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Kitchen Extension Cost: 2021 Rear Price Comparison UK 

Kitchen extensions vary in size and convenience depending on your requirements and budget. But, you can be certain of one thing. In the UK,  you’ll reap the money you spent out building a kitchen extension, many times over. Both, in terms of a better lifestyle and getting your money back when you eventually decide to sell. 

An average cost of a kitchen extension lies between £18/m2 to £144/m2 and might be even more if you choose a bespoke kitchen extension design. Furthermore, if you live in London and southeast, the cost can increase by 20%. But, even a relatively modest kitchen extension price of around £18000, will potentially add around 5% to 10% to your property value. 

How Much Does A Kitchen Extension Cost? 

If you don’t know what you want from the extension, youll find it very difficult to price a contemporary kitchen and calculate the costs. So, you must have somewhere to start. First, measure the space you have available. And, decide how much money you can afford. We’ll talk about planning later on.  

But, for now, the following table will show how much you can expect to pay when extending your kitchen. The figures relate to a medium-quality, single-storey extension. Combined with, a compilation of various standard layouts, for kitchen extension ideas priced between £7000 and £20000. Although, you can find DIY kitchens costing a lot less than that. So, regard the totals as guidelines 

Kitchen extension size  Area  Estimated kitchen price  Estimated extension price 
Small kichen extension   15m2  £7000  £18000 
Medium kitchen extension  24m2  £10000  £29000 
Large kitchen extension   48m2  £20000  £57000 

Alternatively, you can choose from basic or premium quality kitchen units, with corresponding variations in price. And, as with most construction quotations, we don’t include VAT. 

Small Kitchen Extensions 

Although you can have very small kitchen extensions. You could say that the expenditure wouldn’t be worth the extra space. So, if you intend to build an extension, it’s best to build a decent size one. Now, a typical rear kitchen extension, with sliding doors onto the back garden, measures between 10m2 and  18m2. also, you need wall and base units, a sink, and a laminate worktop to suit the size. Depending on its dimensions, the small kitchen extension might not have enough space for a washing machine and tumble dryer so these could be installed in the garage or a utility room. Even so, don’t forget the electrics for the fridge, freezer, and plumbing for the sink and dishwasher. Usually, you can’t have too many electrical sockets in a kitchen. 

Windows range in price from £250 for a 100cm x 80cm Velux roof window to £900 for a 1.2m x 1.2m uPVC fitted into the wall. Also, patio doors would be around £350 to £400. And, basic vinyl flooring costs from £70 to £130. 

Medium Kitchen Extensions 

Typical mediumsized extensions ranging from 20m2 to 30m2 are a good choice if you want to provide room for a dining area as well. And, open plan kitchen extensions of these dimensions, don’t usually increase the amount of storage space, except for the addition of a small island. This separates the kitchen from the dining area and contains an extra worktop, as well as sometimes the sink, a single oven priced from £500 to £1000 or a hob costing from £150 to £900. Thus, the extra storage provided by the island might allow more room for a larger freezer, or many other built-in appliances. 

Large Kitchen Extensions 

Improving your kitchen with a large rear kitchen extension increasing in area from about 30m2, is a major project costing many tens of thousands of pounds. The majority of the total cost will go towards building the shell, especially foundations and roof. Unless you are a professional chef or have an extremely large family, you’ll probably find that a kitchen this size will be wasted space. However, you can turn the area into an open plan kitchen, dining room, and breakfast bar without any trouble. And, if there’s space, you can add a couple of small easy chairs too. 

Usually, with an extension of these dimensions, you must ensure you don’t break the planning rules relating to currently Permitted Development rights. Based on these regulations, you will probably require planning permission unless you already have a large house, with plenty of land. If you intend building a large extension, costing so much money, it would be ideal to make the most of it by including a set of large bifold doors to open your kitchen into the garden. So, depending on the style, material and dimensions, these can cost between £1400/m and £1800/m. 

Kitchen Extension Cost Factors 

Many factors affect the total costs. So, as every kitchen extension has a different design, we’ll look at a few of the main components:  

The style of the roof affects the cost. You can choose between a flat roof, pitched gable roof, or hipped roof. But, the planning department will have the final word. And, specify what roof type you can have depending on what looks in keeping. 

Kitchen units and worktop. Usually, costs depend on the style and number of units, appliances, and worktop. 

Bi-fold doors link the indoor and outdoor spaces. Depending on the style, accessories, and material, typical costs will vary between £1400/m to £1800/m. 

You can design the lighting system yourself for free. Or, commission a professional lighting designer. Although they typically cost around £100/hr, a professionally designed scheme will add the finishing touches. 

Concrete floors are hardwearing and look good. Especially when beneath one of the modern floor coverings. Usually, you can expect to pay between £120/m2 and £150/m2. 

Kitchen tiles are a must-have. And, theres a huge range of designs and prices to choose from. You can buy floor or wall tiles from DIY stores for as little as £10/m2 or as much as £70/m2 

Heating is another essential. But, you should already have a boiler for your existing central heating. So, check with a registered heating engineer whether your boiler has enough capacity to handle more radiators. Usually, a no-frills replacement gas boiler will cost around £2300. But, you might be eligible for Government funded help. So, look on the Energy Saving Trust website for help with choosing an up to date boiler. And, why not try underfloor heating instead? 

Decorating will finish everything off to match your kitchen. Decorating costs around £75/m2. 

Finally, flooring comes in at between £25/m2 to £50/m2. 

UK Planning Permission & Building Regulations 

When building an extension, you don’t need to apply for planning permission as long as you follow the Permitted Development rules, and apply for ‘prior approval’. Let’s have a look at a few of the requirements. 

Single storey kitchen extension 

Normally, you can extend from the original house wall by up to 6m if it’s a semidetached or terraced house. Or, 8m for a detached property. However, if the property sits in Article 2(3) designated land or any land designated as an SSSI (Site of Special Scientific Interest) the distances reduce to 3m and 4m respectively. The extension must also be less than 4m to the highest point of the roof.  

Article 2(3) land 

Article 2(3) land is defined as: 

  • Conservation area. 
  • Area of outstanding natural beauty. 
  • National Park. 
  • World Heritage Site. 
  • The Broads. 
  • Any other area specified by the Secretary of State. 

Also, if there is less than 2m distance between your extension wall and your neighbour’s property, the extension’s eaves must not be higher than 3m. 

Double-storey kitchen extension 

A double-storey extension can’t be higher than your existing roof height. And must not extend beyond 3m from the existing house. Moreover, any wall must also be at least 7m from any boundary. Also, you must not build double-storey extensions onto the front elevation or on any wall parallel to a public road. Furthermore, under Permitted Development rules, you can’t build a double-storey extension that extends beyond the side elevation. 

If your proposed extension breaks any of these single or double-storey extension conditions, you must apply for planning permission in the usual way with a full set of kitchen extension plans and associated documentation. 

However, whatever your circumstances, you must contact your planning department before the project begins to confirm whether it falls under the Permitted Development rights criteria, or not. 

Building Regulations 

Repairs and maintenance in your home don’t usually need Building Regulations. But, depending on the project, you must comply for anything new or a conversion from an existing room into something else. In the case of a kitchen extension, you will first build the shell, then add the kitchen fixtures and fittings. The shell needs foundations, a concrete floor, walls, windows, doors, and roof. As it’s a kitchen it’ll also need drainage, hot and cold water, electricity and ventilation. All of these components come under the Building Regulations. 

List of relevant regulations 

Also, all plumbing materials, appliances, procedures, and workmanship must comply with the UK Water Supply (Water Fittings) Regulations or the Water Byelaws in Scotland. These regulations and bylaws protect public health, safeguard water supplies, and promote water efficiency. 

Professional Fees 

When building a kitchen extension, you not only have the costs of materials and labour needed to build the extension, you also have professional fees to consider.  

Design fees 

These fees mainly go to the architect. To design the extension will cost between 3% and 7% of the entire build cost.  

Planning department drawings 

Usually, drawings necessary for the Planning Department will cost at least £2500. But, might extend to around £4000, depending on the number of plans required and the level of detail and documentation. 

Construction drawings 

These are for the Building Regulations approval and for the contractors to work from. Usually, these cost the same as Planning drawings, namely £2500 to £4000. 

Survey 

Your existing house must be accurately surveyed for the plans. And, will cost between £500 and £1500. 

Structural engineer 

A structural engineer must calculate the loads and dimensions of the foundations, roof, lintels, and any structural changes to the existing house. Fees for this will go from £500 to £1000. 

Planning permission 

If your project needs planning permission, the fees will be about £200, depending on what you propose and your whereabouts in the UK. If you need planning permission, you will also need: 

  • A tree report costing at least £200. 
  • Flood risk assessment costing at least £600. 
  • Ecology report costing from £720. 
  • If you live in areas of archaeological interest, you will need an archaeological report. Its cost depends on many factors, which will be decided upon on a case by case basis. But, they can cost many thousands of pounds. 
  • If you live in a listed building, you will need a historic building report, costing from £750 to £2000 depending on the property. 

Building regulations 

This fee depends on the size of the extension and whether you also use competent persons who can self-certify their work. You can find registered tradesmen on the Competent Persons Register. For a typical extension with an area of up to 10m2, the fee will be around £250. Or, for an extension of area 80m2 to 100m2, it will be around £900. 

Party wall agreement 

If your extension adjoins your neighbour’s property, you will need a chartered surveyor to sort out this agreement. Typically, a party wall agreement costs between £700 to £1000 per neighbour. 

Does A Kitchen Extension Add Value?

A kitchen extension will always add value to your home. However, the amount it adds depends on: 

  • The quality and workmanship of the kitchen extension.  
  • How it was maintained.  
  • And, how the condition of the extension lasts over time.  

Make sure that the amount you spend adds value to your house. And, don’t be tempted to spend any more than that. So, don’t become engrossed in spending a lot on detail unless it’s guaranteed to give a return on your investment. It might look pretty, but it’ll work out as a waste of resources. 

The added value will vary depending on the overall situation in your area. So, it’s a good idea to speak to a local estate agent and find out what type of extension is in demand. But, don’t forget that the type of extension in demand might change over time. Having said that, an extended kitchen will always be useful, whoever buys your home. 

A typical singlestorey kitchen extension might add between 5% and 10% to the value of your property. Also, you might consider building a twostorey extension, with a kitchen on the ground floor and a bedroom upstairs. An extension such as this might add as much as 20%. 

How Do I Plan A Kitchen Extension? 

The planning and construction of your kitchen extension must follow a set procedure and timeline or else there will be holdups that cost time and money. And, the Planning and Building Control offices will get upset, as certain inspections must follow others. Once the Building Control office have the construction drawings, they will give you a list of milestones where you must pause work to allow for inspections. 

Although there are many details within the process, the following are the major points. 

The money & budget

First, calculate how much you have to work with. A typical basic singlestorey kitchen extension costs around £15000/m2 to £17000/m2. But, if you decide to choose expensive flooring, windows and doors and a bespoke kitchen, you could be paying from £1900/m2 to £2300/m2. 

Plans and documentation 

Speak to an architect about what sizes and styles are feasible for the extension. But don’t forget to choose internal wall lengths to make the best use of standardsized kitchen units. 

The architect will guide you on what the local planning authority will allow in your area and whether you have to apply for permission. Alternatively, you could ask the Planning office, without any help from anyone else. 

There will be documentation to complete. Mainly, to do with how the extension affects the local environment. Once again, the architect will help you there.  The various people involved at this stage of planning will usually report to the architect. Or, if you have one, the project manager. You can read about the various professionals, their output, and their costs in a previous section on Professional Fees. 

Choose the contractor 

Once you have the legal stuff in order, it’s time to finalise your choice of building contractor. You should by now, have contacted contractors and asked for 3 quotations for the work. Choose the best overall deal (not necessarily the cheapest) which aligns with your expected start date, contractor’s experience and price. 

Then, once you have written permission back from the council. And, the finance is in place, start building. 

Prepare site and excavate 

The contractor sets out the proposed dimensions for the foundations. Remove any shrubs or trees that might be in the way and dispose of them, or replant elsewhere. 

Excavate the foundation trench to the required depth and prepare for concrete premix delivery.  

Before, pouring the concrete, call in the Building Control inspector. He will check the trenches are of suitable dimensions to comply with the Regulations, depending on soil type and the height of the water table. 

Pour concrete footings and lay foundations 

Pour the pre-mix concrete so the footings are the required thickness and at the correct level. Allow the concrete to cure. Build the brickwork up to damp proof course level, incorporating sewer pipes and any service pipes along the way. Building control inspection of foundations and drainage pipes required at this point. 

Concrete floor 

Lay damp proof membrane, insulation and galvanised steel mesh before pouring premix concrete for the floor. Bring the level up to the required height on the brickwork, taking into account brickwork damp proof course. 

Build walls 

Build the brickwork walls up to the required height, tying into the walls of the existing house. Incorporate window and door openings as required. 

Roof 

Set out roof onto the wallplate and fix roof trusses in place. At this stage open the existing roof so the new roof can be successfully incorporated into it.
when the trusses are fixed, install initial roof coverings and roof tiles. Make good the existing roof, incorporating lead valleys at the junction between new and existing roof. 

Doors and windows 

Install door and windows to make the extension watertight. Now work can commence indoors. 

First fix  

The carpenter, plumber and electrician arrive to install their ‘first fix’ work. That is, internal stud walls, pipework, and cables. 

Plasterboarding 

All internal walls now covered with plasterboard. 

Break through into the house 

Make the opening between the extension and the original house. The amount of work will depend on what has to be done. You might be cutting a hole in brickwork, or timber frame and inserting lintels. Or, removing an existing window and using the existing lintel. 

Plastering 

Plaster all internal walls and make good around the opening into the existing house. 

Second fix 

After the plaster has set, the carpenter, plumber and electrician arrive to finish off their work. This includes skirting boards, installing light fittings, switches, drainage, and water pipes, heating pipes and radiators. 

Install kitchen 

Kitchen fitters install agreed kitchen. Installation of base units, wall units, sink, fitted appliances and worktop. When finished, protect all surfaces from damage until all work has been completed. 

Final building regulations check 

The Building inspector will know that you have used as many ‘competent persons’ as possible during the construction of the extension, so will not check their work.  By now the building control office should have the certificates from the various selfcertifying tradesmen, so will know what else needs checking.   

Decorating 

Wait until the plaster on walls and ceiling has cured. Then paint the ceiling, walls, and woodwork. Do the wall tiling at this stage too. 

Flooring 

Floor covering laid. Then painters touch up any slight damage done to paintwork. 

Hand-over 

The building contractor checks for snags and problems, and puts them right. Then, he formally hands over the kitchen extension to you.  

Get Quotes From Experts 

If you want to have a new kitchen extension, and who doesn’t? You must use a qualified building contractor and associated tradesmen to do the work. This job is far too complex to have a go yourself, so choose someone who knows what they’re doing.  

Just complete the form on this page and you’ll receive 3 to 4 quotes from local contractors, so you can choose the best kitchen extension costs around. 

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