Due to their bespoke construction, it can be difficult to determine exactly how long an annexe building will take from initial consultation to finished product, but a timescale of between three and eight months is to be expected.

Developing any habitable building, from a small garden room to a two-floor annexe, requires a lot of work, regulatory compliance and planning approval, but the results are very much worth it if you know what you want and you have a plan for the extra space.

Whilst far from a new concept, the idea of multi-generational homes where children, parents and grandparents live under the same roof has become increasingly desirable, and with more space often equating to significantly higher house valuations, an annexe could be a sensible financial choice.

However, quality takes time to build, and it is important to have realistic timescales for the creation of your annexe building, as well as how these timescales can vary depending on whether you opt for a modular prefabricated structure or a more bespoke design based on specific needs.

Typical Timescales For An Annexe Building

These timescales do not take into account adjustments, additional consultation meetings and other delays, but provide an outline of how long each stage is expected to take. Some of these stages overlap, meaning that the final timescales can be less than this:

  • Initial Enquiry and site survey – One to two weeks.
  • Finalising design and ordering components – One to two weeks.
  • Planning permission – Between eight and 13 weeks.
  • Construction of parts – Four to six weeks.
  • Site preparation – One to two weeks.
  • Delivery – One to two weeks.
  • Installation, finalising and connecting utilities – Two to three weeks.
  • Total timescale from initial consultation to completion – Four to eight months.

Do You Need Planning Permission For A Garden Annexe?

One of the biggest variables when it comes to house extensions, especially garden annexes, is planning permission, which can add up to 16 weeks of extra time whilst applications are examined by the local planning authority.

It depends largely on the scale of development, and whether it fits into one of five categories:

  • Permitted development – No time
  • Most types of development – Eight weeks
  • Development which requires technical details consent – Ten weeks
  • Major development – 13 weeks
  • Development applications subject to Environmental Impact Assessments – 16 weeks

We can help with this by designing the optimal garden annexe in a way that minimises the planning process as much as possible; in many cases, even a two-storey granny annexe can be developed as a permitted development depending on your local planning authority.

What Can Speed Up The Annexe Building Construction Process?

The four-to-eight-week timescale is somewhat broad, and there are many cases where the construction process takes significantly less time, something that is often compounded when there is a lack of planning hurdles to have to jump over.

Whilst there are a lot of streamlining factors, here are the ones that have the biggest impact on construction schedules:

  • Using prefabricated components – Relying on factory-built components means that they may be immediately available rather than having to be constructed to order.
  • Standard or modular designs – Being able to use pre-built and easy-to-assemble assets is far quicker than bespoke buildings.
  • Easy garden access – The easier it is to deliver components and clear the space, the less time it takes to start building.
  • Easy utility connections – If your electrician can easily wire up the new building, it significantly saves time before you can move in.
  • Ordering out of season – If you order your annexe building from now up to the start of spring, you avoid the peak demand and have shorter lead times.
  • Responding quickly to enquiries – As with any other planning project, having paperwork and responses in order rapidly speeds up the process.

What Can Slow Down The Annexe Building Construction Process?

The timescales above assume relatively typical conditions, but not every garden is the same, and each project needs to be managed on a case-by-case basis.

Because of this, here are some factors that can extend the construction process, besides extended planning delays:

  • Complex gardens – if it is hard to get people and equipment into the back garden, it can lead to delays as alternative methods are developed.
  • Utilities installation – If you need to extend the cables to wire up the granny annexe, this can take longer and require specialist help.
  • Poor drainage – If you need to build nonstandard foundations, it will take far longer to build the annexe.
  • Personalisation – If your annexe building is a one-off, it may take longer to fabricate the needed components.
  • Peak season – If you order in summer, there may be a lack of manpower that delays your start date.
  • Weather delays – Heavy rain, wind or snow can slow down or stop a construction site.