Prefabricated Building Modules for AI Data Centres: Technological Feasibility, Global Practice, and the Multi-storey Stacked Data Hall

The modular data centre has moved, in roughly five years, from an edge-computing curiosity to the default delivery method for multi-hundred-megawatt AI campuses. The market reflects it: modular data centre revenues stood at US$31.24 billion in 2025, are put at US$35.44 billion in 2026, and are forecast to reach US$116.53 billion by 2034 — a compound annual growth rate of 16.0% over 2026–2034, or 15.8% measured from the 2025 base. North America alone accounted for 37.04% — some US$11.57 billion — of the 2025 total.¹

That growth is not driven by cost. Factory integration and proprietary power and cooling assemblies carry a reported premium of 20–30% per megawatt against conventional site-built construction. It is driven by time, by labour scarcity, and increasingly by thermal physics. When an accelerator rack draws 100–200 kW and the roadmap points at 600 kW, the cooling system stops being a service routed through a building and becomes a structural element of it. Factories build that kind of assembly better than construction sites do.

This paper is about one specific answer to that problem: the prefabricated building module — the structural bay that is the building, manufactured complete with its frame, envelope, services and cooling, then set and connected on site. It is the family that delivers gigawatt-class AI capacity, it is the family that makes stacking an architectural option rather than a container-yard expedient, and it is the family that Japanese, Australian and Southeast Asian projects are converging on. The paper sets out what it is, how it differs from steel-frame construction and from container-scale MDC, what the delivery sequence actually looks like, who builds it, and — the question that decides land economics on a constrained site — whether AI data halls made this way can be stacked two levels high. It is also the method Grid Apex has adopted for its own multi-storey AI data centre campus, and section 11 sets out why that produces a permanent Japanese building capable of housing the current and next generations of AI hardware.

01 What MDC means — and which family matters

MDC — modular data centre — denotes a data centre whose functional building blocks are manufactured, assembled, integrated and tested in a factory, then transported to site and connected together. The defining characteristic is not that the building is made of repeated parts. It is that the factory, not the site, is where integration happens.

In a conventional project, a contractor erects a structure and then installs equipment inside it: switchgear arrives, is positioned, wired, commissioned; chillers are craned onto a roof and piped; containment is built around racks. Every one of those operations happens outdoors, in sequence, subject to weather, trade availability and site congestion. In a modular project, those same operations happen on a production line under cover, in parallel with the site works, and the resulting unit is factory-acceptance-tested before it is ever loaded onto a truck.

Three families are commonly grouped under the term, and conflating them causes most of the confusion in the market.

The third family is the subject of this paper. The distinction from the first is not one of size but of structural role. A container-scale module is a piece of equipment that happens to have walls; the building, if any, goes around it. A prefabricated building module is a piece of the building: its frame is primary structure, its floor is the data hall floor, its envelope is the external wall and fire-rated line, and its roof is either the roof of the finished hall or the deck that carries the level above. That is what allows prefabricated building modules to be assembled into continuous data halls of tens of thousands of square metres, and to be stacked — neither of which a yard of shipping containers can do.

A single project frequently uses all three families. NEXTDC's S4 Sydney — a 30,743 m² facility of 350 MW across two four-storey buildings, under construction by Multiplex for mid-2027 completion — is conventionally framed but uses prefabricated mechanical plantrooms, prefabricated electrical switch rooms and prefabricated main services reticulation pathways, alongside precast lift cores, columns and façade.² It is simultaneously the largest modular data centre project in Australia and not a “container” project at all.

02 Anatomy of a prefabricated building module

A prefabricated building module for an AI data hall is a steel-framed volumetric unit sized by what can move on the road — typically 3–4.5 m wide, 12–16 m long and 3.5–4.5 m high — and designed to be joined to its neighbours so that many modules combine into one continuous hall. The unit that ships is therefore not the unit that operates: capacity is quoted per hall or per campus, not per module, and a data hall of 2,000 m² is simply a hall built from more of them. It is best understood as four systems manufactured as one object:

• The chassis: A welded steel frame — base grillage, corner and intermediate posts, roof frame — fabricated to millimetre tolerance. It is simultaneously primary building structure, the transport frame, the equipment support and the lifting rig, and it must satisfy all of those load cases independently.
• The envelope: Insulated composite panel or rainscreen on a fire-rated substrate, with the module-to-module joint detailed as a continuous fire, air and water line. Because the joint is the one element made on site, its design governs the quality of the finished building far more than the panel specification does.
• The services layer: Containment, busway or cabling, switchboards, cooling distribution — CDUs, manifolds, primary and secondary coolant headers — fire detection and suppression, monitoring and controls, all installed and terminated at fixed interface points on the module face.
• The interface: Four families of connection cross the module boundary: power, coolant supply and return, network, and controls. These are the only genuinely site-made joints in the whole building, which is why they are engineered as repeatable quick-connect details rather than as drawn-and-measured site work.

Module dimensions must be resolved against road and sea transport conditions together. Japan's general vehicle limits under the Vehicle Restriction Order (車両制限令 Art. 3) are 2.5 m width, 3.8 m height, 12.0 m length, 20 t gross, 10 t per axle and 5 t per wheel, with a 12 m minimum turning radius. Two qualifications matter. Height rises to 4.1 m on designated 高さ指定道路 and gross weight to 22–25 t on expressways and 重さ指定道路 according to axle spacing; but the 12.0 m length is measured over the tractor and trailer together and has no designated-road exemption. A 40 ft module is 12.19 m before the tractor is attached, so module transport in Japan is a permit exercise from the first drawing, under 特殊車両通行許可 or the confirmation scheme that replaced part of it in 2022, with permit ceilings for the standard exempted vehicle types running to 16.5 m and 36 t on expressways. Route and overhead clearances are verified case by case. Cross-border delivery additionally requires that vessel type, loading and discharge method, lashing and salt-spray protection be settled at the design stage, and that port transhipment, sailing schedules and the final road leg be planned as one sequence. Where a manufacturer quotes a large single figure — Daiwa House's approximately 200 m² Module DPDC — that denotes a design bay, which must be divided into several shipping pieces and mated on site.

03 How it differs from steel-frame construction

The distinction most often misunderstood is between a prefabricated modular data centre and a steel-frame building that happens to be erected quickly. Both use steel. The difference is what the steel is doing, and when the mechanical and electrical content arrives.

In a steel-frame building the critical path runs through the structure: nothing else can start until the frame is up and clad. In a prefabricated modular building the critical path runs through the factory line and the foundations, in parallel, and the two converge at the crane. That is the whole of the schedule advantage, and it is also the whole of the risk: a module that arrives before its plinth is ready, or a plinth built to construction rather than manufacturing tolerance, destroys the benefit immediately.

04 From factory line to live hall: the delivery sequence

The plates that follow document the sequence in a working prefabricated-module data centre programme, from the bare chassis on a factory line to a liquid-cooled hall in service. They are reproduced here because the argument of this paper — that integration has moved from the site to the factory, and that this is what makes stacking tractable — is easier to see than to assert. Read them as five stages: manufacture, integration, assembly, plant, operation.

STAGE 1 · MANUFACTURE — THE CHASSIS ON THE LINE

PLATE 1 The module begins as structure, not as a box. A welded steel chassis — base grillage, corner posts, roof frame — on a powered transfer pallet at station 28 of a production line, tare weight marked at 1,900 kg. The floor deck is already laid and drilled to the equipment setting-out. Everything that follows is added to this frame while it advances down the line, in a covered, lit, climate-controlled environment with overhead lifting on every station. This is the single most important image in the sequence: the object on the pallet is simultaneously the building's primary structure, its transport frame and its lifting rig.

STAGE 2 · INTEGRATION — SERVICES INSTALLED

PLATE 2 Mechanical and electrical fit-out inside the module. Overhead containment, cable ladder, ductwork and hangers being installed at ceiling level within the module volume. Work at this stage is done from a stepladder in a protected space, to a repeated detail, rather than from a mobile platform in the open.

STAGE 2 · INTEGRATION — SWITCHBOARD WIRING

PLATE 3 Switchboard termination inside the module box. Power cabling dressed into distribution boards, with tray, busway and pre-formed cable sets overhead. The stamp records the work as 模块箱 (module box) / 配电柜接线 (switchboard wiring), Johor Bahru, Malaysia, executed by PSG Construction Sdn. Bhd.

COOLANT INTEGRATION · FACTORY-TESTED HYDRAULICS

PLATE 4 The pre-piped coolant gallery — the clearest single argument for factory integration. Stainless primary headers on a fabricated support frame, actuated control valves on every branch, flexible 30-bar coolant hoses to the rack-side manifolds, and segregated power and control containment below. In a site-built hall every one of these joints would be made outdoors by a different trade at a different time; here they are made on a jig, pressure-tested as an assembly, and delivered proven. A closed liquid loop is only as reliable as its worst field joint, which is why moving those joints indoors is not a convenience but a reliability strategy.

STAGE 3 · ASSEMBLY — SETTING THE BUILDING

PLATE 5 A data hall being assembled from prefabricated building modules. At the left, modules already set and joined, with the roof and plant deck being completed over them; in the centre, a crawler crane working the setting face; at the right and rear, several hundred completed modules in laydown awaiting their slot. This is what distinguishes the prefabricated building module from every other form of modular delivery: the units are not parked next to each other as separate machines, they are knitted into one continuous building. The laydown yard is, in effect, the project's inventory of finished floor area — and the reason the programme is limited by crane cycles rather than by trade availability.

STAGE 4 · PLANT — THE DECK ABOVE THE HALL

PLATE 6 Completed envelope with the rooftop plant deck under installation. The modules are set on plinths that lift the floor clear of the ground and form a continuous service undercroft beneath the hall; above, a steel deck carries cooling plant and the primary pipe racks. Power and coolant therefore arrive from below and heat leaves from above, over the shortest possible vertical path — the same logic that, taken one step further, produces the stacked hall.

STAGE 4 · GENERAL ARRANGEMENT

PLATE 7 The configuration in general arrangement. A modular hall with its IT volume enclosed at ground level and the full cooling plant carried on an elevated steel deck directly above and alongside it, arranged in repeating bays that mirror the module grid below. Vertical zoning of this kind — plant over IT, services dropping rather than running — is the intermediate step between a single-storey modular hall and a genuinely two-level stacked one.

STAGE 5 · OPERATION — THE LIQUID-COOLED HALL IN SERVICE

PLATE 8 A direct-to-chip liquid-cooled hall, live. Colour-coded supply and return hoses run from the rack-side manifolds to each cabinet, with overhead containment carrying power and network separately above the cold aisle. This is the load the building exists to serve: at 100–200 kW per cabinet the coolant distribution is no longer a service routed through the building — it is part of the building, and it is the reason the whole assembly is manufactured rather than constructed.

05 The container-scale case, and why it is different

Container-scale MDC is the most constrained variant and, for that reason, the most instructive contrast. Its logic runs as follows:

The envelope is set jointly by sea and road transport conditions. A container-scale module has to satisfy the ISO box format, ship loading, port lifting and the final road leg at once, and its internal layout, aisles and service clearances are constrained accordingly. The 40 ft format is convenient precisely because it connects sea and land carriage, but adopting it does not mean every leg of the journey is permit-free.

The difference from the prefabricated building module is architectural, and it is decisive at scale:

A container is a machine placed on a site: it carries only itself, its walls are not a building line, and a yard of them does not become a hall. A prefabricated building module is a piece of a building: it is designed for module-to-module joints, for continuous fire and acoustic lines, for a shared roof and plant deck, and for superimposed load from a module above. That is why the container is the right answer for 2 MW at the edge and the wrong answer for 80 MW on a campus — and why every gigawatt-class programme in this paper's section 8 uses building modules, prefabricated plantrooms, or both.

06 Technological feasibility: what has been proven

Three questions determine whether prefabricated modular delivery is technically viable for AI workloads rather than merely for traditional colocation: can it carry the thermal load, can it satisfy structural and life-safety codes, and can it be certified repeatably.

Thermal Feasibility

This is settled. Direct-to-chip cold plates, rear-door heat exchangers and single-phase immersion all now ship as sealed factory-integrated units capable of carrying current 700 W accelerators with roadmap headroom toward 1,000 W devices. Vendor claims of liquid-cooling-enabled PUE approaching 1.15 are credible in principle, though they should be read as design-point rather than annualised figures. The significant point is architectural, and Plates 4 and 8 make it: because the coolant loop is assembled and pressure-tested on a jig in a factory, prefabricated construction is arguably better suited to liquid cooling than site-built construction, where thousands of field-made joints in a closed loop represent a serious leak-risk surface.

Structural and Seismic Feasibility

Here feasibility is jurisdiction-dependent, and Japan is the strictest case in the world. Japanese data centre practice targets seismic performance at importance factor 1.5. It is worth being precise about the status of that figure: 重要度係数 does not appear in the Building Standards Act, and a privately owned data centre can lawfully obtain building confirmation at 1.0. The 1.5 / 1.25 / 1.0 ladder is the Ⅲ・Ⅱ・Ⅰ classification of MLIT's 官庁施設の総合耐震・対津波計画基準, a standard whose own scope is government facilities; it reaches data centres because JDCC's facility standard adopts 耐震性能Ⅰ類相当 — the 1.5 grade — as its Tier 4 criterion, after which tenants and developers specify it contractually. Importance factor 1.5 is therefore a de facto market standard enforced through tenant specification and tier certification. What is statutory is the verification route: building confirmation plus structural calculation conformity review (構造計算適合性判定, “tekihan”) under Article 6-3, carried out by the prefectural governor or a designated agency. Two Japanese products demonstrate that prefabricated building modules clear this bar:

• Daiwa House Module DPDC: Announced 8 December 2025 and on sale nationwide from 5 January 2026, is a steel-framed seismic-resistant building module of approximately 200 m² and 6.6 m height, delivering 1–2 MW per module on high-voltage supply, built to importance factor 1.5, with its structural frame in conformance with (準拠) JDCC Tier 4 for robustness and availability, and delivery approximately one year from contract against a conventional programme of several years.³
• NTT Facilities, with Nippon Steel Engineering: Developing a modular building method for hyperscale data centres that targets a reduction of up to approximately 50% in the period from application and design through to completion, for facilities in the tens to hundreds of MW range, with practical implementation targeted within FY2028.⁴

Certification

The repeatability question is answered by type approval. Where a module type is certified once and manufactured repeatedly, the approval burden collapses from per-building to per-type. Japan provides this through type conformity approval (型式適合認定, Art. 68-10) followed by certification of the type-component manufacturer (Art. 68-11 / 68-12). Canada certifies factory-built construction through CSA A277, and a binational safety standard dedicated to prefabricated modular data centres — ANSI/CAN/UL 2755, from UL Standards & Engagement — entered development in February 2026 (UL 2755:2025 Outline of Investigation). The United States combines state-level factory certification with local installation permitting around ICC/MBI 1200, 1205 and 1210. Europe works through CE marking under the Construction Products Regulation (CPR). China has gone furthest with T/CIEP 0205—2026.

07 The EPC layer: who actually assembles the building

Discussion of modular data centres tends to concentrate on the module manufacturer, which is the wrong end of the problem. Delivering a prefabricated-module AI campus requires three distinct capabilities, and only the first is widely available:

1. Module manufacture: Steel fabrication, envelope, production-line discipline. Widely available from the modular-construction and shipping-container industries.
2. In-module MEP integration: Switchboards, busway, containment, coolant headers, controls, terminated to fixed interfaces and factory-acceptance-tested. Available from data centre MEP contractors, but rarely at production-line cadence.
3. Site EPC and assembly: Foundations and plinths to manufacturing tolerance, transport and craneage planning, module setting, the module-to-module joints, the four boundary connections per module, the plant deck, and integrated testing of the assembled building. This is the scarce capability, because it is the only one that cannot be bought as a product.

The third capability is where programmes are won or lost. A module that is perfect in the factory is worth nothing if the plinth is 40 mm out, if the crane cycle is slower than the delivery convoy, or if the joint between two modules is detailed as a site improvisation.

08 Example projects across nine markets

The momentum toward modular and prefabricated construction in AI infrastructure is worldwide. Below are representative projects across nine key geographies:

09 The stacked data hall — and the two-level case

Stacking is where prefabricated modular construction stops being a procurement strategy and becomes an architectural one. The motivation is straightforward: on a land-constrained or power-dense site, megawatts per hectare is the governing metric, and the only way to raise it without raising rack density further is to build upward. It is also the point at which the container and the building module part company for good — only a module engineered for superimposed load can carry another module.

The Proof Point

The most significant demonstration to date is Huawei's 3D Data Centre, unveiled on 15 September 2026 at the AIDC Industry Development Conference in Wuhu, Anhui. It organises the facility into four vertically stacked functional layers — cooling, IT equipment, power supply and backup power — rather than distributing those functions horizontally across a site. It is architected to support Ascend supernode clusters of 100,000 cards and above (十万卡以上).⁵

STACKING PROOF · FIVE LEVELS IN ELEVATION

PLATE 9 Five levels of stacked volumetric modules. The module grid reads directly in the elevation: each bay is one factory-built unit, with its own chassis posts and edge beams, set on the unit below and spliced at the corners. The pale blue members are the modules' own structural frames; the panelised infill between them is envelope, not structure. Every module carries its share of the superimposed load from the levels above.

SUBSTRUCTURE · MANUFACTURING-TOLERANCE GRID

PLATE 10 Stacking in progress, over a foundation grid built to manufacturing tolerance. In the foreground, the prepared substructure: a regular grid of reinforced strip footings and pile caps with starter bars, set out to the module grid so that every unit lands on a prepared bearing. Behind it, modules already set two and three high, with a crawler crane and a tower crane working the setting face.

Why Two Levels Specifically

Two levels captures most of the benefit at a fraction of the regulatory and structural cost, for four reasons:

1. The structure stays conventional: A two-level assembly can be built as modules-on-modules or as modules set into a simple frame, with load paths a structural engineer can verify by inspection. Beyond two or three levels, the lower modules become primary structure carrying substantial superimposed load, the frame becomes a moment-resisting system in its own right, and the design leaves the realm of repeatable type approval.
2. Seismic demand scales faster than height: Under a seismic regime, mass at height attracts lateral force, and the overturning moment grows with the square of height. At two levels the centre of mass stays low and foundations remain economical. This is the binding constraint in Japan.
3. Fire strategy remains tractable: Two levels permits direct external escape from both, straightforward fire-brigade access and simple smoke control.
4. Density roughly doubles without changing the module: The same certified module, the same transport envelope, the same factory line, the same setting cycle — twice the megawatts per hectare.

10 The Japanese case

Japan is simultaneously the hardest market in which to stack and one of the most compelling in which to build with prefabricated building modules — and the two facts share a cause.

The drivers are acute: construction labour is severely constrained, and grid connection in the Tokyo core carries waiting times of five to ten years, pushing projects to regional sites where local trade capacity is thinner still. Against that, a one-year delivery programme is the difference between a viable project and an unviable one.

The Japanese industry's answer across its two most credible products is instructive: keep the building low and solve the seismic problem with isolation rather than with mass. NTT Facilities isolates the data hall floor only while applying vibration control to the main equipment; Daiwa House uses a single-level 200 m² steel building module engineered to importance factor 1.5, with its structural frame in conformance with JDCC Tier 4.

Structural steel must be a designated building material conforming to a JIS named in Notification 1446 of 2000 under Article 37, item (i) of the Building Standards Act. SN grades (JIS G 3136, typically SN400B and SN490B) are the Japanese design convention and effectively mandatory in practice for seismic-resisting and welded members, because only SN specifies yield-ratio caps, impact values and weldability control. Repeatable factory manufacture of a certified module type runs through two sequential approvals: type conformity approval of the design (型式適合認定, Art. 68-10), then certification of the manufacturer (Art. 68-11, or Art. 68-12 where the factory is overseas).

11 Grid Apex's adopted approach

Grid Apex is building its multi-storey AI data centre campus using prefabricated building modules. The campus is designed as two-level stacked data halls assembled from factory-manufactured, factory-tested structural modules, set on permanent foundations, joined into continuous buildings, and served by a rooftop plant deck.

Why the Building is Permanent

“Modular” is often heard as “temporary”, because the word is associated with site cabins and container yards. A prefabricated building module campus is a different object in every respect that matters:

Why it Houses the Latest AI Equipment

A data centre does not need to anticipate the specific accelerator it will host; it needs a shell whose four capacity envelopes — floor loading, power path, coolant path and heat rejection — are specified above the hardware roadmap rather than to the hardware of the day:

12 Conclusion

Prefabricated modular delivery of AI data centres is no longer a question of technical feasibility. The thermal case is closed: liquid cooling at 700–1,000 W per accelerator ships as a factory-integrated, pressure-tested assembly. The structural case is closed in every major market, including Japan's importance-factor-1.5 standard. The certification case is closing fast through type approval in Japan, CSA in Canada, state certification in the United States, CPR in Europe and T/CIEP in China.

For a large AI campus in Japan, the two-level stacked data hall built from prefabricated building modules is therefore the point of maximum advantage: roughly double the megawatts per hectare, shorter vertical service runs, compartmentation given by the structure, and maintenance separated from operations — all within a structural form that the Japanese approval system has already accepted.