How Long Does a Home Extension Take in Greenwich?
A Realistic Timeline

If you've typed "how long does a home extension take" into Google recently, you've probably come back with answers ranging from four months to over a year which isn't exactly useful when you're trying to plan your life around building work in Greenwich. The families extending Victorian terraces behind Greenwich Market, or adding rear extensions to the larger period houses off Crooms Hill and Maze Hill, face a very specific set of local variables that no generic UK guide ever addresses.

Greenwich's planning rules are among the most stringent in South East London. The Royal Borough sits entirely within the World Heritage Site buffer zone established around Maritime Greenwich a UNESCO designation that extends Ordinary planning scrutiny into something considerably more demanding. On top of that, the Greenwich Conservation Area covers a vast swathe of SE10's most sought-after streets, Article 4 Directions have removed PD rights across significant parts of the borough, and the Royal Borough's conservation officers are among the most active in London. Extension proposals that would sail through in a neighbouring borough often attract detailed design commentary in SE10.

This guide breaks the full timeline down phase by phase from first design meeting to final Building Control sign-off with the real Greenwich-specific figures you need to plan properly.

What's the Full Timeline for a Home Extension in Greenwich?

For most Greenwich properties the Victorian terraces off Greenwich High Road and the streets around East Greenwich, the larger period houses on Maze Hill and Crooms Hill near the park, and the Edwardian semis toward Charlton a standard single-storey rear extension runs between 6 and 10 months from first consultation to handover. A double-storey build adds three to five months on top of that.

The construction phase is only one part of the picture. Planning applications, structural calculations, party wall matters, and building regulations approval all sit in the calendar before groundworks begin. Most Greenwich homeowners underestimate this pre-build period by two to three months largely because the UNESCO buffer zone layer and the depth of conservation area assessment in SE10 aren't apparent until the planning process is already under way.

Here's how those months break down across the seven main phases:

Before committing to a timeline, understanding the cost picture is equally useful. See our guide on how much a home extension costs in Greenwich → Full cost guide for a breakdown of what to expect at each build stage in SE10.

Phase 1 Design, Feasibility & Planning Prep (3–6 Weeks)

This phase is where Greenwich projects most consistently run into their first avoidable delay. It covers the period from your first conversation with an architect to the moment the application is formally submitted and in SE10, it routinely takes longer than anywhere else in this part of London.

What actually happens in this phase

Your architect will carry out a measured survey, develop concept drawings, and produce the planning drawings the Royal Borough needs to assess your application. A rear extension in a location outside the Greenwich Conservation Area might get through this in four to five weeks. A project within the conservation area which covers almost all of the historic SE10 core, from the streets around Greenwich Market and the Cutty Sark, out along Crooms Hill and Maze Hill toward Blackheath needs six to seven weeks minimum. And because the majority of SE10's most attractive residential streets sit within the World Heritage Site buffer zone, a World Heritage Site Statement is frequently required on top of the standard Heritage Statement and Design and Access Statement before the Royal Borough will validate the application.

Greenwich's pre-application advice service is one of the most valuable in South East London for this very reason. A planning officer's early view on how your proposal sits within the World Heritage Site setting, and what design adjustments the council is likely to require, is worth considerably more here than in a borough where the planning environment is less layered.

The Greenwich planning context you need to know

The householder planning application fee is £206 as of 2025 (Royal Borough of Greenwich). Your architect's time to prepare drawings, Heritage Statements, and where required a World Heritage Site Statement is additional and in Greenwich often more involved than in neighbouring boroughs.

Unsure whether your project sits within the World Heritage Site buffer zone, or which design requirements apply to your SE10 address? Our guide on planning permission for a home extension in Greenwich → Full planning guide covers the key thresholds specific to the Royal Borough.

Phase 2 Royal Borough of Greenwich Planning Permission (8–13 Weeks)

Once submitted, the Royal Borough targets a decision within eight weeks from the date your application is validated not the date you submitted it. Validation is the council's check that all required documents are present and correctly formatted, which takes one to two weeks after submission.

In practice, budget ten to thirteen weeks between submission and a decision in SE10. This is longer than the equivalent outer London borough timeline, and the reason is structural: World Heritage Site buffer zone applications involve a mandatory consultation with Historic England, which the Royal Borough must accommodate within its assessment process. Applications that trigger Historic England commentary even supportive commentary can run to thirteen weeks before a decision letter is issued.

How the Royal Borough planning process actually works

• Validation (1–2 weeks): The Royal Borough checks all documents including any required World Heritage Site Statement are complete before formally registering the application. Missing documentation specific to the WHS buffer zone resets this clock.
• Neighbour consultation (21 days): Statutory requirement. On Greenwich's tightly packed Victorian terrace streets, objections from adjoining owners are not uncommon and are taken seriously by the case officer.
• Historic England consultation (where applicable): Applications within the World Heritage Site buffer zone that affect its setting are referred to Historic England. This is a parallel process but it adds to the overall assessment period.
• Decision: Most Royal Borough householder applications are determined under delegated officer authority rather than at a planning committee making outcomes predictable when submissions are thorough, the design rationale addresses both conservation area and WHS requirements, and the Heritage Statement is substantive.

The permitted development position in Greenwich

If your rear extension falls within PD limits 3 metres deep for an attached house, 4 metres deep for a detached Prior Approval applies rather than a full planning application, with a statutory 42-day decision deadline. That's a meaningful time saving in theory.

In Greenwich, the practical availability of this route is limited. The Greenwich Conservation Area removes PD rights for most visible external alterations in the historic SE10 core. Article 4 Directions in parts of the Royal Borough remove further PD categories. And any extension in the World Heritage Site buffer zone that affects its setting may require assessment regardless of whether the works would otherwise qualify for PD. Verify your specific address before designing around Prior Approval.

Phase 3 Building Regulations, Party Walls & Pre-Construction (4–8 Weeks)

A planning approval letter doesn't mean construction can begin. Two further processes sit between your decision and the first day on site and in Greenwich, where party wall obligations are essentially universal on terrace stock, both need to be initiated as soon as planning approval arrives.

Building Regulations approval covers structural and safety compliance: foundations, steelwork, insulation values, fire separation, drainage. Your builder and structural engineer submit Full Plans to the Royal Borough's Building Control team or a licensed approved inspector. Initial approval typically takes four to eight weeks depending on complexity and current caseload.

The Party Wall Act applies to the overwhelming majority of rear extensions on Greenwich's Victorian terrace stock the streets off Greenwich High Road, Trafalgar Road, the roads around Greenwich station, and the Victorian terraces of East Greenwich. Any extension within 3 metres of a shared or neighbouring foundation requires a Party Wall Notice served at least two months before work starts.

When a neighbour disputes a party wall notice and appoints their own surveyor, add four to eight weeks to pre-construction and expect costs on both sides. According to RICS guidance on the Party Wall Act, disputed notices are among the leading causes of pre-construction delay on London domestic projects. On SE10's dense terrace streets, it's a real and regular risk.

Phase 4 Construction: What Gets Built and When (12–24 Weeks)

Here's where visible progress happens. Construction runs from groundworks through to snagging and depending on the type and scale of the extension, it takes between 12 and 24 weeks once work starts on site.

The build moves through distinct stages in a logical sequence:

• Groundworks and foundations (Weeks 1–3): Excavation, concrete pour, and drainage connections. SE10 sits on Thames Terrace gravel in parts and London Clay in others the difference matters for foundation design and should be established by a structural survey before drawings are finalised. Weather sensitivity is real; groundworks started in December or January in waterlogged London Clay carry more programme risk than a spring start.
• Structure goes up (Weeks 4–7): Blockwork, structural steelwork where required, roof structure, and external walls. Conservation area projects in SE10 that specify matching stock brick, lime mortar, or heritage-grade render take slightly longer in this phase than standard material builds lead times on these materials need to be factored into the pre-build programme.
• Weathertight (Weeks 8–10): Roof covering, windows, and external doors installed and sealed. Once weathertight, internal work proceeds independently of weather a significant milestone that keeps the build on track through autumn.
• First fix (Weeks 11–13): Electrical wiring, plumbing pipework, and central heating installed before plasterboard goes up. Getting service routes right at this stage avoids costly remedial work later.
• Plaster, insulation and second fix (Weeks 14–15): Walls and ceilings take final form. Skirtings, sockets, switches, and kitchen or bathroom fittings where applicable.
• Decoration and snagging (Weeks 15–16): Final finishes, tiling, decoration, and Building Control sign-off.

For a standard single-storey rear extension on a Greenwich residential property, on-site construction typically runs 12–16 weeks. A double-storey extension extends this to 18–24 weeks. Conservation-specification materials for SE10 terrace projects matching stock brick, lime render, heritage glazing should be ordered during the design phase, not after planning, to avoid a structural-phase hold. (Source: Checkatrade; Buildaway project experience)

Considering single or double storey? See our comparison of single storey vs double storey extension for Greenwich for the full timeline and cost breakdown.

What Actually Delays a Greenwich Home Extension?

Every extension encounters a delay somewhere. In Greenwich, four causes account for the large majority of overruns on SE10 projects and the first is unique to this postcode in South East London.

The World Heritage Site layer. Greenwich is the only borough in this part of London where a UNESCO World Heritage Site designation actively shapes residential extension assessments. Homeowners who don't know their property sits within the buffer zone which is most of SE10's historic residential fabric discover it when the Royal Borough requests a World Heritage Site Statement after submission. Adding this document mid-assessment extends the validation period and resets the decision clock. Producing it during the design phase, before submission, is the only way to avoid that delay.

Conservation area requirements underestimated. The Greenwich Conservation Area appraisal is detailed and actively applied. Extensions proposing materials, proportions, or roof forms that conflict with the period character of the host building attract requests for further information from the Royal Borough's conservation team extending the decision period from eight weeks to thirteen. Working with an architect who has read the Greenwich Conservation Area appraisal before producing drawings, and who treats the Heritage Statement as a substantive design document rather than a checklist, eliminates this risk almost entirely.

Party wall notices served too late. Greenwich's Victorian terrace stock the rows around East Greenwich, the streets off Trafalgar Road, and the terraced roads between Greenwich station and Deptford triggers party wall obligations on almost every rear extension. The two-month notice period is a legal minimum, and it doesn't start until the notice is formally served. Homeowners who finish the planning process and then begin party wall discussions face a mandatory wait at the point they most want to move. Serving the notice the day planning approval arrives is the practice that keeps SE10 projects on programme.

Late material decisions on conservation-specification builds. Matching stock brick, lime-based mortar, heritage-grade sash windows, or conservation-approved render for a SE10 Victorian terrace typically requires four to six weeks of lead time from order to delivery. Leaving these decisions until the structural phase is under way creates a programme hold that is entirely avoidable. Specifying materials during the design phase before planning is submitted allows delivery to coincide with the start of the structural works.

When Is the Best Time to Start a Greenwich Home Extension?

The short answer: start your planning and design in September or October, target a planning submission in November, receive your decision in January or February, and break ground in March or April.

Spring is the best construction window in SE10. Soil conditions improve after winter, daylight extends, and a full dry season ahead gives the structure the best opportunity to reach weathertight before autumn. There's also a practical reason to plan well ahead good builders working across SE10 and neighbouring SE3, SE7, and SE12 postcodes book six to ten weeks ahead through the spring and summer peak. Starting your design process in autumn lets you confirm a contractor and lock in a start date before that window closes.

One Greenwich-specific addition: if your project requires conservation-specification materials matching brick, lime mortar, or heritage glazing placing orders during the design phase rather than after planning keeps the structural timeline intact from day one.

Putting It All Together

A Greenwich home extension is a more involved process than in most neighbouring postcodes but it's entirely achievable when the planning is done properly at the outset. The honest summary for SE10 projects:

• Single-storey rear extension in Greenwich: 6–10 months total from first consultation to handover
• Double-storey extension: 10–15 months greater structural complexity and extended planning scrutiny
• World Heritage Site or conservation area position: Add 5–7 weeks to design prep, produce the WHS Statement during design not after submission, and allow 10–13 weeks for a planning decision
• Party wall obligations: Universal on terrace stock serve the notice the day planning approval arrives; disputed notices add 4–8 weeks
• Best start time: Design in autumn, submit in November, break ground in spring

At Buildaway, every Greenwich project runs with a single point of contact one person who coordinates your architect, structural engineer, building control officer, and on-site team. No chasing separate contractors. No gaps between phases. A clear timeline and a project that completes when it's supposed to.

Once you understand the timeline, the next step is understanding the costs. See our full breakdown of home extension costs in Greenwich for a realistic budget picture across all extension types in SE10.