Your Property Wizard

What’s The Cost Of a Flat-Pack Extension?

If you’re a homeowner, you’ll know that space is always at a premium. You might even be thinking about moving in order to gain a little more room. However, wouldn’t it be so much easier if you could just stay put but expand your home?

Prefab extensions are literally prefabricated extensions that are delivered in a modular format, ready to be assembled in as little as a week. Flatpack extensions are similar in premise, but they usually require some light building before connecting to your home.

Choosing a prefab or flat-pack extension is often a more affordable way of adding space. These types of extensions typically cost 25 per cent less than conventional extensions.

In this article, we’ll cover how much prefab or flat-pack extensions cost by size, what affects the cost of building this type of extension, how you can save money on a prefab or flat pack extension, other extension options; and how to find and hire a builder to complete your project.

If you want to make your dreams of having more space a reality, keep reading to learn more.


How Much Do Flat Pack and Prefab Extensions Cost?

The table below estimates how much your flat-pack extension could cost, by size:

Single storey extension (15 sqm)£18,900 to £25,200£150 to £250 per person per day1 week£19,950 to £26,250
Single storey extension (20 sqm)£25,200 to £33,600£150 to £250 per person per day1 week£26,250 to £35,350
Single storey extension (25 sqm)£31,500 to £42,000£150 to £250 per person per day1 week£32,550 to £43,750

On average, prefab or flat-pack extensions cost between £1,260 and £1,680 per square metre. These estimates include VAT because most extension builders are VAT-registered. However, our estimates don’t include the cost of any fittings or finishings since these will vary according to how you plan to use the new space and your own personal tastes.

In general, building a single-storey 15 square metre prefab extension should cost anywhere from £19,950 to £26,250.

For a slightly larger single-storey flat-pack extension measuring 20 square metres, you can expect to pay between £26,250 and £35,350.

Or, if you’re planning a grand prefab extension of up to 25 square metres, then you will likely pay between £32,550 and £43,750 to complete your project.

Labour costs normally range from £150 to £250 per person per day, and our estimates include the cost of hiring two labourers for seven days.

Are you ready to get started on your flat pack extension? HouseholdQuotes can help you find the right supplier.

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What Affects the Cost of Flat Pack and Prefab Extensions?

The costs of any extension, regardless of whether it is prefabricated or traditionally built, are going to differ depending on a wide range of factors that are specific to the circumstance.

Design and Planning Fees

Whenever you plan to make structural changes to your house, it’s always a good idea to speak with an architect or a structural engineer.

Some architects and structural engineers charge a fixed fee for their services, such as making a site visit or creating drawings and plans for planning applications. Others charge a percentage of the total build cost.

For an extension or conversion, you should allow an additional £300 to £500 for a site visit, plus an extra £2,000 to £6,000 for drawings and plans to help you achieve your dream extension.

Building Costs

As we saw in the table above, the cost of building a flat-pack or prefab extension can vary considerably based on size. This reflects the cost of digging and excavating the site in preparation for your extension, as well as pouring foundations and building the shell.

There is also a large number of other factors that can impact the overall cost of your extension. No matter how you plan to use your extension, you’ll need to account for the cost of adding a roof, gutters, downpipes, doors and windows, flooring, internal plumbing, heating, and electricity, as well as basic painting and decorating.

If you plan on using your prefab extension as a kitchen or bathroom, you’ll also need to consider the cost of those finishings and fittings which can quickly add up.

Main House Alterations

Building any type of extension means making structural changes to your existing home.

To ensure your home remains structurally sound, you may need to add new RSJ or universal support beams to support the structure after knocking through external walls.

RSJs cost anywhere from £430 to £1,160 to install, depending on the size you need. To learn more about the costs of installing universal beams, check out our guide here.

Miscellaneous Costs

Building a prefab or flat-pack extension is simpler than adding a conventional extension, but it’s still a messy business. So, be sure that you budget for the costs of hiring a skip (including any necessary permits) or hiring a waste clearance company.

Once your extension is complete, you may also need to tidy up your garden so you may need to hire a gardener or professional landscaper to lay new turf or add flowers and shrubs.

Since you’re making structural changes to your home, it’s a good idea to contact your mortgage and home insurance providers to notify them of the new addition and make sure you’ve still got adequate cover. Depending on the changes you’ve made, your home insurance costs could increase.

Finally, there are almost always unforeseen costs involved in any building project. That’s why it’s always a good idea to set aside an extra 10 per cent for unexpected expenses.

How Can I Save Money on a Flat Pack or Prefab Extension?

Extensions aren’t cheap, and there are a lot of cost factors involved in determining the final price. However, modern technology is making extending your home more affordable, and with flat-pack options increasingly available you could get your dream property without even moving.

Lower the Cost with Flat Pack Options

Flat pack extensions are becoming increasingly popular, not only because they’re simpler to instal but due to the lower costs.

There are other benefits, too. Other than foundations and laying utilities, a lot of the work can be done off-site, reducing the noise and impact on your everyday life.

In addition, advanced technology means that prefabricated extensions can come with integrated soundproofing, insulation and temperature controls.

Other Extension Options

There are several other options to consider if you’re trying to get an extension on a tight budget. For instance, glass extensions can be a modern and stylish feature that makes quite a statement.

Not to be confused with conservatories, exterior glass rooms come with all the mod cons and can be seamlessly integrated into your home. A 10.5m² glass extension, complete with three frameless sliding doors, could cost around £17,000.

Alternatively, you might like to consider an orangery. Though orangeries might be perceived as extremely expensive, if you’re already thinking of paying for an extension, then an orangery could be affordable too.

Averaging around £20,000, you could get a functional and usable room that makes the most of indoors and out.

Comparing quotes is a great way to potentially reduce the cost of flat pack extensions. HouseholdQuotes can help you get quotes from multiple flat pack suppliers near you, so that you can find someone that suits your budget.

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What’s Involved in Building a Flat Pack and Prefab Extension?

The general answer is a lot less building work than is required for a traditional extension – but let’s get into the nuts and bolts of the two different types:

Flat Pack Extension

Flat pack extensions take a little more time than prefab simply because they don’t arrive on site fully assembled.

Professionals will piece sections together, much like a flat pack set of furniture, to create the structure. While finishing off a piece of furniture might just need a few screws in the wall to fix it in place, flat pack extensions sadly require a little bit more work.

To connect the extension to your home, some structural work will need to take place. This can either be for structural foundations like excavating and digging all the way through to demolishing existing outside walls and adding in new support beams to your home.

Then, once in place, you’ll have to finish the extension off with whatever amenities you need – be that electricity, water, gas, heating – the list goes on. You’ll also have to make good the space with cosmetic additions after the flooring has gone down.

Prefab Extension

Prefab extensions are great for adding extra space into your home in a fraction of the time a traditional extension would require.

Generally, less excavation is needed, and they can be ready to use within a week, and designs can be made bespoke to you and your specific size or needs.

As before, the structure will need to be affixed to your property, and then you’ll need to connect any relevant energy supplies as well as finish the space off with cosmetic items.

How Do I Find and Hire Tradespeople to Build My Extension?

Has someone on your street had a prefab or flat pack extension recently added to their property? Go and ask them for a recommendation of their trader or firm – it’s your best bet for finding a good professional to work with; and if not that, it’ll teach you who you need to avoid!

Seeking recommendations from family, friends, and neighbours is a great way of trimming down your search time and (hopefully!) securing leads that are already vetted and trusted by your friends and family.

If this isn’t possible, or no one can come forward with good reviews, then turning your attention online can be the next best route of action.

Using HouseholdQuotes you can complete one simple search and then compare lots of traders across one website – meaning you don’t need to keep track of multiple tabs on multiple traders and websites, as all the information you need will be in one place.

Then it’s just a case of choosing someone who fits what you’re looking for – be that a trader specialising in prefab or flat pack extensions.

Finding the right flat pack extension supplier can be challenging. At HouseholdQuotes, we can connect you to companies in your area.

Click the button below to tell us more about your project, and we’ll help you find someone quickly and easily:

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Ensuring the Professional Is the Right Fit

No matter how nice someone is to your face or how trustworthy they seem, never agree to accept a verbal contract with them to ‘save time’ on writing up a proper quote or proposal.

Not only is it unprofessional, but it leaves you and your wallet wide open for manipulation as traders can keep adding on ‘extras’ that need to be done, but were ‘missed’ off the original verbal quote.

If it’s written down and agreed it can’t be disputed, and it’ll give you some security in your job, the time it’ll take and the amount it will cost you. If a trader refuses to give you a written quote, refuse to work with them.

Much like a job application, you’ll then want to know about their experience. Have they completed work like this before, and was it successful? Where possible, ask to see photos or videos of their previous work to make sure their words match up to their actions.

Following on from this, seeking out their references can be a good way of finding the truth amongst their claims – where possible, use unbiased reviews like TrustPilot to see legitimate reviews and not just ones they can control on their website by adding themselves.

Finally, any trader worth their salt should have insurance for the job they’re proposing to undertake. Just make sure they do have this before getting started to avoid any nasty surprises or unwanted liability charges further down the line.

Final Checklist

If you’ve been dreaming about extra space for far too long and want to make it into a reality, installing a prefab or flat pack extension can be a great way to achieve your desires.

Here’s our final checklist to make sure you don’t forget anything in the process:

  • What’s right for you? Do you want something bespoke to your exact specifications or are you happy to pick an off-the-shelf option?
  • Check with your local council and building regulations to make sure what you’re proposing is within guidelines for a permanent extension structure
  • Make sure all fees are included in the quote, including waste removal and skip hire if necessary
  • Find a trader you feel confident in using HouseholdQuotes and enjoy savings of up to 40% on your project’s bill
  • Enjoy the extra space in your home without the hassle of having to move house!

Use HouseholdQuotes to find local flat pack extension suppliers and potentially save money on your home’s extension.

Comparing Quotes Could Save You Up To 40%:

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Frequently Asked Questions

Do I Need Planning Permission for a Flat Pack or Prefab Extension?

As the structure is permanent and lasts for longer than 28 days, you will need to seek planning permission for prefab or flat pack extensions.

Specific details will be available at your local council, so make sure you speak to them in the first instance before purchasing anything to save yourself from wasting both time and money.

Are There Any Building Regs for Flat Pack or Prefab Extensions?

Similar to above, standard building regulations for extensions will need to be taken into consideration with both prefab and flat pack extensions.

If you’re unsure about anything, speaking to a professional in the first instance will help to ease your concerns, and they’ll be able to advise on the best structure for your space while considering building regulations and planning permission factors.

Are Flat Pack and Prefab Extensions Cheaper Than Conventional Extensions?

In general, an extension that’s prefabricated off-site will cost between 10 and 25 percent cheaper than the traditional on-site construction. It means that a project costing £25,000 can suddenly drop to under £20,000, which often makes an extension far more affordable.

For more information on the cost of traditional extensions, see our dedicated page here.

Can I Build a Flat Pack or Prefab Extension Myself?

While it is possible to build a flat pack extension yourself, it’s best to leave it to the professionals to ensure the job is done correctly. As this will eventually form a large part of your home and be a permanent structure, you don’t want to cut any corners to reduce costs by skipping out involving professionals.

What’s the Difference Between Flat Pack and Prefab Extensions?

Flat pack extensions define themselves: they need to be put together much like flat pack furniture before becoming a structure.

Prefab – short for prefabricated – extensions skip out the building stage, and are delivered to your home fully built, and just require attaching to your existing home.

What Is a SIPs Extension?

A SIPs extension is similar in premise to a prefab extension, in that it is made out of panels that are prefabricated for you. Structural prefabricated panels are measured before arriving at your home and are then connected by professionals during the build and assembly of your extension.

Ready to start your project? We can help!

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