work, and £2,700 to £3,800 for a structural-glazing wrap-around. These are our own quoting ranges for BR5, and they include structure, envelope, services, finishes and VAT.
Do I need planning permission for an extension in Petts Wood, or is it permitted development?
It depends on where in Petts Wood you are. Away from the original estate, most houses can extend under permitted development - a single-storey rear extension up to 3 metres deep on a semi or 4 on a detached house, a two-storey rear within limits, and a rear dormer loft. But on the original 1930s estate, Bromley has made Article 4 directions to protect the uniform interwar character, and those remove some permitted development rights, so work that would normally be permitted needs a full planning application. Always check whether an Article 4 direction applies to your address before you assume permitted development. (Planning Portal; London Borough of Bromley)
What does the Article 4 direction mean for my Petts Wood house?
An Article 4 direction removes specified permitted development rights so the council can control changes that would otherwise not need permission. In Petts Wood the directions were made to protect the 1930s garden-suburb appearance, and they typically cover things visible from the street - front porches, roof alterations, cladding and changes to the frontage - meaning those need planning permission even though they would be permitted elsewhere. A rear extension out of public view is often less affected, but the safest first step is to ask Bromley exactly what your direction covers. (London Borough of Bromley)
Do I need a party wall agreement for an extension in Petts Wood?
Only where the work is close to, or on, a shared boundary. Many Petts Wood houses are semi-detached, so a two-storey side extension, a rear extension near the boundary, or a loft cutting into the party wall brings the Party Wall etc. Act 1996 into play. A party structure notice needs two months' notice, and an excavation notice one month. Each neighbour can appoint a surveyor at your cost. A detached house set back from its boundaries may need none. (GOV.UK)
How long does a home extension take in Petts Wood?
Allow four to nine months from first call to handover for most Petts Wood extensions. On site, a single-storey rear extension takes eight to fourteen weeks, a two-storey extension fourteen to twenty-two weeks, and a wrap-around with structural glazing sixteen to twenty-six weeks. The build is predictable here because there is usually driveway access, room for a skip and, where needed, a crane. The pacing items are planning determination, which runs to eight weeks for a householder application, along with any Article 4 application, party wall awards, building control and material lead times. (London Borough of Bromley)
Do I have to pay the Community Infrastructure Levy on a Petts Wood extension?
Only where the scheme creates 100 square metres or more of new internal floorspace, or creates a new dwelling. Bromley charges its own CIL, and the Mayoral CIL applies on top because Petts Wood is in Greater London. Even where CIL is triggered, a residential extension exemption can be claimed on an extension to your own home, but it must be claimed and granted, and a commencement notice served, before work starts. Miss that sequence and the exemption is lost. (London Borough of Bromley; Mayor of London)
So What Should a Petts Wood Extension Cost You?
Petts Wood's costs are moderate for London, and the rule that shapes them most is the Article 4 direction on the 1930s estate. A cost you can predict is a cost you can plan for.
- A home extension cost in Petts Wood starts around £45,000 for a single-storey rear extension. A two-storey full-width scheme reaches £230,000 to £430,000. Per square metre that is £2,300 to £3,300 for single-storey and £2,200 to £3,000 for two-storey work. (Buildaway 2026 quoting data)
- National guidance of £1,800 to £3,000 per square metre is close to the mark here. (Federation of Master Builders)
- Check for an Article 4 direction before you ask what it costs. On the original 1930s estate, some permitted development rights are removed, so work that is automatic elsewhere needs a planning application. (Planning Portal; London Borough of Bromley)
- Budget for the design and consent layer - fees, any Article 4 application, party wall surveyors and loft fire works - which a per-square-metre rate never contains.
- Plan for four to nine months end to end. Planning and party wall awards are the pacing items, not the build.
- The strongest signal of a competent contractor here is fluency on Article 4, permitted development, the 1930s character and party walls on the first visit.
At Buildaway we price Petts Wood extensions against an approved scheme rather than a hopeful one, and we build them under one fixed quote. To talk through your Article 4 and planning position, get in touch or see the areas we cover across London.