The Complete Step-by-Step Guide to Planning a Home Extension in Dorset

(Everything you need to know before you start your project)

If you’re thinking about extending your home, you’re not alone. Across Dorset, homeowners are increasingly choosing to improve rather than move - adding valuable space, functionality, and long-term property value through thoughtful home extensions.

But where do you start? 

Planning an extension can feel daunting, especially when you’re juggling permissions, budgets, timelines, and contractors.

This guide walks you through every key stage of planning a home extension in Dorset - from your first idea to the final handover - so you can approach your project with confidence.

Step 1: Define your goals and vision

Before diving into quotes or designs, start with clarity. Ask yourself:

• What’s driving the need for more space - lifestyle, family, work, or value?

• How do you want the extension to feel and function?

• Are you adding space for living, entertaining, or working?

The clearer your vision, the easier it is to brief your builder or architect - and the better the end result will align with your lifestyle.

👉 Tip: Gather inspiration images on Pinterest and think about how the new space will connect with your existing rooms.

Step 2: Understand planning permission and building regulations in Dorset

One of the biggest early questions is: Do I need planning permission for my extension?

In many cases, you might not - thanks to “Permitted Development Rights.” However, this depends on your property type, location, and size of the proposed build.

Here’s a quick breakdown:

• Single-storey rear extensions are often permitted if they don’t exceed 3–6 metres (depending on house type).

• Side extensions must not be wider than half the width of the original house.

• Two-storey extensions or those near boundaries usually require formal planning approval.

You’ll also need to comply with Building Regulations, covering structure, insulation, drainage, ventilation, and electrical safety.

At Rooster Construction, we handle this entire process for you - from drawings to approvals - ensuring your project stays compliant and stress-free.

Step 3: Set your budget (and be realistic)

Extensions are an investment - but careful budgeting avoids unpleasant surprises later.

Average extension costs in Dorset (2025 guide):

• Single-storey extension: £1,800–£2,500 per m²

• Double-storey extension: £2,000–£2,800 per m²

• Loft conversion with dormer: £40,000–£70,000+

• Full renovation with extension: £100,000+ depending on finish

Always factor in: 

✅ Professional fees (architect, structural engineer, planning)

✅ Materials, finishes, and fixtures 

✅ Site access and waste disposal 

✅ Contingency fund (10–15% for unforeseen costs)

Rooster Construction provides detailed fixed quotes - no hidden extras, no inflated day rates - so you know exactly what your investment covers before work begins.

Step 4: Choose your builder carefully

Your builder will make or break your project.

When comparing quotes, look for more than just price. Ask about:

• Experience with similar builds in your local area

• Insurance, certifications, and references

• Communication and project management style

• Transparency around timelines and payment schedules

As a family-run Dorset business, Rooster Construction takes pride in delivering trusted, local service. Our clients choose us because we handle everything - from design and structure to finishes and landscaping - keeping your build seamless from start to finish.

Step 5: Plan your design and layout

Once your builder and budget are in place, it’s time to finalise the layout.

Think beyond square footage - focus on how the extension integrates with your home’s flow, light, and energy efficiency.

Consider:

• How will natural light enter the space?

• Does the design complement your home’s style and materials?

• Are you future-proofing (for resale, accessibility, or sustainability)?

Our in-house design and planning team at Rooster Construction helps you visualise the end result before a single wall is built - saving time and costly changes down the line.

Step 6: Secure approvals and schedule the build

Once your plans are ready, it’s time to apply for any necessary permissions.

Depending on complexity, planning approval in Dorset can take 6–10 weeks. Once approved, building control will need to inspect key stages (foundations, structure, insulation, etc.) to ensure compliance.

During this stage, Rooster Construction coordinates all parties - keeping communication clear between you, the council, and our construction team.

We also help you plan the logistics:

• Temporary access or scaffolding

• Site security and safety

• Timeline and phase breakdown

• Managing utilities (electric, plumbing, etc.)

  
  

Step 7: Construction phase - what to expect

This is where your plans become reality. 

A good builder will keep disruption minimal, provide regular progress updates, and maintain site cleanliness.

At Rooster Construction, our build process typically includes:

1. Site preparation and foundations

2. Structural work and framing

3. Roofing, insulation, and external finishes

4. Windows, doors, and interior fit-out

5. Plumbing, electrics, and heating

6. Finishes and snagging inspection

We pride ourselves on timely delivery, attention to detail, and consistent communication - so you’re never left guessing what’s happening next.

Step 8: Completion and handover

When your extension is complete, we’ll carry out a final inspection with you to ensure everything meets your expectations. We’ll also issue any necessary certificates and guarantees.

But our relationship doesn’t end there - our aftercare team is always available for future advice, maintenance, or additional projects

Final thoughts: A successful build starts with planning - and the right team

A home extension is one of the best ways to increase comfort, functionality, and property value. But success isn’t just about materials - it’s about planning, trust, and execution.

At Rooster Construction, we bring together expertise, local knowledge, and end-to-end service to make your build seamless from concept to completion.

📍 Serving Bournemouth, Poole, Christchurch, and across Dorset 

📞 Contact our team today to book your free on-site consultation and turn your home extension ideas into reality.