Select Page

Home improvement Quote

Rear Extension Cost

Rear Extension Costs

We used a number of web quotation tools to ensure that the information on pricing reflected here is as accurate as possible. The figures mentioned here should give you a good estimate of how much out of pocket expenses you need to shell out for a house extension project.

It wouldn’t hurt though to gather quotations from people who engage in these services across the UK so you will at least get a fairly accurate pricing based on your specific personal requirements if your more interest in a porch rather than extension please check this page Build A Porch.

Average material costs for the installation of rear extensions will greatly depend on a variety of factors. This includes how big or small the extension is as well as the quality and type of materials involved.

If you’re planning on a kitchen extension, £3,000 to £10,000 may be added to your overall expenses. You might want to add another living room to your home— in this case, costs will be largely focused on additional furniture.

A building specialist charges for every square metre— usually around £1,000 to £1,500. For single or double-storey extensions, several tradesmen may be required to take on the job.

You’ll need planning applications for this project too so, an experienced structural engineer or an architect will be needed. They will also help in making the reports as well as ensure that necessary building regulations are adhered to. In addition, a roofer and a builder will be necessary for completing the work involved.

You’ll also need the services of a professional electrician to make sure that the lights, sockets, switches, cabling, and heating are properly installed.

For the pipework and radiators installation, a plumber of a heating specialist is needed. If you want to install a fireplace or a cooker— in the event that a living room or a kitchen is in the works, he is also the specialist to call.

For the floors, ceilings, and walls, you’ll need to call in a decorator, plasterer, flooring specialist and a tiler. If you need some kitchen fitting done or are interested in the installation of some bespoke furniture, you’ll need the services of an expert joiner. With all the details involved in this project, you may need a few months to get everything set up, installed, and fitted in.

Cost Breakdown

If you want to add a 25 square metre rear extension that is medium-sized, total costs could amount to £30,000. Half of that will go to materials, £13,500 will cover the tradesmen fees, and the remaining £1,500 should cover the costs for waste removal. The service costs and the length of time it would take for the project to get completed will be highly dependent on the job size. The accessibility of the area where the installation will take place and your location will have to be factored in as well.

Supply Costs

Another important cost consideration for rear extension installation has to do with the supplies. Depending on the kind of installation you want, the supply costs can be broken down as follows:


There are several types and styles of bathroom sinks that are available out there. If you’re trying to minimise the costs involved as best as you can, go for a pedestal sink at £50, a wall-hung type at £60, or a drop-in style which retails at £70.

If you’re looking for something more luxurious, you can choose vessel sink at £80, and under-mount type at £110 or you can go for the console type at £260.

When installing a shower for a bathroom extension, an electric type will cost £50, shower baths cost £50, power showers generally cost £150, steam showers are retailed at £250, or you can go digital for £550.

If you’re planning on a larger extension to your bathroom, there may be enough space to fit in a bath. Among the choices you have are acrylic baths at £80, steel baths at £120, fibreglass baths at £200, a cast-iron bath at 300, stone baths at £1,000 and the luxurious marble baths at £1,200.

A very important bathroom fixture, there are cheaper options including the low-level type and the wall- hung one at £150. You can go mid-range by getting a two-piece for £170 or you could go high-level for £180.

A one-piece toilet will usually cost £170 or you could go high-level for £180. A one-piece toilet will usually cost £200 and the priciest of them all, the smart toilet will usually retail at £500.


If you want better insulation yet also bringing as much light into the rear extension, windows that are double-glazed are ideal. Average per window cost is at £300, but this could be largely influenced by the size you prefer.

More upscale installations usually feature windows that are triple glazed with costs at about £400. This is ideal if you want to really crank up the insulation and energy efficiency in your home. The addition of another layer of glass panel to the windows will result in even lesser heat loss.


You can choose a stock unit which is priced at £300. This usually features more generic designs and is pre assembled. If you want some flexibility in the design, you can go semi-custom at £500. If you want

cabinets that are ideal to your kitchen type, you can go for the custom ones at £1,000. With this, you can choose to customise the cabinets based on your preferred material, colour or size.

A number of options are available as far as worktops go. Laminate is easily the most preferred choice with prices ranging from £20 to £40 per square metre. Solid woods command a £75 to £100 per square metre pricing, quartz at £225 to £475 per square metre, and granite is retailed at £150 to £400 per square metre.

You’ll need appliances for the kitchen extension. An oven can cost around £300 to £16,000, a washing machine retails around £200 to £1,500, a fridge freezer is priced at £200 to £2,000, a dishwasher costs around £300 to £600 and a dryer can cost between 150 and £1,000.


Decide what kind of door you’d prefer. For external doors, steel is usually the most preferred at £300. Softwood will cost about £700, fibreglass is usually retailed at £1,500, a sliding door costs £900, and a French patio external door can cost around £1,600.

You need internal doors to connect the rear extension to the rest of the house. Timber will usually cost you £50, aluminium is usually priced at £90, glass is retailed at around £100 and PVC could cost around £200.

Bringing in natural light is a great way of enhancing the rear extension. This can be achieved by adding more mirrors or windows. Full-length mirrors could cost £60 – £150. For a bathroom extension, wall- hung mirrors can be positioned over your sink would be more ideal. These mirrors usually retail at £40 or £200.

If there isn’t much natural light to bring in, artificial lighting is an option to consider. Floor and table lamps can cost around £30-£120. For £15 to £60, you can install wall-mounted lighting fixtures. Downlights would cost you around £10 – £50 or you can go for smart lighting at £25 to £500. Smart lighting can be a bit expensive but if you want a lower carbon footprint, this is the choice to go. It can help lower your electricity bill as well.



A new system will usually be required in order to keep your extension warm and heated. Costs could be around £2,000 to £3,000. These figures already include the price for the new boiler as well as the pipework and various extra parts.

For keeping your expenses low, an electric system could work as it can only cost around £20 to £150 to get a baseboard heater that is electric-powered. If you’re looking for something even more affordable, a wall heater is another alternative which should cost you around £50 to £100.

If you want to add new radiators, you’ll likely have to shell out around £100 for the low-level type. Vertical radiators can cost around £400. How many of these radiators are needed will depend on the dimensions of the room. You’ll need more of these units if the room is bigger to ensure that enough heat is produced.

Underfloor heating is a great choice if you want something more luxurious. This allows heat circulation around the entire room. You can choose between wet underfloor heating which can cost around 100 per square metre or the dry type which is often priced at £60 per square metre.


If the extension is for a new bathroom or kitchen, floor tiles may be the most ideal. You should have more freedom as far as choice materials go although ceramic remains the most popular choice at £20 per square metre. Porcelain is another choice at £55 per square metre or you can get stone ones at £105 per square metre.

If tiling is not for your taste, wood is a good flooring alternative. It is highly durable too, making it even more ideal. Solid wood can cost 15 to £80 per square metre. Engineered wood usually costs more at £19 to £160 per square metre. You can go for reclaimed wood too at £25 to £100 per square metre. Lastly, there are parquet wood floors at £25 to £110 per square metre.

Another option is laminate flooring. Maple, white oak, and red oak will generally retail at £5.50 per square metre. If you want to look at mid-range alternatives such as cherry, beech, and acacia, be prepared to pay around £10 per square metre. Hickory is usually more expensive, often priced at £20 per square metre.


Carpets are also a common option and a comfortable one as well. You can get Wilton or Axminster  woven carpets at £60 per square metre. If tufted carpets are more of your preference, they cost even less at £12 per square metre.


Getting your wall ready for decorating usually requires carrying out some plasterwork. Costs could run between £20 and £25 per square metre.

There are several paint styles for you to choose from for wall decoration. Matte paint costs £5 a litre, gloss is priced £6 per litre, and semi-gloss can cost around £6 per litre. Satin paint can cost more at £14 a litre and eggshell can cost around £15 per litre. Note that the final price will still vary based on the specific colour you choose.

If you’re looking for something that will last longer, wallpaper is the way to go. A liner paper can cost between £3 and £5 per roll. You’ll also need to choose your preferred wallpaper style and this could cost as low as £8 to as high as £60 per roll.

Additional costs
When considering a house extension, be prepared to shell out more funds on additional costs. For instance, if a house rewiring is needed, it can cost around £1,200 to £3,00. If there are structural issues that need fixing, additional costs can range from £3,000 to £10,000. In cases where a new heating system needs to be installed, expect to add around £1,000 to £3,000 to the total cost.

Rear Extension Job Details
Installing a rear extension can be considered a major project. It’s a rather messy one too so expect some major upheaval, especially in your rear garden what with all the foundation work that will need to be carried out.

1. Design and planning
Before carrying out an extension project, you need to plan and design how the whole thing will be carried out. You’ll need professional help to do this. In some cases, advice and guidance from an architect or an established structural engineer will do. This is also the point where you decide how much you’re happy to spend to get the project into fruition. Find out if there is a need to secure a planning permission too.

2. Layout
You’ll need the presence of experts in construction including joiners and builders to set the layout. Along with the structural engineer and architect, they will work together to ensure that building regulations are adhered to in the installation of the extension. The amount of work involved at this point would all

depend on the kind of rear extension you want to build. In some cases the ground may require levelling out, your pipes may need renewing or blocking, a block floor may also be laid out, or in some cases, vapour and weed barriers may be added.

3. Insulation and brickwork
The next step is laying out the bricks while closely following what is specified in the project plan. At this point, expansion joints may also be added to ensure that the bricks will not move despite the fluctuations in the temperature. Insulation will also be added along the inside of the bricks to ensure that water damage is prevented and that heat is kept within. Steels and joists will be used to hold the entire structure in place.

4. Roofing
Roofing of the extension will be installed by fitting in a frame made of timber to the original roofline and then expanding it out. The material used will need to be cut off and then attached whilst paying attention to the specific measurements. This process covers roof frame, soffit, and underlay installation.

5. Flooring
If you want underfloor heating installed, it will need to be laid down beforehand. This job will require the presence of an electrician in the event of a dry system installation or plumbers for a wet system. The floor will then be levelled out after covering it with screed. Your preferred flooring material will then be laid out afterwards.

6. Heating

If underfloor heating isn’t in your plans, you’ll need to choose a different type of heating system for the extension. An electric system or a central heating system can be installed instead where radiator instalment will be part of the process.

8. Walls
To get the walls ready for decoration, it needs to be covered in plaster first and then sealed with an emulsion or a sealant. A decorator or a painter can do this job. After it has properly dried off, wallpaper or paint can be added to finish things up.

9. Electrics
You’ll want to have all the right power outlets inside the extension. An electrician would be most helpful at fitting in the necessary light switches and plug sockets. They will ensure too that these fixtures are legally-compliant.

10. Lighting
After the electrics have been fitted in, you have the choice to add your preferred lighting. Make the most of your choices and determine whether you want smart lighting, wall lights, or a chandelier fitted in.

11. Windows
Windows are perfect at opening up space. What you choose will usually depend on how much you can afford to spend and what your preferred style is as well as the style of the room.

Have the windows measured first before having a glazier fit them in. The steps mentioned above can change based on the extension you want to fit in.

For instance, when installing a kitchen extension, you’ll need to make sure that units, worktops, and appliances are fitted in. A lounge or a dining room might also be a good idea so you’ll need to factor in whatever furnishings are necessary.For bathroom extensions, plumbers are necessary so the toilet, bath, sink and shower get properly fitted in, he will also see to it that necessary the pipes are connected and installed appropriately.

Don’t forget to decide on the kind of door you want as well as where you’d want them added too. If you want the extension to be an open-plan type, keeping everything open is ideal so a door for exit and entry purposes is all you’ll likely need.

Ready to get a quote from local tradespeople?

Can You Add a Rear Extension?

Most homeowners shouldn’t have a problem adding rear extensions to their properties as long as they
follow certain regulations.

• The extensions shouldn’t extend to more than half of the property’s entire area.
• Use only materials that are similar to the ones used in the original property.
• The new fixture shouldn’t extend more than 3 metres from the original rear wall for attached properties or 4 metres for detached properties.
• Extensions shouldn’t go over 4 metres in height.

Can I DIY a Rear Extension Installation?

While having the professionals plan, design, and construct your extension project can be more on the expensive side, you’ll find that as long as it is properly executed, it will pay for itself over time. Well-built extensions will add value to the property. It will add more to its aesthetics as well.

Whilst you might want to consider the possibility of making this a DIY venture in the hopes of minimising the costs, this is certainly one of those undertakings that are beyond the skills of even the most seasoned DIY enthusiast. There is so much that can go wrong if you attempt to do this on your own. So, contact the right professionals to help you out instead.

You can, instead, contribute to the project in other ways. You can do the decorating and painting part. Also, be prepared to purchase additional tools that may be required for the project including a brush set for £10, step ladder for £60, self-adhesive film for £10, seam roller for £5 and masking tape for £2.

Steer clear from difficult jobs too including roofing, plumbing, or fitting electrics. These are best left to the hands of the experts. This ensures that expensive complications are avoided whilst the project is being carried out and it helps you avoid unnecessary legal complications too.

Rear Extension Types

Different kinds of rear extensions will vary in terms of costs. It helps to find out what the average costs are for the specific type and kind of extension you want so you will at least get an idea how much of your budget you must set aside for the project.

The quality and size of your rear kitchen extension will influence how much the costs are going to be. Small-sized one can cost between £12,000 and £30,000. Medium-sized extensions can cost between £19,000 and £48,000. If it is a large extension, the costs could be around £38,000 to £100,000. Variations on the prices will be based on whether you want something basic, average, or deluxe.

Open-plan spaces are becoming a trend these days so if this is the kind of extension you want, a small diner and kitchen extension will cost around £18,000 to £25,000. Medium-sized ones will cost £25,000 to £38,000 and Large-sized extensions will cost £38,000 to £60,000.

If you want a lounge space extension, a small-sized project would cost between £15,000 and £22,500. Medium extensions will usually be priced at £22,500 to £36,000. Meanwhile, large lounge space extensions are going to cost between £36,000 and £58,000.

These types of extensions are generally going to cost more since it requires a bathroom suite which can add about £5,000 to the costs. Small extensions can cost £15,000 to £25,000, mediums ones can cost £25,000 to £35,000 and large ones are usually going to cost between £35,000 and £45,000.

If you’re not keen on an extension made of bricks, you can go for a conservatory instead. This is ideal if you want to add more light into your home. Lean-too can cost between £5,000 and £8,000, Victorian extensions can cost around £8,000 to £11,000, Edwardian conservatory extensions can cost £7,000 to £10,000 and Orangery types will usually cost between £15,000 and £25,000.

Glass extensions have gained considerable popularity in recent years too although they can get a bit pricey. Small ones will cost you around £14,000 to £26,000, medium extensions will usually be priced around £24,000 to £38,000 and large ones will likely cost between £33,000 and £70,000.

If your after a garage rather than an extension we break down the costing over here at how to build a garage

Is an Architect Necessary?

There is no legal requirement for an architect when completing the installation of a rear extension. However, it is always better that you do to ensure that you get a finished product that looks great and functions exactly how you intend it to be.

Errors are also prevented when there is a professional on- board and this will help you save a lot of money in the long run. Having to redo certain stages of the construction because you made the wrong calculations or there were errors in the design will only cost more.

They can also help in choosing the right materials so you make the most out of the extension, especially where the aesthetics of your home is concerned.

Architects will usually charge around £50 to £60 an hour for their services. This has the potential to add up to something really substantial if this is a large extension you are planning on building.

Alternatively, some people also hire the services of a structural engineer, they often charge a per hour rate of £50. Another alternative to consider is an interior designer although they do charge rather hefty rates of up to £110 an hour.

They do focus on a different aspect of the project as their expertise lies more on furnishings and decoration.

Lighting Costs
If you want artificial lighting installed in your extension, an electrician is the man for the job. They will  usually charge around £50 per hour for lighting and wiring. You may need the services of a glazier for your window installation.

They are known to charge £16 an hour. These prices are expected to vary though depending on the lighting type you prefer.

Heating Costs
For heating installation, plumbers will charge an hourly rate of £50 but this could change based on the heating type you want fitted in. The cheapest would be plug-in heaters at £40.

Among the cheaper options include Gas and il radiators at £200 and £300 each respectively. Electric radiators can cost around £470. A regular boiler is usually priced at £900 while system boilers cost around £1,000.

If you want a combination boiler, be prepared to pay £1,800. There is also the option to install underfloor heating which can cost you £100 per square metre.

Fire Safety

Certain regulations on fire safety must be considered when installing rear extensions. Among these are:
• Provide an escape route
• Prevent fire from spreading through appropriate internal lighting
• Care must be taken to ensure that the extension will never collapse
• There must be proper suppression and separation
• Any unseen fire should be prevented from escaping from the cavities
• Fire must be restricted from reaching over the outside walls
• Fire should be prevented from going over other neighbouring homes

A carbon monoxide and smoke alarm is also needed for better fire avoidance. The alarm must be fitted in every floor of the structure and must be fitted at a distance of 7.5 metres from bedroom doors in hallways or in landings.

Smoke alarms generally cost £12 each while smoke alarms often retail at £90. If you want to better protect your home against fire, then fire-resisting doors may be worth looking into. They can cost around £70 – £300 depending on your style preference.

Effects of Rear Extensions to Your Home Value

If you want to be sure that your extension is going to bring about all kinds of good things to your property, see to it that it is properly planned and designed.

Even the simplest extension can add so much to your property’s overall value when done right. If it is a bathroom extension that you’re adding, a return as high as to 6% can be expected.

A lounge extension has the potential of adding 12% to your property value. Meanwhile, a large extension kitchen can offer up to 50% added property value. Expect to get even better returns when you only use materials with top-notch quality.

Planning Permission

Whether you will require planning permissions will be based on the type of property you own or the size of your ideal extension you plan on installing. Based on a homeowner’s permitted development right, a home extension can be installed without the need for a planning permission provided that it meets specific criteria.

A detached property may be extended along the rear by no more than 8 metres and at a height that doesn’t go beyond 4 metres than the existing structure.

Two-storey extensions need to be installed using the same materials as the existing structure and should not go beyond 7 metres to the boundary at the rear. It is your responsibility to ensure that all the papers and permits are secured before the project starts, so it is best to check with the experts ahead of time so you’ll be guided accordingly.

If there is a need for a planning permission, applying for one would cost you £206. When a project requires a permission, but you choose not to apply, you will be subjected to a fine and the extension may be removed or amended to ensure that the standards set by the local authority are properly met.

Building Regulations

You want the extension to comply with all the necessary legal requirements. So, consider securing a warranty that covers every element of the job. You’ll also have to file for a building notice or the submission of a full plan.

This process involves sending a design plan for the project to the local authority. They will then have somebody come to the site to carry out inspections whilst the process is going on.

Meanwhile, a building notice seeks to inform the local council that you plan on making all these changes to your property and how they are well within the building regulations. A 48-hour notice is also required to be extended to the local building control agency before work is started. Once the job is commenced,

inspectors will be sent by the local authorities to the premises ensure that the job has adhered to certain standards. Note that homes tagged as a Grade II building cannot be changed.

For other listed buildings, changes may be possible provided that the work isn’t going to cause considerable deviation to the original design. Non-conformance to these rules could lead to hefty fines with work carried out needing to be reversed with you shouldering the costs.

Party Wall Agreement

This legal document seeks to protect your neighbours and you as it allows you to do whatever work that needs to be done in relation to the project at hand.

At the same time, your neighbour agrees to allow the construction to carry out and to not take any step to dispute the work. The agreement covers walls that you share with your neighbours as in the case of semi-detached, attached or terraced properties.

Among the details included in the agreement are:
• The award for the party wall agreement
• A list of the conditions of the rest of the nearby properties
• Plan and drawings of the work to be carried out
• Insurance and liability details of the contractor
• Surveyor’s fee for you and the neighbours
• Addresses of the parties involved
• Building owner protection favouring the neighbours
• Specific hours when the work will be carried out
• Time limitations

Obtaining this agreement requires a professional surveyor and will usually cost about £300

Rear Extension Benefits

A rear extension is a cheaper alternative to finding and moving to a new place simply because your current home doesn’t have the necessary living space you want.

With all the necessary costs figured in, it is still cheaper to just extend your living space than to have to pay for all the moving costs including removals, stamp duties, and even solicitor’s fees.

The addition of rear extensions also leads to better garden access. It is also one way of increasing the overall value of your property especially if the project meant adding a more spacious bathroom or kitchen.

This is also one way of bringing more natural light into the house— as is the case in open space extension that aims to expand the living space inside your home.

Keeping the Costs Down

To make the most of the presence of all the tradesmen working on the project, have them do other jobs around your property that also need their attention.

For instance, if your rear extension is intended to match an already existing structure, have them paint or clean the outer walls especially since the construction work can make the facade look dirty and grimy.

An extension can be an extensive project with so many tradesmen carrying out the labour. It also involves rather complicated legislation.

This is why it is always advised that you secure the guidance of the right professional to avoid turning the job into an absolute financial disaster.

Many of the problems that tend to plague extension installation often have to do with poor planning and design or getting the job done by less than trustworthy builders.

Always have an architect and a structural engineer asset you in designing the extension. They will be most helpful at figuring out not only the entire process but also in determining the appropriate costs to get your vision to come to life.

More importantly, make sure that you will only have a highly reputable builder do the work to avoid unnecessary problems. If you can, try to manage the project.

While you’ll need to seek out the help of subcontractors to carry out the different bits and stages of the extension project, taking on the job of a project manager will help you save valuable money in the process.

Rear Extension Removal Costs

There are a number of reasons that you want to remove an extension. For instance, if it isn’t compliant to building regulations, then you will be required by law to take it down.

You might also want to completely rebuild it so demolishing the original one is necessary. A job like this could use the help of demolition contractors.

Cost is often calculated on a per square metre basis with most charging £55 per square metre. The figures already include waste disposal cost.

Note that prices can vary based on the specific items and materials that need to be removed. For instance, bathroom or kitchen extensions tend to be more complex since there are plumbing and electric cabling involved.

You do have the choice of doing the demolition work yourself. This could take longer to complete though, not to mention, riskier when you end up hitting pipes or wires. If this happens, it may end up being costlier than what you’d have spent hiring demolition experts due to the repairs that will need to be done afterwards.