The process

The 8 steps from idea to builder starting on site

Step 1

Establish your planning route

Before you speak to a builder, draw anything, or spend any money, you need to know which of the three planning routes applies to your extension. This single decision determines everything that follows.

To establish your route, you need to know: your property type (detached, semi, terraced, flat); whether your property is in a conservation area, AONB, or listed; the proposed depth of any rear extension; whether any previous extensions have already been added to the property; and the proposed width of any side extension relative to the original house width.

Don’t assume. The most common and expensive mistake on extension projects is assuming PD applies (or doesn’t) without checking. Previous extensions count against your PD allowance. Conservation areas remove PD rights for side extensions. New build properties may have planning conditions that restrict what you can build. An architectural designer checks all of this as a matter of course — a builder generally does not.

💡 Free check available: Call us or use our PD checker tool. Establishing your planning route takes minutes and costs nothing. It is the single most important thing you can do before starting any extension project.

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Step 2

Appoint an architectural designer and agree a fixed price

Once you know your planning route, you need an architectural designer (also called an architectural technologist or architectural technician) to produce the drawings. For most householder extensions, you do not legally need a RIBA-registered architect — an experienced architectural designer produces the same drawings at lower cost.

What to look for when choosing an architectural designer for an extension:

• Fixed price agreed in writing upfront — avoid hourly rate arrangements for standard extension drawings
• Experience with your local council — someone who knows what Middlesbrough, Stockton, or Redcar & Cleveland planning officers expect will get your application right
• A track record of approvals — ask for the approval rate on submitted applications, not just examples of drawings
• The full drawing package included — confirm that site location plan, block plan, existing AND proposed plans and elevations are all included in the price
• Planning application management included — the designer should submit to the council on your behalf and monitor the application through to decision

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Step 3

Site survey — accurate measurements of the existing property

Your architectural designer visits your property to carry out a measured survey. This is the foundation of the entire drawing package — and it is where poor-quality services cut corners. A proper site survey involves measuring all relevant dimensions of the existing house: floor plans for all affected floors, all external elevations, ridge and eaves heights, boundary distances, and any existing extensions or outbuildings.

Why this matters more than you might expect: Planning applications that use incorrect existing dimensions — which typically happens when designers work from estate agent floor plans or unverified owner measurements — fail in one of two ways. Either the council notices the discrepancy between the drawings and what actually exists, leading to an invalid application. Or the discrepancy isn’t noticed at planning stage but emerges when building control inspects the build, causing expensive remediation.

For two storey rear extensions, the survey must also precisely measure the distance from the rear wall to the rear boundary — the 7 metre boundary rule for PD eligibility depends on this measurement. For loft conversions, the survey establishes the existing ridge height — which determines the maximum permitted height of any dormer or roof alteration.

💡 What to prepare for the site survey: Clear access to all rooms the designer needs to measure, access to the loft if a loft conversion is proposed, and knowledge of where the rear boundary fence is (in gardens where this isn’t obvious). The survey typically takes 45–90 minutes for a standard semi-detached house.

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Step 4

Design development and draft drawings

Your architectural designer produces the full set of planning drawings: existing floor plans and elevations, proposed floor plans and elevations for all affected floors, site location plan, and block plan. For two storey extensions, a design and access statement may also be produced. For extensions in conservation areas, additional heritage justification documents may be required by the council.

Draft drawings are shared with you for review before anything is submitted. This is your opportunity to make changes — internal layout adjustments, window position changes, roof form decisions — while the cost of revision is minimal. Once drawings are submitted to the council, changes become more expensive and time-consuming.

Key things to check on draft drawings before signing off:

• The existing plans accurately reflect your home as it currently stands
• The proposed extension is the size and shape you discussed
• Internal room layouts work as you intend
• Window positions, sizes, and opening directions are correct
• The roof form (pitched or flat, ridge height) matches your expectations
• Materials noted on the drawings match what you plan to build

💡 Design decisions that matter for planning approval: Materials are the most common reason for planning conditions. Specify matching brick, roof tile, and window styles explicitly in the drawings and your application is less likely to face a materials condition or pre-commencement discharge requirement. Your designer should advise on this.

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Step 5

Planning application submission — and what happens next

Once you’ve approved the drawings, your designer submits the planning application via the Planning Portal (planningportal.co.uk) — the national online system for submitting planning applications in England. The application includes the drawings, a completed application form (the 1APP householder form), ownership certificates, and the application fee.

The application fee from 1 April 2026 is £528 for a householder application in England. Prior Approval applications (Larger Home Extension Scheme) cost £120. Lawful Development Certificate applications cost £258. These fees are paid directly to the council at submission and are separate from your designer’s fee. (all excluding VAT)

After submission, the council validates the application — checking that all required documents are present and correct. Validation typically takes 1–5 working days for straightforward applications. Only once the application is validated does the statutory 8 week clock start.

Once validated, the council issues a case officer, publishes the application online, and sends neighbour notification letters to adjacent properties. Neighbours have 21 days to submit comments. Statutory consultees (highways, drainage, heritage) may also be consulted depending on the nature of the proposal.

💡 Track your application: Every council publishes planning application details online. Once you have your application reference number, you can track the status, view uploaded documents, and read any comments submitted — on your council’s planning portal. Your designer should send you the reference number on the day of submission.

⚠️ No free resubmission: Since December 2023, all English councils have removed the “free go” for planning applications. If your application is refused, resubmitting costs another £528. This makes getting the application right first time — with drawings that address the council’s known assessment criteria — significantly more important than it was before 2023.

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Step 6

Planning officer assessment and decision

A planning officer is assigned to your application and carries out a site visit — typically within 2–4 weeks of validation. They assess the proposal against the Local Plan policies, the National Planning Policy Framework, and any relevant supplementary planning documents. For householder applications, this almost always happens under delegated powers — meaning the officer can make the decision themselves without referring to the planning committee.

What the officer is assessing:

• The visual impact on the street scene and the character of the area
• The effect on neighbouring properties — loss of light, overlooking, overbearing impact
• The scale of the extension relative to the original house
• The materials and design quality
• Highway and parking implications where relevant
• Heritage impact if the property is listed or in a conservation area

Most well-prepared householder extension applications receive a grant of planning permission within the 8-week statutory window, often with one or two conditions attached (commonly: materials to match; obscure glazing to specified windows; no further extensions without prior approval). These conditions are generally straightforward to comply with.

If the officer has concerns: They may contact your designer to discuss minor amendments before issuing a decision. Since councils removed the free go in December 2023, most councils are more cautious about allowing amendment discussions — they may simply decide the application as submitted. This is another reason why getting the design right before submission matters more than it used to.

The national approval rate for householder applications in England in 2026 is approximately 83%. Well-prepared applications in straightforward suburban locations have significantly higher approval rates than this average — the 17% refusal rate is weighted towards conservation area applications, listed buildings, and poorly prepared submissions.

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Step 7

Building regulation drawings — the technical stage

Planning permission is granted. You now need a completely separate set of documents before your builder can start: building regulation drawings and building control approval.

What building regulations cover — and why they’re completely different from planning drawings:

Planning drawings show what the extension looks like from the outside. Building regulation drawings show how it is constructed on the inside. They are detailed technical documents covering:

• Structure:foundation depth and type; structural calculations for any beams, lintels, or steel work; floor construction
• Thermal insulation:U-values for walls, roof, and floor to meet Part L (energy efficiency); specification of insulation materials and thickness
• Fire safety:30-minute fire-rated construction where required; mains-wired smoke alarms; fire doors on habitable rooms connected to the main house
• Ventilation:Part F ventilation requirements; background ventilators, extract fans, and trickle vents
• Drainage:connection of any new rainwater drainage and foul drainage to the existing system
• Damp proof course:DPC installation and connection to the existing house DPC
• Accessibility:Part M threshold levels and access considerations

Building regulation drawings are submitted to building control — either your council’s building control department, or a private Approved Inspector. Building control issues an approval notice (typically 5 working days for a Full Plans application) and then carries out inspections at key stages during the build.

Timing: You can apply for building regulations approval in parallel with the planning application — this is worth considering on straightforward projects to save time. Most homeowners, however, wait for planning approval before commissioning building regulation drawings, to avoid paying for drawings if planning is refused.

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Step 8

Construction, inspections, and completion certificate

Once building regulations are approved, your builder can start on site. Building control will carry out a series of inspection visits at the key stages of the build — you (or your builder) must notify building control before each stage is covered up:

• Commencement notice:notify building control when work starts on site
• Excavation inspection:before foundations are poured — the building control officer checks depth and bearing capacity
• Foundation inspection:concrete poured and ready, before backfilling
• DPC inspection:damp proof course installed at low-level
• Structural frame inspection:any steel beams or lintels in place, before wall construction covers them
• Insulation inspection:wall and roof insulation in place before plasterboard is fixed
• Drains inspection:new drainage laid before backfilled
• Completion inspection:all works complete — building control officer walks around and signs off

On satisfactory completion, building control issues a completion certificate. This is one of the most important documents the project produces — it confirms the extension was built to building regulations standard and is required by solicitors and mortgage lenders when you sell or remortgage. Keep it with your property documents.

Construction timescales: A single storey rear extension typically takes 8–16 weeks to build from groundworks to completion, depending on size and specification. A two storey extension takes 12–20 weeks. A loft conversion with dormer takes 6–10 weeks. These are realistic timescales for 2026 — homeowners who are told a project can be completed in 4–6 weeks should treat this with caution.

⚠️ Don’t skip building control inspections: If your builder covers up work before building control inspects it, the inspector may require it to be uncovered at your expense. More significantly, without a completion certificate, you cannot sell or remortgage the property without either obtaining a retrospective regularisation certificate (expensive, not always possible) or taking out indemnity insurance (an ongoing cost and flag for buyers).