A 1930s detached on a generous corner plot, three small rear rooms merged into one 48m² open-plan kitchen-diner-living space — with a 2.5m roof lantern, a 5-leaf bi-fold opening, and a single steel ring beam doing the work of four lintels.
A 1930s detached family home in WA14, on a generous corner plot with the rear garden facing south and a side return that had been doing nothing but holding wheelie bins for the previous fifty years. Inside, the back of the house was carved into three small rooms — a galley kitchen, a poky dining room, and a utility-cum-breakfast room — each with its own door, none of them big enough to fit a family of five at once.
The clients had been quoted by a local builder for a straight rear extension at £65,000. The new room would have been a more generous version of the existing rear sitting room. We walked the site, mapped the existing internal layout, and proposed a wrap-around: take the side return as well, demolish the two internal walls, and finish with a single 48m² family space rather than three small rooms plus an extension.
The price went up by twenty-two thousand pounds. The usable family living area more than tripled.
Three children under ten and two parents working from home most days. The brief was about merging the family's working day into a single shared space, not about adding rooms:
Wrap-arounds are a category of extension where the boundary, the drains and the structural decisions all interact — and getting any one of them wrong derails the others.
The rear bi-fold opening, the lantern aperture, the side return roof load and the existing rear elevation lintel were originally drawn as four separate steels. Our structural engineer redesigned the lot as a continuous welded steel ring beam — a single member taking all four loads with one set of padstones at each end. Cleaner detail, faster install, and a flat soffit across the entire opening.
The existing 100mm clay foul drain ran diagonally under the proposed side return footprint. United Utilities build-over consent application was lodged in the pre-construction phase, with a detailed manhole-survey and engineering calc showing concrete encasement of the surviving line. Consent issued before scaffold went up.
The side extension brought our build line within 2.4m of the adjoining boundary. A formal 45-degree rule analysis was prepared and shared with the neighbour at design stage, demonstrating no significant loss of light to their habitable rooms. Pre-empting the conversation removed it from the planning consultation period entirely.
Merging three rooms meant taking down two internal load-bearing walls within the existing house. Each required temporary acrow propping, a new RSJ on padstones, and Building Control inspection before the props came out. Sequencing mattered — one wall at a time, not both at once, with an interim props-and-tarpaulin period of three days.
The 2.5m x 1.5m roof lantern aperture had to be trimmed cleanly within the warm-roof build-up. We used engineered timber trimmer joists with proprietary hangers, a continuous airtight membrane lapped and taped to the lantern frame, and a thermal break at the lantern upstand. No cold-bridge condensation in the second winter post-completion.
Removing all radiators from the new 48m² floor plate meant the wet UFH had to do all the heat lifting on the coldest February days. Heat loss calculations were done room-by-room before pipe spacing was finalised. Output capacity sized to 75 W/m² against a typical 50 W/m² spec, ensuring comfort even with the bi-folds open in shoulder seasons.
A wrap-around isn't a bigger rear extension. It's a different category of project, and we approached it as one.
One ring beam, not four lintels. The single biggest design decision was structural. The original engineer's scheme called for separate lintels above the bi-folds, the lantern, the side window run and the corner. We commissioned a redesign as a continuous welded ring beam. More expensive in steel by £3,800 — but it removed three padstone positions, gave a flat unbroken soffit across the entire rear, and let us push the bi-fold aperture from the originally specified 4.2m to a final 5.4m without changing the foundation footprint.
Drainage and right-to-light, finished at design stage. Both the United Utilities build-over consent and the 45-degree right-to-light analysis sat in our pre-construction scope. By the time the planning application went to the council, both had been resolved on paper. The approval came back without conditions.
Internal walls phased, not simultaneous. Removing two load-bearing internal walls in a single sequence is faster on paper. It also leaves the upper floor on temporary props for longer. We split the works into two phases — new RSJ to wall one, propped, signed off; new RSJ to wall two, propped, signed off — so the upper floor was always carried on at least one permanent member.
Underfloor heating sized for an open plan. A 48m² open-plan space behaves differently to three small rooms heated by radiators. The UFH design used a 75 W/m² output target, 100mm pipe centres in the perimeter zones, and a separate manifold loop for the kitchen-island area. Result: even temperature distribution from breakfast to bedtime.
Sixteen weeks from soft strip to handover. The wrap-around shape meant a longer foundation phase but a faster roof phase than a rectangular extension.
Existing rear conservatory and the side-return lean-to demolished. Existing kitchen units removed. Wheelie bin store relocated. Hoarding erected to side and rear elevations. Building Control commencement notice issued.
Strip foundations excavated to 1.0m depth around the L-shaped perimeter. Existing 100mm foul drain encased in 150mm of mass concrete to satisfy build-over consent. Reinforced concrete pour, cured to specification before brickwork.
Cavity wall construction: 100mm Celotex PIR, 100mm concrete block inner, 102mm facing brick outer matched to original 1930s stretcher bond. Interior dry walls and drainage second-fix prepared. Wall plate level reached on day 38.
Welded steel ring beam (203 x 133 UB sections, site-bolted at corners) craned in and bolted to padstones. Engineered timber rafters spanning ring beam to existing rear wall. Lantern aperture trimmed and prepared. Warm-roof build-up: vapour control, 200mm PIR, EPDM weatherproof membrane.
Aluminium roof lantern (2.5m x 1.5m, triple-glazed) installed and flashed. 5-leaf bi-fold door system (5.4m total opening) installed and adjusted. Building reached weathertight stage on day 70 — nine days inside the contracted target.
Phase 1 internal wall removal: temporary props installed, kitchen-to-dining wall demolished, new RSJ on padstones, props removed after Building Control sign-off. Phase 2 repeated for dining-to-breakfast room wall four days later. First-fix electrical, plumbing and UFH manifold installation.
Skim plaster to all walls and ceilings. 75mm liquid screed poured over UFH loops, 28-day cure period. Engineered oak floor laid with appropriate expansion gaps and underlay rated for UFH compatibility.
Bespoke handle-less kitchen installed across rear and island. Quartz worktops templated and fitted on day 108. Final decoration. UFH commissioned and balanced. Building Control completion certificate issued. Snagging walk-through with the family. Keys returned with full project file.
The technical detail behind a 48m² wrap-around.
Reinforced concrete strip foundations 1.0m deep around the L-shaped perimeter. Existing foul drain encased in 150mm mass concrete per United Utilities build-over consent.
Cavity construction: 100mm Celotex PIR, 100mm concrete block inner, 102mm facing brick outer matched to original 1930s stretcher bond.
Continuous welded ring beam (203 x 133 UB), site-bolted at corners, taking bi-fold lintel, lantern aperture, side roof and corner loads. Two internal RSJs (152 x 89 UB) for wall removals.
Warm flat roof: vapour control layer, 200mm PIR insulation, EPDM weatherproof membrane. Roof U-value 0.13 W/m²K.
2.5m x 1.5m aluminium-framed roof lantern, triple-glazed self-cleaning units, anthracite grey RAL 7016, thermally broken upstand, U-value 1.2 W/m²K (whole assembly).
5-leaf aluminium thermally-broken bi-fold system, 5.4m total opening, anthracite grey RAL 7016, double-glazed argon-filled, whole-assembly U-value 1.4 W/m²K.
Wet underfloor heating, 100mm pipe centres, sized to 75 W/m². 75mm liquid screed. 22mm engineered oak top layer with UFH-rated underlay, expansion gaps to perimeter.
Bespoke handle-less kitchen, soft-close drawers, 4m island with seating for four, 30mm quartz worktops, integrated appliance bays, downdraft extraction to island.
A 48m² open-plan kitchen-diner-living space replacing three small rooms, with a 5.4m bi-fold opening to the south-facing garden, a 2.5m roof lantern centred over the dining position, and a flat unbroken soffit across the entire rear elevation thanks to the single ring beam. Building Control completion issued on day 110.
Final account £87,400 against contract sum £87,400. No variations. The local Altrincham agent assessed the property at a 14% market valuation uplift versus the un-extended 4-bed comparable on the same street.
The original quote we had from another firm was for a basic rear extension that would have given us a slightly bigger version of what we already had. Building Group were the only company who looked at the floor plan and asked why we wanted three rooms in the first place. The single steel beam idea on the rear elevation is invisible — you can stand in the kitchen and see straight through to the garden with no posts, no break, nothing. We use this room every single day, all five of us, and the kids actually do their homework at the island while we're cooking. Cannot fault it.
If you've got a side return doing nothing and a back of house carved into rooms that no longer suit you, we'll come out for a free site visit, walk the existing layout, and put a fixed-price quote on the table for the wrap-around you actually need.
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