Building an Extension 2024: Full Guide 

Introduction 

‘Building an Extension’ to your property includes a vast number of extensions and renovations that can be carried out. This guide takes you through all of the key considerations you must encounter for when planning an extension. 

Let’s start at the beginning… Ask yourself what it is that you want from your extension. What frustrates you about your property? Maybe its the size of your kitchen, the fact you have no downstairs loo or you need another bedroom upstairs. Make sure you are clear on what you need from your extension from the very beginning. If he extension you are planning does not resolve your main frustration, re-think your extension. 

Get inspired before you start your works. There is no such thing as a cheap home extension anymore so make sure you have looked at other designs, styles, layouts and materials so that you have an idea of how you want your extension to the look, from the offset. 

Different Kind of Home Extensions 

There are so many different kinds of extensions: 

• Single Storey Extensions 
• Double Storey Extensions
• Side Extensions 
• Front Extensions
• Roof / Loft Conversions / Extensions
• Garage Conversions 
• Basement Conversions 

You need to consider what kind of property you have and which kind of extension does the property lend itself to. If you need another bedroom and your loft is a ‘cut roof’, then changing this space into another bedroom is going to be much easier and much less expensive that a two-storey house extension, to gain the same space. 

Timescales

For any home renovation / extension project, timescales are continuing to increase - irregardless of the size of the project. It is obvious that the larger the project, the more time it will take to build, but this is not the only consideration. 

Finding a good, reputable builder for a large extension project within a year can be a massive challange these days, and even when you have a builder lined up, it is likely that due to materials, permissions etc. the projects they are working on between now and your project beginning, are likely to overrun. 

Here is a basic timeline that can indicate your rough project timeline: 

Planning: Your Discretion 

The planning phase accounts for the time you spend planning what you would like your project to be. This can be anything from the basic requirements of your extension, to the design style you want to achieve and what features / materials you might want to include. 

Design: 4-8 weeks 

The Design phase is the process of either finding your architect, or the the design service / route you chose to take and the creation of your plans / designs for the extension. This can vary massively depending on the size of the project, its complexity and your property. A large glass extension on a listed building is going to take significantly more time to design than a simple, single-storey extension to a detached home. 

Planning Permission: 8-10 weeks 

Planning permission is likely to be a requirement for your home extension. There are a number of extensions / altertions that do not require planning permission that fall within Permitted Development Rights which we have outlined in more detail below. Planning permission is required for all other extensions and is required on every project, no matter how small in areas such as a conservation area or Area of Outstanding Natural Beauty. 

In order to make the planning process as simple as possible, we recommend using an architect or planning professional, and filling out the application form in as much detail as possible. Planning applications can be refused, which can then mean you need to go to appeal and the process can extend, becoming months long. More on planning permission later on. 

Technical Design: 1-2 months 

Once you have planning permission, you need to make sure you comply with building regulations and have your plans checked by a structural engineer. This is particularly important in insuring the renovations you are making to your property does not effect the structure of the building. More on this later. 

Party Wall: 1 week - 3 months

Our top tip here is to be on good terms with your neighbours, before the project begins. A party wall agreement includes any renovations that might impact your neighbours. Party Wall agreements are needed if you share a wall with your neighbour, if you’re building on a shared boundary or excavating within 3meters of one. More on this later. 

Tender Process: 2-4 weeks 

The ‘tender process’ is the process of finding a builder for your project, if you don’t already have one. Your design professional, such as an architect, will help you with this - depending on the design route you chose. More on this later. 

Building: 2-6 months 

Building an extension can take anything from 2 - 6 months, depending on the size and complexity of the project. The key to keeping the build-time as quick as possible, is to have materials on site, all the right professionals lined up and a good project manager. More on this later. 

Budget 

Budgets are tricky and very rarely does any project stay within the original budget. Remember to always include VAT (20%) in your calculations and allow for a contingency - we recommend 20%. When you budget your project, try to go into as much detail as possible. There are always more costs that occur along the way.

We always recommend you include any other upgrades you might make to your home during the project. When you have builders on site, it is always recommended that you use this time to make other upgrades to your home, such as improving your home insulation. 

Our top tip when it comes to budgeting is to make sure you fit your extension and renovations to your budget and not the other way around. 

Costs

The cost of your project can depend on a number of factors: 

• Size of the project 
• Complexity of the project
• Where you are in the country 
• Choice of materials 

As a general rule of thumb, single-storey extensions work out to be slightly more expensive than double storey extensions. Single-storey extensions can roughly cost between £1,800 - £2,400 per square metre, white two-storey extensions can cost roughly between £1,500 - £2,000 per square metre. 

However, it would not be recommended to plan your extension based on any figures that you read online that are not specific to your project / location etc. For example, areas in the South compared to areas in the north can double your labour costs, which will have a massive impact on the cost of your project. 

This can also be true for the size, scale, complexity and finish of your project. A small, brick extension to extend the back of a detached property is going to cost significantly less than a large timber frame rear and side extension to a home in a conservation area. 

The Design Process

There are a selection of different ways that you can design / have your project designed. Your options are: 

• Architects 
• Architectural Technicians 
• Design & Build Contractors 
• DIY Design 

Your choice of designer depends massively on the vision that you have for your project, the design that you imagine and the end result to desire to have. If you are unsure of design of your project but desire the best results, it will always be recommended to use an architect due to their holistic approach. More on working with an architect later. 

Although architects are always good value for money, they are not always allowed for within peoples budget, which is when you may turn to a technician to draw out the exact plans you have imagined, you may hire a design and build contractor (at the risk of a ‘one size fits all’ result) or you may learn how to DIY the design and plans yourself. DIYing your home design and plans is a time consuming and complicated process but not impossible! 

Hiring an Architect 

Hiring an architect for your project may initially seem like a luxury service, however, as the cost of any project increases, hiring an architect is much more of a necessity than a luxury. Architects are able to asses with you what it is you want from your project from the offset. If cost is a concern, by hiring an architect, they are able to use their experience to suggest materials and practices that can keep costs in check while still achieving the goals of your project. 

Architects also prove to be the best value for money due to their help across the full spectrum of the project. Not only do architects ensure the best design for your project, they are able to help with the planning permission process, tender the work and help manage the project by working alongside the main contractor to ensure the delivery of the end project is as expected (having likely inspected the site throughout the job). 

Consult with an architect on your project today with no strings attached at Space That Inspires.

Professionals

Hiring the right people / professionals for your project is imperative to the success of your project. Whether you are hiring your architect, main contractor, plumber, electrician, decorator etc. the same rules will always apply:

1. Always ask friends and family in the area for recommendations 
2. Always ask to see a portfolio of previous works 
3. Get their opinion on your project and monitor the response (do they think this work is feasible for them?)
4. Use your gut instinct - you need to allow time for any professional to go through your project and quote, however, if you’re receiving slow replies and they’re taking a lack of interest in your project, they probably aren’t the right person for the job! 
5. Check the tradesman you’re working with are insured, particularly your main contractor

Tendering for works can be a lengthy process. If you are working with an architect, they can help you tender the works within their roster of contractors they use regularly. If you are not working with an architect or design and build contractor, then we recommend you tender your work to up to 6 different builders / contractors, which you can whittle down as you compare timescales, price and their vision of your project. 

With every professional that you hire, be very careful to understand exactly what the scope of their work will include and what they are going to charge for that work. Where you can, try to pay at the end of a project, to ensure the works are complete before they leave site. 

Planning Permission 

Planning permission / your planning application can take up to 8 weeks to process, and that is if the application is accepted straight away. Many planning applications fail, which means you can either appeal the decision, or it requires the design to be adjusted, depending on the reason for refusal. 

The planning process can be a lengthy one, and not one you want to make any longer than it has to be. In order to have a successful application, our top tips are: 

• Hire a professional, some text
  • Your architect would apply for planning permission for you
  • If you do not have an architect, you can consult with a chartered member of the Royal Town Planning Institute.
• Provide as much detail as possible on your application 
• Make sure the application is correct - avoid making any silly mistakes
• Use your local plan and ensure the design on your project is likely to be accepted (if you have designed the project on your own)

There are some cases where you can extend your property without the need for planning permission. These extensions and renovations fall within Permitted Development Rights. More on this next. However, if your design is on the cusb of not being accepted, we always recommend to get planning permission anyway, or at least a Permitted Development Certificate. 

Permitted Development / Lawful Development 

Permitted Development or Lawful Development is a way of extending or renovating your home without the need for a full planning application. Lawful Development is a set of rules / guidelines that outline simple modifications for the following renovations:

1. Rear Extension 
2. Side Extension 
3. Two Storey Extension 
4. Loft Conversion 
5. Garage Conversion 
6. Outbuildings, Garden Rooms and Porches 
7. Change of Use 
8. Other Permitted Development Rights 

To summarise broadly, you can build up to 8meters out of the rear of a detached property in England, 4meters if not detached. The extension cannot be built higher than the highest point of the original roof. All renovations must be built to the back and side of the property but must not wrap around the property. The area extended cannot be more than half of the land surrounding the existing property and must be built with materials to match the existing property. 

It is very important that if you decide to renovate within the permitted development guidelines, that you are certain you are within the guidelines, otherwise you are at risk of being requested to return your property to its original condition. This is why we recommend to either apply for full planning permission if you are on the cusp, or at least a Lawful Planning Certificate if not, which is beneficial if you ever wish to sell your property.

Learn more about Permitted Development here. 

Neighbours, Boundaries and Party Wall Agreements 

Whenever you embark on a home renovation / extension project, it is always so important to keep your neighbours on side. Best practice is always to discuss your plans with your neighbours from the beginning, so they do not learn about your aspirations when the council are asking for their opinion on your planning application or when you need them to help with your party wall agreement. 

‘Party Wall Agreements’ include anything from a shared wall between you and your neighbour, to informing the neighbours of any ground excavations that will aka place within 6 or 3 meters of your neighbours property - depending on the depth needed for the new foundations. They are mostly needed for loft conversions, side extensions and any extensions where steel supports are required or the digging of new foundations.

Building Regulations 

Every home extension will need to comply with building regulations, however acquiring building regs always seems much more complicated than it is. They are important because you need to ensure that any alterations you are making to your property does not effect the structure of the building and therefore your safety. To meet building regulations, you either have to: 

1. Submit a Full Plan - this means you send all of your plans to your local planning authority, who will send a building inspector to inspect the site, which will determine the approval of your plans. 
2. Submit a Building Notice - this is where you can submit a statement to your local planning authority, informing them that you are complying with building regulations, giving the building control department a 48 hour notice period of your project before you start works, and they will send someone to inspect during the project.

We always recommend to submit a full plan, just because you do not want to begin your project to find out that there are compliance issues with your build which will need to be rectified before you can go any further. 

Building regulations are so important, especially on a listed building, where you need full internal and external plans to be approved before you can make any alterations to the property. 

Project Management

The project manager of your project depends on who you hired to design and construct your extension. If you have an architect and main contractor, the contractor should work as your project manager, referring to the architect if there are any design or technical queries. This is even easier if you chose to use a Design & Build contractor as they will see the project through from the design to completion. 

However, if your budget didn’t allow for either of those options, you might have a lead builder and then be responsible for all the tradesman working together on your project eg. your plumber, electrician etc. The only way for success here is to keep extremely organised. Use your builder to help you build the project timeline and ensure that all materials are on site for when they are needed. Organising this is not impossible, it just needs you to be on the ball with what is happening with each tradesman at each point of the project. You do not want a tradesman on site, unable to do their job due to someone else's hold up. 

Project Stages

A project can be split into 5 stages: 

External Construction 

This phase includes preparing the site eg. scaffolding and skips. Excavating the construction area, preparing the groundwork of the project and building the foundations for the extension which might include connecting the drainage system. Then building the walls and roof, and fitting the windows and doors.

Interior Work

This includes the reconfiguration of the internal space, and installing insulation to the property.

Internal Fit Out 

Plastering the walls and ceiling, laying the floor and fitting / installing electrics and plumbing. This also includes the fitting of large applications such as the oven etc. 

Interior Decor

Painting, decorating, adding the light fixtures and furniture. 

Final Inspections 

This is where you cover any ‘snagging issues’ with your contractors, as there might still be things that are missing or not quite right that need to be completed before the project is deemed complete. A final inspection also needs to take place to ensure the building complies with all safety and building regulations. 

Insurance 

Make sure your home insurance company is aware of the project and the chnages you are making to your property. Depending on the size of the renovations, it is unlikely that they will not insure the build, however the cost of your insurance may change due to the changes you are making. Also, getting a warranty on your project is advisable as you want to ensure that you are covered for any structural defects or fault workmanship. 

Keeping Costs Down 

If you are looking to keep the cost of your project down, here are some of our top tips: 

• Keep your home extension design simple and small. A lot can be achieved in a small amount of space so be smart with the design and don’t get carried away with the size. 
• Think about the materials you wish to use, are they the most efficient and cost effective options. 
• Make your extension work for you - don’t forget about the importance of insulation etc. 
• Stick to the plan! Costs always shoot up when homeowners start making changes to the project as it is being built as it becomes extremely difficult to monitor costs and prices. 
• Upcycle, a new extension does not need to be filled with all new items.
• Get a professional opinion, those that have experience in the industry eg. architects and builders and going to be able to suggest ways of keeping your project costs down. Consult with an architect today at Space That Inspires.

Financing

Depending on the amount of money your require, there are lots of different ways you can finance your project. The obvious choices are: 

• Credit Cards: the best option for when you just need a few thousand £. You can compare the different cards available online. 
• Personal Loan: This might be the best option if you need to take out more than £10,000 
• Remortgage / Home Improvement Loan: These are a great option if you are looking to do a significant project that will also increase the value of your property. 

Our top tip: Always keep a close eye on your finances. Once a project begins, it is very easy for finances to get confusing and hard to track and this leads to money disappearing on the project. Make sure you keep a close eye on the project finances, from the beginning, throughout and to the very end. 

Adding Value

If you are hoping for your home extension to add value to your property, then you should consult with a local agent once you have the plans. Although it is likely that added space would increase the value of any property, there is also a ceiling that can depend on many external factors. If this is the goal of your project, be sure to check this before you begin works.

Conclusion 

If building an extension is something you desire for your property then take the first step and consult with an architect and your project now, its time to take the first step by speaking to an architect for a one-time fee with no strings attached. It’s time to figure out what can be achieved!

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