Clarifying a Shared Language for Offsite Construction

The terms in this glossary reinterpret familiar words through the technical lens of offsite construction — where manufacturing logic reshapes how we build, coordinate, and deliver. These definitions are not drawn from a single discipline, but emerge from the CfOC’s effort to harmonize vocabulary across architecture, engineering, construction, and product manufacturing. Our team consulted a wide range of sources in the U.S. and U.K., including the Offsite Construction for Housing: Research Roadmap (HUD & MODX) and the Product Platform Rulebook (Construction Innovation Hub). The result is a reference that acknowledges the industry’s legacy while building a foundation for its future. These definitions aim to clarify offsite construction’s core methods and how it is practiced.

Assembly A combination of components. NB: Widely recognized as the third part of the division of 21st-century construction into [1] Fabrication, [2] Assembly, and [3] Installation. Assembly refers to the integration of prefabricated elements into coherent units—such as modules or pods—prior to final delivery. It often occurs at intermediary hubs or finishing facilities and plays a critical role in ensuring interoperability across systems and trades.
Authority Having Jurisdiction (AHJ) Commonly defined as the Federal, State, local, or other governmental entity with statutory or regulatory authority for the approval of fire safety systems, equipment, installations, or procedures within a specified locality. (See 15 USC § 2225(d)(3))
Building Envelope The physical separator between the conditioned and unconditioned environment of a building, including the resistance to air, water, heat, light, and noise transfer.
Building Information Modeling (BIM) A process involving the generation and management of digital representations of the physical and functional characteristics of buildings and other physical assets. NB: See software AutoDesk Revit, Bentley Architecture, etc.
Cartridges Assemblies used as floors, walls, and ceilings, usually pre-fabricated and integrated with many of a building’s systems. NB: Though these assemblies have thickness, they lend themselves to 2D thinking in early design stages, and flat-packed shipping methods. (Contrast this with “block” as a component of 3D design thinking.)
Component A constituent part of a building (or other built asset) which is manufactured as an independent unit that can be joined or blended with other components to form a more complex item. ND: From a building delivery team’s perspective, components are ‘self-contained’ and sourced from a single supplier.
Continuous improvement process (CIP) A formal system for improving the quality of products, processes and/or services continuously over time. CIP initiatives, particularly in manufacturing and lean construction processes, include: Quality First Attitude; Plan Do Check Act Cycle; 7 Tools of Quality; Audits and Inspections; and Poka-yoke (a Japanese term for mistake-proofing assembly operations). Manufacturers generally aspire to achieve ‘Six Sig ma’ levels of performance to obtain high production yields of products with many components.
Construction A legacy term rooted in the Engineer-to-Order (ETO) paradigm of the 19th and 20th centuries. Under this model, raw commodities—lumber, pipe, wire, etc.—are shipped to a jobsite and then cut, hoisted, placed, and finished in situ. “Construction” connotes an improvisational, labor-intensive process where nearly every decision is resolved in the field. In contrast, the Center for Offsite Construction favors terms that describe industrialized, manufacturing-informed workflows.
Construction industrialisation The process of adopting more manufacturing practices, including specialized tooling, mechanization and automation, to make the construction industry more efficient and productive, with better quality assurance for better-value, more reliable and more sustainable long-term outcomes. See also MMC.
Demand The use of product platforms requires aggregation of demand across a range of assets – typically where there are high volumes of similar features – and an ability to rationalize design requirements. This is done away from the project environment and is critical to establishing requirements and providing confidence to the supply chain that the solutions they develop will have a market.
Deploy (Product Platform) The development of product platforms happens away from the project environment and hence is not undertaken in relation to the requirements of one specific asset. The deployment of product platforms on projects therefore relies on how well the requirements collected during the development stage reflect the specific needs of that project (and the flexibility of the product platform). Once a product platform is developed, a significant proportion of design is replaced by ‘configuration’ of these standardized components and assemblies, although an element of bespoke design is always likely to be required. A Product Platform Deployment Manual will be produced for each particular product platform using the Product Platform Rule book. (As referenced within the Product Platform Development Framework)
Design for Assembly (DfA) A process by which products are designed with ease of assembly in mind. If a product contains fewer parts it will take costs.
Design for Deconstruction (DfD) A process by which products are designed to increase the quality and quantity of materials that can be re-used at the end of a building’s life. This focus can be used in conjunction with DfMA in order to optimize construction products and product platforms for dis-assembly, maintenance and deconstruction. This enables re-circulation of materials, components and assemblies in the sector.
Design for Maintenance A process by which products are designed to ensure that maintenance and intended service life is factored into the design process to reduce whole life costs. It can include the use of smart components, i.e. ones that are equipped with sensors and are linked to the Internet of Things in a way that allows them to be monitored and controlled.
Design for Manufacture (DfM) The general engineering practice of designing products in such a way that they are easy to manufacture.
Design for Manufacture & Assembly (DfMA) An engineering methodology that focuses on reducing time-to-market and total production costs by prioritizing both the ease of manufacture for the product’s parts and the simplified assembly of those parts into the final product – all during the early design phases of the product life cycle.
Design for Standardization Focuses on the functional, interface, dimensional and geometric design of components and assemblies to, for example, rationalize the number of variants and drive commonality to achieve economies of scale, this is in line with a Product Platform approach. The AIMCH project highlights the benefits of adopting this design philosophy for an industrialized housing sector.
Develop (Product Platform) IThe process through which product platforms are developed is not widely understood or consistent in construction. The product platform rulebook will set out this process, ensuring different product platforms use the same language, share the same data, and thus allow for comparison, ease of configuration, and levels of interoperability/interchange. As part of the develop stage, all product platforms will produce a Product Platform Specification and Deployment Manual in line with the Product Platform Rulebook. (As referenced within the Product Platform Development Framework).
Digital Twin A dynamic, digital replica of a building or system that is continuously updated to reflect its real-world condition. Digital twins enable simulation, monitoring, and optimization across a building’s lifecycle. In Modular 2.0, they support integration across design, manufacturing, and facility management, using BIM and sensor data. CfOC promotes digital twin use to validate modular assemblies, track lifecycle performance, and support predictive maintenance. This is an emerging area of research and development in offsite construction.
Engineering Bill of Materials (EBOM) An engineering bill of materials (EBOM) is developed during the product design process. It’s generally created automatically from engineering and design software, such as CAD tools, and it lists the parts and subassemblies necessary to build the product. It usually includes more detailed engineering information, such as manufacturing tolerances, related engineering standards, and product specifications.
Fabrication The precise manufacturing of components or subassemblies in a controlled environment. Fabrication occurs upstream of the jobsite, often within specialized factories, and emphasizes accuracy, repeatability, and quality control. In the CTO paradigm, fabrication allows modules, panels, or parts to be created independent of site constraints, reducing weather risk and labor variability.
Field factory A temporary manufacturing facility established near to the construction site to manufacture modules or pre-assembled flat pack components before assembly on site. The work carried out in them counts as offsite construction. They can also help with transportation logistics.
Flying factory See Field factory.
Finishing The final detailing and adjustment of a product prior to occupancy. In traditional ETO construction, finishing was highly labor-intensive, involving drywall, paint, fixtures, and trim work performed on site. In a CTO model, finishing is relocated upstream—completed within factories or assembly hubs—so that site work is minimized. Where finishing occurs onsite, it is limited to minor touch-ups and functional tests rather than core craftsmanship.
Hoisting The act of lifting prefabricated or assembled components—such as modules, panels, or assemblies—into their final or intermediate position using cranes or similar equipment. In the CTO paradigm, hoisting is a logistics operation, not a construction task. It marks the moment when offsite precision meets onsite execution, and its success depends on clear interface standards and engineered rigging points.
Hybrid construction system Any construction system that combines two or more categories of MMC.
Indoor Construction (pejorative) [1] The use of 19th-century (ETO) construction technologies in a 21st-century offsite construction workflow. [2] Constructing panels or modules, in an offsite setting, with the same ETO steps and trades, instead of re-arranging production into an EBOM, by also blending trades in a fabrication and assembly hierarchy.
Industrialized Construction A building methodology that aims to optimize the construction process by integrating automation and mechanization in a factory production environment. It involves the use of precision technology and lean production methodologies to fabricate building components with high accuracy and quality. Industrialized construction (IC) is a building methodology that aims to optimize the construction process by integrating automation and mechanization in a factory production environment. It involves the use of precision technology and lean production methodologies to fabricate building components with high accuracy and quality.
Installation The final act of placing prefabricated and pre-assembled elements into their permanent position on site. Installation does not involve cutting, welding, or field-engineering; instead, it focuses on coupling, alignment, and commissioning. In a mature CTO ecosystem, installation is fast, clean, and governed by interface standards rather than jobsite improvisation.
Interface (Design Rules) A formal boundary where two or more components connect, governed by a set of rules that define how information, material, or force flows across the boundary. NB: As described by Clark and Baldwin in Design Rules, an interface partitions a system into discrete, substitutable modules while preserving overall coherence. In offsite construction, interfaces are not just physical (e.g., mechanical fasteners or utility couplings) but also digital (e.g., BIM object standards) and procedural (e.g., inspection protocols). Standardizing interfaces enables parallel development, reduces coordination cost, and allows innovation to scale without reengineering the entire system. See essay “What Modularity Really Means” (above).
Interoperability A characteristic of a product, component, assembly or system, whose interfaces are completely understood, which allows it to work with other products, components, assemblies or systems, at present or in the future, in either implementation or access, without any restrictions. Just-in-time logistics Planning to ensure that deliveries arrive on site only when they are needed, thus avoiding the overheads and added risks involved in on-site storage, improving overall build efficiency.
Kit of Parts [1] A collection of repeatable, standardized building components that are pre engineered and designed to create a variety of assemblies which define part or all of a finished building. [2] A system of separate proprietary parts manufactured off site, conceived to be efficiently assembled on site. The rationale for keeping the parts separate is to allow more efficient, safer handling and transportation, and to allow flexibility (within certain constraints) in their final configuration.
Lean An adjective used in industry to describe processes where waste (of materials, time, cost, handling, intellectual property and so on) has been eliminated or minimized, improving efficiency and productivity.
Manufacturing The industrialized production of repeatable components or systems in a controlled environment, governed by pre-established design rules and interface standards. Unlike traditional construction—which relies on site-based, project-specific improvisation—manufacturing emphasizes predictability, quality control, and throughput. Within the Modular 2.0 paradigm, manufacturing encompasses fabrication (making parts), assembly (joining components), and preparation for installation (onsite integration). Manufacturing is enabled by design-for-repeatability, supply chain coordination, and automation—not by field coordination. It replaces the variability of construction with the scalability of productization.
Manufactured housing The practice of building housing with 3D offsite manufactured building products. Specifically, by fabricating and assembling all discipline’s contributions into one product, and installing the product as a complete home solution. Single-wide and Double-wide Mobile Homes are the most common form of Manufactured Housing.
Manufactured homes Houses built in the controlled environment of a manufacturing plant and are transported in one or more sections on a permanent chassis. Manufactured homes are constructed according to a code administered by the U.S. Department of Housing and Urban Development (HUD Code).
Mass customisation A process that allows manufacturers to customize products by varying production processes without affecting their ability to charge low mass-production prices.
Mass production The production or manufacture of goods in large quantities, especially by machinery.
Material handling design The detailed planning of the packaging of components and assemblies manufactured off site and the logistics of getting them to their final destination on site, with the objective of making the process as efficient as possible. It can result in incorporating physical features on the components, assemblies or their packaging, including lifting points or positioning aids to facilitate handling or assembly
Mods See: Modules
Module (Design Rules) [1] A component designed to be developed, manufactured, and improved independently, provided it conforms to a shared interface. [2] A separable component, frequently one that is interchangeable with others, for assembly into units of differing size, complexity, or function. NB: In Clark and Baldwin’s framework, a module hides its internal complexity behind a stable interface, allowing others to rely on its function without needing to understand its construction. In Modular 2.0, modules can take the form of physical building blocks (like bathrooms or kitchens), software tools, or even roles within a supply chain. The power of modularity lies not in uniformity, but in the freedom to vary internally while remaining externally compatible. See essay “What Modularity Really Means” (above).
Modular construction A process that allows manufactured components to be configured in multiple ways by exploiting standardized interfaces.
Modular housing The practice of building housing with 3D off-site building products. Specifically, by fabricating and assembling large parts of repeating elements (i.e. kitchens, bathroom, etc.) in a manufacturing facility to speed building assembly on site.
Modern methods of construction (MMC) Building methods designed to improve productivity and safety or reduce the need for labor, or both. They have the specific objective of improving efficiency compared to business-as-usual techniques. Whereas the term is most commonly associated with volumetric offsite construction, it actually includes many other outputs, including on site process innovations.
Near-site factories See Field factory.
Off-Site construction (OSC) [1] A project-delivery process used to realize a building project using large, offsite-manufactured products. [2] A collective term for construction processes that are carried out away from the building site in a way that adds value compared to business-as-usu al construction. Offsite construction can happen in a factory or in a specially created temporary production facility close to the construction site (see Field factory).
Off-Site manufacturing (OSM) A process of delivering a singular product for multiple off-site construction projects and realizing that product with late-20th century manufac turing principles. Critically, these products combine more than one construction discipline (framers, plumbers, electricians, etc), and the products are realized with principles from Design for Manufacturability (DfM) and Design for Assembly (DfA).
Off-Site production (OSP) Largely interchangeable terms referring to the part of the construction process that is carried out away from the building site. This can be in a factory or sometimes in specially created temporary production facilities close to the construction site (or field factories).
Open Interface A documented and publicly accessible connection standard that allows independently designed components to interoperate. Open interfaces allow modules and systems from different manufacturers to connect without custom engineering. They are essential to reducing project-specific coordination and enabling marketplace dynamics in offsite construction. CfOC promotes open interfaces as the backbone of Modular 2.0’s interoperability goals. This is distinct from proprietary interfaces, which restrict component substitution.
Panelized Construction The practice of building housing with two-dimensional off site manufactured building products.
Panelized Systems Two-dimensional building elements — such as walls, floors, or roofs — that are manufactured offsite and assembled on site. These systems may include framing, sheathing, insulation, windows, or cladding. Unlike volumetric modules, panelized systems require structural integration during onsite assembly. They are often used in hybrid modular projects and are subject to digital coordination rules to ensure consistency and accuracy. Panelization enables transportation of flat-packed components and supports higher configurability.
Platform A term that is widely used but with consistent elements including: a set of low variety core assets (i.e. components, processes, knowledge, people and relationships); a complementary set of peripheral components that exhibit high variety; stable interfaces that act as a bridge between the stable core and variable peripherals; and a set of rules or standards governing how components can be integrated.
Platform-based design for manufacture and assembly (P-DfMA) The process by which designers develop and make use of platform construction systems to create new bespoke built assets.
Prefabrication To fabricate the parts at a factory so that construction consists mainly of assembling and uniting standardized parts.
Pre-manufactured value (PMV) A proxy measure of project efficiency calculated as the project’s gross capital cost less the cost of prelims (site overheads) and site labor, divided by the gross capital cost, expressed as a percentage. The business-as-usual benchmark is 40%; anything higher has more of its operations conducted off site.
Process control and monitoring A formal system of statistical controls and standard ized procedures to ensure that the journey from design to construction is consistent and repeatable, thereby assuring quality and reliability. Production is monitored and vari ations plotted between control limits which, if exceeded, trigger corrective actions before critical limits are reached.
Product A thing produced by or resulting from a process.
Product Family The product family is a group of related products that share common features, parts and systems, yet deliver variety.
Product Line A group of products of the same manufacturer having similar or related characteristics and intended for similar or related markets.
Product Platform Development Framework A common framework to support the development of product platforms. The framework sets out a series of activities across three stages (Demand, Develop, Deploy) covering the identification of market demand through the development of a product platform to its eventual deployment on multiple projects.
Product Platform (PP) A kit of parts, associated production processes, and the knowledge, people and relationships required to deliver all or part of construction projects using a platform approach. A product platform provides a stable core which is configured and combined with complementary components (via defined interfaces) to suit a particular project. A product platform also includes the processes tools and equipment required for assembly.
Product Platform Roadmap A detailed breakdown of activities to inform planning and investment decisions, that sets out the order in which the product platform provid er needs to develop product families and constituent parts.
Product Platform Specification The component, interface and production specifications for a particular product platform, developed using the Product Platform Rulebook and based on the rules set out in the Product Platform Definition
Product Variants Working within the framework of the platform, individual products can be variants or derivatives.
Pods A prefabricated volumetric element, fully factory finished and internally complete with building services. Types of pod include bathrooms, shower rooms, office wash rooms, plant rooms and kitchens. Pods use volumetric construction principles, but are smaller in size than modular units and are typically installed into traditional structural frames.
Rigging The strategic arrangement of lifting equipment—slings, shackles, spreader bars, and anchor points—used to safely and precisely hoist modular components. Rigging design is an integral part of the hoisting process, ensuring that loads remain balanced, modules are not damaged, and interface alignments are preserved. In a CTO workflow, rigging is not improvised onsite but engineered in advance, often co-developed with the product’s structural and interface logic. Effective rigging translates digital intent into physical precision at the moment of lift.
Scaffold A temporary structure for holding workers and materials during the construction, repair, or decoration of a building. Any framework or system of such frameworks for supporting other materials.
Staging The organized preparation of prefabricated components for installation. Staging includes layout sequencing, temporary positioning, and just-in-time coordination with other trades. In modular workflows, effective staging ensures that site crews handle pre-finished units with care and efficiency, avoiding rework and maintaining schedule integrity. It is a key transitional step between delivery and installation.
Skids A low mobile platform on which goods are placed for ease in handling, moving, etc.
Standardization In the context of DfMA, standardization involves quality-assured systems and processes that govern design, manufacturing and assembly inputs with the objective of improving the reliability, speed, consistency and efficiency of digital and physical outputs, making it possible to achieve economies of scale. With CIP, the extent of the benefits is refined over time.
Structurally Insulated Panels (SIPs) A panel consisting of two face sheets of wood panel bonded together by plastic foam core.
Sub-assemblies Major building elements that are manufactured off site, potentially comprising a combination of components. Examples include walls, floors, roofs, balconies, balustrading assemblies, façade cassette panels and pre-assembled M&E elements.
Supply chain A generic term describing the contractually linked people and companies who supply the services, materials, parts, components and equipment that are used to make larger components, assemblies and whole buildings for a head client.
Supply chain integration (SCI) A process for improving the efficiency and effectiveness of the supply chain’s performance by setting the conditions for cooperation and collaboration. When successful, supply chains run projects safely, quickly and without rework, and deliver the client’s requirements for quality and reliability on time and on budget.
Vertical Integration A business model in which a single firm controls multiple stages of the construction process — from design to manufacturing to installation. While this can ensure quality and accountability, it also limits interoperability and scalability. Modular 2.0 aims to reduce reliance on vertically integrated firms by promoting shared standards and distributed collaboration. Vertical integration is often contrasted with open platform models, where independent actors operate with defined roles but shared rules.
Virtual Design & Construction (VDC) Is the management of integrated multi-disciplinary performance models of design–construction projects, including the product (facilities), work processes, and organization of the design – construction – operation team to support explicit and public business objectives.
Volumetric An adjective describing large scale assemblies constructed offsite in such a way that they enclose a three-dimensional volume of space. In the context of MMC, the term tends to be restricted to assemblies that incorporate primary structural elements, i.e. that fall into Category 1 of the Categories of MMC.
Volumetric modular unit A volumetric modular unit is a self-contained, three-dimensional building module that can be used to create various structures, ranging from residential homes to commercial buildings. These units are manufactured off-site and delivered to the project location in their entirety, complete with finishes, fixtures, and fittings. Each module is built with the intention of seamlessly integrating with other modules to form the final building.
Volumetric Modules Three-dimensional factory-built units that include structural systems, mechanical/electrical/plumbing (MEP) components, and interior finishes. These modules are transported to the site and connected to form part or all of a building. Volumetric modules typically arrive enclosed and nearly complete, requiring minimal finishing on site. In Modular 2.0 workflows, they are treated as pre-assembled units, governed by interface standards to ensure interoperability. Also referred to as “boxes,” “pods,” or “units,” depending on context.