Imagine a space where family dinners flow into relaxing evenings, where the boundary between indoors and garden melts away, and where natural light fills every corner. That’s the promise of an open plan living-dining conservatory extension. Our clients, a family in West Sussex, wanted exactly that: a spacious, versatile area that would serve both as a bright dining space for entertaining and a comfortable lounge for everyday relaxation—while keeping their original living room as a cosy retreat.

In this comprehensive guide, we’ll walk through their project, exploring every design decision, structural consideration, and finishing touch that turned their vision into reality. Whether you’re planning a similar extension or just gathering ideas, you’ll find detailed insights on roof styles, door configurations, utility integration, and the technical side of removing an external wall.

Seamless Flow Between Indoors and Outdoors

The defining feature of this project was the decision to remove the entire external wall between the existing house and the new extension. This single change transforms the experience: from the kitchen, your eye travels uninterrupted across the dining table, through the lounge, and out into the garden. No step, no narrow doorway—just a smooth transition that makes both spaces feel larger.

But removing an external wall is not a DIY task. It requires:

• Structural assessment: A steel beam (or RSJ) must be designed to carry the load of the upper floor. In this case, a 4.5m galvanised steel beam was installed, recessed into the ceiling to keep the profile clean.
• Foundations: The new extension’s foundations were tied into the existing footings, with additional depth where the original wall was removed.
• Building Regulations approval: All structural work must be signed off. Your builder or architect typically handles this.
• Temporary propping: During installation, the upper floor was supported with Acrow props to ensure safety.

A Stylish & Functional Conservatory Design: The Gable Feature

The roof design can make or break an open plan space. A standard lean-to roof (sloping in one direction) is simple and effective, but our clients wanted something with more architectural presence. The solution? A central gable-end roof feature that rises above the lean-to slope, creating a dramatic triangular focal point.

Why combine lean-to and gable?

• Visual interest: The gable breaks the monotony of a flat roofline, drawing the eye upward.
• Extra light: The vertical face of the gable can be fully glazed, flooding the centre of the room with sunlight.
• Height and space: Inside, the ceiling soars in the gable section, making the room feel grander—ideal above a dining table or lounge seating.
• Symmetry: When placed centrally, the gable anchors the whole extension, giving a balanced, elegant facade.

To maximise comfort, the entire roof was fitted with solar-control, self-cleaning glass (U-value 1.0 W/m²K). An electrically operated skylight in the gable face provides automated ventilation—fresh air at the touch of a button.

Perfect Symmetry & Garden Access

The footprint was designed to be highly functional while maintaining a pleasing aesthetic from both inside and out.

Zoning the space

• Left side (utility): A separate utility room was tucked to the right (as you look from the house). It houses washing machine, dryer, and storage, hidden behind a partition wall but accessible via a half-glazed door. This keeps laundry noise and clutter away from the open plan area.
• Central dining zone: Directly ahead as you enter, with space for an 8-seater table.
• Right side lounge: A comfortable seating area with two floor-length windows overlooking the garden.

Door configuration – symmetry matters

From the outside, the white timber-framed conservatory presents a perfectly symmetrical elevation:

• Large French doors open from the lounge onto a round mosaic patio – perfect for stepping out with a morning coffee.
• Double patio doors on the left connect the kitchen to the garden via the utility room, creating a handy route for bringing in shopping or muddy boots.
• Two floor-length windows on the right mirror the patio doors opposite, maintaining visual balance.
• Decorative dwarf brick walls match the existing house brick, tying the extension to the original structure.

Year-Round Comfort: Insulation, Heating & Glazing

An open plan living-dining space must be usable in January as well as July. Here’s how we achieved that:

Insulation

• Below floor: 100mm PIR insulation board beneath the screed, with edge insulation to prevent thermal bridging.
• Walls: Cavity walls with blown bead insulation (U-value 0.18).
• Roof: Triple-layer low-E argon-filled glazing with warm-edge spacers.

Heating

Underfloor heating (water-based) was installed throughout the extension, zoned separately for the lounge and dining areas. This provides gentle, even warmth without radiators breaking up the glazing. The system runs off the existing gas boiler, with an independent thermostat.

Glazing specification

• G-value: 0.35 (blocks 65% solar heat, reducing summer overheating)
• Light transmission: 72% (keeps the space bright)
• Self-cleaning coating: photocatalytic layer that breaks down dirt – rain washes it away.

Planning Permission & Building Regulations

Most single-storey rear extensions in England fall under Permitted Development if:

• Single storey, rear extension ≤4m (detached) or ≤3m (semi/terraced)
• Maximum height ≤4m, eaves ≤3m
• Materials similar to existing house

This project sat within those limits, so no full planning application was needed. However, because we removed an external wall, Building Regulations approval was mandatory. Key aspects checked:

• Structure: Steel beam design and calcs.
• Thermal performance: U-values of glazing, floor, walls.
• Ventilation: Opening skylight (equal to 5% of floor area) for purge ventilation.
• Electrical safety: Part P certification for all new circuits.

Listed buildings, Conservation Areas, AONBs always require permission. See our full planning guide for details.

How Much Does an Open Plan Living-Dining Conservatory Cost?

Costs vary significantly based on size, specification, and site conditions. For a medium-sized extension (25-35m²) similar to this project:

• Timber frame & glazing: £35,000 – £55,000
• Foundations & groundworks: £8,000 – £15,000 (depends on soil type)
• Steel beam & wall removal: £3,000 – £6,000
• Underfloor heating & screed: £4,000 – £7,000
• Internal finishes (plastering, flooring, electrics): £6,000 – £12,000

Total estimated range: £55,000 – £95,000 + VAT. Gable roof features, bifold doors (instead of French), and high-end glazing add to the cost.