The Complete Guide to Modular Data Centers: From Skids to Containers explains how prefabricated data center modules are built, shipped, set, and anchored, with particular attention to the skid-based modular data center. Demand for compute capacity and short deployment schedules has pushed many owners away from facilities built entirely on-site over many months or years. The modular alternative moves fabrication into a factory and leaves the site work to foundations, utilities, and final connections. This guide defines what “skid-based” means, compares skids with containerized and prefabricated modules, describes the common skid types, and sets out where structural engineering under the International Building Code (IBC) and ASCE 7 is required.
Need engineering for a specific skid-mounted unit? ISTA provides a dedicated skid data center structural engineer service covering foundations, anchorage, lifting, and seismic design. Call (720) 740-4060.
The sections below move from basic definitions and the advantages of prefabrication through transport and rigging, foundation and anchorage design, and a short FAQ. Whether the project involves a single skid-mounted UPS inside an existing white space or a fully containerized data center set on a new pad in Denver or Colorado Springs, the same structural questions apply: what loads the frame carries, how it is lifted, what it sits on, and how it is held down.
Table of Contents
What Is a Skid-Based Modular Data Center?
A skid-based modular data center is a facility whose key components, such as power distribution units, UPS systems, or cooling units, are pre-assembled in a factory onto a structural steel frame, or “skid,” and then transported to the site for final assembly and commissioning. The skid frame carries the equipment during shipping and lifting, provides the points where the assembly is bolted to a slab or foundation, and serves as the permanent base once the unit is in service. A skid-based facility may consist of a single skid that augments an existing building or of many skids arranged into a complete data hall.
The term “modular data center” covers the broader family: any facility composed of prefabricated data center modules that are manufactured off-site in a controlled factory environment. These modules, containing everything from IT racks and cooling systems to power distribution, stand in contrast to traditional “stick-built” data centers, which are constructed entirely on-site from the ground up. Skids are the most open form of module, since they usually have no walls or roof of their own and are intended to sit inside a building or under a canopy. ISTA Engineers evaluates the integrity of these prefabricated frames through its Structural Inspection service, both at the fabricator and after the unit is set in place.
The two most common forms of module are skid-mounted and containerized. Skid-mounted units are often used as functional blocks within a larger data center white space. Containerized data centers house a complete data center within a standard ISO shipping container, providing an all-in-one, portable, and weather-resistant solution. A third category, the purpose-built prefabricated module, is a custom steel or concrete enclosure fabricated to the owner’s dimensions rather than to ISO container sizes.
Skids vs. Containerized vs. Prefabricated Modules
The three module formats differ mainly in enclosure, structural behavior, and the code path used to design them. A skid is an open frame, so the building or canopy around it resists wind, snow, and rain, and the skid itself is treated as an item of mechanical or electrical equipment anchored under ASCE 7 Chapter 13. A containerized unit is a closed steel box built to ISO 668 dimensions, typically 20 ft or 40 ft long and 8 ft wide, which can be set outdoors and must therefore carry environmental loads on its own shell. A purpose-built prefabricated module is a custom enclosure that is usually designed as a small building or as a nonbuilding structure under ASCE 7 Chapter 15.
Format also drives logistics. Skids and ISO containers fit standard flatbed and chassis trailers and can often move without oversize permits, while custom modules frequently exceed the 8 ft 6 in legal width used by most state departments of transportation and require permitted routes. The table below summarizes the comparison; the modular versus traditional comparison appears later in this guide.
| Feature | Skid-Mounted Unit | Containerized Data Center | Purpose-Built Prefabricated Module |
| Enclosure | Open steel frame; relies on host building or canopy | Closed ISO shipping container shell | Custom steel or concrete enclosure |
| Typical Location | Inside white space, electrical room, or mechanical yard | Outdoors on a pad, or inside a shell building | Outdoors on a foundation; often stacked or ganged |
| Governing Design Path | ASCE 7 Chapter 13 (nonstructural component anchorage) | ASCE 7 Chapter 13 or 15 depending on setting | IBC Chapter 16 building design or ASCE 7 Chapter 15 |
| Environmental Loads | Carried by host structure | Wind, snow, and seismic carried by container shell | Wind, snow, and seismic carried by module structure |
| Transport | Flatbed; forklift pockets or lifting lugs | Standard container chassis; corner castings | Often oversize; permitted routes and crane set |
| Weather Protection | None inherent | Inherent, with field-sealed penetrations | Inherent, designed to project specification |
Common Skid Types in a Modular Data Center
Skids are grouped by the system they carry. Each type places a different kind of demand on the frame and on the structure below it, and each is usually fabricated by a different vendor to a different specification. The four groups described below cover most of what arrives on a data center site.
Power skids carry switchgear, transformers, UPS modules, and power distribution units on a common frame with pre-terminated bus or cable. Transformers concentrate most of the mass at one end of the frame, so the center of gravity is rarely at the geometric center and must be marked for the rigging crew. Power skids are generally designated as components required for continued operation, which under ASCE 7 Section 13.1.3 raises the component importance factor to 1.5.
Cooling skids include chiller packages, pump skids, cooling distribution units, and dry coolers. They introduce vibration from rotating equipment, fluid loads that change between empty and operating conditions, and piping that connects to the building and must accommodate relative movement. Isolation springs or pads, when used, change how seismic forces reach the anchors and must be accounted for in the anchorage design.
Energy storage skids carry battery cabinets, either as UPS strings or as larger battery energy storage systems. Lithium-ion and lead-acid batteries are dense, so floor loading and anchor demand are high relative to the footprint. Fire separation and ventilation requirements from the International Fire Code frequently dictate skid spacing and enclosure, which in turn affects the foundation layout.
IT skids are pre-populated rack rows, sometimes with integrated containment and in-row cooling, mounted on a frame that can be rolled or lifted into a data hall. Rack rows are tall relative to their depth, so overturning during a seismic event is the governing check, and the frame must be tied to the slab or raised-floor structure rather than resting on casters alone.
Why Build a Modular Data Center From Prefabricated Modules?
Prefabrication shortens schedules, allows capacity to be added in increments, and produces more consistent quality than field construction. Factory fabrication occurs concurrently with on-site preparation, such as pouring the foundation, slashing overall project timelines by 30-50%. This accelerated deployment speed allows businesses to respond to market demands or internal growth in weeks or months, not years. Every module is built to the exact same specifications and undergoes stringent quality checks before it ever leaves the facility.
Scalability is baked into the design. Organizations can start with the capacity they need today and add identical data center modules as demand increases, following a “pay-as-you-grow” model. This eliminates the massive upfront capital expenditure on overbuilt infrastructure that might sit unused for years, and it reduces the environmental impact of construction because less material is placed before it is needed. Modular data centers also tend toward higher energy efficiency, with cooling and power trains optimized for low PUE at the factory rather than tuned in the field.
The structural side of adding capacity is often overlooked. A pad designed for two skids may not have the reinforcing or the frost protection to accept a third, and a slab inside an existing building may need thickening or new footings before another UPS skid is rolled in. ISTA Engineers addresses these changes through its Structural Modification Design service, which covers slab reinforcement, new equipment pads, and the openings or supports needed to bring a new module into an occupied facility.
Modular vs. Traditional Data Centers: A Clear Comparison
Traditional data centers are built entirely on-site over many months or years with a fixed capacity. Modular data centers are built from pre-engineered modules constructed off-site in a factory, leading to much faster deployment and greater flexibility. The two approaches also differ in how risk is distributed: a stick-built facility concentrates schedule risk in field trades and weather, while a modular facility shifts most of that risk to the fabricator’s shop and to the coordination of shipping and setting.
From a structural standpoint, the host building or pad for a modular facility is often simpler than a conventional data hall because the modules carry their own equipment supports. The trade-off is that the interface between module and foundation becomes a design item in its own right, with anchor layouts, leveling tolerances, and grounding details that must be coordinated between the fabricator and the engineer of record. The table below highlights the key differences between modular and traditional data centers:
| Feature | Modular Data Center | Traditional “Stick-Built” Data Center |
| Construction Time | Weeks to a few months | 12–24+ months |
| Scalability | Incremental, on-demand growth | Fixed capacity at initial construction |
| Initial Cost | Lower and phased | Very high, all upfront |
| Flexibility | Relocatable and reconfigurable | Fixed, permanent, and rigid layout |
| Energy Efficiency | High; optimized for low PUE | Often lower efficiency; harder to optimize |
| Build Location | Off-site prefabrication | Entirely on-site construction |
How Modular Skids Are Transported, Lifted, and Set
A skid leaves the factory on a flatbed or step-deck trailer, secured under the Federal Motor Carrier Safety Administration cargo securement rules in 49 CFR Part 393. Road transport imposes accelerations in braking, cornering, and over rough pavement that the frame must resist with the equipment already mounted, so the fabricator’s structural calculations should cover the shipping condition, not just the installed condition. Containers travel on standard chassis and use their corner castings for both tie-down and lifting.
At the site, skids are lifted either by forklift through engineered pockets in the base frame or by crane through lifting lugs welded to the frame. A four-point lift with a spreader bar keeps the slings near vertical and avoids crushing equipment at the top of the frame. Lifting lugs and spreader bars fall under ASME B30.20 for below-the-hook lifting devices, and the rigging plan should show the marked center of gravity, sling angles, and the resulting load at each lug. Lugs that were sized only for the bare frame are a common cause of field problems once transformers or battery cabinets are installed.
Setting places the skid on a reinforced concrete pad, a thickened slab, a set of piers, or a structural steel platform. The bearing surface must be level within the tolerance the equipment manufacturer requires, which is tighter for switchgear and chillers than for a general-purpose frame. Once set, the skid is anchored with cast-in-place anchor bolts or post-installed mechanical or adhesive anchors designed under ACI 318 Chapter 17, and the anchor installation is subject to the special inspection requirements of IBC Section 1705. ISTA Engineers verifies anchor embedment, torque, and edge distance in the field through its Construction Inspection service.
Where Structural Engineering Is Required for Skid-Based and Containerized Data Centers
The benefits of modularity cannot be realized without sound structural engineering. A modular data center must be engineered to withstand its operational loads, the rigors of transportation and lifting, and the environmental loads assigned by the IBC and ASCE 7 for the site. Neglecting this phase can lead to catastrophic failure, turning a strategic investment into a liability. ISTA Engineers has written about why data center structural engineering underpins every successful facility; the four areas below are where that work concentrates for skid-based and containerized projects.
Responsibility for each area is split between the fabricator and the engineer of record for the site. The fabricator typically stamps the skid or container frame and its lifting points, while the site engineer stamps the foundation, the anchorage, and any host structure. Gaps appear when neither party has been assigned the interface, so the contract documents should state who designs the anchors and who provides the reactions.
Skid and Container Frames in a Modular Data Center
The frame is a structural steel assembly designed under AISC 360 to carry equipment dead load, operating loads such as fluid weight and vibration, and the transport and lifting cases described above. Members near lifting lugs and forklift pockets see concentrated forces and are often the governing elements. For a containerized unit, the ISO shell was designed for stacking and corner-lifting in marine service, and cutting openings for doors, louvers, and cable entries removes part of that strength, so the modified shell must be re-analyzed.
Fabricator drawings should show member sizes, weld symbols, lug plate thickness and hole size, and the design reactions at each anchor location. ISTA Engineers reviews these submittals against the project specification through its Shop Drawing Review service, confirming that the stated reactions match the equipment actually being mounted and that the frame can be anchored in the pattern the site engineer has detailed.
Foundations and Pads for Prefabricated Data Center Modules
Foundations for modules are designed under IBC Chapter 18 and depend on the geotechnical report for the site. Options range from a thickened slab-on-grade for light skids, to isolated spread footings or a continuous grade beam under container corners, to a reinforced mat for a row of heavy power or battery skids. The foundation must extend below the local frost depth and must account for the differential settlement limits of the equipment, which for rigid bus connections can be more restrictive than code minimums.
Along the Colorado Front Range, expansive clays and bedrock of the Denver and Pierre formations are common, and geotechnical engineers frequently recommend overexcavation, moisture conditioning, or drilled piers to control heave under slabs and pads. These recommendations carry directly into module foundations in Denver, Aurora, and other Front Range municipalities. ISTA Engineers provides this design within its Commercial Structural Engineering Services, coordinating pad geometry with the skid anchor layout before concrete is placed.
Seismic and Wind Anchorage for Skid-Based Data Centers
Seismic anchorage of skids inside a building follows ASCE 7 Chapter 13, referenced through IBC Section 1613. The seismic design force depends on the mapped spectral accelerations for the site, the component amplification and response modification factors from Table 13.6-1, the height of the skid within the building, and the component importance factor, which is 1.5 for equipment required for continued operation of the facility. Most of Colorado falls in a low to moderate seismic design category, but a Risk Category III or IV data center under IBC Table 1604.5 can still see anchorage demands that govern over gravity, particularly for tall rack rows and battery cabinets.
Containers and modules set outdoors must also resist wind under IBC Section 1609 and ASCE 7 Chapters 26 through 30. A closed container behaves as a low-rise building for pressure purposes, and the anchorage must resist both sliding and overturning from wind on the long face. The Front Range experiences strong downslope winds, and ASCE 7 wind speed maps for Boulder and the foothills reflect higher basic wind speeds than the Denver metro core, so the same container may require a different anchor pattern depending on where it is set.
Snow Loads on Containerized and Prefabricated Data Center Modules
Snow is a design load for any module with its own roof. IBC Section 1608 directs the designer to ASCE 7 Chapter 7, where the ground snow load is converted to a flat-roof load and then adjusted for exposure, thermal condition, and importance. Colorado jurisdictions frequently publish their own ground snow loads, and the Structural Engineers Association of Colorado maintains a statewide snow load study that local building departments reference, so the value used must come from the authority having jurisdiction rather than from a generic map.
Containers present two snow-specific problems. The flat roof of an ISO container was not designed as a building roof, so snow plus rooftop cooling equipment can overstress the corrugated top panel and its side rails. Drifting also occurs where a module sits beside a taller building or where several containers are ganged with a gap between them, and ASCE 7 Section 7.7 requires those drift surcharges to be included. Mountain sites outside the Front Range can carry snow loads several times those in Denver, which changes both the module shell design and the foundation reactions.
What Engineers Commonly See With Modular Data Centers: From Skids to Containers
The most frequent gap on modular projects is a missing owner of the interface. The fabricator assumes the site engineer will design the anchors, the site engineer assumes the fabricator’s drawings include them, and the skid arrives with hole patterns that do not match the pad. A related issue is a frame designed for the shipping condition only, with no documented seismic reactions, which forces the site engineer to either reverse-engineer the frame or specify conservative anchors that may not fit the base plate.
Other recurring findings include lifting lugs sized for the bare frame rather than the loaded unit, containers modified with large openings and no compensating framing, pads poured without the frost depth or reinforcing needed for a planned future module, and rack rows placed on raised access floors without a load path to the slab below. Each of these is a design coordination problem rather than a fabrication defect, and each is resolved by assigning the frame, the lift, the foundation, and the anchorage to named parties before fabrication begins.
Skid-Based Modular Data Center FAQ
The following questions come up repeatedly from owners, general contractors, and electrical contractors who are specifying or receiving modular equipment for the first time. The answers are short definitions suitable for scoping discussions, followed by the detail that affects engineering.
Terminology in this market is inconsistent between vendors, so the same product may be called a skid, a module, or a block depending on who is selling it. The definitions below follow the structural distinction used throughout this guide: an open frame is a skid, a closed ISO box is a container, and a custom closed enclosure is a prefabricated module.
What Is a Skid in a Data Center?
A skid in a data center is a welded structural steel base frame on which electrical, mechanical, or IT equipment is mounted, wired, and tested at a factory so that the entire assembly can be shipped, lifted, and bolted down as one unit. The frame provides forklift pockets or lifting lugs for handling and anchor holes for attachment to a slab or foundation. Typical skids carry switchgear and UPS systems, chillers and pumps, battery cabinets, or pre-populated rack rows.
Structurally, a skid is treated as a nonstructural component under ASCE 7 Chapter 13 when it sits inside a building, meaning the building resists wind and snow while the skid anchorage resists seismic and operating forces. The frame must also be checked for the transport and lifting conditions, which often govern member sizes near lugs and pockets. Because the skid is open, it has no inherent weather protection and is usually placed indoors or beneath a canopy.
What Is a Skid-Based Modular Data Center?
A skid-based modular data center is a facility assembled from factory-built skids, each carrying a power, cooling, energy storage, or IT subsystem, that are shipped to the site and connected inside a host building or shell to form a working data center. The approach lets fabrication proceed while the foundation and shell are built, and it allows capacity to be added by setting additional skids rather than by constructing new rooms.
The skid-based approach differs from a containerized facility in that the skids share a common building envelope rather than each carrying its own. That shifts the environmental load design to the host structure and simplifies each module, but it also means the host slab, pads, and anchor layouts must be engineered for the specific skids being installed and for any planned future additions. The modular versus traditional comparison table earlier in this guide applies equally to skid-based and containerized facilities.
Modular vs. Containerized Data Center: What Is the Difference?
A modular data center is any facility built from prefabricated modules, while a containerized data center is the specific type of modular facility in which each module is a standard ISO shipping container fitted out with racks, power, and cooling. Every containerized data center is modular, but a modular data center may instead use open skids or purpose-built enclosures that are not shipping containers.
The engineering consequence is where the environmental loads land. A container set outdoors carries wind, snow, and seismic forces on its own shell and corner castings and is anchored as a small structure. A modular facility built from skids inside a shell building places those loads on the shell and anchors the skids as equipment. Purpose-built modules fall between the two and are usually designed under ASCE 7 Chapter 15 as nonbuilding structures or under IBC Chapter 16 as buildings, depending on their size and occupancy.
Conclusion: Modular Data Centers From Skids to Containers Rest on Structural Design
Modular data centers represent the future of scalable, efficient, and rapid IT infrastructure. From skids to containers, these solutions provide unmatched flexibility and speed compared to traditional builds. Those benefits are only realized when the frame, the lift, the foundation, and the anchorage are each engineered to the IBC and ASCE 7 for the site and coordinated between fabricator and site engineer.
Owners planning a skid-based or containerized facility in Colorado should settle the structural scope before fabrication starts: who stamps the frame, who provides the reactions, who designs the pad and the anchors, and who inspects the installation. ISTA Engineers, a firm of Colorado-licensed Professional Engineers, provides each of those services for modular projects and can be reached at (720) 740-4060 or through the contact form below.
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