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Things You Need To Know Before Extending Your Home

Home extensions: 15 things everyone needs to know


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Last updated Thursday 4th March 2021


Before you embark on creating your dream extension, there are a few things every homeowner should sit down and consider. After all, even modest extensions are a big project for a homeowner to undertake, and the last thing you want to encounter is surprises.

From budget to regulation, design to contractors, here’s a breakdown of everything you need to know before extending your home...

Will it add value to your home?

Even if you’re not planning to sell your home anytime soon, it’s important to understand what your project may or may not do for the value of your home. Extending is an expensive project, but can in many cases reward your investment when it comes to selling.

However, an extension doesn’t always result in a bigger house price. How much value you add will depend on the quality of the work, what (if any) additional rooms you’ve created, and whether or not your area has a ceiling price - meaning, there’s a limit on how much a property can be worth in your location. To work out if your home is affected by a ceiling price, checking in your local estate agents to see for what price homes with extensions are selling at around you.

Have you got enough budget?

You’ve put money aside, but have you got enough for everything that will be required? While many people plan for the builder’s fees, and materials, there are a lot of hidden costs that some aren’t prepared for. Such as…

  • Legal fees
  • Stamp duty and land tax
  • Measured survey
  • Architecture fees
  • Structural engineer fees
  • Planning application fees
  • Building regulation fees
  • Warranty
  • Services
  • Waste removal
  • External works

Learn more: How much does an extension cost?

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Do you understand the timings?

Extending your home isn’t a quick job, in fact, you might be surprised by how long the whole process can take. There’s a lot of stages involved with extending, and each one can vary on the time it takes.

For instance, you might need to get a Party Wall Agreement with your neighbour. This can take anywhere between a week and 3 months to sort. Similarly, who you hire can also have an effect.

Depending on the size and scope of your extension, on average your project will take between 7 and 15 months to complete.

Check out our blog on the timeline of home extension.

How much can you do yourself?

If you know your way around a power tool or have a way with piping, you could potentially save yourself a lot of money when it comes to construction. For the actual build of your extension, there are four routes you could take…

  • DIY
  • Self manage with subcontractors
  • Main contractor with subcontractors
  • Main contractor

Learn more about your options in this blog.

Each of these routes has its pros and cons. The more you do yourself, the more money you’ll be able to save. Not only that, you’ll have greater control over your project and be able to know where your materials come from, as well as assess the standard of work throughout each stage. However, it’s likely your build will take a lot longer to complete, and you run the risk of having to undertake expensive repair work if your work isn’t up to a high professional standard.

Should you project manage your own extension?

A typical project manager will oversee…

  • Preparing your tendering package
  • Interviewing / reviewing potential contractors
  • Preparing your construction contract
  • Devising a payment plan based on milestones
  • Site supervision
  • Work assessment
  • And general relationship management

Taking on this role for yourself will ensure that you’re able to keep a close eye on your project, while also saving you money from hiring a professional. However, this isn’t a small job. You’ll need to make sure you have the time to commit to visiting the construction site often, the knowledge to know when works aren’t being correctly executed, and the confidence to deal with tricky situations. If confrontation isn’t your strong suit, you might struggle when faced with a contractor who isn’t fulfilling their contractual obligations.

Learn more: what is a project manager and do you need one?

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Do you have permitted development rights?

Permitted development rights were created by the Government to allow homeowners to extend their home, without the need for planning permission, as long as said development follows a strict set of guidelines. These rights do not extend to all homes. For example, no one living in a flat or maisonette has permitted development rights. Nor do some homes that are located in conservation areas.

Having permitted development rights makes planning a lot easier. Though you won’t require planning permission, you will need to get a lawful development certificate, in order to prove your build was done legally to future buyers. Not having to worry about planning rejection will also mean you won’t have to worry about repeated application and revision fees.

Learn more about your Permitted Development Rights here.

Don’t forget building regulations

While many people understand the need for planning permission, building regulations can often be forgotten about. These regulations set out all the safety standards your property must comply with, if you fail to meet these standards you could face penalty fines or even be asked to demolish your build.

Building regulations are extensive and cover…

  • Structure
  • Fire Safety
  • Site preparation and resistance to contaminants and moisture
  • Toxic substances
  • Sound
  • Ventilation
  • Hygiene
  • Drainage and waste disposal
  • Combustion appliances and fuel storage systems
  • Protection from falling, collision and impact
  • Conservation of power and fuel
  • Access to and use of buildings
  • Electrical safety in dwellings

To ensure these guidelines are met, we highly recommend commissioning a building regulations package. This can be put together by your architect or by some structural engineers (more on these guys below), and it basically involves adding technical details to the drawings you had put together for the planning stage. These highly detailed drawings can then be used by your contractor to meet these requirements.

You will need a structural engineer

All extensions require input from a structural engineer, who will provide the key structural calculations your contractor will need to put your project together. These technical specialists will assess your project and provide guidance on…

  • Materials you plan to use
  • The site location
  • Weight of the build
  • Structural support needed

Learn more about all the professionals involved.

The more details you have, the better

It’s important to go into the construction process fully prepared. One of the reasons why we advise you to commission a building regulations package is because it protects you from bad builds. Many builders will claim they’re able to meet building regulations, but if they should make a mistake, it will be very easy for them to lay the blame on your side if these technical details weren’t provided.

By providing highly detailed drawings for a contractor to work from, you’re demonstrating the builder had all the information they need to provide a quality extension - this will give you strong legal grounds, should anything go wrong.

Kitchen extension project

Where will you live during construction?

It’s a factor often overlooked by homeowners, but will your home be habitable during the construction of your extension? Depending on the work, your water may have to be shut off, you’ll have builders moving material and waste through your home, and you may lose vital space - like your bathroom or kitchen.

When it comes to facing construction, you’ll have a few options. If the work is happening at the rear, and your garden allows your contractors to avoid going through the rest of your home, you could stay put. Alternatively, you might opt to rent another home with a short-term contract. Moving will be a pain, but will let you have a normal home life for the length of the build. Caravans are another option if you have space nearby. However, families with kids might not relish the idea of such close quarters.

Can your boiler handle a larger home?

If you’re creating more space, you need to think if your boiler can handle the extra pressure this presents. Whether your extension will mean an additional room or creating a large open-plan layout, this will add extra strain to your existing system. To avoid your boiler having an unexpected meltdown, it would be wise to check in with your provider to understand what your boiler can and cannot handle.

It’s worth bearing in mind, the UK government is pushing for the removal of gas boilers to help tackle the climate crisis. If you’ve got a dated gas boiler, now might be the time to make a switch!

Who will do your designs?

The obvious and most recommended option would be that you get an architect to design your extension. However, there’s no law that says you have to go down this route. Some people get a contractor to draw their designs, or you could even do them yourself.

So why choose an architect? For starters, it means you and your home have much better protection from bad practises. Unlike contractors, architects are held to a statutory code of practice and undertake years of training before being allowed to produce designs. Not only that, they’re able to act as your planning agents, meaning you have a much better chance of securing planning approval.

Ultimately, if you’re extending your home, you want to make sure you’re getting the best build possible. That means utilising the most space, getting the best layout, and avoiding as many admin headaches as you can. All this should come into consideration when it comes to your early design decisions.

How much do architects charge? Get a Resi Quick Quote!

You’ll need to take out insurance

Fun fact, your current home insurance will stop covering your home the minute you start to construct your extension. In fact, it stops being applied for any structural change. For this reason, you’ll have to take out site insurance, to make sure you’re still protected.

You’ll also need to check what your contractor’s liability insurance covers - if they have insurance at all! To make sure you don’t fall foul of cowboy builders, we recommend looking into Developer Insolvency Insurance. This will protect you in the event your contractor goes bust - which is more common than you might think.

Learn more: A guide to insurance, construction, and protecting your home


Have you got any potential obstacles in your way?

Sometimes there are forces out of the homeowner’s control that can derail their extension. What impacts a build can sometimes come as a surprise, as to anyone not in the industry, they can seem harmless.

For instance, did you know that some trees are protected? It’s known as a TPO (Tree Preservation Orders), and if you have a protected tree in your garden it’ll mean you lose your permitted development rights and will need to look into getting planning permission. Altering a protected tree is even a criminal offence.

Other obstacles you’ll need to consider…

  • Sewers under your home
  • Nearby roads
  • Conservation areas

Learn common reasons why planning permission is refused.

Are you on good terms with your neighbours?

Your neighbours could play a big part in your project’s success if you share what is known as a ‘party wall’. Put simply, a party wall is any wall, boundary, or structure that straddles your and your neighbour’s land. If you plan on building on, or next to, this party wall, you’ll be required to come to a ‘party wall agreement’ with the person next door.

As we’ve touched on, this can go one of two ways. Your neighbour could give consent straight away, or you could be looking at a lengthy (and costly) legal process. Therefore, it doesn’t hurt to start buttering them up sooner, rather than pay for it later.

Learn more: Our guide to serving a party wall notice


Want to start your home extension fully prepared? Remember to double-check this to-do list…

  • Research property prices in your area and check for ceiling prices
  • Make sure your budget includes every stage of your project
  • Are your timescales realistic?
  • What are your DIY options?
  • Do you have what it takes to be a project manager?
  • Check with an architect to understand your permitted development rights
  • Protect yourself with a building regulations package
  • Don’t forget you’ll need a structural engineer too
  • The more details you have for a contractor, the more protected your home will be
  • Remember to plan your accommodation for the construction stage
  • Can your boiler handle powering an extended home?
  • Who will design your project? Remember, an architect is always the best choice
  • Protect yourself with the right insurance plans
  • Ask an expert about the planning hurdles you might face
  • If you have a party wall, make sure you butter up the neighbours!

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