Kitchen Extension Ideas and Structural Steel: What to Know Before You Knock Through
A kitchen extension is often the project that changes how a London home feels, and almost every open-plan scheme involves structural steel. An RSJ, or rolled steel joist, is the beam that carries the weight of the house above once you remove a wall. This post covers layout ideas and the structural points to understand before you start, so conversations with your engineer and builder are easier.
Kitchen extension layout ideas
The best layouts follow how you live. Common approaches include:
Open-plan kitchen-diner: removing the wall between kitchen and dining room, or extending to the rear, to create one social space.
Kitchen with island or peninsula: gives workspace, seating and a natural divide between cooking and living areas.
Side-return kitchen: widens a narrow Victorian kitchen and adds daylight. See our comparison of rear, side-return and wraparound extensions, and our extensions page.
Zoned family space: kitchen, dining and sofa areas in one room, with a utility or boot room tucked beside.
Garden connection: large sliding or bi-fold doors that open onto a patio.
Rooflights and glazed sections: bring light into the centre of the plan.
Think about workflow, storage and where plumbing and drainage can realistically go before you fall in love with a layout.
What an RSJ actually does
When you take out a load-bearing wall, something has to carry the load above. A steel beam spans the opening and rests on supports at each end. Beams sit on padstones that spread the weight into the walls below, and sometimes on steel posts or columns. Not every wall is load-bearing, which is why you must never assume. Only a structural engineer can confirm it.
The structural process
Survey and assessment: an engineer inspects the house and identifies what each wall carries.
Calculations and drawings: the engineer specifies the beam sizes, supports and any foundations. Building control usually asks to see these.
Temporary support: before removal, the floors above are propped, often with adjustable props and needles.
Beam installation: the opening is formed, padstones placed and the steel lifted in.
Making good: fire protection, usually plasterboard or intumescent coating, and then plastering.
Inspection: building control checks the steelwork before it is covered.
Good builders handle this routinely, but it requires planning, a clean site and sequencing with other trades.
Things to plan for
Ceiling heights and flush beams: a beam can be hidden within the floor depth, or it can drop below the ceiling. A flush beam is neater but may cost more.
Party Wall notices: if the steel bears on a shared wall, notice is normally required.
Dust and disruption: knocking through is messy, so plan for sealing off rooms.
Drainage and services: moving a sink or hob can affect pipes and flues.
Ventilation: open-plan kitchens need good extraction.
Heating: underfloor heating, radiators and insulation levels need to fit the new space.
Planning and regulations
Single-storey rear and side extensions can sometimes be built under permitted development, but not always. Building regulations apply to both the extension and the structural alterations. Check with your local council and building control. Our guide to building regulations outlines the usual stages.
Open-plan layouts also change fire safety. If the stairs now open into a large kitchen-living space, building control will want to see that people upstairs can get out safely, which can mean fire doors, interlinked alarms or protected routes. It is far easier to design this in than to retrofit it.
Finally, think about the details people notice daily: lighting over the worktops, flooring that runs continuously from old to new, and enough sockets in the right places. A good kitchen is as much about these things as the size of the room, and a joiner who understands how the pieces fit together can make the finished result feel seamless.
If you are weighing up where to add space overall, compare the kitchen extension with other options. Some households find that a loft conversion above and a kitchen extension below, planned together, share steel design, scaffold and access, which can make the whole programme more efficient. Ask your builder whether combining stages makes sense for your house.
Ask your engineer to explain the design in plain English, including where the loads go and why. It is your house, and understanding the reasoning helps you make better decisions about finishes and layout.
Frequently asked questions
Do I need an engineer to remove a wall?
If it could be load-bearing, yes. The calculations also keep building control satisfied.
How long does it take to fit an RSJ?
The installation itself is often quick, a matter of days, but design, notices and approvals come first.
Will a beam be visible?
It can be, or it can be hidden in the ceiling. Decide early as it affects the budget and finish.
Plan your kitchen with TNK
Our carpentry, building and project management skills sit under one roof. Try the cost calculator, then get in touch to talk through your kitchen extension.
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