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House extensions: The Ultimate Guide



When it comes to a house extension, you’ll always want to make sure your home stands out from the crowd. If you’re a fan of home makeover shows you may know all about how to wow your guests by creating something impressive with your home décor.

An extension is a great way to create more living space without having to move house, making it a much cheaper and more convenient option. Extensions can add value to your property in addition to that much-needed living space, and with the help of an expert team, you can be sure that the extension you add to your home will be perfect for your needs.

Home extension types

Good news! When it comes to extending your home there are infinite possibilities. But with so many options to choose from, where do you start? To help give you some ideas our architects have created some 3D examples of the most popular extension types.

Front house extension

Hallways are often a depository for takeaway leaflets, muddy wellies and kids’ scooters. What better way to hide them away than with a front extension or porch? They’re also perfect for making those smaller downstairs offices a little roomier, letting you get away from the hustle and bustle of the main house. Not only this, but it’s the first part of your house people will see when they come to visit.

Semi-detached house extension

Semi-detached house extensions are the most popular type as there is often space to both the side and rear. They’re also separated from the neighbours so there is often scope to have a single storey extension or even a two storey side extension (if there’s space). In some circumstances you can even create wraparound extensions which add a huge amount of space. The best part is that lots of semi-detached house extensions can be built without planning permission through permitted development.

Terraced house extensions

Although terraced houses can often be a little narrower than other types, there is still lots of scope to be creative. Both rear extensions and loft conversions are a fantastic way to get a little bit of extra living space or a new bedroom. Some terraced houses benefit from those narrow alleyways to the back. A terraced house extension is the perfect way to extend and make that narrow kitchen a little wider…. perfect for entertaining!

Rear house extensions

Rear extensions, conservatories and orangeries are without doubt the most popular type of house extension, and there is so much scope to be creative. There is also lots to consider: The depth, height, width, materials, amount of glazing. The good news is that rear extensions can be built without planning permission in some case. They can also be used for so many different things. Perhaps you want a huge dining table to host dinner parties or a huge sofa for movie nights!

Loft extension

Loft conversions are one of the most cost-effective ways to add space to your home. This is for the simple reason that as most of your loft already exists, there are minimum building works required to make the loft usable. Most lofts in the UK are built through Permitted Development without Planning Permission, which allows up to 50 cubic metres to be added. This is loads of space, and usually means you can fit in an extra master bedroom and en-suite bathroom to add a whole new living area to your home.

House extensions costs

Estimating how much an extension will cost depends on a number of different factors (which we will go into in more detail below). The most accurate way to estimate the total cost is to first work out how big you would like your extension to be.

Let’s say it would measure 4m x 5m (20m2 in total). The next step is to estimate the average construction cost per m2. The average cost/m2 for an extension is approximately £2,700/m2.

So…20m2 x £2,300 = £54,000.

That would be the average cost for both the materials and construction.

Factors affecting the cost of an extension

  • How big will your extension be?
  • No. of storeys?
  • How much glass would you like?
  • Materials and finishes – basic, medium, stunning
  • Ground conditions – clay, sand, chalk?
  • The build route you’ll take – how involved in the project you’ll be?

How can you save money when building an extension?

You might be worried that while you want impressive results, you don’t necessarily have an impressive budget to match. Not to worry! We’ve been doing this a long time and our team know lots of tips and tricks to help you save money on your extension.

Get Professional Advice: Step 1 in any extension project…find yourself a good architect. It’s important because they will be able to take all your ideas and work out how to deliver them while also sticking to your budget.

Choose a simple design: We know that after watching an episode of Grand Designs the aspirations of homeowners goes sky high. Glass roof extensions and huge expanses of cantilevered glass can look fantastic, but can cost a huge amount of money. Simple designs can also look stunning and should never be underestimated.

Stick to your budget: Once your architect has prepared the initial design and confirmed that it is within your budget, do your best to make as few changes as possible. Making changes once your builder has already started means costs can quickly mount up – so maybe stop yourself from watching property shows once your plans have been submitted.

Manage the project yourself: Builders will usually charge an extra 15% – 20% on top of labour and building materials to manage the project themselves. You can save a huge amount of money by managing the project yourself and sourcing the various tradespeople.

Source your own materials: If your builder has offered to purchase all the materials for your extension, the chances are they are marking those prices up which is common practice. By picking materials yourself you can avoid that.

Financing a house extension

It’s easy to take to Pinterest, watch an episode of Grand Designs and start planning your dream extension. The slightly trickier part is making sure you have sufficient funds to pay for all your incredible ideas. Below are 4 of the easiest ways to finance your home extension project:

1. Remortgage your home

As long as you have enough equity in your home and can afford the repayments, it is possible to remortgage to pay for your renovations or extensions. There are remortgage brokers who specialise in helping people raise money for home improvements. Most homeowners usually remortgage in advance of carrying out the work, but if you have the cash, another great option is to remortgage after the extensions have been completed. The advantage of this option is that the extensions will increase the value of the property. This means you might have access to more equity.

2. Second charge mortgages

Second charge mortgages are sometimes referred to as ‘homeowner loans’ or ‘secured loans’.  They are a good option if you have a decent amount of equity in your home. Equity is the amount of your home that is mortgage-free. For example, say your property was valued at £400,000 and you had £100,000 outstanding on your mortgage, you would have £300,000 worth of equity. A second charge mortgage is a separate facility to your existing mortgage. You could either go to your current lender or a new one.

3. Take out an unsecured loan

An unsecured personal loan can be a convenient way of financing an extension. The loan isn’t secured on your house or other property, so you tend to need a good credit rating and the costs will generally be higher than secured borrowing. Typically, you can borrow up to £30,000 (sometimes more).

4. Use savings

If you have savings to cover the costs of your extension, that’s great! However, interest rates are not very competitive for savers at the present time and it’s worth assessing whether you want to outlay such a large amount of your own money in one go. Think carefully about any interest you may be paying if you borrow the money. Everyone’s circumstances are different, so it really is a personal choice.

House extension ideas

Play with Brick colours

Our client was in a similar situation to lots of families. They had lots of kids and needed the extra space to hide some toys and give them space to run around. Their main brief was that they wanted something ‘different’ which is our favourite sort of challenge.

We love the juxtaposition between contrasting materials. We decided to go for a grey brick which looks incredible against the house’s existing beige colour. This was quite a simple idea but creates an elegant and modern finish. Oh, and as the family like to have friends and family over for dinner we designed a sunken firepit which is great for sipping hot chocolate (with marshmallows) on those winter nights.

Timber cladding

This is one of our favourite extensions. When the couple first move din, the rear looked more like a jungle than a garden. Our client liked the natural look so we opted for timber cladding. We chose a type which is untreated which means it will naturally weather over time for a more natural look. On the interior we also decided to leave exposed brick on one side. The irregularities and natural imperfections of exposed brick is what makes it so special… it’s perfectly imperfect.

Interior design must haves

We’re a fan of anything different, and every project we design is unique. Here are some interior design features we love.

In floor wine cellar

Love your wine and want to make your friends and family jealous? There is no better answer than a spiral wine cellar in your new kitchen extension. It also serves a practical purpose as it will keep your wine at the right temp and humidity levels. A word of warning though – you will definitely have to host more parties if you have one of these!

Hidden book case door

How have I gone my whole life without a hidden bookcase door?! There are so many reasons to use it. Perhaps you’re trying to escape some noisy kids. Or you need a place to secretly wrap Christmas presents. A hidden room is the perfect option, and definitely reminds you of something from an Enid Blyton novel.

Indoor slide

We’re not saying stairs are dull, but no house should be without its own slide. We know what will happen… it’s built for the kids but we have no doubt the adults will be using it just as much.

What is the house extension process?

The design and planning process can appear a little daunting if you’ve never been involved with an extension before. We try our best to make it as simple as possible by breaking it down into simple stages.

  1. Digital measured survey: Our meticulous surveyors will come to your house and take a digital scan to make sure we have all the measurements and distances perfectly. Our architects will use these measurements to create a 3D model of your existing house.
  2. 2D & 3D Design: Once your existing house has been modelled, our architects will sit down with you and begin to design your dream extensions. All our designs are in 3D so you will be able to see it before you even move in.
  3. Planning: At this stage most of the hard work has been done. Our expert planners will complete all the necessary forms and submit them to your local planning authority.
  4. Building regulations: This is the technical part. Your architect will prepare a set of technical drawings to make sure your new extensions meet all the relevant British Standards.
  5. Structural engineer: A structural engineer will then produce a set of structural drawings and calculations to make sure your new extension is safe and secure.
  6. Party wall agreement: You might need a party wall agreement if you’re building close to a shared wall or foundations with your neighbour.
  7. Start building: Now your builder can start their part and you can see your plans come to life.

Do you need an architect for a house extension?

A good architect will be super creative and have lots of ideas. They’ll play a huge part in your renovation or extension project and if you have lots of exciting ideas yourself, you can definitely bounce off each other in the design process. Here’s a few reasons why they’re so important.

Creative: This is the most important part. Your architect will be great at taking all your ideas and making them a reality. They will also be able to suggest some incredible and innovative ideas you might not have thought of.

Skilled and professionally trained: Architects undergo years of training and are hugely practical. Delivering even the most ambitious of ideas can be challenging, but in the hands of the right architect it will be easy.

Guide you through the process: The design and planning process can be complex to manage. Architects will have a huge amount of experience at navigating that process, making your journey as smooth and easy as possible.

Problem solving: Given how technical the design, planning and building process can be, unexpected problems will always raise their heads. Your architect will be a skilled problem solver to make sure your project stays on track and looks incredible when finished – so there’s no need to panic when something doesn’t quite go as planned.

House extension regulations

There are quite a lot of technical hoops your new extension will have to jump through to make sure the entire process runs smoothly.

There are three main categories to consider.

1. Planning permission or permitted development

Permitted development: There are certain types of house extension you can build without planning permission through ‘permitted development’. These include loft conversions, rear/`side extensions and porches (and lots of others). If your design meets the relevant Permitted Development legislation, you can apply for what’s called a ‘Certificate of Lawful Development’. It’s a sort of planning permission but rather than saying ‘approved’ your local planning authority will confirm your designs don’t require planning permission.

Planning permission: If your designs don’t meet the permitted development criteria you would need to apply for planning permission. That’s not necessarily a bad thing! There are quite a few advantages, the main one being that planning policies are less restrictive and can be applied in different ways. This means there can sometimes be some wiggle room, whereas permitted development is more rigid. The planning permission route often allows for more scope for you to be creative.

2. Building regulations

Once your new extensions have been approved, next comes the technical stage which is Building Control. This stage requires three main parts.

Detailed drawings: These are detailed drawings showing all the specifications and all relevant building notes for your planned extensions. Your builder will then have a clear and detailed set of plans to work from.

Engineers’ drawings/calculations: Your engineer will also prepare structural drawings and calculations. These will take into account the weight of the materials and the level of structural support required for your extensions or any other structural works.

Build Regulations submission: Once you have a set of detailed plans from your architect and calculation from your engineer, you are then able to submit your application for Building Regulations approval.

3. Party wall matters

A party wall is a shared wall between you and your neighbour’s property. For example, if you live in a semi-detached house, you will have one party wall separating you from your neighbour. If you live in a mid-terraced property, you will have one party wall on either side of you. If your extension involves building on or near a party wall, you would need to serve a party wall notice. This can be done yourself or there are specialists called Party Wall Surveyors who deal with such matters.

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