Glossary

Methods & categories

Volumetric modular construction

Construction in which three-dimensional, room-sized modules are structurally completed and largely finished in a factory, transported to site and assembled — stacked, set or slid — into a building. The subject of this site. Category 1 in the UK MMC framework.

Modern Methods of Construction (MMC)

UK umbrella term for off-site and productivity-improving construction methods, formalised in a seven-category definition framework: 1 volumetric; 2 panelised; 3 non-systemised structural components; 4 additive manufacturing; 5 non-structural assemblies and sub-assemblies (e.g. bathroom pods); 6 traditional building-product-led site labour reduction; 7 site-process-led improvements. Adopted in Canada by UNB's Off-site Construction Research Centre.

Panelised construction

Factory-built two-dimensional wall, floor and roof panels — open or closed — shipped flat and assembled into volumes on site. Ships densely, suits irregular buildings, leaves more finishing work on site than volumetric. MMC Category 2.

Hybrid

A building combining volumetric modules (typically kitchens and bathrooms, where labour and tolerance are most demanding) with panelised or conventional construction for the rest.

Permanent Modular Construction (PMC)US

MBI's term for modular buildings intended to remain in place, as distinct from relocatable buildings (site offices, temporary classrooms). The $20.5 billion 2025 US figure on this site is PMC.

Relocatable buildings

Modular structures designed to be moved and reused — site trailers, temporary classrooms, medical units. A different market with different economics, often lumped into "modular" statistics.

PPVCSingapore

Prefabricated Prefinished Volumetric Construction. Singapore's term for volumetric modular; mandated by the Building and Construction Authority on designated government land-sales sites, which is why Singapore builds 40-storey volumetric towers routinely.

MiCHong Kong

Modular Integrated Construction. Hong Kong's term, used across its public housing programme targeting roughly 20,000 flats.

Manufactured housingUS

Factory-built homes on a permanent chassis regulated by the federal HUD Code, which pre-empts local building codes. Not modular. The distinction matters for wind design, appraisal, financing and stigma.

Prefabrication / off-site construction

Any construction work performed away from the final site. Includes everything above plus trusses, precast and curtain-wall units. When a market report says "prefab," ask which categories it counted.

Standards & approvals

ICC/MBI 1200-2021

Standard for Off-Site Construction: Planning, Design, Fabrication and Assembly. Joint International Code Council / Modular Building Institute consensus standard; the first US-wide referenceable document for how off-site work should be planned and built.

ICC/MBI 1205-2021

Standard for Off-Site Construction: Inspection and Regulatory Compliance. How authorities and third-party agencies inspect factory work they cannot see on site.

ICC/MBI 1210-2023

Standard for Mechanical, Electrical, Plumbing Systems, Energy Efficiency and Water Conservation in Off-Site Construction. Published March 2024; explicitly excludes HUD-code housing. All three consolidated in the ICC's 2025 publication.

CSA A277Canada

Procedure for Certification of Prefabricated Buildings, Modules, and Panels. Certifies the factory's quality programme via a Standards Council of Canada-accredited body so modules leave labelled as code-compliant. Mandated in Alberta, Quebec and Yukon; recognised or accepted elsewhere at provincial or municipal discretion. Modules must still meet the code at the installation location.

CSA Z240 / Z250Canada

Standards for manufactured (mobile) homes and for park-model / relocatable structures respectively. Not the code-built modular pathway; the Canadian analogue of the HUD-code distinction.

Third-party inspection agency (TPIA)

A private agency approved by a state or province to inspect factory work on behalf of the authority having jurisdiction. Many states keep their own rosters; approval in one state does not transfer to another.

Authority Having Jurisdiction (AHJ)

The local official or body with legal power to approve a building. In modular, often two: the state or provincial programme that approves the factory and design, and the municipality that approves the site and foundation.

Reciprocity

Acceptance by one jurisdiction of another's factory approvals or inspections. Largely absent in North America; the industry's most under-discussed cost driver.

Housing Design CatalogueCanada

CMHC's October 2025 library of fifty standardised low-rise housing designs (rowhouses, fourplexes, sixplexes, ADUs), pre-reviewed by fourteen cities, intended to compress design and approval time. Standardises the building, not the permit.

BOPASUK

Buildoffsite Property Assurance Scheme — a durability and process accreditation for off-site systems intended to give mortgage lenders confidence in non-traditional construction.

Factory & design

Module

One volumetric unit. In North America typically up to about 15' 9" wide and 68–72' long, dimensions set by road-transport rules rather than architecture.

Mate line

The joint where two modules meet. Where corridor finishes, structural connections, fire-stopping and MEP tie-ins are completed on site; the quality of a modular building is largely the quality of its mate lines.

Degree of completion

The share of construction value finished in the factory before shipping — MBI cites 60 to 90 percent. The single most important number to press a factory on.

DfMA

Design for Manufacture and Assembly. Designing a building from the start around how it will be produced in a factory and assembled on site — module grid, repetition, tolerances, connection details — rather than converting a conventional design afterward.

Floor cassette / ceiling cassette

The prefabricated floor and ceiling assemblies that, with wall panels, form the structural box of a module. The floor cassette is typically the first station on a line.

Line / station

The sequence of fixed workstations a module moves through — framing, MEP rough-in, insulation and board, finishes, wrap. A stopped station is the most expensive square footage in construction.

Utilisation

The share of a factory's capacity actually in production. Determines whether fixed costs are covered; the reason factories fail with full order books of one-off projects.

Double wall / double ceiling

The condition where adjacent stacked modules each carry their own wall and ceiling, creating air-gapped double-leaf assemblies. Widely claimed to improve acoustic separation; we have not found a modular-specific STC/IIC test report and say so.

Light-gauge steel (LGS) modular

Modules framed in cold-formed steel. Stacks highest (44 storeys at Croydon), non-combustible, heavier and higher in upfront embodied carbon than timber.

Wood-frame modular

Modules framed in dimensional lumber or engineered wood. Dominates North American mid-rise; constrained by combustible-construction height and area limits rather than by the method.

Bathroom pod

A factory-finished bathroom shipped as a unit and set inside a conventional or panelised structure. MMC Category 5; the most common hybrid element.

Site & logistics

Set / setting

Craning modules into position on the foundation or on lower modules. Croydon reached about a floor a day; the AC NoMad design targeted the same.

Oversize / superload

Road-transport classifications for loads exceeding standard width, height, length or weight. Above roughly 14 feet wide, permits; above roughly 16 feet, escorts, route surveys and sometimes night moves. Set at schematic design, paid for at shipping.

Pilot car / escort

Vehicles required to accompany oversize loads. In one MBI-documented Idaho case, late planning for escorts raised shipping costs 300 percent.

Transport radius

The distance beyond which shipping cost erases modular's advantage. Commonly quoted as 300–500 miles; we could not find a primary source and treat the figure as industry lore.

Site readiness

Foundations, utilities and crane access complete before modules arrive. The point where public-sector projects — Toronto's, for instance — most often lose the schedule the factory kept.

Finance

Material deposit

A payment, typically 25 percent or more, due roughly three months before production so the factory can buy materials. Precedes any work on the collateral site — the core of modular's financing friction.

Progress billing

Factory invoicing at module start and completion (commonly 30–35 percent each), every 15–30 days, ahead of a conventional lender's site-based draw schedule.

Loan-to-cost (LTC)

Share of project cost a lender will finance. CFMA reports modular projects commonly receive LTC 5–10 points below site-built comparables because factory work is treated as unsecured.

Retainage

A share of each payment withheld until completion as security for performance. Manufacturers frequently refuse it, shifting risk and equity to the developer.

Pipeline / backlog

Prospective versus contracted orders. Factories fail on pipeline and survive on backlog; investors should price fixed costs against the latter.

Carbon & sustainability

Embodied carbon

Greenhouse-gas emissions from producing, transporting, installing, maintaining and disposing of building materials, as distinct from operational emissions. Vancouver has required its reporting at permit since 2023 and reductions since 2025.

Whole-building life-cycle assessment (WBLCA)

Quantification of a building's environmental impact across its life. The method behind both the favourable modular carbon studies and the unfavourable steel-high-rise ones.

Environmental Product Declaration (EPD)

A verified document reporting a product's life-cycle impacts. A standard module can carry one EPD reused across projects — a structural advantage in embodied-carbon permitting.

Design for disassembly

Designing connections so modules can be unbolted and reused rather than demolished. The mechanism by which steel modules' upfront carbon penalty may be recovered at end of life — if anyone does it.

Buy Clean

Procurement policies favouring low-embodied-carbon materials, especially steel and concrete, in public construction. Adopted federally in Canada under the Greening Government Strategy.