How to buy a garden room: step by step, from first enquiry to sign-off

Most garden rooms are bought from the firm that designs and builds them, but it isn’t the only route. The difference between the three is how much of the project the seller takes on, and so how much is left to the buyer.

Annexe buyers follow a different sequence, because a self-contained annexe always needs formal approval: see how to build a granny annexe.

Start with finished buildings rather than brochures. The directory of companies links each one to the projects the Guide has featured, which show how they build, what their interiors look like and how they handle difficult gardens. Brochures fill in the ranges and prices (brochure requests), and a show site or a past customer’s room shows the quality of the finish in a way photographs can’t.

Check early that a company works in your area, because not all of them cover the whole UK. It is also reasonable to ask for a ballpark price at this stage, giving the size and the main features. Many modular companies have online design tools that price a room as it is configured, and the price calculator gives a guide figure for any size before any company is contacted.

Most buyers take three or four companies through to a design consultation. Fewer gives little to compare, and more takes a lot of time for little extra. Consultations are usually free and carry no obligation. A few companies charge for an in-person visit and refund the fee if the room is ordered.

The consultation can happen at a show site, at home or by video call. Either way, the designer will want to know how the room will be used, which features matter and what the budget is. Sharing the budget lets them design to it, and pictures of rooms the buyer likes, or doesn’t, save a good deal of explaining.

An in-person survey is worth insisting on. Some companies survey from photographs, video and measurements sent in by the buyer, but if the site turns out to be different on installation day, the cost of putting it right usually falls on the buyer.

After the consultation, the designer prepares floor plans and elevations, often with 3D visuals, and a specification and quote. Some build a 3D model into a photograph of the buyer’s own garden, which shows the room at its true size from the spot it will be seen from.

Each quote should come with drawings, a specification and a price. Compare them line by line rather than on the total, because two quotes for rooms of the same size can include quite different things. The items most often left out are the foundations, the electrical connection, delivery beyond a set distance and VAT.

The warranty matters as much as the price. Cover varies: some companies pass on the manufacturers’ warranties for materials such as the roof membrane and glazing, while others also cover their own workmanship, such as cracks in plastered walls. An insurance-backed warranty keeps that cover in place if the firm stops trading.

How a company has dealt with the enquiry so far is a fair guide to how it will run the project. After Crusoe Garden Rooms met a Derbyshire client, they returned a revised plan within two days, fully itemised, with a fixed price and a build date.

Before ordering, check that the drawings, specification and quote match everything agreed, because changes after production starts are harder and dearer to make. The order confirms the design, the payment schedule and an expected installation date.

A deposit is due on ordering, often 25–50% of the price. Some companies take a smaller reservation payment first, typically £100–£500, to hold an installation slot while the order is finalised or planning permission is sought. It is worth asking whether that payment is refundable.

There are two common ways to protect a deposit. Many established companies offer deposit insurance, which covers the money if the firm stops trading before the room is delivered, though on larger projects the deposit can exceed the cover limit. Paying by credit card brings protection under Section 75 of the Consumer Credit Act, for purchases with a cash price between £100 and £30,000.

Most garden rooms don’t need planning permission, because they are built under Permitted Development. The rule that shapes most designs is height: within 2m of a boundary, the room can be no taller than 2.5m. Listed buildings, conservation areas, National Landscapes and National Parks have tighter rules, and some homes have had their Permitted Development rights removed. The builder should advise, but responsibility for the building being lawful rests with the homeowner.

Where permission is needed, the council’s target for a decision on a householder application is eight weeks. Many companies prepare and submit the application themselves; others leave it to the buyer or bring in a planning consultant. Garden Spaces’ Cambridge gym needed permission because it sits close to the boundary with a pitched roof, and they prepared the application with images showing the finished building in the garden, which help both the planning officer and the neighbours picture it.

Even where Permitted Development applies, a Lawful Development Certificate confirms in writing that the room is lawful, which helps when the house is sold. Building Regulations don’t usually apply to a garden room, with three exceptions: a room over 30sqm, a room used for sleeping and a room over 15sqm within 1m of a boundary.

These are the rules in England. Wales is similar, and Scotland and Northern Ireland have their own.

Once the order is placed, the room goes into production. Most companies make the panels or sections in their own workshop or factory and assemble them in the garden. Others build entirely on site, which suits bespoke designs and gardens with difficult access. A few deliver a finished building on a lorry and crane it into place.

From order to finished room typically takes 6–8 weeks for a pre-designed building, 8–12 weeks for a modular one and 12 weeks or more for a bespoke design. The time of year makes a difference too, as busy companies book installation slots further ahead.

A stage payment is usually due just before the team arrives, and it is normally the largest of the three.

Installation starts with the foundations. Most garden rooms now stand on ground screws, which need no concrete and suit sloping ground; concrete pads and slabs are the alternatives. The structure, roof and cladding follow, then the interior finishes and the wiring.

How long the team is on site depends mostly on how much of the room is made beforehand. Cabin Master’s year-round garden bar was installed in two days by their own team. Crusoe Garden Rooms spent two weeks on site for their Derbyshire client, Vita Modular’s Rugby office took three weeks with the electrics included, and Swift Unlimited’s Cornish office, on a sloping garden, took three and a half.

The room arrives wired inside, but it still has to be connected to the house supply, usually by a cable laid in a trench. With a turnkey service, the builder’s own electrician makes that connection, as Cosy Garden Rooms did on their London terrace project, so the room is ready to use as the team leaves. Many companies don’t include it, and the buyer arranges a local electrician once the room is built.

Where it isn’t included, the connection typically costs £1,500–£3,500, depending mainly on the distance from the house. The installation must be certified by a qualified electrician, and the certificate belongs with the house’s paperwork.

Before the team leaves, walk round the room inside and out with them. Check that the doors and windows open, close and lock smoothly, that the sockets and lights work, and that the finishes are clean. Anything that isn’t right goes on a snag list, with photographs, and is best agreed with the team while they are still on site.

The team will then ask for the room to be signed off as complete, and the balance is due. It is usually the smallest payment. Keep the warranty, the electrical certificate and any Lawful Development Certificate together with the house’s documents.