RIBA Stage 3 on a mews house: Spatial Coordination at Bathurst Mews

Stage 3 of the RIBA Plan of Work is where a project stops being a promising concept and becomes a coordinated, buildable design. The 2020 Plan of Work calls it Spatial Coordination; many people still know it by its older name, Developed Design.

It is the stage where structure, services and architecture are brought into one resolved whole, and on most projects it ends with the planning application going in.

Our retrofit of a mews house on Bathurst Mews in Bayswater shows what that actually involves, because a small, tight, historic building is Spatial Coordination at its most demanding.

The Bathurst Mews palette in one frame: limewashed lime plaster, reclaimed timber cladding, limestone at the stair and a stone worktop. At Stage 3, every junction between these materials was coordinated on paper first. RISE Design Studio.

What Stage 3 involves

By the end of Stage 2 you have an agreed concept: the form, the layout, the character of the thing. Stage 3 tests that concept against reality and tightens it. The structural engineer's steels, the routes for pipework, ventilation and electrics, the build-ups of walls, floors and roof, all of it gets drawn into the same model and made to work together. Where the disciplines clash, and they always clash somewhere, the conflicts are found and resolved on paper, where they cost hours, rather than on site, where they cost weeks.

What it looked like at Bathurst Mews

A mews house concentrates the problem. The building is small, the party walls are shared on both sides, the floor-to-floor heights are tight, and the fabric is old and characterful, which is exactly why it is worth keeping. We are retrofitting the house to the EnerPHit standard, and at Stage 3 that ambition had to be reconciled with the building's constraints, decision by decision.

The material palette is natural throughout, and that shaped the coordination as much as the performance target did. The wall build-ups had to deliver EnerPHit performance while staying breathable, lime plasters and limewash finishes over the insulation, so the original brickwork could keep doing what it has done for a century without trapping moisture. The airtightness line had to be drawn, literally, as a continuous line through every junction of an irregular old structure. The limestone floors at ground and basement level had to be reconciled with the floor build-ups, the levels and the tight head heights, which on a mews house is a millimetre game. The MVHR needed duct routes through a house with no spare space, which meant threading them through floor voids and joinery so the system disappears. The triple-glazed timber windows had to sit correctly in the wall build-up to avoid thermal bridges, and the reclaimed timber cladding had to be detailed so it weathers well and sits naturally against the retained brick. Every one of those moves had to be coordinated with the structure and checked against the cost plan, so the design that went forward was one the budget could actually carry.

None of this is glamorous. It is hundreds of small decisions made in the right order, and it is the quality of those decisions that determines whether the build runs smoothly. Most of the expensive problems that surface during construction, the beam that doesn't fit, the duct with nowhere to go, the detail that can't be built as drawn, are Stage 3 problems that weren't caught at Stage 3.

Why the timing matters

Stage 3 is also the last point at which changing your mind is cheap. Move a wall now and it is a drawing revision. Move it on site and it is a variation, a delay and a bill. We encourage clients to engage hardest here, walking the design in 3D and VR and questioning everything, precisely because this is the stage where questioning everything costs nothing. On a mews house there is nowhere to hide a mistake, which makes that discipline worth even more.

The planning application

Stage 3 concludes with the planning submission, and the coordinated design is what gives the application its substance: accurate drawings, a resolved form, a credible energy strategy, and the supporting documents the council needs. In a conservation setting like Bayswater that matters doubly, because the officers want to see that the performance ambitions and the character of the building have genuinely been reconciled, not just asserted. An application built on a properly coordinated design has already survived contact with the structure, the services and the budget, and it shows.

Stage 3 rewards patience. Give it the time it needs and everything after it, the technical design, the tender, the build itself, goes noticeably better. If you are heading into this stage, on a mews house or anything else, we'd be glad to talk it through.

→ Email us at architects@risedesignstudio.co.uk
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