Who this guide is for
- Homeowners planning a home extension
- People wanting to anticipate build stages
- Anyone coordinating an extension project
- Those briefing a builder or architect
Groundwork and structure
Extensions typically begin with site preparation and groundwork, followed by the structural elements that everything else relies on. This foundation stage sets up the rest of the build.
Structural and groundwork stages must be handled by qualified professionals, since they are safety-critical.
- Site preparation first
- Groundwork and foundations
- Structural elements follow
- Handled by qualified professionals
Envelope and weathertightness
Once the structure is up, the focus moves to making the extension weathertight, including the roof, walls and openings. Reaching weathertightness is a key milestone that enables interior work.
The order within this stage follows what must be sealed before the next step.
Services and first fix
With the shell weathertight, services such as electrical and plumbing are typically routed before surfaces are closed up. This first-fix stage happens before finishes go on.
All services work must go to qualified trades, and the sequence ensures access while walls are open.
- Services routed before closing up
- First fix before finishes
- Access while walls are open
- Qualified trades for all services
Finishes and fit-out
The final stages cover plastering, finishes, fit-out and connecting the extension to the existing home. These follow once earlier stages are complete and access is no longer needed behind surfaces.
Use this sequence to anticipate phases, and rely on your professionals for the actual schedule and any specifics.
Extension sequence checklist
- 1Understand that stages depend on each other
- 2Expect groundwork and structure first
- 3Look for the weathertight milestone
- 4Plan services before surfaces close up
- 5Sequence finishes after first fix
- 6Coordinate connection to the existing home
- 7Route structural and services work to professionals
- 8Rely on professionals for the actual schedule
Common mistakes to avoid
- Expecting finishes before the shell is weathertight
- Closing up walls before services are in
- Underestimating the groundwork stage
- Treating the sequence as fixed in duration
- Overlooking the connection to the existing home
- Attempting structural or services work without trades
When to involve a professional
- Structural and services work must go to qualified professionals
- The actual sequence varies by project and property
- Timelines vary widely and are not fixed
- Safety-critical stages need qualified trades
- Requirements vary by location
Frequently asked questions
Questions readers ask about this topic
What is the typical order of an extension build?
Generally site preparation and groundwork, then structure, then making the extension weathertight, followed by services first fix and finally finishes and fit-out. Each stage depends on the one before, but the actual sequence and timing should be planned by professionals.
How long does an extension take?
Durations vary widely by project, property and many factors, so this guide describes the order of stages rather than timings. Rely on your builder and professionals for realistic scheduling for your specific extension.
Why does sequence matter?
Each stage tends to depend on the previous one, such as services going in before walls are closed up. Following a logical sequence keeps access available when needed and avoids costly rework, which is why the order is important.
Can I do parts of the build myself?
Structural, services and other safety-critical work must go to qualified professionals. This guide is an educational overview of the sequence; the actual build and any specialist stages should be planned and carried out by qualified trades.
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