Guide to extensions

Many homeowners will at some point think of extending their property. It may be as an alternative to moving or to accommodate additions to the family either children or elderly parents. It may be that you want to do something very specific with your extra space, such as a utility room or a larger kitchen.

An extension should of course add re-sale value to your property, however a badly designed or ugly extension can have the opposite affect. Ideally the extension should look as though it has always been part of the house. You cannot assume that the cost of the extension will be recovered when you sell the house. What a well designed and built extension should do is to make your house more saleable. This means that your property should sell more quickly than otherwise and that you will be more likely to achieve the highest price possible for the type of property in your area. The secret to building a good extension is not to rush into it before you have ensured you have achieved some basic points.

Getting started

1. Decide where you think the extension could or should be built around the perimeter of the property. This may dictate the maximum size you can achieve.
2. Decide what type of extension you like and what it is going to look like. Look around your neighbourhood and see what your neighbours have done with a similar style property.
3. Get information to enable you to get plans produced and to find who will build your extension. See our related article on Planning Procedures.
4. Work out whether your ideas will require planning permission and building regulations. The differences are that all new buildings are subject to building regulations and either you or your builder will have to pay the local authority to have the progress of the building work inspected and approved. Also the regulations dictate the quality of many materials and the level of thermal insulation you must have in the floors walls and ceilings and windows. Planning permission is required if the extension exceeds 15 per cent of the existing volume or 70 cubic metres. An existing terrace house needs planning permission if the volume exceeds 10 per cent or 50 cubic metres whichever is the greater.
5. Work out the likely cost before you start. Talk to friends or neighbours who have an extension and find out what the final cost of the build came to and also how big the extension was in terms of square metres. You will then have a rough cost per square metre and can work out what your extension could cost you. For a very rough rule of thumb a brick built extension with basic internal finishing will cost approx. £50 per square foot or £500 per square metre. So if you think you will need an extension measuring say 8 foot by 15 foot the square footage will be 1200 square feet and the cost at £50 per square foot will be approx. £6000. You need then to add the cost of any new fittings and increase the cost for any special items like hand made tiles or bricks and hardwood floors etc.

Plans & planning permission

Take photographs of all elevations of your property and put on graph paper to scale. Next obtain an Architect. A recommended architect is the best. Without a recommendation contact the Royal Institute of British Architects on 0131 580 5533 or Architects Registration Council on 01604 404121. You can also find local architects in your local Yellow Pages. Many architects will agree to give you a free first consultation to talk about your plans. Ask to see details of his previous work of a similar nature and talk to one or more of his previous clients. Take this whole stage slowly and do not proceed if you have any doubts either of the architect or his proposals. It is easier to walk away at this stage than at a later date.

Architects fees are around 5 per cent of the total building cost, for an extra fee he may be able and willing to find and recommend a suitable builder, oversee the building work and settle all disputes and payments with the builder. For peace of mind it is not unreasonable to add 15 per cent to your estimate of final cost to allow for unforeseen items and unplannable hitches. They do quite often occur but don’t let anyone else know you have made this financial provision. It is not advisable to attempt to supervise the work yourself unless you have experience of construction and you can give the building your full attention.

Remember to talk to your home insurers or your insurance broker before commencing work to let them know what you are doing and to get their advice. Ask them to ensure that new construction is covered by your policy as you proceed. Ensure you understand what the builder’s insurance covers, e.g. whose policy is meant to cover for materials on-site in the event of their theft. Etc.

Finally think of your extension as the same as building a mini house for it contains all the elements which your main building required and think about access to the area of building and how excavated soil and rubbish will be removed from the site etc. The more thinking you can do for yourself the more likely you will end with a successful extension which could add value by as much as 50 per cent of the total building cost to the price of your house.