How long do house extensions take

The Timeline For Your House Extension
- By An Industry Expert

Posted by Craig | Updated May, 2024 | 10 Min Read Time

At a glance 

  • As a rough estimate, your house extension could take anywhere between 6 – 12 months


In this article, you’ll find the following:

    • An explanation of different stages that are involved in a house extension 
    • Hurdles you may have to overcome for your extension to stay on your predicted timescale

Greetings, dear homeowners and aspiring renovators! For many of us, extending our home isn’t just about adding extra space. It’s about enhancing our living experience, improving our property’s aesthetic appeal, and increasing its market value.

One crucial step in this process is to be aware of the common mistakes to avoid when planning a house extension, ensuring your project runs smoothly and meets your expectations.

However, before you dive into this transformative journey, it’s prudent to understand the timeline you might be looking at and to plan ahead based on my extensive experience in the industry, here’s a detailed timeline to guide you through the process of extending your house.

A side angle photo of a resent ground floor extension

As A Rough Estimate, Your House Extension Could Take Anywhere Between 6 - 12 Months To Complete

This is subject to planning and neighbourly permissions going ahead without delays

Wondering whether you have enough time this year to go ahead with your house extension?

1. Preparation and Planning Stages (12 - 19 weeks)

2. Building Preparation (2 - 4 weeks)

Before any brick is laid or a blueprint is drawn, you need to do some groundwork (quite literally!). Begin by setting a clear budget. Understand your motivations – are you looking for extra living space, a design overhaul, or a seamless transition to your garden?

Familiarising yourself with the typical house extension timeline is essential, as it helps manage expectations and plan for stages from design to completion.

Once you have a clearer picture, you can start scouting for architects. I always recommend shopping around, getting multiple quotes, and assessing portfolios. This initial groundwork will generally span a couple of weeks.

Design (2 - 5 weeks)

Once you’ve chosen your architect, it’s time to dive into the design process. If you already possess existing property drawings, you’re in for a smoother ride. Otherwise, you might need to commission a measured survey to get the necessary dimensions for your extension.

Planning (8 - 10 weeks)

Ah, the planning stage. This is where patience becomes a virtue. The bare minimum for awaiting planning approval is between 8-10 weeks, but sometimes it could be more. Keep an eye out for any Permission Conditions that accompany your approval. Remember, your project won’t get off the ground until these are sorted.

An oversized ground floor extension on Collyer Road

2. Technical and Legal Aspects (1.5 - 5 months)

Technical Design (1 - 2 months)

Once you’ve received the green light for your plans, you’ll wade into the technicalities of building. This step entails understanding building regulations and consulting a structural engineer – these are the folks ensuring your new space won’t come tumbling down. Depending on the company, you could be looking at a 2-month wait. 

Party Wall Agreements (1 week - 3 months)

Depending on your property and the nature of your extension, you might need a Party Wall Agreement. This can be straightforward, taking just a week if you’re fortunate. However, if disagreements arise or consent isn’t promptly given, brace yourself for a longer haul.

Tender Process (2 - 4 weeks)

In simpler terms, this phase is all about hiring your builder. I suggest reaching out to multiple contractors to gauge prices and evaluate their past work. Visiting properties they’ve worked on and speaking to previous clients can give you a better sense of their expertise and reliability.

We recommend reaching out to your local building authorities to obtain the precise requirements and regulations for your house extension, ensuring you have all necessary planning in place.

Building Work (2 - 4 months)

Now, for the grand finale! The duration of the building phase hinges on the size of your extension and its intricacies. For instance, if you’re incorporating substantial glazing, it will naturally require more time.


Every house extension is unique, and while this guide offers a structured timeline, always remember the golden rule: *understanding the process is crucial*. By familiarising yourself with what to expect, you’re better equipped to make informed decisions and address potential hiccups. Here’s to a successful house extension journey!

If you are still interested in finding out more about house extensions, consider reading our blog on >> Do house extensions add value


Craig Smith

The founder of CJ Smiths Construction Company for over 14+ years and a proud citizen of St Albans City.

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