So, How Much Does a Garden Annexe Cost

A garden annexe typically costs from around £27,000 fully installed for a compact open-plan layout, rising to roughly £59,500 or more for a larger two-bedroom design, with most fully self-contained annexes landing somewhere in between depending on size, layout and fit-out. That figure includes the insulated building, internal walls and the base, but the kitchen, bathroom and connections to services are usually costed separately, which is exactly where many people underestimate the total. This guide breaks down what drives the price so you can budget realistically.

A garden annexe is a fully self-contained living space in the garden, with its own sleeping, living, kitchen and bathroom areas, built to be lived in all year round. From working with families planning annexes, we’ve found the headline building price is only ever part of the conversation, because the cost of making it genuinely habitable, the kitchen, the wet room, the services and the groundwork, is what shapes the final budget. Understanding those layers early is the difference between a realistic plan and a nasty surprise.

What the base price actually includes

Our annexe prices start from around £27,000 inc VAT for an open-plan layout of roughly 6.4m x 3.3m, fully installed. That price covers the parts that make it a proper building rather than a shell. You get fully insulated 70mm composite walls in a choice of four colours, double-glazed PVCu windows and doors with Low-E argon-filled units, composite internal partition walls to create a bathroom space, a black EPDM rubber roof with 100mm insulation, five pre-routed sockets with spotlights, wiring and a fuse box, a 43mm Styrofloor insulated floor, and the base itself built on treated timber joists on concrete posts. VAT and full installation are included.

In other words, the base price gives you a warm, weatherproof, electrically wired and partitioned building, ready for the rooms to be fitted out inside. What it does not include is the kitchen, the bathroom fittings, and the connection of water, drainage and a dedicated electrical supply, which is where the next layer of cost comes in.

The fit-out is where budgets move

This is the part people most often miss, so it is worth being clear. A shower and kitchen fit-out is a significant cost on top of the building. As a real reference from our own range, shower and kitchen units fitted to an annexe, including fixtures, fittings, pipework and the electrical connections to a water heater, shower, extractor and towel rail, run to around £15,800 to £18,640 inc VAT depending on the layout. Luxury vinyl flooring throughout adds roughly £1,520 to £3,040, and air conditioning, which we usually recommend for year-round comfort, adds around £2,040 for a single unit up to £5,760 where several are needed.

In our experience, fitting the kitchen and bathroom through the supplier as part of the build works better than arranging it separately afterwards because the pipework, electrical connections and partition layout are all designed together from the start, rather than retrofitted around a finished shell. Doing it piecemeal almost always costs more in the end and risks compromises in the layout. It is not the only way to do it, and some clients prefer to fit out themselves, but for most people the joined-up route is smoother and more predictable.

Real examples to budget against

Because every annexe is configured differently, the most honest way to understand cost is through real completed layouts. A 1-bedroom annexe at 8m x 3.3m comes in from around £32,000 inc VAT for the building. A separate living and bedroom layout at 8m x 4.2m is from around £41,050. A 1-bedroom L-shaped design at 6.5m x 6.5m is from around £43,000, and a 2-bedroom L-shaped at 9.7m x 6.5m from around £59,500. Larger luxury builds with wet rooms, canopies and decking can run to £64,000 to £65,000 and beyond once fully fitted.

These are building and base prices, so remember to layer the fit-out, flooring, air conditioning and service connections on top to reach a true all-in figure. The armoured cable connection and the water and sewer connections are not included in any of these, because those costs vary entirely with the distance from your home to the annexe.

The costs people forget

A few items sit outside the building price and catch people out, so factor them in from the start. Connecting electricity via armoured cable and connecting water and drainage both depend on how far the annexe sits from existing services, so a position close to the house keeps these down. Groundwork beyond the standard base may be needed on difficult plots, though our no-dig base approach using a treated timber and concrete-post system keeps this simpler than a full concrete raft. And if you want decking, canopies or extra insulation to the base, these are priced as add-ons.

There is also the approval process to budget for, which leads to the most important cost consideration of all.

Planning, approval and why it affects cost

An annexe someone will actually live in is treated very differently from a garden room used as an office, and this affects both cost and timescale. For annexes, we generally recommend building under the Mobile Homes Act rather than relying on permitted development, and we work with the National Annexe Providers Consultancy on this. Obtaining a certificate of lawfulness from the council can take around ten weeks and carries a fee, so it needs to be built into both your budget and your timeline.

Getting this right is not optional, because an annexe built on the wrong basis can create problems with the council and with council tax later. It is always worth checking your specific plans against the official guidance on the Planning Portal and taking the recommended approval route from the outset. The reassurance of a building designed to last, backed by our guarantee, matters most on a structure intended for long-term living.

Payment, delivery and getting an accurate quote

We ask for a 50% deposit to begin production, with the balance due on completion, and delivery is typically within four to six weeks, free within a 70-mile radius of our EN2 0QX base, which covers St Albans and the wider area. Because the all-in cost depends so much on layout, fit-out and your site, the only truly accurate figure is a quote built around your actual plans.

If you are weighing up an annexe, the best next step is a conversation about what you need and where it will go. You can read more about our granny and garden annexes, request a callback at a time that suits you, or call us on 07816 898512 to talk through a realistic budget.

You can also browse finished annexes and walkthrough videos on our Facebook page and YouTube channel.