A kitchen extension goes well when the design, the permissions, the structure and the finishes are planned as one job. They go badly when each is treated as a separate problem. This guide takes you through the whole journey in the order it happens on site, with the decisions that matter at each stage. It is written for homeowners in Warrington, St Helens, Wigan, Worsley and the towns around them.
TL;DR
- Settle the layout, the services and the steelwork together, before anyone digs. Late changes are where budgets slip.
- Most extensions need Building Regulations approval, even when planning permission is not required. Check both early.
- Expect a typical kitchen extension to cost roughly £30,000 to £50,000, depending on size and finish. Ask for a detailed written scope with exclusions and staged payments.
- Agree who supplies the kitchen, flooring and decoration before work starts, because the answer changes both the price and the programme.
- Book a site visit. A builder who has stood in your garden will quote far more accurately than one working from photographs.
Table of Contents
- Start with how you live, not how many square metres you want
- Layouts that work in typical North West homes
- Budget: what to expect and how to keep control
- Permissions: planning, Building Regulations and your neighbours
- Foundations and structural work
- Roofing, glazing and light
- Electrics, plumbing and lighting
- Finishes: the details people live with
- A realistic timeline
- Why a detailed written scope matters
- Common mistakes we see
- Perspective: what we have learned from building kitchens
- Working with Complete Property Solutions
- FAQs
- Arrange a site visit
- Sources
Start with how you live, not how many square metres you want
Most people begin with a number: 4 metres out the back, or knock through the side. Architects tend to say the opposite. Successful extensions improve how a house feels and functions, rather than simply adding floor area. A bigger room that is dark at one end and awkward to cook in is a worse result than a smaller room with good light and a sensible layout.
Before you talk to anyone, answer a few plain questions:
- Who cooks, and how often do two people cook at once?
- Do you want a dining table in the room, or a place for the children to do homework while you cook?
- Where does the garden sit in relation to the sun? A room that catches morning light feels different from one facing a north fence.
- What do you hate about the current kitchen? Write it down. It is the best brief you will ever give a designer.
Our kitchen extension layout ideas guide goes deeper on rear, side return and wraparound options. If you are weighing a kitchen-diner, our page on what a kitchen diner extension is will help.
Layouts that work in typical North West homes
Many homes in Warrington, St Helens, Wigan and Worsley are 1930s semis, post-war family homes or newer estate properties with a narrow rear kitchen and a separate dining room. That suggests a few common layouts.
Rear extension
The simplest shape. The kitchen pushes out into the garden, and the old kitchen wall is opened up with a steel beam. It suits houses with a reasonable garden depth and gives you the most straightforward build.
Side return or side extension
Useful on semis and detached homes with a passage alongside. It widens a narrow kitchen without taking much garden. Rules on width and height differ here, so read our guide to side extension permitted development first.
Wraparound
A rear and side extension combined. It gives the largest open-plan space and the most design freedom, but it needs more structural work and more careful coordination of trades. We build these, and you can see the range on our house extensions page.
Islands, storage and the working triangle
The classic idea is the working triangle between sink, hob and fridge. It still helps, but it is a starting point and not a rule. A good primer is this guide to the kitchen work triangle measurements and island clearances. A few practical points we raise with clients:
- Islands need room on every side. If you cannot leave comfortable walking space around one, a peninsula or a slim breakfast bar is often the better choice.
- Storage is cheaper to plan now than to add later. Tall larder units, deep drawers and a utility corner keep worktops clear.
- Services come first. Where the sink, hob and appliances sit decides where pipes, cables and extraction go. Early coordination of gas, electrical and water services with the structural steelwork avoids clashes on site.
Budget: what to expect and how to keep control
We do not publish fixed prices for kitchen extensions, because every one depends on the size, ground conditions, glazing and finish. For a general benchmark, one national price guide puts the average kitchen extension at £30,000 to £50,000, with basic builds starting around £2,200 per m² and more complex or premium projects reaching £3,300 per m² or more. Treat these as national averages, not a quote for your home.
What moves the figure most:
- Size and shape. A wraparound costs more than a simple box because of the extra structure and roof complexity.
- Glazing. Large bi-folding or aluminium sliding doors, and rooflights, add cost but transform the room.
- Structure. Removing a load-bearing wall means steelwork and calculations.
- Ground conditions. Foundations are the biggest unknown until the ground is opened up or investigated.
- The kitchen itself. Cabinets, worktops and appliances can range from modest to very expensive.
A sensible habit is to hold back a contingency, because older houses sometimes reveal surprises such as unmarked drains or poor existing brickwork. Ask your builder how unforeseen items are handled before you sign.
Permissions: planning, Building Regulations and your neighbours
These are two separate systems, and people regularly confuse them.
Planning permission
Many extensions can go ahead under permitted development, which means no full planning application, but only within strict limits on size, height and position. These limits come from the General Permitted Development Order, as explained on the Planning Portal. Homes in conservation areas, listed buildings, and houses where permitted development has been removed have tighter rules. Our guides on permitted development for extensions and permitted development versus planning permission explain how to check where you stand. If you want a certificate to prove it, a lawful development certificate is one route.
Building Regulations
This is the part you cannot skip. Most extensions need Building Regulations approval, whether or not planning permission is needed. It covers structure, drainage, fire safety, insulation and electrics. You can apply through your local council or a private approver, and under the full plans route a decision is expected within five weeks, or two months with your consent. Official guidance on how to apply is on GOV.UK.
Kitchens bring their own points. Simply refitting a kitchen with new units does not generally need approval, but drainage or electrical work might. In an extension, ventilation and new electrical circuits must comply, and leaving them out of the original scope can delay sign-off. Opening up walls between the old kitchen and a dining room can also trigger extra fire safety requirements, such as interlinked detection.
How we can help
We can help arrange planning advice, Building Control applications and structural calculations as part of a managed project. These fees are identified separately in your written scope, so you can see exactly what you are paying for and who is responsible for what. If your build is close to a boundary, ask us about neighbour notices and any party wall matters early, since they can affect the start date.
Foundations and structural work
Every extension starts in the ground. The depth and type of foundation depend on the soil, nearby trees, drains and the size of the building. Some of this is only certain once the trench is open, which is why a good scope explains how changes would be priced.
One piece of design advice worth hearing: economy of means, such as keeping to a clear plan and avoiding structural change that brings little everyday benefit, often gives a better result than spending heavily on dramatic alterations.
Where the old rear wall comes out, an RSJ or steel beam carries the load above. A structural engineer calculates the size, Building Control approves it, and temporary supports hold the house up while the steel goes in. Our structural alterations page covers this in more detail. Plan the beam position and the service routes together, so pipes and cables do not end up fighting the steel.
Roofing, glazing and light
Roof choices
Flat roofs with a rooflight or lantern give a clean, modern look and are common on single-storey extensions. Pitched roofs tie in with the existing house and can offer higher ceilings. Your choice depends on the existing roof line, the budget and the planning rules for height.
Rooflights and doors
A deep extension can end up gloomy in the middle, because vertical windows only reach so far. Rooflights bring daylight into the core of the room, and the same guidance suggests keeping total glazing at around 15 to 20 per cent of the floor area to balance brightness against overheating, particularly on south-facing rooms. Plan for ventilation too: openable rooflights and good cross-ventilation stop a bright room turning into a hot one in July.
Garden access
Bi-folding doors, aluminium sliding doors and French doors all connect the kitchen to the garden. Think about where the door lands in relation to the patio, the step level and the kitchen run, so your worktop does not end up blocking the route outside. We install a range of replacement windows and doors, including bi-folding, aluminium, composite and French doors, so glazing can be part of the same managed project.
Electrics, plumbing and lighting
This is the stage that makes or breaks a kitchen in daily use.
- Electrics: new circuits must meet the regulations, and work in wet areas needs particular care. Allow for enough sockets at worktop height, appliance circuits and an island supply if you are fitting one.
- Plumbing: the sink, dishwasher and washing machine need supply and waste. Moving them far from the existing drain adds cost.
- Extraction: adequate ventilation over the hob is a Building Regulations point, not a finishing detail.
- Lighting: layer it. Use bright task lighting over worktops, softer lights over the dining area and pendants over an island. Decide the positions before plastering, because moving them afterwards is messy.
Underfloor heating is worth deciding early too, as it affects the floor build-up and the type of flooring you can choose.
Finishes: the details people live with
The finishing stage is where the room becomes yours: plastering, flooring, worktops, tiling, decoration and the final fit of the kitchen. Choosing the performance specification and finishes early helps prevent budget creep and keeps deliveries in step with the build.
Whether we supply and fit the kitchen, flooring and decorating, or you buy some of it yourself, depends on the scope agreed for your project. Neither route is wrong. What matters is that it is written down. Typical decisions at this point:
- Worktop material and thickness, which affects the cabinet structure underneath.
- Flooring type, and whether it runs continuously from the old kitchen into the new space.
- Paint colours and finishes on any exposed steel or rooflight surrounds.
- Appliance sizes, confirmed before the units are ordered.
A realistic timeline
Every project differs, so we do not promise a standard programme, but the sequence is predictable:
- Design and measured survey. Layout, elevations and first ideas.
- Permissions and calculations. Planning if needed, Building Control and structural design.
- Groundworks and foundations.
- Walls, steelwork and roof.
- Windows, doors and rooflights, making the building weathertight.
- First fix: electrics, plumbing and heating routes.
- Plastering and drying time.
- Second fix and kitchen fitting.
- Decoration, flooring and Building Control sign-off.
The permissions stage often takes longer than people expect, so start it early. Our house extension planning guide and building a home extension page set out the stages in more depth.
Why a detailed written scope matters
The single best protection for you and your builder is a clear written scope. A good one covers:
- What is included, stage by stage.
- What is excluded, such as kitchen units, appliances, flooring or decorating if you are supplying them.
- Who supplies and fits each item. Agreeing early who provides the kitchen, flooring and appliances affects both budget and timeline.
- How variations are priced and approved.
- Staged payments linked to completed milestones, so you pay for progress you can see.
This stops scope creep and keeps everyone aligned on the expected quality. It is also why coordinated trades matter. When one managed contract covers groundworkers, bricklayers, roofers, glaziers, electricians and plumbers, fewer regulatory requirements are missed, and nobody is left waiting for someone else to finish.
Common mistakes we see
- Choosing size over light and orientation.
- Fixing the kitchen layout after the steel and drainage are already planned.
- Leaving extraction and electrical requirements out of the original scope.
- Assuming planning permission and Building Regulations are the same thing.
- Comparing quotes that cover different things. A cheaper price often just leaves items out.
- Deciding finishes late, so deliveries hold up the programme.
- Skipping a contingency for hidden problems.
Perspective: what we have learned from building kitchens
We are a family-run company with more than 35 years of experience, and the pattern is consistent. Kitchen extensions rarely go wrong because of one dramatic failure. They go wrong in the gaps: between the designer and the engineer, between the plumber and the steel, between what the homeowner thought was included and what the quote actually said.
That is why we manage projects from design through to completion, and why we put fixed-price quotations in writing, with the scope and exclusions spelled out. Our customers are mostly local, from Warrington, Great Sankey, Penketh and Culcheth to St Helens, Rainhill, Haydock, Wigan, Lowton and Worsley, so we know the typical house types and the usual surprises. Our advice is simple: decide the layout and services early, be honest about your budget, and never sign a scope you do not fully understand.
— Gareth
Working with Complete Property Solutions
We design and build kitchen extensions across the North West, as part of a fully managed service. We are a member of the Guild of Master Craftsmen, an approved HUP! Building System partner, and an authorised REHAU installer. If you are ready to move from ideas to a proper plan, see our kitchen extensions page or ask for a cost estimate through the site. The best next step is a site visit, where we can look at your house, your garden and your plans together.
FAQs
Do I need planning permission for a kitchen extension?
Not always. Many rear and side extensions fall under permitted development, but only within limits on size, height and position, and not for every property. Conservation areas and listed buildings have extra restrictions. Check with your council or a lawful development certificate before you start.
Do I need Building Regulations approval?
Almost certainly yes. Most extensions need it, even where planning permission is not required. It covers structure, drainage, ventilation, electrics and fire safety, and we can help arrange the application.
Will the builder supply the kitchen?
That depends on the scope we agree with you. Some homeowners want supply and fitting included, others buy the kitchen, flooring or decoration separately. Whichever you choose, it is written into the scope and exclusions so there is no confusion.
How should I pay for the work?
Staged payments tied to completed milestones are the sensible approach, because you pay as the work progresses. The stages and amounts should be set out in the written contract before work begins.
How much will it cost?
It depends on size, design, ground conditions, glazing and finish. National guides suggest £30,000 to £50,000 as an average range, but your own figure needs a site visit and a detailed scope.
Arrange a site visit
If you are in Warrington, St Helens, Wigan, Worsley or nearby and are thinking about a kitchen extension, get in touch with us to arrange a site visit. We will talk through layouts, permissions and budget, and give you a clear, written fixed-price quotation. Start on our kitchen extensions page.
Sources
- Kitchen extension costs, MyBuilder
- Planning permission for extensions, Planning Portal
- Is Building Regulations approval needed for an extension, Planning Portal
- Is Building Regulations approval needed for work to a kitchen or bathroom, Planning Portal
- Building regulations approval: how to apply, GOV.UK
- The Regs: Don’t get your fingers burnt on a kitchen project, Architects’ Journal
- Checklist: specifying domestic kitchens, RIBA Journal
- The secret to better open-plan extensions, RIBA Journal
- Kitchen work triangle: measurements and islands, House A-Z
