Planning and costing your single storey extension

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1. Decide what you need

Use our checklist to think about the features you would like to include in a main bathroom or en suite.

Your essential elements:

• Fitted bath
• Freestanding bath
• Shower bath
• Shower
• Pedestal basin
• Console basin
• Twin basins
• WC
• Bidet
• Built-in storage
• Freestanding storage
• Heated towel rail or radiator
• Waterproof television
• Built-in hi-fi
• Lighting controls
• Automated bath filler
• Underfloor heating

2. Work with professionals

You could choose a bathroom design specialist firm or employ individual contractors. ‘All of your products and features need to be considered before your installation team quotes for the renovation,’ says David Smith, senior designer at Ripples. ‘Forward planning will allow for accurate pricing and a realistic project schedule of works.’

3. Employ expert designers

A bathroom specialist can manage the entire renovation project for you. ‘The specialist company will be qualified in all aspects of the installation, including tiling, electrics and carpentry,’ says David. ‘Check whether the company has experienced tilers and plasterers, or whether it contracts this work out – an inexperienced tiler or plasterer may take three times longer. Will your installer take responsibility for all the work and oversee the quality? Check for recommendations from friends; ask for quotes before signing contracts, and don’t be afraid to request references.’

You should spend time discussing the space with your designer. ‘A site visit is imperative to take the dimensions of the room, check the direction of the floorboards, the heights of ceilings, and to measure water-pressure systems, along with observing the style of the house,’ David explains.

4. Pick individual contractors

If you have decided to employ individual contractors for your project, ask for personal recommendations, and make sure that anyone you use is accredited.

For builders, tilers, plasterers and electricians, look to trade organisations, such as the Federation of Master Builders, or government-licensed TrustMark.

You can also find local electricians through trade bodies, such as NICEIC. For electrical, heating and hot-water contractors, visit ELECSA, while NAPIT provides a list of electricians and plumbers.

5. Agree on the plans

You will need to assess the feasibility of your plans at an early stage. ‘Discuss options with your installer and bathroom designer,’ says David. ‘Loft conversions lend themselves to large, light bathrooms that make a real design statement. Often the best place is directly above your existing bathroom, as this should ensure that you can connect into the existing drainage and water supplies without requiring excessive pipework.’

6. Organise necessary permissions

You probably won’t need planning permission for a new bathroom, but if it’s part of a loft conversion, check whether this needs an approved application or falls under the permitted-development regime. If you live in a terraced or semi-detached house, the Party Wall etc Act may apply. Look at planningportal.gov.uk and check with your local authority.

Drainage and electrical works may be subject to building regulations. If you are using a room where there isn’t a bathroom now, approval will probably be needed. The floor may have to be strengthened if you are fitting a bathroom suite where there wasn’t one. A structural engineer or surveyor can create the documentation needed. A surveyor (see rics.org) can arrange agreements, or find details on planningportal.co.uk.

7. Employ specialist designers

A new bathroom may place more demands on plumbing. ‘Ensure that the boiler produces enough hot water for the shower and bath,’ says Dorian Bowen, director of design consultancy Project One. ‘For an unvented system, go for a low-pressure thermostatic mixer or install a pump.’ Also, check that your water system will cope if the new bathroom is in the loft.

8. Select fittings and features

The location and size of your bathroom will affect the choices that are available. ’With limited space, consider made-to-measure products,’ says David Smith. ‘Where there are height restrictions, use a bespoke glazing company. They will template the space and know how to provide easy entry to the shower, and so water doesn’t splash out.’

Budget

Bathroom suite and installation

The specification of the suite or individual pieces will have a big influence on your final costs, whereas plumbing costs will be much the same whether you choose a less expensive bath, basin and WC or designer fittings. However, if you are refitting an existing bathroom, remember that your final costs will also be influenced by the layout.

‘Installation prices will vary depending on whether you are simply replacing items – such as removing an old sink and bath and installing a new one in the same place – or redesigning the bathroom,’ says David.

For a bathroom with WC, basin and bath, costs range from around £4,000 to around £10,500, depending on where you source the pieces. For a shower room with WC, basin and shower cubicle, budget from around £4,500 to around £11,000, depending on where you shop, from DIY stores to high-end showrooms.

Bathroom specialist

If you’re working with a specialist bathroom company, the price should include all elements. ‘The ideal place to start any project is with a budget,’ explains Dorian Bowen. ‘A good company will then design and install to that figure.’

Planning

If you’re putting a bathroom in a loft conversion and cannot carry out work under permitted development rights, budget £172 for a householder planning application in England. When making use of your permitted development rights, a certificate of lawful development costs £86 (England). See planningportal.co.uk for other fees.

Party walls

If your bathroom is in a loft conversion and the Party Wall etc Act applies, plus you need to employ a surveyor, factor around £850 per neighbour into your budget.

Building control

If you’re converting the loft, building control fees are likely to be around £960 to £1,200 for a standard conversion. Otherwise, budget for around £300, but check with your local authority.

Heating

You may have to upgrade your boiler to meet your new bathroom’s needs. According to the Energy Saving Trust, a straightforward gas boiler replacement will cost around £2,300.

Underfloor heating

For an electric system for your new bathroom, factor in from around £14 to £22 per square metre. If your bathroom is going to include a wet underfloor heating system, the costs are likely to be from £36 to £48 per square metre.

Electrical

‘You might have to upgrade your consumer unit if you have no residual current device on your electrics,’ says Dorian. ‘An average cost would be £400 to £500.’

Decorating

‘Tiling is a huge contributor to what can go wrong in a bathroom,’ explains Dorian. ‘Factor in the correct materials over using the cheapest product. If your project is a wet room, make sure that you use the right tanking system.’

If tiling is not part of your overall project cost, allow from around £28 per square metre upwards to cover it.