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When it comes to extending your home, there are a number of criteria that need to be considered to ensure project success. These can range from the legalities of the project through to crucial design details that are often forgotten.
Here we reveal 25 things that all extenders need to know — and probably don’t. If you’re planning on your own extension project, this is essential reading.
1. Living on Site Could Slow Down Your Project
Many people choose to live in their house while the work is done, and this is certainly possible. But it could still include plenty of dust, mess and dirt in the house — and it may also slow down the project as builders work around your life.
Consider looking for temporary accommodation: whether a short-term rent, hotel or calling in a favour from the family if you aren’t prepared to live with the disruption. Depending on the extent of the work, it could perhaps save you money to live elsewhere.
2. Choose a Designer Wisely
When it comes to the design of your extension, there are a number of options you can choose from.
- architectural technicians
- specialist designers
- package build companies’ in-house design teams
Start your search by asking 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.
You should have a good rapport with your chosen designer and make sure that they understand exactly what you are looking to achieve. A good designer will take your brief and identify feasible solutions within your budget that you may not have even considered.
3. Access Restrictions May Affect Design Choices
The available access to your home may have an impact on what work can be done to it. If your site has restricted access (for instance, if you live in a terraced home) you may not be able to use certain construction methods, for example, or agreements may need to be made with neighbours to use their land for storage or for fence panels to be removed.
4. Don’t Forget Site Insurance When Extending
Many people don’t know that most home insurance providers will not cover the building if you are changing the structure of the build — for example extending, doing a conversion or renovation. When carrying out the works you need to have site insurance with an A-rated insurer to cover the existing structure and the new works until you complete the works.
Builders will often say they have insurance but it is important to check their documents as the majority have liability cover which will require you to prove fault in the event of a claim, which can mean a lengthy legal battles. This may also not cover any natural events claims, such as fire, flood and storm damage.
If you are vacating the property during the build, you will require site insurance or unoccupied buildings insurance which will usually be a minimum six month policy. Always contact your existing insurance provider to notify them of works before you start.
Your build choices may also affect your insurance: “The materials you choose for your extension may have a bearing on your insurance, so it’s worth checking this before you build,” says Andrew Reardon of ProAktive.
“High value and theft-attractive items such as zinc or more flammable items will impact on your ability to get insurance and the premium you will pay for it. Flat roofs can also be an issue for household insurers.”
5. The Importance of Connecting the Old and New
Understandably, how the additional space sits alongside the original property will 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 the extension to complement or contrast with the main building.
Bear in mind, that if you want the extension to match the existing property, you need to choose materials very carefully as one slight mismatch could make the whole extension look wrong.
6. Rebuilding Might be the Better Option
You will need to ensure that the value created by adding the extension is greater than the build cost for the project to make financial sense. This can be difficult to assess, but it’s worth looking at the various resources online to see what similar properties with extensions in your area are worth. There is always a ceiling as to how much value can be added to a property, so you may need to revise your initial plans to ensure the best return on investment.
Remember, it may pay to knock down the existing house and rebuild, if you feel the house is no longer fit for purpose, or it may simply make sense to sell and move.
7. Plan Your Kitchen Layout Before You Extend
When planning a kitchen extension, 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.
By considering these aspects early on, you can avoid the headache of expensive, time-consuming and frustrating changes that may need to be made when it comes to the more practical aspects of the project.
8. Can Your Boiler Cope?
Adding an extension to your home will also add demand to your current hot water system — 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.
9. Know the Building Regulations for Extensions
Even if you do not need planning permission for your extension, because you are using permitted development rights, you must get building regulation 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 the 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 Building Regulations.
Typical Examples of Work Needing Approval:
- Home extensions such as for a kitchen, bedroom, lounge, etc
- Loft conversions. Internal structural alterations, such as the removal of a load-bearing wall
- 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
(MORE: Building Regulations Guide)
10. It May Save Time to Build Off-Site
Off-site construction systems, including cross laminated timber (CLT), oak frame, structural insulated panels (SIPs) and timber frame, often work well on extension projects. As the name suggests, the majority of work happens in a factory off-site, and components are then delivered to site ready for erection.
11. Locate the Sewers
If your 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.
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12. Know the Rules for Extending in Conservation Areas
If you live in a Conservation Area your Permitted Development rights are restricted. Each local authority has its own policy for Conservation Areas but generally the basis of the policy is to prevent the loss of character of the Conservation Area. So, if you are thinking about extending your home, always contact your local conservation officer first.
Consequently planning permission is required for the addition of dormer windows or any other change to the shape or height of the existing roof, including the addition of Velux rooflights if they face the highway. This means that loft conversions will almost always require planning permission in a Conservation Area.
(MORE: Dormer Windows)
13. You Could Be Your Own Project Manager
“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.
14. Plan Carefully if Extending Above
While it may seem appealing to extend above a single storey extension or garage, these structures may not be able to support the load. According to chartered surveyor Ian Rock there is good news, though: “Most extensions built in the last 25 years should have sufficiently deep foundations to accommodate an extra storey at a later date, assuming they complied with Building Regs.
“However, building over garages is rarely a practical proposition without substantial additional support because of their limited loadbearing capacity.”
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.
15. A Community Infrastructure Levy May Apply
Before building you should establish if you will be liable to pay the Community Infrastructure Levy (CIL). Some councils operate this scheme, and it’s applicable to extensions over 100m² in gross internal area (even if they are built under Permitted Development).
However, a self builder’s relief can apply, as Jonathan Durndell of Milton Keynes Architectural, explains: “To benefit from the self builder’s relief the applicant does not have to physically construct the extension themselves but they must intend to live at the property as their main residence for a minimum of three years from completion. It is advisable to check with your local council to establish if any CIL charges are applicable and the route to apply and claim relief before you start construction.”
16. Design in Efficiency
By focusing on the fabric of your new 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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17. Understand 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 etc. 1996 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 extension involves building or digging 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.
(MORE: The Party Wall Act)
18. The Importance of Privacy
The glazing choice may have an impact on how private your home is and how exposed you are to glances in from passersby and your neighbours. 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.
19. Beware TPOs
Some trees are protected by Tree Preservation Orders (TPOs). Even if an extension does not 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.
(MORE: Tree Preservation Orders)
20. You Probably Can’t Claim VAT Relief
Most extensions will be subject to VAT on labour and materials at the standard rate of 20%, especially if you use a contractor to undertake the work. If you use local tradesmen who are not VAT registered you can save the 20% VAT on their labour, but you will still have to pay VAT on materials at the standard rate.
Some extension projects are eligible for VAT relief, such as work to listed buildings (zero rated), the conversion of an existing dwelling that changes the number of units (reduced rate of 5%) and work to a building that has been unoccupied for at least two years (reduced rate of 5%).
To benefit from VAT relief if you are extending a listed building or renovating an unoccupied home, you must use a VAT registered builder — you cannot reclaim the VAT yourself.
(MORE: Reclaiming VAT)
21. A Healthy Contingency Budget is Vital
A good first port of call to work out a rough budget is our Extension Build Calculator, which will factor in your build route, geographical location, desired quality of finish and size of the extension to give you a rough idea of the total build cost.
You’ll also need to set 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%.
22. Don’t Forget Building Control
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.
Ian Rock suggests that a full plans application is more suitable for most extension projects: “The best advice is to submit a full plans application in advance to building control so they can confirm that the design meets all the required standards before work starts — it will also mean you will have an approved set of plans to work to on site.”
23. Solar Gain Can be a Problem
Though bringing more light into a home is often a desired outcome of an extension project, unmanaged light ingress can create problems associated with solar gain.
Designers should be aware of this when designing glazing features into an extension and mitigate for the solar gain to avoid the situation where, like poorly designed conservatories, the extra space is usable for only a small part of the year. Screen fabrics can also be used to reduce glare and diffuse light.
24. Bigger isn’t Always Better
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 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. “Sometimes lots of additional floor space is not necessary and the property can be made to feel more spacious by using natural light and improving links to outside spaces,” advises
Leila Westrope of Roderick James Architects.
25. It Can’t be All Glass
“Part L of the Building Regulations limits the total area of glazed elements in an extension to a maximum of 25% of the extension’s floor area,” says Jason Orme, experienced extender and Homebuilding’s Editorial Director.
“Particularly on small extensions, this poses a problem. A small kitchen extension, perhaps adding 20m² of space, could easily have its allowance taken up by a set of bifolds – 4m(W) x 1.8m(H) = 7.2m² or 36% of the floor area – and will therefore be rejected by building control.
“There are several ways around this. First of all, you need to deduct the total area of the windows and doors that are being lost as part of the extension from your additional total. If that doesn’t get you below 25%, then you’ll need to show that the new glazed extension can meet the energy performance standards achieved by a non-glazed extension in other ways. If that still fails, then you’ll need to commission a SAP assessment to show that the CO2 emission rate from your glazed extension would be no greater than the emission from a fully compliant extension of the same size.”