The Brief

A young professional couple in Southampton had recently purchased a 1970s detached property with good bones but uninspiring architecture. They wanted to transform the ground floor into a contemporary open-plan living space that reflected their minimalist taste — somewhere that felt more like a design magazine than a suburban semi. The brief emphasised clean lines, maximum natural light and high-quality materials.

Our Design Approach

We designed a 40m² single-storey extension with a dramatic flat roof that extends beyond the building line to create a covered outdoor terrace. The rear elevation features floor-to-ceiling glazing — a combination of fixed panels and a minimal-frame sliding door system with sightlines of just 20mm, maximising the glass area and the connection to the garden.

Internally, we removed the wall between the original living room and dining room, creating one continuous space that flows from the front of the house through to the new extension and garden beyond. The kitchen occupies a sleek handleless run along one wall, with a cantilevered concrete-effect island providing preparation space and casual seating.

Planning and Approvals

The extension qualified under Permitted Development rights. We obtained a Lawful Development Certificate from Southampton City Council and secured Building Regulations approval covering the structural steel frame, flat roof construction, thermal performance of the extensive glazing, and drainage design for the flat roof.

Key Design Features

• Minimal-frame glazing: Ultra-slim 20mm sightlines maximising the glass area and views
• Extended roof overhang: Creates a covered terrace and provides solar shading in summer
• Concrete-effect island: Cantilevered island with waterfall ends creating a sculptural centrepiece
• Handleless kitchen: Push-to-open cabinetry in matt grey for a seamless, clutter-free aesthetic
• Polished concrete floor: Continuous flooring from inside to outside, blurring the boundary

The Result

This Southampton extension demonstrates how thoughtful contemporary design can completely transform an unremarkable 1970s property. The open-plan space feels twice its actual size thanks to the extensive glazing and uninterrupted floor plane. Our clients describe it as their favourite room in the world — high praise for what was previously a dark, compartmentalised ground floor.

Cost and Package Guidance

For a 40m² modern extension in Southampton, the biggest budget variables are usually structural steelwork, glazing specification, drainage changes, foundation conditions and final kitchen, bathroom or joinery choices. Hampshire Build's fixed-fee design packages give homeowners clear design-cost certainty before construction begins, with Essential, Pre-Build and Premium options depending on how much technical documentation and contractor support is needed. The design fee is separate from builder costs, planning fees, Building Control fees and any third-party specialist reports, so clients can make informed decisions without confusing design work with the wider construction budget.

Local Context and Practical Considerations

Projects in Southampton benefit from early attention to neighbouring amenity, overlooking, daylight, access for builders and material choices that sit comfortably with the existing street scene. On this project, the drawings needed to communicate not only the look of the extension but also how it would work technically: roof drainage, insulation build-ups, structural openings, floor levels and practical circulation through the home. That level of detail helps planning officers, Building Control and builders understand the proposal clearly, reducing avoidable questions and giving the homeowner a stronger basis for the next stage of their extension journey.

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