Architect Drawings for House Extensions & Renovations (UK): What You Need, Costs, and How to Get Them

Thinking about a house extension or full renovation? At some point you’ll be asked for architect drawings. But what exactly are they, do you always need them, and how much should you expect to pay in the UK? Here’s a clear, practical guide from the build team at Clarkson Construction.

Already have your plans in place? Get in touch to start breaking ground.

A contemporary double-storey rear extension by Clarkson Construction, featuring open-plan living, full-width sliding doors and architectural glazing — designed to maximise light and connection to the garden.

What are architect drawings — and why do they matter?

Architect drawings are scaled plans, sections and elevations that communicate how your extension or renovation will look and be built. Good drawings help you:

• Get accurate quotes (not guesswork).

• Secure planning permission (where required).

• Comply with Building Regulations.

• Avoid costly on-site decisions and re-work.

• Keep everyone — you, the designer, the builder, and Building Control — on the same page.

Tip: For straightforward projects, you might only need a measured survey and planning drawings; for complex structural changes, you’ll typically also need Building Regulations drawings and structural calculations.

Planning drawings vs Building Regulations drawings (what’s the difference?)

• Planning drawings show the overall concept — layouts, size/mass, external appearance, and how the extension relates to neighbours/streetscene. They support applications for householder planning or to confirm permitted development.

• Building Regulations drawings go deeper into technical detail: foundations, insulation, fire safety, structure, drainage, ventilation, U-values, etc. They’re checked either by Local Authority Building Control or an Approved Inspector.

  
  

Many homeowners think one set of drawings “does both”. In practice, planning drawings get you permission, while Building Regs drawings tell the builder how to build it.

Do I always need architect drawings for an extension?

Short answer: almost always — especially when adding floor area or altering structure.

• Simple internal refurb (like redecorating or replacing a kitchen in the same footprint) typically doesn’t require formal drawings.

• Removing structural walls, adding bi-folds, converting a loft, garage conversions, single/double storey extensions, or reconfiguring layouts benefit massively from drawings and structural calcs.

• If you’re applying for planning permission, your council will require drawings that meet its validation checklist.

  
  

Typical UK costs for architect drawings (realistic ranges)

Every project is unique, but these ballpark figures help you plan:

• Measured survey: £300–£950+ (size/complexity dependent)

• Planning drawings for a single-storey extension: £900–£2,200+

• Double-storey or complex geometry: £1,800–£4,500+

• Building Regulations drawings & notes: £1,200–£3,000+

• Structural engineer (if needed): £450–£1,500+

• Planning fees: typically ~£258 for householder applications in England (plus site notice/printing/validation extras)

• Building Control fees: vary by council/inspector and project value

Cost-saving tip: A well-coordinated design + build workflow can reduce duplication and speed approvals.

How long do architect drawings take?

• Measured survey: 1–3 hours on site; 3–10 working days for CAD.

• Planning drawings: 1–3 weeks (revisions add time).

• Planning decision: 8 weeks typical (householder), longer if amended.

• Building Regulations package: 1–3 weeks after planning sign-off.

• Build start: after Building Control acceptance and tendering.

  
  

Start the design phase early — it’s the cheapest time to make changes.

The step-by-step process (what to expect)

1. Discovery call & brief — goals, budget, constraints, timeline.

2. Measured survey — accurate dimensions and levels captured.

3. Concept & layouts — options to choose from.

4. Planning drawings & application — council submission if required.

5. Building Regs drawings — detailed construction notes and specs.

6. Structural design — beams, lintels, load paths, padstones.

7. Tender pack — drawings + scope + specification for builders.

8. Construction — site setup, inspections, sign-offs.

   
   

What should good architect drawings include?

• Accurate existing and proposed plans, elevations and sections

• Dimensions, levels, and gridlines

• Material call-outs and key details (insulation, DPCs, lintels)

• Openings schedule (windows/doors)

• Drainage and ventilation notes

• Fire safety measures and escape strategy

• Thermal performance notes (Part L)

• Acoustic considerations (where relevant)

  
  

The goal is clarity. The more that’s clear on paper, the smoother (and cheaper) it is on site.

Do I need an architect, or can a designer/technologist do it?

In the UK, architects, architectural technologists, and experienced designers can prepare drawings.

What matters is:

• Proven residential experience with extensions/renovations

• Evidence of planning approvals and Building Regs compliance

• Ability to coordinate structural engineers and Building Control

• Drawings that builders can actually build from

  
  

If you want a seamless journey from concept to completion, a design-informed builder like Clarkson Construction can coordinate the whole process and de-risk the build.

How can Clarkson Construction Ltd help?

We’re a specialist renovation and new-build contractor. If you already have drawings, we’ll price and build them. If you don’t, we can coordinate a measured survey, produce planning and Building Regs drawings, manage structural design, and provide a fixed, transparent build quote — all in one joined-up process.

• Renovations & extensions: kitchens, open-plan spaces, rear/side/double-storey

• Loft and garage conversions: habitable rooms, dormers, en-suites

• New builds & investor projects: programme, cost control, quality delivery

  
  

Enquire now to book a site visit and get your project moving or view all our projects here.

FAQs: Architect Drawings for Extensions & Renovations

Do I need architect drawings for a single-storey rear extension?

Almost always. You’ll need planning or permitted development drawings to show massing and elevations, plus Building Regs drawings for insulation, structure and drainage.

How much do architect drawings cost in the UK?

For a typical extension, budget £2,100–£5,500+ across survey, planning drawings, Building Regs drawings and structural calcs. Complexity and revisions affect cost.

Can I build from planning drawings alone?

We don’t recommend it. Planning drawings lack the detail a builder needs to price and build accurately. Use Building Regs drawings to avoid surprises.

How long does it take to get drawings done?