How much does a granny annexe cost?

The short answer

From £54,000 to £90,000 including VAT, as a self-build kit.

A granny annexe — also called a granny flat, or simply a garden annexe — is a self-contained building in the garden of an existing house, with its own bedroom, kitchen and bathroom. What it costs depends on how big it is and on how much of the work you take on yourself.

We sell it as a kit with the engineering already done. The three published sizes are:

28 m² — Studio, home office, or a compact one-bed annexe. £54,000

35 m² — A comfortable one or two-bed annexe. £72,000

45 m² — A genuine two-bed annexe with room to breathe. £90,000

All three include VAT. These are consumer prices, and the number shown is the number you pay for the kit.

What is in the price

The kit is a weathertight, insulated shell on an engineered foundation — not a bare frame, and not a finished house. It covers:

• Ground screw foundation and precision steel ring beam — screws installed by our approved installer
• Insulated beam and block floor system
• Full ICF wall system, Building Regulations compliant
• Windows and doors, fitted openings, precast lintels
• Roof structure, insulation and EPDM weatherproof covering
• Soffit, fascia and guttering
• Internal partition walls and plasterboard, ready for your own finish
• Full drawings, staged build sequence and wait periods
• Video instruction library

What is not in the price

These are left out deliberately rather than to make the headline figure look smaller. They are the parts where your taste and your budget should decide, not our production line:

• External cladding or render
• Electrics, plumbing and heating
• Kitchen and bathroom
• Decoration
• Drainage and utilities connections

Drainage, utilities and heating are quoted separately once your site has been assessed. How far the annexe sits from the house, the fall across the garden and what you are connecting into all change that number, and a single figure quoted before anyone has walked the site would be wrong for most plots. There is more on this in our frequently asked questions.

Optional extras

Published for the same reason as everything else on this page — so you can budget before you enquire rather than after.

Staged delivery £5,000

Ground and lawn protection £850 – £950

Underfloor heating upgrade from £4,300

If you would rather not build it yourself

Solvere, our sister company, will take the whole job — built and project managed start to finish. A 45 m² managed build is £129,995 including VAT, and the two smaller sizes are priced on application. The target programme is 28 days, which is a target we work to rather than an average we have measured.

It costs more than the kit. It is a real alternative rather than an upsell — if you already have a builder you trust, use them.

How this compares

A traditionally built annexe of the same footprint is usually more, because the foundation is excavated and poured and the shell is built wet on site. A factory-finished pod is often less, but arrives with its specification already decided for you and is a lighter form of construction.

This sits between the two on purpose: a solid reinforced concrete wall with insulation permanently on both faces, on a foundation wound into the ground rather than dug, with the last twenty per cent of the specification left to you. What you are buying is the difficult engineering, done — and the freedom to spend the rest of the budget where you actually want it.

The costs beyond the building

Worth budgeting for from the start, and none of them are ours:

• A householder planning application, which a self-contained annexe needs — see planning permission for an annexe.
• Building control, either your local authority or an approved inspector, who signs the finished building off.
• Council tax, which may be banded separately once the annexe is finished — see annexe council tax.
• Your own fit-out: kitchen, bathroom, cladding and decoration.