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16 December 2020

How to build a summer house or garden room

Follow our expert tips on installing a garden room or summer house, how to prepare the foundations and how to look after your outbuilding for years to come.
SI
Sarah Ingrams

Installing a garden room, summer house or garden office in your garden is a big job. Aside from deciding on the type of room you want and where to put it, you’ll need to consider planning permission, foundations and construction before your new space can take shape.

If you’re planning on assembling it yourself or building from scratch, we share top tips from people who already have.  

Unsure what type of summer house, log cabin or garden office would suit you and your garden? See our guide on how to buy the best garden room.

Building a garden room  

Many garden buildings can be bought in pieces for you to construct yourself. Instructions should be provided, although you'll need basic tools to complete the job.

These will probably include a handsaw, screwdriver, mallet, hammer, spirit level, tape measure, drill and ladder – but check the instructions or ask the company you buy it from to make sure you have everything you need before you start. 

If you’re planning to build from a kit, also check the following:

  • Are all the fixings (screws, nails etc) included?
  • Is wood pre-cut and planed, or will you need to do this yourself?
  • What is the construction method (for example tongue and groove)?
  • Are electrics and lights included (if you plan to have these)?
  • Are full instructions provided?
  • Are parts labelled (so it’s clear what is what)?
  • How many people are required for assembly?

If you’re more confident with DIY, you might decide to build your garden room from scratch, rather than buying a kit to assemble. Which? members in our survey* who have done this give the following tips:

Get the best roof possible even if you need to source it from another supplier.

Ensure the doors and windows are weathertight, foundations are level and gutters are fitted. Electrical installation should be incorporated in the design otherwise all the cables will end up being on external / surface conduits.

With DIY installation ensure the roof is fully secured to the walls and doors are well-fitted fitted. High winds lifted my roof off and it was heavy - it needed two people to lift one side so that the roof could be disassembled for reinstall.

Building your garden room or summer house yourself will mean you won't need to pay for installation, but think carefully whether you are confident that you can complete the job. 

One Which? member wishes they had used a professional installer:

Get it installed/ assembled professionally - we managed a DIY job but some of the pieces were very heavy, and the extra cost would have been worth it to avoid injury, and get the thing done and finished quickly.

If you have no experience with assembly or construction work, it’s worth hiring a professional carpenter or builder. Use Which? Trusted Traders to find a reliable trader near you. 

How long does it take to assemble a DIY garden room? 

Garden rooms are popular at the moment. Several firms state delivery times are between eight and 14 weeks (correct in December 2020). Depending on where the firm is delivering from, and where you live, timings will vary.

If the firm will also be installing it, or you’re planning to hire a trader to do so, add on the time they say this will take. As a rough guide, professional installation can take between one and five days, depending on the size and complexity of the structure.

Assembling a garden room yourself will take several days. As an example, a small 4.5x2.5 metre garden office with a flat roof, 25mm insulation, double-glazed windows and sliding door would take approximately four to five days, according to the manufacturer’s estimate.  

Simpler log cabins or summer houses can take closer to one to three days. 

These times are based on two adults and don’t include fitting lighting, plumbing, heating or internal decoration. The exact time it will take you depends on the season and weather you’re working in, the type of foundations you choose, and your DIY skills.

With either option, you’ll need to factor in time for foundations, or a base, for the room if this isn’t part of the agreed installation. 

Foundations for garden rooms and offices 

Garden buildings need a solid, level base to sit on. If you’re hiring a firm to assemble your room, it may request that this is ready before they will deliver it. Some specify the type of base they require, for example paving slabs or concrete, and may even send you a plan for the base when you have ordered your room.

Don’t skimp on foundations if you want your structure to last. They support the structure of the building. Good foundations are particularly important if you plan to put heavy items in it such as gym equipment, a snooker table or hot tub.

One owner of a garden room in our survey* said: 

Invest in a professionally laid base – it makes the erection of the building much easier, makes it stable, and a flat base will reduce the chances of leaks etc. which could result from an uneven base.

Subsidence is a risk if your foundations are poor or you omit them altogether, warns Gareth Jones, managing director of UK Leisure Living, a Which? Trusted Trader that focuses on foundations for garden rooms.

Concrete foundations are the traditional approach to create a sturdy base for your new structure. This typically involves digging a trench and filling it with concrete. 

Ground screws are a newer option for foundations, Jones explains. Large screws (up to 2.5 metres long) are driven into the ground to support the structure above. You can move ground screws if you decide you want to relocate your garden room in future. They can also be installed without heavy equipment – getting cement mixers or diggers into your garden to build concrete foundations can be a challenge if your home has limited access.

It’s important to take into account the type of soil that the foundations will sit on, to make sure that it can take the weight of the foundations and building, and to factor in how it reacts when it’s very wet. Speak to a structural engineer or building control for advice on what your garden room will need.

Looking after your garden room or summer house 

Check the maintenance instructions when you buy your garden building, so you know what you’ll need to do to keep it in good shape for many years to come. Many rooms are guaranteed for 10 years or more, and some Which? members have owned summer houses for much longer.

Wooden buildings can come pre-treated, or you may need to treat them yourself with paint or preservative when you first assemble them.

Then they typically need re-treatment, sometimes as often as every year. This is important to maintain the weatherproofing, structure and look of your garden room.

Wooden buildings can shift and settle over time. After the first few weeks, you may need to re-adjust the doors or windows if they have started to rub or stick. Wood can sometimes warp if exposed to the sun or moisture for a long time, especially if the wood isn't treated. Wood will also change colour as it weathers.

If you want a specialist to treat your wooden outbuilding or to preserve the structure's timber, check out Which? Trusted Traders to find reliable traders in your area.

Garden room guarantee 

Garden rooms come with different lengths of guarantee, including five and 10 years. Check what it covers – for example, is the structure of the building covered – and what rights you have if there’s a problem with your room in future.

Find out what you need to do for the guarantee to remain valid. Some guarantees specify essential maintenance - for example, treating the wood.  

Also remember to keep your proof of purchase and any other documents you’ll need for the guarantee.

Our garden room research

*In September 2020 we surveyed 11,539 Which? members about garden rooms, including 1,264 people who own one.