Kitchen Extension Ideas: Open Plan Living Guide

Why open-plan kitchen extensions work

The open-plan kitchen-diner-living space has become the most sought-after home improvement in the UK, and for good reason. It fundamentally changes how a home functions - cooking, eating, socialising and family time happen in one connected space rather than in separate rooms divided by walls and corridors. For families with children, it means keeping an eye on homework while cooking dinner. For anyone who entertains, it means the cook is no longer isolated in a separate room.

At RCB Design & Build, open-plan kitchen extensions account for the majority of our rear extension projects across London and the South-East. As FMB and TrustMark accredited contractors, we have delivered dozens of these spaces and have learned what works in practice - not just on paper. The design decisions you make at the start determine whether the finished space feels connected and functional or just big and echoey.

This guide covers the key design ideas and practical considerations that turn a kitchen extension from a construction project into a space you genuinely enjoy living in every day.

Bi-fold doors, sliding doors and rear glazing options

The rear glazing system defines the relationship between the kitchen extension and the garden. Bi-fold doors remain popular and fold neatly to one side, creating a wide opening that effectively removes the boundary between inside and outside in summer. Standard aluminium bi-fold systems in 2026 cost GBP 3,500-GBP 7,000 for a 3-4 metre opening. Slim-framed systems with narrower sightlines run GBP 6,000-GBP 12,000 for the same span.

Sliding doors are increasingly preferred over bi-folds for larger openings. A three-panel sliding system where one or two panels slide behind a fixed pane delivers a clean, minimal aesthetic with better thermal performance (fewer seals and joints). Lift-and-slide systems from manufacturers like Schuco, Origin or Reynaers offer excellent weather sealing and smooth operation. Budget GBP 5,000-GBP 14,000 depending on size and specification.

Roof lanterns and skylights bring light deep into the plan where the rear glazing cannot reach. A standard aluminium roof lantern over the dining or kitchen area costs GBP 2,500-GBP 6,000 installed. For maximum impact, consider a long, narrow rooflight running parallel to the side wall - it creates a band of light that visually separates the new extension from the existing house while flooding the centre of the space with daylight.

Kitchen layout options: island, L-shaped, galley and U-shaped

The kitchen layout needs to work with the extension footprint, not against it. An island layout is the most popular choice for open-plan extensions because the island serves multiple functions: food preparation, casual dining (with bar stools on one side), visual separation between the kitchen and living zones, and often housing the sink or hob. A functional island needs a minimum of 1.2 metres clearance on all sides for comfortable movement - plan for this before committing to the size.

An L-shaped kitchen runs along two walls and leaves the centre of the space open. This works well in narrower extensions where a full island would feel cramped. It keeps the working triangle (sink, hob, fridge) compact and efficient while leaving floor space for a dining table.

A galley layout - cabinets running along two parallel walls - is efficient for cooking but less suited to open-plan living because it creates a corridor feel. It works best in side-return extensions where the kitchen occupies the narrower section and the wider rear section becomes the dining and living area.

U-shaped kitchens wrap cabinets around three walls and offer the most storage and worktop space. They work in larger extensions where the kitchen zone is clearly defined. Combined with a peninsula (a U-shape with one arm extending into the room), this layout gives you the storage of a U-shape with the sociability of an island.

Structural considerations: load-bearing walls and steel beams

Creating an open-plan space almost always means removing load-bearing walls, and that means structural steelwork. The rear wall of a typical UK house is load-bearing - it supports the first floor and often the roof structure above. Removing it requires a steel beam (or twin beams for wider spans) to transfer the load to new supports at each end.

The size and weight of the steel depends on the span, the load from above, and the bearing conditions at each end. A typical rear wall removal on a London terrace might require an RSJ (rolled steel joist) weighing 200-400 kg, installed by crane or manually manoeuvred into position. The steelwork and associated pad foundations typically cost GBP 3,000-GBP 8,000 depending on complexity.

Where the extension meets the existing house, the junction needs careful structural design to prevent differential settlement (the new foundations moving at a different rate to the old ones). Your structural engineer will specify the foundation type and depth - strip foundations for standard ground conditions or piled foundations where ground conditions are poor or trees are nearby.

At RCB Design & Build, we commission structural engineering early in the design process so that steel specifications and foundation designs are locked before construction begins. This avoids the expensive mid-build redesigns that plague projects where structural design is treated as an afterthought.

Lighting design for open-plan spaces

Lighting is one of the most underestimated aspects of kitchen extension design. A single open-plan space needs to serve multiple moods - bright task lighting for cooking, ambient lighting for dining, and softer background lighting for evening relaxation. This requires a layered lighting scheme with separate circuits for each zone.

Over the kitchen work surfaces, recessed LED downlights on a dedicated circuit provide clean, even task lighting. Under-cabinet LED strips add a second layer of work surface illumination. Pendant lights over an island or dining table add warmth and visual focus - and because they hang at a lower level, they create a sense of intimacy within the larger space.

In the living zone, consider a combination of wall washers, table lamps on switched sockets, and a feature pendant or track system. Dimmer switches on every circuit are essential - they cost very little to install at first-fix stage but transform the flexibility of the space. Our electricians wire every kitchen extension with zoned, dimmable circuits as standard because retrofitting lighting control after plastering is disruptive and expensive.

Flooring and heating strategies

Flooring in an open-plan kitchen extension needs to handle cooking spills, dining chair movement, and bare feet on a Sunday morning. The most practical choices in 2026 are large-format porcelain tiles (extremely durable, water-resistant, and available in realistic stone and wood-effect finishes), polished concrete (industrial aesthetic, seamless, works perfectly with underfloor heating), and engineered wood (warm, natural, quieter underfoot than tile but needs more care around water).

Underfloor heating is strongly recommended in a rear extension for three reasons. First, it eliminates radiators from walls, freeing up space for furniture and cabinetry. Second, it distributes heat evenly across the large floor area rather than creating hot and cold zones. Third, it works at lower water temperatures than radiators, making it more efficient - particularly when paired with a heat pump.

Wet underfloor heating systems installed within the floor screed typically cost GBP 60-GBP 90 per m² including the manifold and controls. Electric mat systems are cheaper (GBP 30-GBP 50 per m²) but have higher running costs. For a 25 m² extension, wet underfloor heating adds roughly GBP 1,500-GBP 2,250 to the build cost - a modest investment for the comfort and design flexibility it delivers. RCB Design & Build installs underfloor heating on the majority of our kitchen extension projects and our Checkatrade reviews consistently highlight the quality of our heating installations.