Finishes & Fit-Out

The defining feature of a fully-developed volumetric module is how much of the interior is complete before it leaves the factory. Beyond the structure and the services of the previous lessons, a module can arrive with its floor finishes laid (tiles, vinyl, timber, screed), its walls lined, skimmed and painted, its ceilings finished, its skirtings and architraves fixed, its joinery installed (wardrobes, vanities, kitchen units, shelving), its sanitaryware and kitchen fittings plumbed in, its light fittings, switches and sockets live, and in some cases its loose fit-out too — furniture, blinds, even artwork for a hotel room. A bathroom pod is the archetype: a complete, tiled, fitted, water-tested wet room delivered as a single unit. The module is, in effect, an interior delivered whole.

The reason to finish this much off-site is the same reason prefab exists, and it applies with special force to finishes. Finishing work is fiddly, quality-sensitive and traditionally done late on a crowded site, overhead and in the wet, by trades queuing behind one another. Do it instead at a bench, in a dry, lit, dust-controlled factory, with the work at a comfortable height and an inspector at the end of the line, and the quality tends to be higher and far more consistent — the tiling is truer, the paint is even, the joinery fits, and a defect is caught and corrected where fixing it is cheap. It is also faster in programme terms, because the fit-out happens in parallel with the foundations and superstructure rather than sequentially after them, and the queue of finishing trades is compressed into the factory line.

As with services, how far to push the factory fit-out is a genuine decision, not a default. The more you finish off-site, the more quality and speed you capture, but the heavier, more fragile and more transport-sensitive the module becomes, and the earlier you must lock the design. Some projects deliberately leave certain finishes to site — a feature wall, a floor that runs continuously across module joints, a facade finish — precisely because they cross boundaries or benefit from being completed as a whole. The judgement of where to draw that line is a core DfMA-for-interiors decision, and it is taken early, with the manufacturer, because the factory builds what is frozen when the line starts. The finished interior is a real prize; it is earned by designing for it.

A finished interior is a fragile thing, and between the factory bench and its final resting place a module is driven down rough roads and swung through the air on a crane. The central practical problem of factory finishing is therefore protection: keeping the completed interior undamaged through transport, handling and the lift. A scratched floor, a cracked tile, a chipped worktop or a popped skirting discovered after installation is a repair done the hard way — on site, at height, in the very conditions the factory finish was meant to avoid — so protection is not an afterthought but part of the design.

The threats are specific. Road transport subjects the module to vibration, jolting and dynamic loads that can crack rigid finishes and loosen fittings. The crane lift is worse in one respect: as a module is lifted, it can flex, rack and twist slightly under its own weight and the geometry of the slings, and that movement can crack tiling, open joints in joinery, and craze brittle finishes — which is why modules are often designed with temporary bracing or lifting frames to keep them square during the lift. Weather is a constant threat to an open or partly-open module, and handling — setting down, nudging into position — risks knocks to corners and edges.

The responses are a mix of design and process. Finishes are protected physically: floors covered with boards or sheet, corners guarded, glazing and joinery taped and wrapped, fragile fittings sometimes shipped loose and installed on site. Modules are wrapped or covered against the weather, and open faces closed with temporary end panels. The module is designed to be stiff enough to survive the lift without distorting the finishes — a structural and lifting-design question that belongs to the engineer and the manufacturer. And the sequence is managed: fragile final finishes may be held back, and the lift and transport route planned to minimise handling. For the designer, the lesson is that finish choices have a transport dimension — a brittle, unforgiving finish that cracks if the module flexes is a riskier specification than a more tolerant one — and that the protection and the stiffness needed to deliver a finish intact are part of designing it. The binding transport, lifting and bracing design, as ever, belongs to the transport and lifting specialists and the manufacturer's system.

For the interior designer, factory fit-out changes the most fundamental thing about the process: when the interior is decided. On a site-built job, interior finishes are among the last decisions — selected, sampled and sometimes changed late in the programme, fitted after the building is weathertight, adjusted on site as the client sees the space. Factory fit-out inverts this. Because the finishes are installed as the module is built, months before the building exists, the interior design has to be complete, specified and frozen early — the flooring, the wall finishes, the paint colours, the joinery design, the fittings, the fixtures, all decided before the factory line starts, and all but unchangeable once it does.

This is demanding, but it carries a distinctive reward that is pure prefab logic: repetition makes the early design worth perfecting. When the same hotel room, flat or ward is built a hundred times, the value of getting that one interior exactly right — the ergonomics, the detailing, the material choices, the buildability — is multiplied a hundredfold, and a mock-up or prototype room can be built, reviewed, lived-in and refined before the production run commits. The interior designer's craft shifts from resolving each space individually on site to perfecting a repeated prototype and designing the variety that a kit of finished modules can still produce. It also demands tight coordination with the factory: the finishes must suit the manufacturing sequence and the fixings available, and the design must be delivered in the disciplined information sequence the factory needs.

The honest caution is the loss of late flexibility. A client who wants to change a finish after production has started faces the same expensive choice as a services change — open up, rework or scrap a finished module. The response is the one this course keeps returning to: decide early, when change is cheap; prototype to get the repeated design right before committing; and keep genuinely client-variable or uncertain elements in site-finished zones rather than buried in the factory build. Interior design for modular work is not less design — if anything it demands more rigour and earlier resolution — but it is design done in a different order, front-loaded and prototype-driven, with the discipline of the module and the factory shaping it from the first mood board. The binding compliance of finishes (fire performance of linings, slip resistance, acoustic build-ups) stays with the specialists; the quality, detail and buildability of the interior within the module's discipline is the designer's.

However complete the module, a modular building is never entirely finished in the factory, because modules meet each other and meet site-built work, and those junctions have to be finished *after* assembly. Knowing where the factory finish stops and site finishing begins is essential to detailing a modular interior that reads as one coherent space rather than a set of boxes bolted together.

The clearest case is the marriage line — the joint where two modules meet, side to side or stacked. At the marriage line the factory-applied finishes stop short, because a continuous finish cannot be applied across a gap that only closes on site. So the junction is made good on site: the floor finish is run across or trimmed at the joint, the ceiling is made continuous and skimmed, skirtings and cornices are completed across the line, and wall finishes are joined and decorated so that, ideally, you cannot see where one module ended and the next began. This site making-good is skilled work and it is where a modular interior can betray its construction if it is detailed or executed poorly — so good design either conceals the marriage line deliberately (aligning it with a natural break, a change of plane, a shadow gap) or plans the site finishing carefully so the join disappears.

Two other zones are typically completed on site. Facades are often clad or finished after the modules are stacked, partly because a continuous, weathertight, well-aligned external skin is easier to achieve over the assembled building than module-by-module, and partly because the facade is where the building presents itself and benefits from being resolved as a whole (this also relates directly to weathertightness, the subject of the next lesson). And the interfaces between the modular part and any in-situ or site-built elements — the ground floor, the core, the podium, the entrance, the roof — are finished on site, because that is where the factory world meets the conventional one. The designer's task is to plan these site-finished zones deliberately: to decide what is finished where, to detail the junctions so the transitions are clean, and to concentrate bespoke or expressive finishing effort where it counts (often the entrance, the ground floor and the shared spaces) while the repeated accommodation above carries its factory finish. The binding performance of any finish — fire, acoustics, weather — remains with the specialists and the manufacturer's tested system.