How long do house extensions take to complete?

Starting a house extension project is a thrilling journey that holds the potential to revolutionize your home environment.

 However, it also comes with its share of complexities, particularly regarding timelines. Understanding how long your house extension might take is crucial for planning and managing expectations. This post dives deep into the factors influencing the duration of extension projects, aiming to provide a comprehensive overview for homeowners.

Preparation and Consultation: 2-4 Weeks

Every successful house extension begins with meticulous preparation. During this initial phase, homeowners should define their vision, set a budget, and prioritize their needs. Consulting with architects and obtaining multiple quotes is essential. This stage is also the time to discuss your project with local planning authorities to understand any specific requirements or restrictions. A thorough approach in these early weeks can significantly streamline the later stages of your extension project.

Design Phase: 2-5 Weeks

Upon selecting your architect, the design phase commences. If existing property drawings are available, the design process can start immediately. Otherwise, commissioning a measured survey to obtain these crucial measurements might extend this timeline. The design phase is foundational, setting the stage for planning applications and the construction work that follows.

Planning and Permissions: 8-10 Weeks (Potentially Longer)

Securing planning permission is often the most variable phase, with timelines stretching from 8 to 10 weeks or even longer, depending on the complexity of your extension and local authority processing times. Factors such as site conditions, the property’s location (e.g., conservation areas), and specific local authority requirements can all impact this duration. Engaging an architect skilled in navigating planning applications can mitigate potential delays.

Technical Design and Building Regulations: 1-2 Months

Following planning approval, detailed technical designs, including structural engineering plans and compliance with building regulations, are developed. The complexity of your extension and the responsiveness of your chosen professionals can influence how long this takes. Proactively selecting your structural engineer and other necessary consultants during the planning phase can expedite this process.

The Tender Process: 2-4 Weeks

Choosing the right builder is critical. The tender process involves submitting your detailed plans to various contractors to receive accurate quotes. This phase is not just about finding a cost-effective solution but also ensuring the chosen contractor understands your vision and can deliver quality work within agreed timelines.

Construction Phase: 2-4 Months (And Beyond)

The actual build is where your vision starts to become a reality. The duration here varies widely depending on the extension’s size, complexity, and unexpected challenges like adverse weather or discovering unsuitable ground conditions. Large extensions, those with significant structural changes, or projects that include intricate architectural features will invariably take longer. Efficient and experienced contractors can help mitigate some delays, but a buffer for unforeseen challenges is wise.

Post-Construction: Several Weeks

After the main construction is complete, there’s still work to be done. Snagging — the process of identifying and fixing minor issues — and obtaining the necessary completion certificates from local authorities are final, crucial steps. Ensuring everything is up to standard before making the final payments to your contractor is essential.

Managing Delays

Delays can, and often do, occur. Weather, supply chain issues, and unexpected structural challenges can all impact your timeline. Effective communication with your contractor and a clear contract that outlines how delays will be managed can help keep your project on track.


In essence, the duration of a house extension project can vary significantly, often ranging between 7 to 15 months or more, depending on numerous factors. By understanding each phase and the potential for delays, homeowners can better prepare for the journey ahead. It’s also crucial to have a contingency plan and budget to accommodate unforeseen challenges.

Considering an extension project? Don’t hesitate to reach out for a detailed quote. At Muirfield Construction, we’re committed to turning your vision into a reality with our expertise and dedication to quality. Our team is ready to guide you through each step of your project, ensuring a smooth and satisfactory journey to expanding your living space. Reach out to us now to discover how we can make your ideal extension a reality.