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Updated: Nov 22, 2022

The problem with open plan kitchen extensions is that once you have lived in one there is no going back. It is what leading designers have been claiming for years that the homes we live in can influence and shape our behaviour.

My home is open plan, it has been enlarged with a modern kitchen extension and I can tell you it was love at first sight for my wife and I when we first went to see it. That was back in 2013 and now seven 7 years later I am a complete convert and carry the flag for the march of neuro architecture and specifically open plan kitchen extensions which everyone can relate to.

Open plan kitchen extensions look great and really do give you a feel-good factor and what most people don’t realise is that they cost less to build than the type of kitchen extension our parents would have built.

If you look closely at the details of a modern kitchen extension you will see that the beauty has far more to do with good design than it has to do with expensive building methods and materials. In actual fact you could claim that the average modern kitchen extension is one of the cheapest extensions that you can build and to prove my point we are going to break down how to build an open plan kitchen extension and have a good look at the costs involved.


Most of us have a fair idea of what we want when it comes to extending our homes, but we don’t always know how to shape those ideas into design plans that don’t just add space but also kerb appeal and value. Adding an extension sounds simple enough but in this modern age of constantly rising house prices we also need to keep a strong focus on what adds value as well as living space.

Finding the right designer for your project is crucial to the success of the build but having said that you don’t want to be paying out £3k/£5k on expert design fees when an architectural technician will be more than capable of guiding you through the process and will create your design plans for about £1k for a single storey open plan kitchen extension.

I would certainly recommend that you come to us for a quote because at Draw Plans we specialise in adding space and value at low cost and our fees for creating design plans for a single storey open plan kitchen extension start from £795 plus vat.


Most kitchen extensions do not require a planning application as they tend to fall within the permitted development legislation. However, there are a few rules that mostly relate to size that need to be adhered to.

Most homeowners prefer to build within the permitted development framework and generally try to avoid having to put in a planning application. In some cases this may comprise the build so we generally advise homeowners not to be fearful of planning and focus the thinking on what they want or what they like rather than attempting to build what they think the planners will like.

Another aspect of permitted development is that if you do build a kitchen extension under the permitted development rules you may still need to obtain a certificate of lawful development if you sell within 4 years. If, after 4 years, the planning authority has not taken any enforcement action it loses its right to do so. Whilst this does not make your extension lawful it does mean that the planners can’t take any action against the owners of the property.

Under the new relaxed permitted development rules, you can extend up to 8 metres on a detached house and 6 metres on all other houses.

For those larger house extensions, you will still need to provide notification under the Neighbourhood Consultation Scheme. If any of your neighbour’s object you may have to pull back on the size of the extension.

If in the end you do need a planning application or wish to obtain a certificate of lawful development for your project, Draw Plans will be happy to advise and quote for the service.


It is always a pleasure to notify our clients that permission has been granted and that you can now move forward with the build.

The next step should be to create the building regulations drawings for building control but many of our clients instruct us to create the building plans before getting planning approval. This is so that they don’t have to hang around after getting approval whilst we create the building plans and have them approved.

A full plans application to building control is what we normally do for open plan kitchen extensions. It takes about 8 weeks to get the plans passed and once they are passed, we can submit a building notice and get the work underway.


Most people wouldn’t know that when you work on larger or commercial build projects you always get a Specification & Schedule of Works plus plans for the build. This breaks the job down and lists every bit of work that has to be done.

When you want to get quotes you provide the builders with an unpriced copy of the schedule along with a copy of the plans. That way everybody is pricing for the exact same job so there can be no misinterpretation or omissions of the works to be done. It is extremely fair and avoids loads of misunderstandings that can cause problems further down the line.

In a sense when you agree the price with the builder it is a Fixed Price to carry out the works as per the schedule and specification. There will be no extras or additional costs unless you request variations of the schedule or add on additional works which should always be agreed in writing.

Draw Plans offer a Schedule & Specification service to all its clients and we will be happy to quote you if you already have plans and would like a schedule prepared.


Many homeowners are terrified when it comes to choosing a builder for their extension. They know if they get it wrong it will be a nightmare build. For some it will be the time they instruct Draw Plans to project manage the build which we will do for about 6% of net build costs.

However, if you are made of stronger stuff and want to manage your own build here are a few important things for you to know.

There are three main build routes for homeowners wanting to build an extension; they are:

  • · Option 1: Engage a builder who will deal with the entire project

  • · Option 2: Find local tradesmen and split the job up so that you instruct different companies for the different types of work

  • · Option 3: Instruct a Project Manager who will run all or part of the project

Option 1: This a good idea if you want a trouble-free build with minimum input. The builder has the headache of finding the various trades and services and scheduling to complete the build.

The downside is that it is usually the most expensive option mainly because the builder adds his margin on top of each trade to make his living.

Option 2: The option is more of a headache as you have to find the trades and schedule the work yourself. You should be able to save money by using smaller companies.

The downside is that the job usually takes longer, and you have to find all the different trades. There is a lot more input to organise and manage the project.

Option 3: Use a project manager to manage the build. This is the least effort on your part, but you will have to pay 6% / 10% to whoever you instruct.

If budget is tight then option 2 might be the way forward providing you have the necessary skills to manage your own build.

If timing is an issue and you want to get the job done as quickly as possible then instruct a builder or a project manager for the whole project.


To get an idea of costs for an open plan kitchen extension lets take a slightly bigger than average size of 5 metres wide by 4 metres deep. This will give us an overall extension size of 20 sq mts.

Now if you were to read some of the articles on the internet about kitchen extension costs you will most certainly be confused because prices seem to vary from £1200 / £2500 a sq metre which is way too low for a standard quality extension in the London area.

Almost all of the articles I have read refer to extension build cost per square metre but offer up no information whatsoever as to where those costs come from. Not only are the figures vague and misleading they are derived from sources with absolutely no project management or build experience.

Draw Plans project manage house extension build projects routinely and have unrivalled experience within this sector. It is for that reason we are extremely qualified to write a summary of average costs for building a 20 square metre kitchen extension.


Excavations: Dig out 6/7 cubic metres for trench foundations 2,600

Foundation; Pour concrete foundations 7/8 cubic metres 3,000

Dwarf Walls: Walls up to DPC Level 450

Main Walls: Walls / Blockwork from DPC to Roof Level 2,600

Roof: Warm Flat Roof / Structure and EPDM Covering 5,000

Roof: Supply and fit roof lantern 2,500

Flashings: Code 3 / 4 leads flashing 300

Gutter: Standard pvc gutters and rwp 250

Doors: Double glazed 3-metre-wide aluminium folding doors 3,500

Rendering: Render approx 40 sq metres of blockwork 900

Extension Floor: Excavate a further 5/8 cubic metres of ground 1,200

Structural Work: Cutting out approx. 15 sq metres of load-bearing walls 2,800

Structural Steel: Supply and fit steel sections 800

Drainage Excavation: Excavate 3 /4 cubic metres for new gullies and pipe runs 1,000

Drainage: Install new gullies and pipe runs to manhole 500

Plumbing 1st Fix: Install new hot cold and waste pipework 400

Electrical 1st Fix: Install cabling to extend lighting and ring main circuits 400

Gas 1st Fix: Install new gas pipework 150

Heating 1st Fix: Install new pipework for 2 new radiators 250

Floor: Lay concrete floor with dpc and 150mm insulation 1,800

Ceiling: Board over ceiling for plastering 450

Walls: Dryline all walls for plastering 650

Plastering: Plaster out all walls and ceiling 800

Kitchen: Supply standard kitchen units, worktops and appliances from IKEA 4,000

Kitchen: Install new kitchen units, worktops and appliances 1,750

Tiling: Supply and fit tiles to kitchen to form splashback 300

Electrical 2nd Fix: Supply and fit lights sockets and switches 1,000

Plumbing 2nd Fix: Connect up kitchen taps and appliances 350

Heating 2nd Fix: Supply and fit new radiators and valves. Commission system 500

Joinery 2nd Fix: Supply and fit new skirtings 300

Painting Exterior: Paint the exterior of the extension 400

Painting Interior: Paint the interior of the extension 500

Floor Finish Material: Provide 20 sq mts of timber or tiles for floor 900

Floor Installation: Install 20 sq mts of floor covering 800

Patio Materials: Provide patio slabs / bricks for 5mt wide by 3mt patio 500

Patio Installation: Lay 20 sq mts of patio 800

Other Costs:

Skip Hire 1,300

Tool & Plant Hire 250

Toilets Hire 200

Tool Store Hire 200

Professional Costs:

Design Plans 900

Building Plans 900

Planning Application 520

Party Wall Agreements 600

Structural Engineers 600

Building Control 800

Sub Total 50,650

Valued Added Tax @ 20% 10,130

TOTAL COSTS £ 60,780


So there you have it, a breakdown of costs for an open plan kitchen extension. By having a breakdown it can help you to cut down costs if the budget is tight becasue you know where the money is being spent.

At £60,780 for a 20 square metre extension you average out at around £3k per square metre. Prices are based on building an extension in a London suburb in 2020.

So, if you are considering building any type of house extension then get in touch with Draw Plans and we will be happy to advise you on your proposed build and get you costs for all the necessary services you will need to complete your build.

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