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myDouble Storey Extension Cost
At a Glance
- The average two storey extension costs £60,000 in the UK.
- Double storey extensions take up to 14 weeks for builders to complete.
- NEW! A double storey extension cost calculator, which gives you a quick and no-hassle way to get an idea of what this type of job will cost you.
- A breakdown of what you can expect to be quoted for different types of two storey extensions in 2026 (includes double storey extension cost per m²).
- Expert advice about extensions from builders on MyJobQuote.
- How to find and hire a local builder to add an extension to your home.
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£60,000
Table of Contents
- How Much Does a Double Storey Extension Cost?
- Double Storey Extension Prices
- What Is the Cost of Double Storey Extension Labour?
- Factors That Impact Double Storey Extension Costs
- Types of Double Storey Extension
- What Is Involved in Building a Double Storey Extension?
- Checklist: Hiring a Builder for an Extension
- FAQs
How Much Does a Double Storey Extension Cost?
Looking into how much a double storey extension costs in the UK?
The typical cost of building a two storey extension starts at around £40,000, but easily run as high as £100,000. The increase in cost depends mostly on the size of the extension, but will also increase if you are planning to use some of the space as a kitchen or bathroom.
Double storey house extension costs per square metre are between £1,000 and £1,800. This is for your basic building materials including foundations, walls, roofing, plumbing, electrics and finishing.
Once you've roughly calculated your two storey extension cost, you'll need to add between £5,000 and £15,000 for an average-sized fitted kitchen, and a further £4,500 to £9,000 for a standard family bathroom.
A two storey extension not only gives you more space, but it is more cost-effective than moving house and cheaper per square metre than a single storey extension. If both storeys in an extension are the same size, then a double storey extension will cost around 50% to 75% more than a single storey extension.
I have a 3 x 4 m conservatory with three full brick walls and a dwarf wall across the front (3m). My house is built on a raft, is it possible to add a raft to the current building and then convert it to a two-storey to match the back of the house?
"It can be done, but you would need an RSJ beam put in and built up from that. You would need a structural engineer to do the calculations for it. I would say to build the new first-floor walls from timber frames to keep the weight down on the raft."
Double Storey Extension Prices
The cost of a double storey extension will depend on multiple factors. This includes:
- Type of double storey extension (e.g., side return, wrap around, rear.)
- Finish and specification
- Your location in the UK
The illustration below shows the difference in costs based on your extension size and the specification of finish that you choose:
The table below shows average costs for extensions in the UK, including the average price per m² and what you can expect to pay (additional to the base average) if you are adding a kitchen or bathroom to your home.
| Expense | Basic Specification | Average | High Specification |
|---|---|---|---|
| Small double storey extension (30m² total) | £40,000 | £47,000 | £55,000 |
| Medium double storey extension (60m² total) | £65,000 | £70,000 | £75,000 |
| Large double storey extension (100m² total) | £90,000 | £95,000 | £100,000 |
| Cost per m² (up to 30m²) | £1,333 | £1,566 | £1,833 |
| Cost per m² (over 30m²) | £1,083 | £1,167 | £1,250 |
| Fitted kitchen (add-on) | £8,000 | £10,000 | £15,000 |
| Bathroom (add-on) | £4,500 | £7,000 | £9,000 |
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Converting Single Storey Extension to Double Costs
If you already have a single storey extension and want to build above it, costs usually start from £1,200 to £1,800 per m², with a typical total cost of £20,000 to £30,000 for an average-sized extension. Costs vary depending on whether the existing foundations and walls can support a second storey.
In many cases, structural strengthening is needed when changing a single storey to a double storey extension, so converting an existing extension can sometimes cost as much as building a new multi storey extension from scratch.
What Is the Cost of Double Storey Extension Labour?
Labour for a 60m² double storey extension will cost £42,000 on average.
Below are the rough charges for one day’s labour by the various work types.
Labour makes up a significant part of the total cost of a two storey extension as there are many trades involved and most will be on site for at least a week.
| Extension Size | Estimated Labour Cost | Typical Build Time |
|---|---|---|
| 30m² double storey extension | £28,000 | 8–10 weeks |
| 60m² double storey extension | £42,000 | 10–12 weeks |
| 100m² double storey extension | £57,000 | 12–14 weeks |
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The build time is contingent on the efficiency of labour, weather conditions and scheduling of multiple work types simultaneously. You should also factor in extra time for complex additions and a larger extension size.
Here is an estimate of labour costs by trade, and how long each will be on site for a typical extension build:
| Trade | Typical Labour Cost | Typical Time Required |
|---|---|---|
| Bricklayers / structural build | £14,000–£22,000 | 4–6 weeks |
| Roofers | £4,000–£7,000 | 1–2 weeks |
| Plumbers & electricians | £3,500–£6,000 | 1–2 weeks |
| Plastering | £2,500–£4,500 | 1 week |
| Joinery / finishing work | £2,000–£4,000 | 1 week |
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Brickwork and structural work usually make up the largest share of labour costs, while roofing, plastering, and electrical work are completed in shorter stages later in the project.
What costs do you incur for house extension work?
"Around £850 per square metre for labour only or £1,550 per square metre with all structured materials included."
If you need to get planning permission, go to an architect, or gain a Party Wall agreement, you will need to add the relevant time before the building work begins.
In general, is it better to consult with a local authority building inspector or an independent one when you're designing and building a big house extension?
"We would recommend independent inspectors, as if the local authority advises incorrectly there is no action that can be taken against them whereas if independent inspectors advise incorrectly you can take action against them."
Factors That Impact Double Storey Extension Costs
To help you to work out a reasonably accurate overall cost for your extension, here's an overview of how your costs will be distributed.
You should always round up any potential costs, and add around 10% as a buffer - otherwise, any unexpected costs can blow your initial budget.
- Planning - Budget around £13,000. This will cover house surveys, architect hire fees, full plan creation, and overall project management.
- Initial Building Work - Budget around £19,000. This concerns foundations, timber framing, roofing, and exterior finishing.
- Secondary Building Work - Budget around £5,300. Broadly, this will cover your double glazing fees, external door, and landscaping (where necessary).
- Interior Finishing - Budget around £18,000. Depending on your chosen specifications, this cost will include things like your new kitchen, bathroom installation, electrician day fee, and plastering costs.
Want to see those costs broken down line-by-line?
| Expense | Average Cost |
|---|---|
| Foundations | £6,000 |
| Timber Framing | £5,000 |
| Rendered Brick Exterior | £3,500 |
| Roofing (standard shaped roof and tiles) | £4,500 |
| Windows (based on 4 double-glazed uPVC windows) | £2,400 |
| Doors (one external door) | £1,100 |
| Landscaping (an average-sized patio) | £1,800 |
| New Kitchen (medium-sized, mid-range spec) | £10,000 |
| New Bathroom (standard-sized, mid-range spec) | £7,000 |
| Electrics (standard electrician day rate) | £230 |
| Plastering (internal of average-sized double-storey extension) | £700 |
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What can I do to keep architect costs down when planning an extension?
"It might be a good idea to look for a smaller, newly founded practice driven by expanding their business; their overheads should be more modest than other, more established practices.
Consequently, you might expect a lower fee whilst professionalism and quality are not compromised."
Consequently, you might expect a lower fee whilst professionalism and quality are not compromised."
Planning Permission, Building Regulations & Party Wall Costs for Double Storey Extensions
These are three separate costs and considerations. Not all extensions require planning permission or party wall considerations, but building regulations compliance is almost always required.
The costs of each of these is around:
- Planning Permission - £206 in England, £202 in Scotland, and £190 in Wales.
- Building Regulations - Full plans cost around £180, and inspections are £200 to £550.
- Party Wall - If a surveyor is needed to settle a party wall dispute, expect to pay £90 to £450 per hour depending on where you live.
The house I've bought already has planning permission for a double storey extension. There's a few little changes I'd like to make to the plans. Do I need to get the plans updated and resubmitted before building starts?
"You would generally get away with internal changes or alterations. However, you’d be better off getting planning or seeking clarification for any external changes so as not get into problems with the council.
So seek clarification or planning before building starts as if spotted by an inspector once building commences, you run the risk of having to pull down any alterations not in line with what has already been approved."
So seek clarification or planning before building starts as if spotted by an inspector once building commences, you run the risk of having to pull down any alterations not in line with what has already been approved."
Types of Double Storey Extension
There are several options when it comes to your new extension - let's look at the most common double-storey configurations:
Double Storey Side Return
Best for: Detached or semi-detached homes looking to widen living space without losing the garden.
This type of extension is built at the side of the property without jeopardising the garden area. This extension can be implemented on a detached or semi-detached property.
Pros
- ✔ Preserves garden space
- ✔ Makes use of the unused side area
Cons
- ✖ Not suitable for terraced houses
- ✖ May require Party Wall agreement with neighbours
Double Storey Rear
Best for: Adding more kitchen, dining, and bedroom space while extending into the garden.
This extends the rear of a property, usually by extending into garden space. This type of extension is a good choice for semi-detached and detached properties. A terraced that has enough back garden space could also have a double storey rear extension.
Pros
- ✔ Suitable for most property types
- ✔ Great for open-plan kitchen diners with bedrooms above
Cons
- ✖ Reduces garden space
- ✖ May affect light to neighbouring properties
Double Storey Wrap Around
Best for: Maximising space with a combination of side and rear extension.
This type of extension is a mixture of a side extension and a rear extension. If the main reason for you wanting an extension is extra space, then a wrap-around extension can add a lot of space to a property and is the best solution. It's achievable for both detached and semi-detached properties.
Pros
- ✔ Creates the most additional living space
- ✔ Offers flexibility for room layouts
Cons
- ✖ Most expensive type of double storey extension
- ✖ More complex build
Double Storey Flat Roof
Best for: Modern properties or a contemporary look at a lower cost.
A double storey flat roof extension features a horizontal roof rather than a traditional pitched design. This type of extension has become increasingly popular in recent years due to improvements in building materials and waterproofing technology.
Pros
- ✔ More affordable than pitched roof extensions
- ✔ Quicker to build
Cons
- ✖ May not be permitted in conservation areas or on listed buildings
- ✖ Requires proper drainage to prevent water pooling
Double Storey Front
Best for: Adding kerb appeal, entrance space, and extra bedrooms at the front of the property.
This type of two storey extension is most probably the least common. The reason for this is that a front extension has the most impact on the look of a property, and there are stricter Building Regulations to adhere to.
Pros
- ✔ Ideal for adding a porch, hallway, or front bedroom
- ✔ Doesn't reduce garden space
Cons
- ✖ Most likely to require planning permission
- ✖ Can affect light coming into the neighbour's house
What Is Involved in Building a Double Storey Extension?
Below is the standard process of a double storey extension build.
Before the Project Starts
- Permission Check - Before any construction begins, your builder will need to check whether you need planning permission, including if your property is within a conservation area or a listed building, and assess whether the Party Wall Act applies.
- Designing the Extension and Sign-Off - Using an architect (or structural engineer), plans will be made ready for planning and Building Regulations sign-off. At this stage, the builders will finalise their plans for the foundations, incorporating the recommendations by the structural engineer and Buildings Inspector, and also taking into account any pipes, drainage, etc.
- Logistics Planning - All supplies will be ordered and delivered, and your builder will ensure rights of way are adhered to, as well as providing the necessary insurance.
During the Project Build
- Groundworks and Foundations - The ground conditions will be assessed, accounting for drains/services, and foundations will start to be laid.
- Building the External Structure - External walls will be built, attaching to the existing property where necessary, along with the floors and roof. Windows and doors will be added, and the extension will be weatherproofed.
- Structural Opening and Internal Framing - The original external wall will be knocked through into the extension, and a structural engineer will determine what support will be required to reinforce the exposed structure. A carpenter/joiner will build the internal frame of the rooms.
- First-Fix and Plastering - Electrics and plumbing will be installed, with the area being plastered once the services are fitted.
- Second-Fix and Other Installations - Internal components (doors, skirting boards, radiators, kitchens/bathrooms etc.) will be installed, alongside other permanent fixtures.
After the Project Build
- Decorating and Finishes - Your internal finishes can now be added, like tiles, painting/wallpaper, and flooring.
- Final Inspection and Sign-Off - Building Control will carry out a final inspection and hand over a completion certificate. Snags will be addressed, and the site will be cleared.
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You can get multiple free quotes from local extension builders using MyJobQuote, with no obligation to go ahead.
Checklist: Hiring a Builder for an Extension
Before you hire a double storey extension builder, here are some things you should consider:
- Are they qualified? Check they can provide proof of relevant qualifications, including certification for electricians and, where applicable, Gas Safe engineers.
- Do they have insurance? Ask whether they have liability insurance. Liability insurance would protect you if anything were to go wrong while the work is happening.
- Are they experienced? Ask if they have ever completed a double storey extension, and if they have experience working with Building Control and structural engineers.
- Do they offer any guarantees? If any problems arise in the future, check that you’ll be covered by a guarantee. Find out what's included and for how long.
- Have you been given an itemised quote? Ask for a detailed two storey extension cost breakdown to ensure that there are no hidden fees.
- Do they have examples of similar work? Check their previous work by reviewing the photos on their MyJobQuote profile.
- Do they have positive reviews? Take a look at what other homeowners are saying about their work by checking their MyJobQuote reviews.
FAQs
Can I Build a Double Storey Extension Myself?
In short, no, you’ll definitely need to hire relevant tradespeople for certain tasks during the double storey extension build. You can complete some jobs DIY, like painting and decorating, and by doing odd jobs, you can save some money.
How Can I Reduce the Cost of Building My Double Storey Extension?
Keep the design simple to save on specialist or skilled workers, build time, materials and architect time, while staying in keeping with your property.
Is a Single, Double or Three-Storey Extension Best?
The best option depends on how much extra space you need and your budget. A single storey extension is usually cheaper and simpler, while a double storey gives you extra space upstairs and downstairs without taking up more garden space. Although a double storey costs more overall, the cost per m² is often lower than building two separate extensions. Three-storey extensions are less common and usually only practical on larger properties, as planning and structural requirements are much stricter.
Will Building a Double Storey Extension Cause Me Any Problems?
With detailed plans, an experienced project manager and competent labourers, issues should be minor, though ground conditions, weather and materials can still cause problems that teams can work around. Talk to neighbours early about noise, disruption, access and deliveries and keep them informed.
Should I Move Out While Extending?
If builders need access to most rooms, moving out for a few months helps sanity and timescales, and some companies will not work in an occupied house. A caravan in the garden is a popular option, while a hotel or short-term let is quieter and more comfortable but more expensive. Always factor in temporary accommodation costs.
Which Direction Should I Extend My House?
The simplest option is extending to the rear, but you'll need enough back garden space. If not, a two storey side extension may be right for you. Consider where your current rooms sit within the house and what you want to add, as this will determine the best direction to extend.
Is £50k Enough for an Extension?
£50,000 is enough for a small, basic specification extension but if you want to add a kitchen or bathroom, choose higher-quality fittings, or build an extension larger than 30 m², you will almost certainly need a bigger budget.
What Is the Most Expensive Part of a House Extension?
Structural work and foundations are generally the most expensive parts of building a house extension. It's vital to hire trusted tradespeople for these aspects of building the extension to ensure it is structurally sound and durable.
Is It Cheaper to Extend or Move?
Usually extending is cheaper. There are many fees associated with moving house, including estate agent fees, Stamp Duty, legal fees, house surveys, and more.
What Are the Benefits of a Double-Storey Extension?
The main benefits of a double storey extension are increased property value, improved floorplan and functionality, and less loss of garden space than a single storey extension with the same overall m² size. Overall they offer better value for money compared to single storey extensions as they use the same foundations and roof structure to make double the amount of floor space.
