House extensions give you a real opportunity to add space to the home you love. Before you embark on your project, here are the few things you should know

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Toying with the idea of a house extension? If the current situation has seen you spend more time in your home than ever before you might be thinking about how to extend your house to get the most out of it. Reconfiguring your current downstairs layout with a single-storey addition could give you the chance to kick out the floorplan in your kitchen to create a bigger family space. 

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Adding a two-storey extension could create an extra room for that home office you’ll use every day, as well as a master suite to retreat to. Whatever your intention, a house extension needs careful planning before you dive in. From setting your budget to employing trades; to the legalities and logistics of a project — there are lots to navigate.

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Here are the things you need to know before you add a house extension. 

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1. Do House Extensions Add 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.

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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:

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• structural integrity

• fire safety

• energy efficiency

• damp proofing

• ventilation

• and other key aspects that ensure a building is safe.

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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.

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Typical Examples of Work Needing Approval:

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• House extensions 

• Loft conversions

• Internal structural alterations, such as knocking down an internal wall that is loadbearing

• 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

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(MORE: The Complete Guide to Planning Permission)

 

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3. How Big Should I Build my House Extension?

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TOP TIP: MATCHING MATERIALS

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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.

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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.

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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

• package build companies’ in-house design teams

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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.

 

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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.

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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.

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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.

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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,” 

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

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8. Extending 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.2

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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.

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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.

(MORE: Heating: Beginner’s Guide)

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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).

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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.

 

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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.

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14. Factor in Privacy 

If your house is exposed to passersby or to neighbours, you'll need to consider your glazing choice.

One solution would be to consider your boundary treatments, which may need to be adapted to ensure privacy is maintained, while integral screens in your glazing provide privacy without spoiling your view. Moisture resistant roller blinds are perfect for a kitchen extension, shown here for privacy for the main kitchen windows and the rooflights, from English Blinds.

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15. Check if Trees Are Protected

Some trees are protected by Tree Preservation Orders (TPOs). Even if house extensions don’t require planning permission you cannot alter or even prune a tree that has a TPO on it without planning permission.

All trees within a Conservation Area are protected by legislation and effectively have a TPO on them providing they have a trunk of diameter greater than 75mm. Altering a tree that is protected by a TPO is a criminal offence and can result in substantial fines so take care if you are extending your home near to a protected tree.

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16. 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.

We recommend a contingency of somewhere between 10-20%.

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17. You Need to Notify Building Control of Your House Extension

Before any works begin, you will need to submit either a building notice or a full plans application to building control. A building notice will allow work to begin quickly, but you will lack the protection that building control has signed off on the design and you are liable to correct any work that fails to meet Building Regs’ standards upon inspection.

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