House Extensions Tips – Planning An Extension With No Experience


07 Feb 2022


Simon McAuliffe

An extension to your property is one of the most effective home improvements you can make. Yet while some homeowners might be blessed with insider trade knowledge, many people looking to extend their houses aren’t familiar with construction, architecture, or property design.


Without some solid advice – and a few relevant tips to get you started – it can be easy to miss something, make a mistake, or end up spending far more than you originally intended.


We’ve worked with a lot of architects over the years, on a wide and diverse range of projects. If there’s one thing we’ve learned, it’s that when designing and planning a house extension, a lot of questions come up – particularly in the early stages of the process.


So, to provide you with some key house extension tips, we’ve answered some of the more frequent questions that come up during the planning process, and provided some handy tips and advice.



What are the different types of house extensions?

The term ‘house extension’ simply refers to any structure that’s added to the original building. This can be a loft extension, basement extension, a kitchen, a living space, or even a new bedroom. Extensions can be made from a variety of materials: from simple brick & block to more expensive, luxury designs, such as those including structural glass (internal link).

House extensions are usually one or two storeys high, and include everything from conservatories and garage roof extensions to multi-storey annexes, featuring their own kitchenettes, bedrooms, and bathrooms.

Will I need planning permission for my house extension?

The honest answer is that it depends, but usually no, you won’t need planning permission for your house extension. Most properties benefit from what’s called ‘permitted development’, which basically means that you can extend the original building (which is as it stood in 1948) without applying for permission – provided you obey certain restrictions.

These include things like not extending above the height of the roof of the property, and limitations on how far your extension can project outwards, but they will depend on the type of property you own. The full list of permitted development criteria can be found here, along with a handy quick start guide.

If in doubt, the best bet is simply to speak to your local planning authority, which is usually the Council. They’ll be able to explain the process, whether or not your house qualifies for permitted development, and what fee payments and applications – if any – you’ll need to make.

Do I need planning permission for an extension on a listed building?

If your home is a listed building, then it won’t qualify for permitted development – and you’ll need to obtain both planning permission and listed building consent before undertaking any work. It’s a criminal offence not to do this. Speak to your local authority’s Conservation Officer, as they’ll be able to help you understand what restrictions might apply to your specific property.

Do I need planning permission for an extension in a conservation area?

If your home is in a conservation area, such as a World Heritage Site, National Park, or area of outstanding natural beauty, then permitted development rules do apply – but they’re slightly more restrictive.

The entire design process is scrutinised to a much greater degree by the local authority, but this doesn’t necessarily mean you can’t plan for a contemporary extension – just that it’s best to get in contact as early as possible with your planning authority Conservation Officer, to discuss your intentions. For more information, Home Building offer a fantastic guide to check out.

Do I need an architect for my house extension?

There’s a lot to be said about this, but we’ll try to keep it straightforward: the simpler you want to keep things with your extension, the less likely you’ll need to employ an architect. There’s no law requiring you to do so, and it’s all about personal preference.

If you simply want a basic, brick and mortar construction – or are planning something like a humble conservatory – then an architect probably won’t be necessary. If you have a grander vision for your space, or are looking for an expert to design something a little more special, then employing an architect is a sensible idea.

Are there restrictions on where to place toilets in a house extension?

Short answer: there used to be, but there aren’t any more. The Building Regulations (more on those further down) used to insist on a lobby space between a toilet and other rooms, but this is no longer the case.

You can place a toilet anywhere you like, providing there is ample room, that you include a wash basin and that you allow for sufficient ventilation. The same goes for showers, providing they meet minimum size requirements outlined in the Regulations. As a result, the main consideration when planning for a shower or toilet is the proximity to suitable plumbing, as this is one of the largest influences on price.

Do I need to tell my neighbours when I’m planning my house extension?

There is only a legal requirement to tell your neighbour about your extension plans if the work you intend to organise will impact the boundary between your two properties. In general though, it’s just common courtesy to inform your neighbours of any intended construction work.

The disruption caused by the noise of the building work is likely to have an impact on their lifestyle, at least for a short while, and it’s only right to give them the chance to prepare for this – particularly if they have young children.

It’s also worth noting that keeping the neighbours on side is a very sensible thing to do anyway, as it can make it less likely that they’ll take umbrage to your actions, and try to cause problems for the development, such as attempting to invoke their ‘right to light’ (if applicable – see below).

House extensions: The legal right to light

In theory, even if your house extension qualifies for permitted development or you have planning permission, owners of neighbouring properties can block development of your extension by claiming their legal ‘right to light’.

Natural light is hugely important to our daily lives, and the right to light states that a development can be legally prevented if it will block light to a window or door in a neighbouring property – but only if the amount of light it blocks prevents the room being used properly. It doesn’t guarantee people the right to sunlight or bright airy spaces; it basically just prevents extensions from plunging a neighbour’s home into darkness.

It’s unusual for this to present a problem – right to light disputes tend to stem from deliberate, vindictive builds. It’s just good to be aware of your neighbour’s legal rights, particularly if you live in a city or environment in which the houses are very close together.

How high does the ceiling need to be in a house extension?

As is the case with toilet and shower rooms, there is no longer a minimum requirement specified in the Building Regulations as to the height of a ceiling in a house extensions. Your extension can’t be higher than the roof of your home, but other than that there isn’t any legally binding clause as to ceiling height. Your ceiling can be as high or low as you like.

With that in mind, it’s still important to be realistic about things. If your ceiling is impractically low, your extension won’t be a very nice room to inhabit; you don’t want your expensive new space to cause chronic back pain for anyone that walks into it. The normal ceiling height in the industry is 2.4m, around eight feet, and this is a good baseline when making your plans.

What are the building regulations for house extensions?

The Building Regulations are a set of guidelines and minimum standards, determined by government and enforced by local planning authorities, to ensure building work accommodates safety and health and factors. These can include everything from how a structure uses energy and water to its fire protection. The Regulations apply to any new builds, as well as to all extensions and alterations.

If you want an example: one regulation (the ominous ‘Part L’, that sounds rather like something out of the X-Files) relates to energy efficiency. The government has put in new requirements to raise the efficiency of all new buildings and structures by 40%, and so the amount of glass in a structure is now limited to 25% (Don’t worry, this doesn’t mean you can’t opt for one of the glass extensions we construct; you just have to factor in insulation elsewhere, or opt for something like low-e glass or triple glazing).

The full list of regulations is long, technical, and not really the remit of an amateur developer. You can browse all of the restrictions that apply, but in general, when it comes to planning, your architect or building contractor is the go-to contact. Unless you’re willing to study hundreds of pages of documents, it’s best to refer your ideas to the person responsible for drawing up your plans.

How do I choose a builder for a home extension?

Unless you’re really confident in your own ability, you’ll need to hire a builder to… well, build your house extension. This means finding a contractor who you can trust. There are lots of ways you can find a suitable builder, but it’s a good idea to search online for contractors with experience building extensions near you, and look at some reviews. Word of mouth is also a good source, as are local forums.

Once you’ve found someone you think might be suitable, ask to see some examples of their previous work, and if they can put you in contact with someone for a reference. Don’t feel obliged to hire the first person you speak to about a quote, and take as much time as you feel is necessary to find the right contractor.

How do I choose an architect for a home extension?

The same process as above applies: if you decide for a more bespoke or complicated design, and choose to hire an architect, then finding the right firm for you requires a bit of research. Look online (sites such as Houzz can be a good place to start) and draw up a shortlist, then research the architects you like the look of by browsing their website, and speaking to them in person.

Ask to see their portfolio of relevant projects, ask for references, and if possible, request to go and view some of their work in person. Don’t be intimidated by flashy and impressive work – trust your gut. You’re hiring them to design the extension you want, so you need to make sure you’re confident in their ability to deliver what you’re looking for, not what they’d prefer to design.



How much will a house extension cost?

It might sound like a bit of a cop out, but the cost of your extension really does depend on a lot of things. It’s unrealistic to provide an average or benchmark cost of a house extension, as there are too many variables that impact price, but a very rough estimate would be to budget for £1200 – £2000 per m2.

This doesn’t account for professional fees for your builder and/or architect (along with things like planning application), which you can usually expect to run somewhere in the region of 10-15% – and you’ll need to add VAT on top. Extensions in London and the South East will also inevitably cost more.

Once you’ve decided on the kind of design you’d like to opt for, the best thing to do is consult with your architect or builder, and have some preliminary plans drawn up.

From these, you can then approach a number of builders – the more the better – to provide you with cost estimates. You can use this to get a ballpark cost for the house extension you’re planning, and work out if you can actually afford what you’re intending to build.

Do I need insurance for my extension?

The short answer is yes, but the typeof insurance policy you’ll need to take out depends on a number of factors.

You’ll likely need a site insurance policy (or unoccupied buildings insurance if you’re vacating the property when the work is taking place) – and your contractor will need their own insurance too. It’s also a very good idea to take out a structural warranty, which involves having the extension build inspected and passed for any errors – so if the roof caves in a year later, the builder (technically you) isn’t responsible.

Also, your standard home insurance policy won’t continue to cover your home when it’s under renovation, and you’ll need to check on the insurance status of your builder – if they only have public liability insurance, they won’t be covered if an accident takes place that they weren’t responsible for (such as a fire, or tsunami).

You’ll need to notify your home insurance provider well in advance of any works taking place, and it’s a good idea to use this opportunity to speak to them about the relevant policies you’ll need both during the construction of your extension, and after it has been built.

Can I claim VAT relief on my home extension?

You most likely can’t claim VAT relief for work carried out on your house extension project. If you’re using a contractor, then the standard rate of 20% almost always applies. There is sometimes an exception if you’re using independent tradespeople who aren’t VAT registered, in which case you’ll only need to pay VAT on materials used.

If your property is a listed building, and you’ve obtained permission to undertake work on your extension, then you’re in luck – listed buildings are zero-rated for VAT when it comes to improvements.

Will my house extension add value to my property?

One of the main reasons many people choose to extend a property is the prospect of increasing its value when they eventually decide to sell. It’s usually the case that adding more space to a property results in the value of said property increasing – particularly in London and the South East, but this isn’t always true.

One of the best ways to assess whether extending your home will increase its value is to speak to a local estate agent. They’ll be able to tell you the kinds of renovations that are popular in the local area, as well as offer a guideline to what the ceiling value of property in your street tends to be. If your home already approaches this, then it’s possible to ‘overextend’, and cap out the value of your property despite adding multiple new areas.

It’s also worth bearing in mind that as the housing market changes, so does the potential financial benefit of extending a property. It might not be financially viable to extend your home now, but the extension you build could add significant value in years to come.