Building work is rarely straightforward. Even a standard home extension can involve up to five statutory consents. Managing these properly is key to keeping projects on time and on budget.
That’s why we offer a free Zoom consultation for homeowners — to help you understand the process before you commit to your project.
👉 Book a free discovery call here to talk through your ideas and get a clearer picture of what’s involved.
Whether you’re dreaming of a light-filled kitchen extension, a loft with a view, or rethinking your entire layout, carrying out private residential refurbishments and extensions is a big undertaking. It’s costly, time-consuming, and often stressful. The construction industry is complex and fragmented, and without the right guidance, projects can quickly become overwhelming.
A good architect helps untangle all of this — ensuring your vision is realised with fewer surprises, better coordination, and more confidence.
The Three Phases of a Successful Home Project
We divide the project process into three clear stages, aligned with the RIBA Plan of Work:
1. Design Stage (RIBA Stages 0–3)
Here we work together to define your brief and develop a design that reflects your needs, aspirations and budget. This includes everything from initial concept sketches to submitting your Planning Application and acting as your ‘agent’ through the planning process.
2. Detail Stage (RIBA Stages 3–4)
We help with preparation of the technical drawings and documents needed for Building Control and other approvals, and for your builder to price the works accurately.
3. Construction Stage (RIBA Stages 4–6)
This includes working with you on the appointment of your builder, coordinating site works, and ensuring all compliance is met through to the completion of your.
The 5 Key Statutory Consents (That Often Catch People Out)
Depending on your project, the following consents might be required:
1. Planning Permission
Most extensions and lofts will require formal planning approval. Even if your proposals fall under Permitted Development, we recommend a Certificate of Lawfulness is applied for instead, to ensure the Council agrees. Getting the application right the first time is key to avoiding delays later.
2. Building Control Approval
Most projects will also require Building Regulations approval. A ‘Full Plans’ submission is recommended to catch design or compliance issues before works start on site.
3. Thames Water Build Over Agreement
If your project is within 3 metres of a shared sewer, you’ll need permission from Thames Water. This usually involves:
- A CCTV drainage survey and report
- Architectural or design drawings of your proposals for Thames Water approval
- A formal application
4. CDM Health & Safety Compliance
Under the Construction (Design and Management) Regulations 2015, sets out criteria requiring most domestic projects to require a ‘Principal Designer’ to coordinate the health and safety aspects of your project during the design and construction stages.
5. Party Wall Awards
If your works affect a shared wall, boundary, or nearby structure, you’ll likely need to serve Party Wall notices to your neighbours. If they ‘dissent’, you’ll need a Party Wall Award with each relevant neighbour from a party wall surveyor.
Important to note - As the homeowner, you’re legally required to have someone act on your behalf to manage Building Control and Health & Safety design compliance (known as CDM). These are two separate roles, but confusingly, both are called “Principal Designer.”
Your architect can take on both roles — but only if they’re appointed through to the end of the project. If not, someone else needs to step in. This could be your contractor, but make sure they have the right Professional Indemnity Insurance to cover it.
Yes, it’s confusing. Yes, it’s fragmented. That’s why it helps to have someone experienced by your side.
+ Additional Consent for Leaseholders: Freeholder Consent
If you own a leasehold property, you’ll almost certainly need formal written consent from your freeholder before carrying out any alterations — including extensions, loft conversions, or internal reconfigurations.
This is not a statutory planning consent, but it is a legal requirement under the terms of your lease. Failing to get it can cause problems down the line, especially if you plan to remortgage or sell.
Key points:
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It usually involves a formal application with drawings
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Some freeholders charge fees for reviewing or granting consent
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It’s advised to check the lease early — some leases prohibit certain alterations outright
Budgeting Your Project: Two Ways to Look at It
Method 1 – Budget-first:
- Start with your available capital
- Then deduct the following:
- 10% for contingency
- 15% for fees and surveys
- 20% for VAT on construction
- The remainder is your construction budget before VAT - and this is the figure that most builders will give you.
Method 2 – Cost-first:
- Estimate build costs:
- Rear extension: £1,800–£3,500/m² + VAT
- Loft conversion: £1,500–£2,500/m² + VAT
- Interior refurb: £500–£1,600/m² + VAT
- New kitchen £10,000–£50,000 + VAT
- Each new bathroom or shower room £5,000–£15,000 + VAT
- Multiply total area by these rates and add kitchen, bathrooms and shower rooms as required
- Multiply the result by a factor of 1.6 to cover fees + VAT + contingency
Whichever method you use, it’s essential to understand your total capital expenditure before diving into detailed design.
Other Services That May Be Required
Depending on complexity, your project might also need:
- A measured survey
- Structural engineer (for steel design, calcs & drawings)
- Specialist supplier’s information: Drawings and specifications from specialists contributing to the design and construction of your project
- Quantity Surveyor: For managing costs on larger/complex jobs
- Interior design, visuals, and VR: Optional, but powerful for decision-making
Typical Timelines
Here’s a guideline summary of typical time requirements for each step of your project. It might easily take between 6 and 9 months to progress from the start of a design to being ready to start work on site.- Design Stage: 1-2 months
- Planning Permission Process: 3 months including time for ‘validation’ and decision
- Detailing for Building Control and Tender Pack for Builders: 1-2 months
- Confirming a price with a builder and scheduling in the start of construction: 1-2 months+++
- Construction: 3-18 months be pending on the size and scope of the project
A Little Known Item…Your Insurance!
Before construction begins, make sure you have the right insurance. Check your builder has the appropriate insurance cover but this will not cover everything, so it is highly recommended you have your own. Some policies can be extended to cover home renovations, or you can take out a specific contract works policy. Your architect or builder can advise.
Final Thoughts
Your home is likely your most valuable asset — financially and emotionally. Extending or renovating it should be exciting, not overwhelming. Having a qualified, experienced architect by your side not only improves outcomes but saves time, stress and costly mistakes.
If you’re thinking about making changes to your home and want to understand the process properly:
👉 Book a free discovery call here to talk through your ideas and get a clearer picture of what’s involved.
Good luck with your project, and enjoy the process.
Thanks for reading
Phil
DesignBox Architecture
