How Long Does It Take to Build a Granny Annexe?
After cost, timescale is usually the next big question families ask — particularly if there's some urgency behind the project, such as an elderly parent needing to move in sooner rather than later. The honest answer is that it depends on your specific project, but there are clear stages you can plan around, and a realistic overall timeframe to expect.
We build granny annexes and garden annexes for families across Essex and Hertfordshire, as well as the rest of the UK, and we always talk clients through a realistic timeline at the very start of the process — because knowing what to expect at each stage makes the whole project far less stressful.
The stages of a granny annexe build
1. Initial consultation and site survey
This is where we visit your property, carry out a full site and garden survey, and discuss your requirements — size, layout, specification, and how the annexe will be used. This stage also establishes the groundworks needed and the logistics of connecting power, water and sewage.
2. Design and specification
Once we understand your plot and requirements, we work through the detailed design together — room layout, kitchen and bathroom specification, cladding, doors and windows, heating and lighting. This stage typically involves some back-and-forth as the design gets finalised.
3. Certificate of Lawful Development application
As covered in our previous posts, most granny annexes are built under the Caravan Act and need a Certificate of Lawful Development rather than full planning permission. We submit and manage this application on your behalf. Timescales for council determination vary, but this route is generally significantly faster than a full planning application, usually a maximum of 12 weeks.
4. Groundworks and foundations
Once the CLD is granted, work begins on-site — starting with groundworks and foundations, and establishing the necessary utility connections.
5. Construction
The main build phase — structure, roofing, doors and windows, and first-fix electrics and plumbing.
6. Interior fit-out
Kitchen and bathroom installation, flooring, decoration, second-fix electrics, heating and lighting.
7. Snagging and handover
A final check to make sure everything's finished to standard, followed by handover — at which point your annexe is ready to be lived in.
So how long does the whole process actually take?
From initial consultation through to a finished, move-in-ready annexe, most projects take around 12–16 weeks for the build itself once work starts on-site, depending on size, complexity, weather and daylight hours. On top of that, you'll want to factor in time for the design stage and the Certificate of Lawful Development application before construction begins.
Altogether, most families should realistically plan for a few months from first enquiry to moving in, rather than expecting it to happen in a matter of weeks — though a straightforward project with a decisive client and an accessible plot can often move through the process more quickly than a larger, more bespoke build.
What can affect the timeline?
Design complexity. A straightforward, standard layout moves through design and construction more quickly than a highly bespoke design with unusual configurations or multiple storeys.
Council response times. While the Certificate of Lawful Development process is generally faster than full planning permission, different councils can vary in how quickly they process applications.
Site conditions and access. A straightforward, accessible plot with services nearby will generally move faster through groundworks than a more challenging site.
Decision-making speed. Projects tend to move fastest when specification decisions (kitchen, bathroom, finishes) are made promptly, rather than being revisited partway through the build.
Weather. As with any construction project, groundworks and external building work can be affected by prolonged bad weather, particularly over winter months.
Can the process be sped up?
To some extent, yes — the biggest lever most families have is decision-making speed during the design stage. The faster your specification is finalised, the sooner the CLD application can go in and construction can start. Choosing a builder who manages the planning application efficiently (rather than leaving you to navigate council paperwork yourself) also helps avoid unnecessary delays.
If timing is a genuine priority for your family — for example, planning around an elderly parent's care needs — it's worth flagging this clearly from the first consultation, so the whole project can be planned with that timeline in mind from day one.
Planning around your family's needs
Because granny annexes are so often built to support a specific family situation — an ageing parent, a health need, an adult child's housing situation — timing isn't just a logistical detail, it's often central to why the project matters. We always try to understand the full context behind a project, not just the specification, so we can be realistic (and honest) about what timeline is genuinely achievable.
The bottom line
Most granny annexe builds take around 12–16 weeks on-site, with additional time upfront for design and the Certificate of Lawful Development application — meaning a few months overall from first enquiry to move-in is a realistic expectation for most families. Getting a clear, honest timeline from your builder at the outset, rather than an overly optimistic one, is what actually helps you plan with confidence.
Need a realistic timeline for your granny annexe or garden annexe project? Get in touch with Mobile Annexe Ltd for a free consultation. We build across Essex, Hertfordshire and the rest of the UK, and we'll give you an honest, realistic timescale based on your actual project — not just a generic estimate.
📞 07770 365734 ✉️ enquiries@mobileannexe.com
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