The short answer
A kitchen extension is usually a single-storey addition at the back or side of the house that opens into the existing kitchen to make one larger room, often a kitchen, dining and family space. The build itself is a normal extension, with foundations, cavity walls, a roof and new glazing, but the kitchen adds three extra things to plan early: where the drains and soil pipe run, how the old back wall comes out and is supported, and where the sink, cooker and extractor will sit so the services are laid in the right place.
Choosing a layout
Start with how you use the room rather than with the size. Most people want the cooking area near the existing house, where the plumbing already is, and the dining or sofa area towards the garden, where the light is best. An island works when there is at least a comfortable walkway all round it; squeezed in, it becomes an obstacle. Think about where the fridge, bins and storage go, because tall units take up wall space that might otherwise be glazing.
Sketching the layout before the drawings are finalised lets the architect position windows, doors and rooflights to suit the kitchen, rather than fitting the kitchen around openings that were drawn first.
Planning and Building Regulations
Many rear kitchen extensions fall within permitted development, which sets limits on depth, height and materials. Others need a householder planning application, particularly on larger schemes, corner plots or where earlier extensions have used up the allowance. Almost all need Building Regulations approval, with inspections of the foundations, drainage, structure and insulation. If you share a wall with a neighbour or dig near their foundations, the Party Wall Act may apply as well.
Opening up the back of the house
Joining the extension to the kitchen means removing some or all of the existing rear wall. That wall carries floors and roof above it, so a steel or concrete beam is designed by an engineer to take the load, sitting on padstones or piers at each end. The old wall is propped temporarily while the opening is formed. This is usually one of the last structural jobs, so the house stays closed for as long as possible while the new walls and roof go up outside.
Drains, soil pipes and services
Kitchens sit close to drains, and extensions often land on top of them. Building over or near a public sewer needs the water company's agreement, and existing manholes may need moving or replacing with an access chamber outside the new footprint. New waste runs for the sink, dishwasher and any utility need a proper fall. Plan cables and pipes for the island, underfloor heating and lighting before the floor slab is poured, because moving them afterwards means breaking it out.
Light and glazing
Deep kitchen extensions can leave the middle of the house darker than before. Rooflights or a roof lantern over the join between old and new bring daylight into the part furthest from the garden. Large sliding or folding doors open the room to the garden, but they take up wall space, so balance glazing against the units you need. Energy rules limit how much glazing a new extension can have unless the rest of the design makes up for it.
The order of work
A typical sequence is set-out and excavation, foundations, drainage, brick and block walls to damp-proof course, the floor slab, walls up to roof level, the roof and glazing, then the steel and opening into the house. After that come first-fix electrics and plumbing, plastering, screed, second fix and the kitchen itself. Most households keep a temporary kitchen elsewhere in the house for the messier stages.
Common mistakes
Choosing the kitchen units after the walls are built, and finding the window is in the wrong place. Forgetting extraction for the hob, which needs a route to outside. Leaving the drainage survey until the digger arrives. Underestimating how much the floor level has to match the house, which affects the slab depth and any step down to the garden.
Choosing kitchen extension builders
Kitchen extension builders do two jobs at once: they build a single-storey extension and they open the house into it. Ask who carries out the groundworks, the brickwork and the steel installation, and who coordinates the plumber, electrician and kitchen fitter. A builder who does the structural work themselves keeps foundations, drainage and the opening in step. Our house extensions page explains how we work, from foundations to the finished shell.
Is a kitchen extension worth it?
For many households it is the change that makes the most difference to daily life, because the kitchen is where people spend most of their time at home. It is worth it when the new layout solves a real problem, such as a cramped galley kitchen, no room to eat together or no connection to the garden. It is less worthwhile if the extension simply adds floor area without fixing how the room works, so start with the layout rather than the size.
If budget is tight, a smaller extension with a well planned layout often beats a larger one with an awkward shape. Keeping the kitchen near the existing drains and choosing a simple roof form keep costs down. Our cost calculator gives a starting range.
Building on top of a kitchen extension
Adding a room above an existing single-storey kitchen extension is sometimes possible, but only if the foundations and walls were designed for the extra load, or can be strengthened. An engineer checks the existing structure, and the new floor usually needs planning permission. If you might want a room above later, say so when the kitchen extension is designed so the foundations are sized for it.
About us
D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable, with more than 26 years of building experience. Our bricklaying is NVQ Level 2 qualified, we are Federation of Master Builders members and fully insured, and estimates are free after a visit.
Kitchen and dining extensions are part of our regular extension work, which we build from the foundations through to the finished shell and opening.
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Questions people ask
Do I need planning permission for a kitchen extension?
Not always. Many single-storey rear extensions are permitted development within size limits, but larger or unusual schemes need a planning application. Building Regulations approval is almost always required.
Can I build a kitchen extension over a drain?
Often yes, but building over or close to a public sewer needs the water company's agreement, and manholes may need moving. It is best to check the drain layout before the design is fixed.
Will I need a steel beam?
If the existing back wall is removed to open the kitchen into the extension, a beam is normally needed to carry the load above. An engineer sizes it and Building Control checks it.
Can I keep using my kitchen during the build?
For much of the build the house stays closed while the extension shell goes up outside. When the wall is opened and the new kitchen fitted, most people use a temporary kitchen elsewhere.
Why is my kitchen extension so cold?
Common causes are a lot of glazing, gaps in insulation where the extension meets the house, an uninsulated floor or heating that does not reach the new space. Rooflights and bi-folds can also lose heat if they are not well fitted.
Is a side return kitchen extension different?
A side return kitchen extension fills the narrow passage beside the kitchen to widen it, rather than extending out into the garden. Our side return extension guide covers it.
Is a kitchen extension worth it?
Usually, when it fixes how the kitchen works day to day. Start with the layout you want, then size the extension to suit it.