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How much does a home extension cost?

How much does a home extension cost showing sketch design of extended home with yellow chair

How much does a home extension cost?

As residential architects, one of the most common questions we are asked is ‘how much does a home extension cost?’ We work with a range of clients, from experienced developers to young couples embarking on their first project of this kind. Whatever the scenario, the budget question tends to be front and centre.


While there are some typical costs associated with a home extension, there is no one fixed answer. It really depends on the type of project, the size and complexity of the extension and the brief. There’s a saying that the most used building material is money, so it’s important to go into a project equipped with the facts. We’ve put together this article to help you approach budgeting with confidence.



What’s your home extension budget?


As professional architects, it’s our duty to have clear and open discussions about budget with clients. It wouldn’t be ethical or professional to ignore the question or to leave clients to their own devices.


First of all, it’s a good idea to have a ballpark figure in mind. People often ask us, ‘what budget should I allow for a home extension?’ There are different ways to decide upon a sensible budget, though a general figure that you’re comfortable with is a great place to start.



How to set a budget


You may have heard of rates per square foot or square metre. The idea is that for every square foot extended the cost is multiplied by a set rate. This makes budgeting straightforward from a mathematical point of view at least. Your architect can inform you of typical rates once the brief is established.


The trouble with rates per square foot is that they don’t allow for contingencies. Unexpected circumstances which crop up during the planning or building phases have a cost associated with them. Rates per square foot tend to work on the assumption that everything progresses in a linear fashion with no hiccups. Which rarely happens!


The most effective way to set a home extension budget is to have an open conversation with an architect.


They can bring in professionals who are knowledgeable about costs, for example, quantity surveyors or builders.  These professionals can help to generate a list of costs, based on your ideas, the brief and architectural input. This will help give you a more realistic picture and set an accurate budget to work with.



What’s your vision?


With any home extension or home renovation project, cost is always going to be a factor. Be clear about what you want to achieve, even if you don’t have a figure in mind at the start. Clarity will make it easier to decide a budget when you speak to your architect and other professionals.


Architects design according to the brief, with a pencil, artistic flair and design sensibilities. So, if you task an architect with a large project, finished to a very high standard, expect to see a higher figure.



What to consider when planning a home extension


When you’re in the process of defining your brief, there are a few things to consider. These factors may help you decide what would be a sensible amount to spend on a home extension. Your architect can help you sense-check your numbers, if you’re unsure:


  • Where is the property? And what are sales values for the street/area?
  • What type of house is it? How is it situated? For example, is it detached, on a sloped site, etc?
  • What’s appropriate to spend on the property?
  • How long do you intend to live at the property?


‘Appropriate spend’ is often subject to hearsay and rumour. You may have heard the saying that a certain percentage of the property value is an appropriate amount to spend. Twenty per cent of the house’s value is quite a common outlook. There’s nothing wrong with that as a rule of thumb. Do bear in mind, that as with rates per square foot, it’s vague and doesn’t take into account the nuances of the project, or any contingencies.



Home extension costs: a word of warning about hearsay and rumour


Take general rules for the cost of home extension projects with a pinch of salt. You may have spoken to friends and family who’ve had extensions or remodels done. Perhaps they shared with you the costs that were involved in their project. While we don’t want to cast aspersions, figures can be distorted. There are plenty of innocent reasons for the Chinese-whisper effect to skew the numbers you hear, ranging from vagueness, forgetfulness over time, a change in the market, a difference in scope or brief, a difference in material usage or build quality, to name but a few.


It’s always worth speaking to professionals to cost the project that you have in mind. An architect is instrumental in those conversations.



What does your home extension budget cover?


Once you’ve got a ballpark figure in mind, think about what the budget has to pay for. This helps refine your thinking about the project, as well as clarifying whether the budget you have will deliver what you want to achieve.



How far do you want to go with the budget?


Think through the following exercise with your architect and you’ll have a much clearer picture. Professionals who do this work daily bring value, because they have up-to-date costs at hand. They have anecdotal figures of recent projects and live examples. And while your architect might not know the price of everything, they’ll know someone who does.


Remember to factor the following costs in from the beginning, so they don’t come as a shock later on:


  • Architect’s fees
  • Consulting costs: fees for any experts needed, for instance planning experts, or environmental officers, heritage consultants, etc. Find out more about the professionals needed to complete a project in our forthcoming blog post
  • Site overheads: site hoardings, welfare and safety, machinery and plant hire
  • Kitchens and/or bathrooms
  • Furnishings: Furniture and built-in items inside and possibly outside
  • Décor
  • Outside space/garden: if the interplay of the indoors and outdoors is an important feature of the brief, you’ll want to ensure that your budget covers the garden design, furniture and features, possibly even through to outbuildings
  • Ancillary costs that feed into the project, such as legal fees, freehold or leasehold agreements
  • VAT, applicable to services and materials


The building works, labour and materials are only part of the project cost. There may be other things needed to ‘get the job done’. While it can be intimidating to tackle a vast array of costs at the outset, the aim is to get an idea of the total project cost. This puts you in a position of greater certainty, because you’re prepared for all of the elements your budget will need to encompass.



How architects add value


We recognise that for someone who has never been involved in a project like this before, it’s difficult to shape all of your ideas, visions, hopes and dreams into a brief, then into a scope of work, and finally to equate that to a defined budget. This is where an architect proves their value.



Architects can point out red flags


Bear in mind that you always need a contingency plan. Having the funds to deal with unexpected situations makes the experience less stressful. While nobody has a crystal ball, an architect can forewarn of the kind of things that might occur:


Typical contingencies:


  1. Unforeseen circumstances: Once the build has started, structural or service-based concerns may become apparent. These have an impact on the build and the cost
  2. Changes to the brief: You might find that a certain material in a certain room doesn’t appeal or doesn’t work. Perhaps you decide to change the use of the space
  3. Enforced change: The builder, the client, or the architect may make a change to something consciously. There could be a myriad of reasons, relating to time, budget or practicality


A good architect will set these expectations with you at the beginning so as to avoid surprises. We can never eliminate every unexpected circumstance, though it’s good to be aware of possibilities from the outset.



How contingencies impact home extension budgets


If you really cannot go over a certain budget, it’s critical to be honest about it, firstly with yourself, secondly with your architect and build team. By doing so, the professionals can help you create something that’s mindful of your brief and delivered in a way that respects your budget. Being realistic in the beginning gives you the best chance of creating something that meets your vision and doesn’t leave you in a tricky position financially.



The value 50 Degrees North Architects bring to a home extension project


At 50 Degrees North, we’ve worked on hundreds of residential projects. We’ve seen many different types of project and we can supply details of builders who have accurate, up-to-date cost information. We can also commission a cost advisor (quantity surveyor) to provide an indicative budget cost plan in the pre-planning phase or a detailed cost plan later when the project is designed and detailed.


We’re familiar with the kinds of additional costs that come up and, as architects, we have weekly, sometimes even daily, cost conversations with consultants and construction professionals. Architects can also facilitate an ongoing conversation throughout the project and can value the work as the project is built on site.


The best thing that 50 Degrees can offer, particularly in terms of budgeting, is to tell it like it is.


When you engage professionals, you get the warts-and-all approach. It’s not about removing the inspiration or killing the creativity, it’s about ensuring that the inspiration is firmly rooted in practicality.


We keep advising you on where any changes or contingencies lead financially, so you are informed at all times.



Value vs cost: the intangible price of a home extension


One of the least-discussed elements of a home improvement or a home extension is the value. We don’t mean the re-sell value, rental value, or the yield per year. We’re not talking about bang for your buck. We’re talking about what it means to you.


Value means something different to everyone. Value is intangible. The question you need to ask yourself going into any project, is: ‘What is the value of this to me? What is the value of this to my family and our lifestyle?’


For some people, creating a fantastic space, that’s beautiful, unique and inspiring really matters to them. And that has a value.


For others, building something that is going to help their family have a good life, to enjoy the space, and love living in it for many years to come is the most valuable aspect.


Besides the monetary cost, besides all of the pragmatic financial implications, such as the value added to the property, it’s worth thinking about what you would like to gain from the project.


What do you hope to achieve with the project, besides increasing the square footage of your house?


Maybe you’d like to create a forever home? Perhaps you’d love to help out elderly relatives and house them with you? Or maybe you’re simply looking for somewhere to enjoy your retirement.


Whatever your reason for extending your home, the deeper meaning is truly where the value of your project comes to life.



Let us help you set a budget


There’s no straightforward answer to the question of how much the building work will cost. It really does depend on your budget, what you want to achieve and how much you’d like to spend doing so.


One thing we can say, is that budgets don’t have to be scary. Being open and honest with your architect means they can give you the best guidance possible.


And when you’ve got a team of professionals and you’re comfortable with your budget, you can enjoy the process of bringing your vision to life.


We hope that you found this guide to home extension costs useful. If you’re thinking of starting a project, and you’re not sure where to begin, get in touch for an initial conversation. We’re more than happy to listen to your ideas and concerns – perhaps we can even help you see that what you have in mind is possible!