How Long to Build a Ground Floor Extension?
The duration of a ground floor extension can vary depending on design, complexity, and site conditions. Below is a step-by-step breakdown of the main stages, based on years of experience building premium home extensions across Nottinghamshire and Derbyshire.
1. Design and Planning (3 - 8 weeks)
Every successful ground floor extension starts with a strong foundation and we’re not just talking about concrete. Before any building work begins, your ideas need to be translated into precise, buildable plans that comply with building regulations and reflect both your practical needs and aesthetic vision.
This initial phase is more than just drawing lines on a page. It’s where you define how your new space will work for your lifestyle whether that’s creating a bright open-plan kitchen for entertaining, adding a utility room to streamline family life, or making room for a downstairs bedroom or home office. This phase includes:
- Initial design consultation
- Architectural drawings
- Site surveys
- Floorplan development
If you want a spacious kitchen-diner with roof lanterns and sliding glass doors, these choices affect design time. TNBC provides full in-house design services, which reduces waiting time and eliminates miscommunication.
2. Planning Approvals and Pre-Construction Setup (2 - 4 weeks)
With your extension design now agreed, the next step is turning those drawings into formal permissions and preparing everything behind the scenes for a smooth start on site. This phase is crucial—it ensures that the project is fully compliant, legally sound, and ready to break ground without setbacks.
Depending on the size, location, and features of your extension, you may or may not require planning permission. Many single-storey ground floor extensions fall under permitted development rights, which can speed things up significantly. However, for larger builds, those in conservation areas, or homes with previous extensions, a full planning application may be needed. Once designs are approved, we handle:
- Planning permission (if required)
- Building regulations submission
- Party wall notices (if applicable)
- Project scheduling and risk assessment
For permitted development extensions, we can often begin sooner. Still, submitting a Lawful Development Certificate can protect you during future home sales.
3. Foundations and Groundworks (1 - 2 weeks)
This phase marks the beginning of physical construction and sets the literal foundation for everything that follows. While it may not be the most visually exciting stage, groundworks are critical to the strength, safety, and longevity of your extension. Getting it right now avoids costly issues later. Groundworks and foundations typically include:
- Site preparation and clearance – Removing turf, plants, debris, and any existing outbuildings or hardstanding in the way
- Excavation – Digging precise trenches to the correct depth for your foundation type, based on ground conditions and building regulations
- Setting out – Marking the layout of the extension on-site, ensuring everything aligns perfectly with the approved plans
- Pouring foundations – Usually trench-fill concrete, but may involve reinforced pads or piled foundations on difficult soil
- Drainage installation – Diverting or extending existing soil pipes, adding new connections for kitchen or bathroom waste, and ensuring compliance with building control
- Damp-proofing and oversite preparation – Installing damp-proof courses, membranes, and insulation beneath the concrete floor slab
At TNBC, we begin every project with a detailed site assessment to plan for these variables and set a realistic timeline. Our groundwork team works closely with structural engineers to ensure the correct type of foundation is chosen and installed safely and efficiently.
While this stage is often overlooked, it’s where your home extension earns its long-term reliability. A well-built foundation means no shifting walls, no cracking floors, and no problems with damp. It’s the invisible strength that supports your home’s comfort and structure for decades to come.
By the end of this phase, your extension will be ready for brickwork to begin. Concrete is curing, drainage is in place, and the layout of your new space is visible etched into the footprint of your home’s future.
4. Main Structural Build (3 - 5 weeks)
This is the stage where your extension begins to take shape in a visible, tangible way. After weeks of design, planning, and groundwork, the main structural build is where the new part of your home rises from the foundations—walls go up, the roof is constructed, and the space starts to feel real. This stage includes:
- External walls
- Roof structure (pitched, flat, or warm roof)
- Windows and door openings
- Structural supports (steel beams if needed)
The main structural build is one of the most exciting parts of the project for homeowners. You can walk through the space, get a sense of scale, and begin to visualise how each area will be used. For larger extensions, this stage may also involve the creation of vaulted ceilings, gable ends, or architectural features that give the extension its character.
Timing during this stage depends on size, design complexity, and weather. For example, a basic rear extension will progress faster than a wraparound build that interfaces with multiple elevations of the home.
TNBC’s project managers coordinate all trades onsite, ensuring materials arrive on time and that bricklayers, roofers, and structural specialists work efficiently together. Our commitment to tight scheduling and clear communication helps keep this phase within its expected timeline 2minimising disruption while maintaining construction standards.
5. Internal Works - First Fix (2 - 3 weeks)
With the structure watertight and the roof complete, the focus shifts inside the extension. This phase commonly known as the first fix is where the essential infrastructure of your new space is installed. It's less about visual transformation and more about laying the groundwork for a fully functional, modern living environment. This phase includes installing:
- Electrical wiring and sockets
- Plumbing and pipework
- Internal stud walls and insulation
This stage is critical because any design oversight now—like forgetting to allow for enough plug sockets or underestimating heating requirements—can cause delays or costly alterations later. That’s why TNBC encourages early decisions around kitchen layouts, appliance placement, and lighting preferences well before this phase begins.
Although much of the work during first fix is eventually hidden behind plasterboard or beneath flooring, its accuracy and quality are vital. Everything needs to be precisely measured and positioned so that the second fix (the stage where visible fittings are installed) can happen smoothly.
TNBC uses clear site documentation, approved technical drawings, and rigorous trade coordination to keep this phase efficient. By having electricians, plumbers, and framers working from a shared plan—and under one project manager—we avoid clashes and backtracking that often cause delays in multi-contractor builds.
By the end of the first fix, your extension has moved from an empty shell to a fully serviced structure. Though the transformation may not be visible yet, it's the essential layer that supports every light switch, warm floor, and water flow your family will use every day.
6. Interior Finish - Second Fix (3 - 4 weeks)
Once the internal wiring, plumbing, and walls are in place, the build enters one of the most exciting phases for homeowners—the second fix. This is where your extension begins to look and feel like a finished part of your home. Fixtures are installed, surfaces are smoothed and decorated, and the layout becomes liveable, not just structural. The second fixes include:
- Electrical fixtures – light fittings, switches, sockets, extractor fans, under-cabinet lights
- Plumbing connections – sinks, taps, radiators, toilets, and kitchen or utility appliances
- Internal doors and architraves, as well as skirting boards and window sills
- Flooring – whether it's engineered wood, porcelain tiles, LVT, or carpet
- Final kitchen and utility room fitting, including units, worktops, splashbacks, and integrated appliances
- Wall finishes, such as plastering, painting, tiling, or decorative panelling
- Add-ons such as built-in storage solutions, feature lighting, smart thermostats or home controls, accent wall treatments or splashbacks
During this stage, the design choices made early in the project come to life. The colour palette, lighting layout, flooring materials, and finishes all contribute to the final atmosphere of the space—whether you're going for warm and welcoming, sleek and modern, or family-friendly and durable.
TNBC works closely with you and our trusted suppliers to ensure that all fixtures are ready on site at the right time. We schedule trades in sequence to avoid overlap and delays—plasterers finish before decorators begin, and flooring is laid once all heavy work is complete.
By the end of the second fix, your ground floor extension will look polished and ready to use. Unlike earlier stages that focused on what goes behind the walls, this one brings tangible satisfaction—you’ll see your space completed with your personal style and practical needs embedded into every detail.
7. Final Touches and Sign-Off (1 week)
After weeks of planning, building, fitting, and decorating, your extension is nearly ready to welcome you in—but before that happens, there’s one last, essential step: final touches and sign-off. This concluding phase ensures that everything meets not just your expectations, but also legal building standards and TNBC’s own high-quality benchmarks During this final stage, we focus on:
- Snagging inspections – We walk through the entire extension, checking for minor imperfections such as paint touch-ups, loose fittings, door adjustments, or finish inconsistencies.
- Client walkthrough – You’ll be invited to review the space with us and raise any concerns or final requests.
- Professional cleaning – Our team ensures the area is fully cleaned, dust-free, and presentable, ready for immediate use.
- Final sign-off with Building Control – A local authority inspector or approved inspector visits to ensure that all work complies with UK Building Regulations. Once passed, you’ll receive an official completion certificate.
- Handover of warranties, guarantees, and manuals – You’ll be given full documentation covering structural works, appliances, window glazing, electrics, and any specialist installations.
This phase might only take a few days, but it carries significant importance. A proper snagging and handover process separates a rushed project from a professionally delivered one. It’s also an opportunity for you to feel confident that everything is finished not just to a good standard—but to a standard you’re proud to show friends and family.
At TNBC, we don’t consider a project finished until the client is genuinely satisfied. From the first brick to the last clean surface, your peace of mind matters. That’s why our final inspection is thorough, client-focused, and honest so when we hand over your new space, it's ready for life, not just for photographs.
By the end of this phase, your ground floor extension is complete, compliant, and move-in ready. Whether it’s a stylish new kitchen-diner, a quiet family lounge, or a spacious utility room, everything is in place built with care, finished with precision, and delivered by a team that values every detail.
Total Estimated Duration: 10 to 16 weeks for most ground floor extensions.
CONTACT THE NOTTINGHAMSHIRE BUILDING COMPANY
