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Is It Cheaper to Add On or Build New?

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Is It Cheaper to Add On or Build New?

Deciding whether to construct a new extension or knock down an old building and start again from a fresh footprint can be a tough call - and there are all sorts of pricing and timing considerations to factor into your decision-making! So is it cheaper to add on or build new? We explore the benefits of a new build vs rebuilding a house, adding to a house and more.

As a very rough guide, if you simply want to create an extension, a new space of 30 square metres will cost around £30,000 - £48,000.

In comparison, developing a new property of a similar size from a blank canvas costs approximately £213,000. There isn't an obvious answer that will apply to every project since you may find that the second option is more cost-effective when you factor in the saleable value of your current property.

Discover Reliable Cost Comparisons to Add On or Build New  If you're unsure which route is best for you, the ideal starting point is to collate comparable quotes from trusted local contractors to help you analyse the pros and cons and start working on like-for-like budgets.

Complete our simple quote request form, and we'll have up to four contractors in your area send you pricing estimates to help you make an informed decision.

Average UK Costs: Is It Cheaper to Add On or Build New?

There are three main options if you're not happy with the size of your current home or want to reconfigure the layout to better meet the needs of your family:

  • Add an extension to any aspect of the house.
  • Sell up and buy somewhere else.
  • Start from scratch and build something new.

We'll run through a few price comparisons to give you an idea of the budgets involved in each option. However, it's important to remember that the cost of building new doesn't factor into what your current property is worth.

While you can easily add value with an extension, this might not be the best option if it will eat into your garden space or replace a valuable feature such as a driveway or off-road parking.

New Build vs Rebuilding a House - Average Costs to Build a New Home

Build Project Average Cost
Three bedroom home 90 to 120 square metres £126,000 - £300,000
Four bedroom home 140 to 200 square metres £196,000 - £500,000
Five bedroom home 200 to 240 square metres £280,000 - £600,000

Across the UK, a new build costs around £1,400 to £3,000 per square metre, or an average of £1,800 per square metre.

In many cases, those construction costs (albeit a rough guide) will be significantly lower than the price of purchasing a ready-made home with the right layout and number of bedrooms.

Checkout this time lapse video on what's involved with demolishing an old extension:

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Average Costs to Add an Extension

Extension costs are equally as varied, depending on whether your extension is a side return, rear extension, one or two storeys etc.

Extension Project Average Cost
Basic extension of 20 square metres £35,500 - £50,000
Medium extension of 30 square metres £53,250 - £75,000
Large extension of 50 square metres £88,750 - £125,000
Complex or premium extension of 30 square metres £75,000 - £100,000

There are multiple design options and variations on a typical extension design, such as a kitchen extension, loft conversion, extension down into the basement, or even knocking two properties together to create one larger space.

New Build vs Rebuilding a House - Average Costs to Demolish and Rebuild

Knocking down an old building and starting again incurs both the demolition cost and the cost of building from new (you'll find the averages above in our table of indicative new build budgets).

In terms of the demolition, the average prices are as below.

Demolition Project Average Cost
Small property 80 to 120 square metres £5,600 - £12,000
Medium property 150 to 200 square metres £10,600 - £17,000
Large property 200 to 250 square metres £15,600 - £22,000

Comparing the Price of Adding On vs Building New

Price is one of the biggest factors when deciding how to proceed with your planned construction, and it's important to have complete oversight of the budgets for either potential plan before moving forward.

Costs of New Build

When you start with a clear plot of land and build a new property to your specifications, it can be a costly project because you are starting from scratch and will need to begin with the basics, such as site clearance and laying foundations.

Most people use a project manager since a new build is a multi-faceted project which usually involves several contractors and can take many months.

The scope of work is much broader, so you need to invest in the materials, labour hours, planning permission and architectural work required to draw up a comprehensive set of building plans.

However this option can take longer, but it isn't necessarily more expensive than adding to your property or demolishing and building new.

When you consider what your home is currently worth, the cost of adding on, and then the final sale value of your property, it may be, long-term, less profitable than building new - on average, the cost of building a four-bedroom property is £196,000 - £500,000.

In contrast, the average sale price for a pre-built four-bed home is around £426,099 across the UK, but £1.285 million in Greater London.

Costs of Adding On

Renovating a home or adding an extension is generally cheaper than building or buying new, although much depends on the condition of the structure and the size of the extension you'd like to create.

Homeowners that want to build a large extension, especially one over 50% of the current property footprint or exceeding the height of the existing roofline, will need full planning permission.

If you plan to leave the rest of the building as-is, it will be cheaper than renovating the entire property as part of an extension project.

Older homes and period properties can cost considerably more to renovate, and it can be difficult to know what your contractor will find once work begins.

Typical instances where renovation or extension budgets can soar include where you have toxic materials such as asbestos or lead paint within your home, which were used in the original build.

Construction Duration Times for Extensions vs New Builds

Both new buildings and extension projects differ in timescales depending on whether you can live in the property when the work begins and the complexity of the design.

New construction projects will normally take much longer than building an extension since the work will be carried out in stages, starting with preparatory site clearance and groundwork and finishing with the second fit.

Adding on should be much faster because you aren't starting from scratch, and the basic structure will already be in place. You may need your contractor to dig foundations or create a new structural support system, although the scale is likely to be smaller than for a new build.

It is possible for renovations or extensions to take almost as long as constructing a new building, usually where the property needs substantial work to shore up the foundations or improve the structural stability.

Older or poor-condition buildings may not be stable enough to support the weight of an extension, in which case the project will take longer and cost more.

Need more advice on whether is it cheaper to add on or build new? Contact DemolitionCosts today for more information. Alternatively, why not read related questions such as:

Frequently Asked Questions

Next, we'll share the answers to some of the common questions we receive about construction projects where you're deciding whether it is cheaper to add on or build new.

How Much Does It Cost to Build a New Home in the UK?

There are many variables, such as the size of the property, location, architectural design and materials. Still, on average, it costs from £1,400 to £3,000 per square metre to build a new property.

Is It Cheaper to Add On or Build New?

It's impossible to give one answer because it very much depends on your goals - can you achieve the floor space and layout you want by adding an extension to your existing property?

Building new may be the best solution if there isn't the capacity to construct the extension you have in mind.

Please complete our quick quote form if you'd like a clearer idea about the comparable costs of adding an extension to your property or building something new.

We'll put you in touch with up to four approved local contractors who will be happy to steer you through the decision-making process and provide professional advice about the pros and cons of either option.

What Are the Pros and Cons of Building a New Property?

The advantage of building something new is that you can construct your home exactly as you wish, with control over every aspect from the finishes to materials used, internal layout to appearance.

However, a self-build is a big undertaking with a considerable budget, so you must have a team of experienced contractors, surveyors, architects and tradespeople to ensure each step is completed on schedule and within budget.

Why Should I Add On Rather Than Building New?

If you're keen to improve your property quickly, have a small budget, or only want to make minor changes to your home, adding on an extension or converting an attic or garage will be a much easier and faster option than building new.


  • https://www.checkatrade.com/blog/cost-guides/house-extension-cost/
  • https://www.realhomes.com/advice/renovate-or-build-a-brand-new-home https://www.horstconstruction.com/news-and-blog/renovating-vs-new-construction-which-is-better-for-your-project/

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