1. Make Sure Your House Extensions Adds Value

For house extensions to make economic sense, you need to make sure the value added is greater than the cost of the project. It can be difficult to assess, but finding similar local properties and seeing how much they’ve sold for can be a useful guide.

Be aware of the ceiling value in your area, and be prepared to adjust your plans if necessary.

2. House Extensions and Building Regs 

Even if your house extension can be built under Permitted Development rights, work must get Building Regulations approval.

The Building Regulations set out minimum requirements for:

• structural integrity
• fire safety
• energy efficiency
• damp proofing
• ventilation
• and other key aspects that ensure a building is safe.

Most repair work is excluded from Building Regulations, with the exceptions of replacement windows, under­­pinning and rewiring. However, apart from certain new buildings such as sheds, outbuildings and some conser­vatories, all new building work, including altera­tions, must comply with the Regulations.

Typical examples of work needing approval: 

• House extensions 
• Loft conversions
• Internal structural alterations, such as knocking down an internal wall that is load bearing
• New Builds
• Installation of baths, showers, WCs which involve new drainage or waste plumbing
• Installation of new heating appliances
• New chimneys or flues
• Altered openings for new windows

• 3. How Big Should I Build my House Extension?

  TOP TIP: MATCHING MATERIALS

  If you are aiming to match your house extension to the existing property then you need to source matching materials (which is sometimes easier said than done). One mismatch can stand out like a sore thumb.

  Often extenders get preoccupied with only thinking of the project in terms of square metres, not in terms of what that size is adding to the house. Bigger is not always better when it comes to house extensions, and there are often ways of creating the feeling of more space, without adding a large extension.

  This is often achieved through clever design, not only of the new space, but also what is already there.

4. Choose the Right Designer for Your Home Extension

When it comes to the design of your extensions, there are a number of options you can choose from.

These include:

• architects
• architectural technicians
• specialist designers

Ask for recommendations from friends, family and neighbours, but also look online for practices that have designed projects similar to what you are hoping to build. As leading Cheshire home extension builders, we can help advise where necessary.

5. Design in Efficiency Early On

By focusing on the fabric of your new house extension, you may be able to far outstrip the U values and airtightness levels specified by the Building Regulations.

However, appending a thermally-efficient extension to a poorly insulated home will not make it cheaper to run overnight and you should look to improve the efficiency of the main house while the builders are on site.

6. Understanding the Party Wall Act

Your neighbours cannot stop you from build­ing up to, or even on, the boundary between your properties, even if it requires access onto their land (providing you have planning permission to do so, and there are no restrictive covenants).

The Party Wall Act allows you to carry out work on, or up to, your neighbours’ land and buildings, formalising the arrangements while also protecting everyone’s interests. This is not a matter covered by planning or building control.

If your house extension involves digging or building foundations within 3m of the boundary, party wall or party wall structure, or digging foundations within 6m of a boundary, the work will require you to comply with the Party Wall Act. In these cases you may need a surveyor to act on your behalf. The act does not apply in Scotland.

7. Building a House Extension on or Near a Sewer

If your house extension will be built over or in the area of a sewer, you will need to contact your water board before work begins. “The location of sewers needs to be carefully considered,” Jonathan Durndell of Milton Keynes Architectural explains. “If a shared sewer (one which serves more than one property) is within 3m of your extension, then a Build Over Agreement with your local water authority is likely to be required.”

These can be tricky – and costly – especially if a new manhole is needed, or an existing one needs to be moved.

8. House Extensions Above a Single Storey

While it may seem appealing to extend above a single-storey extension or garage, these structures may not be able to support the load.

There are options where the old structure isn’t up to scratch: underpin existing shallow foundations; strengthen or bypass the existing with a steel frame bedded in new concrete pad footings; or demolish and rebuild. The latter is often the most cost-effective option.

9. Planning in Services for a House Extension

If you are extending your kitchen, you need to confirm the position of your units, cooker and white goods before work begins so that electrics, ventilation and plumbing can be planned in.

The same will apply if you’re building a two-storey extension and are including a new bathroom or en suite in the design.

10. Can Your Boiler Cope with a House Extension?

Adding house extensions will add demand to current hot water systems, which may not be able to cope.

It’s advised that you work out what the new extension will need to be heated effectively, and factor in your boiler output, the size of the radiators, hot water cylinder size and the reheat time.

11. Should I Live on Site?

It is possible to live on site throughout a house extension, but aside from all the dust and mess, you may end up slowing down progress as the builders attempt to work around your life.

If you’re not prepared to live with the disruption, then you should definitely consider looking for temporary accommodation (short-term rental, hotel or staying with family or friends).

12. Factor in Access Restrictions

If you live in a terraced home with restricted access, that may affect the options you have for your house extension design. For example, you may not be able to use certain construction methods, or you may need to make arrangements with your neighbours to temporarily remove fence panels or use their land for short-term storage.

13. Connecting the Old and the New

How well the additional space sits alongside the original property will undoubtedly affect the success of the project. While there are no hard and fast rules, you will need to make a decision on whether you want your new house extension to complement or contrast with the main house.

14. Don’t Forget a Contingency Budget

A healthy contingency to cover any unexpected costs — the start of work on an extension project can uncover problems with the existing house that need addressing, for instance.

15. Should I Project Manage my Own House Extension?

“I would always maintain that the best person to oversee an extension that you are proposing to utilise and enjoy is yourself,” says project manager Bob Branscombe. “No one knows the space or the building better than you, and nobody has a greater level of interest in getting it right.”

Project managing any building project requires high levels of patience, organisation, problem-solving and decision-making skills. If you don’t feel confident dealing with the problems associated with a build site or have the time available, a professional PM, main contractor or package company is a must.