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Converting an Outbuilding

shutterstock_194707322Major life changes can have unforeseen effects on your living arrangements: whether because of a growing family, a change in working patterns or a family member moving in. What once was spacious may now be a home that feels small or unsuitable for your lifestyle. While many people in this situation simply decide to move, for others this is not an option. A popular solution for those homeowners reluctant or unable to move is to convert an existing outbuilding into a new living space.

While most people associate outbuildings with stables and barns in rural locations, outbuildings actually include garages, outside toilets and coal sheds that can be found in many smaller urban properties. Since the Government relaxed some aspects of local planning regulations in 2008, it is now possible to convert an outbuilding in your garden into a residential annexe without planning permission, as long as the building does not become an independent residence. This means that you can build a guest room, garden room, home office, greenhouse or children’s playroom without planning permission, although you will have to make sure you comply with building control regulations. This law only applies if the outbuilding has been on the land for at least four years and has not been used as a residence during that time.

While you can use your outbuilding for many purposes, if you intend to convert it into a habitable room it must be upgraded to meet the building regulations requirements for ‘a material change of use’. This means that you will have to insulate the building structure, and that doors and windows will have to be double-glazed. If you intend to install heating, plumbing or electrics all of these will also have to comply with building regulations. In order to make sure this is the case, you will have to inform the local authority, complete some paperwork and pay a fee.

Types of Conversion

The amount of time, money and effort that you will need to convert your outbuilding will depend on the type of building that you hope to convert and what you intend to use it for. The cheapest options can be a summer garden room or a greenhouse (which would not need heating, plumbing or electrics). In these cases the existing fabric of the building will need to be structurally secure and have proper ventilation.

If you plan on using the outbuilding all year round the building may also need to have a functioning heating and lighting system. If the outbuilding will be used as a guest annexe or as a home office, artist’s studio or children’s playroom you might also want to install electric sockets, internet access and running water, so that you can make a cup of tea and use computer equipment or other electrical goods.

You should make a careful assessment of what amenities you think you will need before you proceed. Calculate the costs of buying and installing all of the services you will require, including the cost of qualified tradesmen to install electric sockets, plumbing and drainage systems if required. Be aware that extending heating and electrical systems are likely to require earthworks through your garden and will cause disruption.

If you would like to convert your outbuilding into an independent residence (with a proper kitchen and bathroom) you should be aware that you will have to apply for planning permission. Once the conversion is completed you will have to pay separate council tax bills for it (at the lowest band). The bills are payable even when the building is empty, although they drop to 50% of a full bill once the property has been empty for more than 6 months.

Insulation and Damp-Proofing

The more you insulate a building the easier and cheaper it is to heat, so investing in good insulation will save costs in the future. Insulation should be added to the interior of a single-skinned building between the original structure and the plasterboard interior. Although this can reduce the living space slightly, it will make the new room much more pleasant to spend time in, making it warmer in winter and cooler on hot summer days.

Damp-proofing will also make the room or building much more pleasant to spend time in, and will help to stop problems such as mould and rising damp developing inside the building. A damp course should be installed during the construction of the inner layer of the building. For timber structures a concrete base with a damp proof membrane can be used, or perhaps the wooden structure can be raised off the ground on blocks with a slate barrier in between the two materials.

Water and Plumbing

If you are planning to use your converted outbuilding as an annexe, studio or home office it will be very useful to have running water or a bathroom. This means plumbing into the drainage and sewerage system, a job that is better left to professionals unless you know what you are doing.

You will need to use a blue plastic water pipe buried under ground, and it will have to be connected to the mains supply somewhere near the stopcock for the main property and have a separate isolating tap. It will be important to install the drainage pipes at the right gradient and connect pipes properly to the correct system.

If you are installing a sink for occasional use you might be able to send the wastewater away with the downpipes the gutters feed into, but in that case you will have to be very careful only to use organic biodegradable soaps and detergents.

Whatever you decide to do will have to comply with building regulations, so check the rules before you install your plumbing.


Installing electricity and heating can make a big difference to ways you can use your conversion. In most parts of the UK you will have to employ a qualified electrician to do the work. shutterstock_83540650Before you start, think about the lighting and electrical needs might be (depending on how the building will be used) and estimate the socket points and lighting that you think you will need. Your electrician will estimate the cost of wiring and installation of the system.

You can choose to do the preliminary wiring etc. yourself, locating the sockets and switches where you think you will need them, but if your electrician disagrees with the location of power points or objects to the quality of your work you could waste time and money getting it fixed.

If you don’t want to connect your electricity supply to the grid, you could use solar panels to power lighting and small electrical goods. Whether you choose to use systems like these depends on how much electricity you will need and whether you will need to use the system all the year round. Solar panels may not be as reliable for producing long hours of electricity and lighting in the winter months, but they may provide all that is needed during the summer.


Unless your outbuilding is next to your house, you will be unable to extend your central heating system to include your conversion. In this case you could choose to have a portable heater to top up in the winter months, such as a fan heater or an oil-filled radiator. It might be possible to install a wood-burning stove, but you will have to consider the fire risk, especially if the building has a wooden structure. The better insulated your building is, the easier it will be to heat and keep warm.

If you are considering using solar panels to provide heating in your outbuilding, remember that light can only provide heat during the day. This kind of system will work well during the long days of late spring to early autumn, but will not work during the winter months. If you do want to use a solar panel-based system, the best way is to use fluid-filled solar panels that circulate heated water through under floor heating pipes. If the floor is thick and well insulated it will retain the heat well and provide heat for an extended period of time during daylight hours. No matter how you decide to heat your conversion, remember it will have to comply with local building regulations.

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