Reciprocity, not regulation, is what modular codes are missing.

For most of its history, the complaint about modular regulation was that there wasn't any — that building officials had no framework for inspecting a wall they could not see inside a module that arrived sealed. That complaint is out of date. Between 2021 and 2024 the International Code Council and the Modular Building Institute published three consensus standards covering planning, fabrication, inspection and building systems for off-site construction. Canada has had a factory-certification standard, CSA A277, for decades. The United Kingdom has a seven-category taxonomy that at least tells everyone what they are arguing about.

The problem now is different and harder. The standards exist; acceptance of them does not travel. A module built under a California-approved quality programme is not presumptively compliant in Texas. A CSA A277-certified module from a Quebec plant is not automatically accepted by an Ontario municipality. Every jurisdiction crossed is a requalification, and requalification is exactly the kind of one-off cost that a manufacturing business cannot amortise.

Two regulatory lines that get confused

Before the standards, a distinction that confuses lenders, buyers and journalists alike. In the US, manufactured homes are built to the federal HUD Code, which pre-empts local building codes; modular buildings are built to the same state and local codes — the IRC or IBC — as site-built construction, and simply happen to be assembled in a factory.⁴ The gap is not cosmetic. MBI notes that HUD Wind Zone III requires a 110 mph design wind speed where the IRC requires 140 to 180 mph for modular in the same regions.⁴ The new ICC/MBI 1210 standard explicitly excludes HUD-code housing from its scope, which is regulators trying to keep the line crisp even as marketing blurs it.²

Everything on this site concerns the second category: code-built volumetric construction. When you see appraisal discounts or lender hesitancy attached to a modular project, it is frequently HUD-code stigma leaking across a line it does not belong on.

The United States: standards without reciprocity

ICC/MBI 1200-2021 covers planning, design, fabrication and assembly of off-site construction; 1205-2021 covers inspection and regulatory compliance; 1210-2023, published in March 2024, covers mechanical, electrical, plumbing, energy efficiency and water conservation.^1,2 The ICC consolidated all three into a single 2025 publication with dedicated chapters on fabrication and on-site installation.³ These are, for the first time, referenceable documents a state can adopt by name.

Adoption, however, remains state by state, and the states that had modular programmes before the standards existed have kept their own machinery. California's Department of Housing and Community Development regulates Factory-Built Housing under its own programme, separate from manufactured housing, and the state is funding a $10 million Factory-Built Housing Pilot into its third round in 2026.⁵ Texas runs volumetric modular through the Department of Licensing and Regulation's Industrialized Housing and Buildings programme, with its own manufacturer and installer certifications.⁶ Utah maintains a roster of approved third-party inspection agencies, updated as recently as January 2026.⁷

Each is a reasonable programme. Together they mean that a factory in Idaho serving five western states holds five approvals, hosts inspectors from several third-party agencies, and maintains design packages annotated for each destination. That overhead is invisible in most cost analyses and is one reason the schedule advantage survives interstate shipping better than the cost advantage does.

Canada: A277 and the provinces

Canada's approach certifies the factory rather than the building. CSA A277, Procedure for Certification of Prefabricated Buildings, Modules, and Panels, has a certification body accredited by the Standards Council of Canada audit the plant's quality programme and inspect production, so that a module leaves with a label attesting compliance with the applicable code.⁸ In principle this is exactly the reciprocity mechanism the US lacks.

In practice, adoption is provincial. According to the Canadian Home Builders' Association, Alberta, Quebec and Yukon mandate A277 certification; other provinces "recognise" or "accept" it through regulation or municipal policy, which leaves the local authority having jurisdiction with discretion over what the label is worth.⁸ And the standard requires compliance with the code in force at the installation location, so a plant in Quebec shipping to Ontario builds to the Ontario Building Code and must satisfy an Ontario official that it did. The national label reduces friction. It does not eliminate the provincial border.

The UK: define first, regulate second

The UK's contribution is taxonomic. Its Modern Methods of Construction definition framework sorts every off-site and productivity-improving method into seven categories, from Category 1 — three-dimensional volumetric primary structural systems — through panelised systems, components, and down to Category 7, site-process improvements.¹⁰ The framework has no force of law, but it has become the shared vocabulary for lenders, warranty providers and government programmes, and it is the reason British market data is less muddled than North American data about what is being counted.

North America has nothing equivalent, and the confusion shows: in market reports that cannot say whether they include panelised systems, in lenders who cannot distinguish a volumetric tower from a manufactured home, and in procurement documents that ask for "modular" without saying which category.

The design-standardisation track

There is a second way to attack permitting friction, and Canada has just taken it. In October 2025 CMHC released the Housing Design Catalogue: fifty standardised designs for rowhouses, fourplexes, sixplexes and accessory dwelling units, intended to compress design and approval timelines, with fourteen cities including Vancouver, Toronto, Ottawa, Edmonton and Halifax committing to pre-review them.⁹ CMHC is candid that each design still needs a local professional to adapt it to site conditions and bylaws — the catalogue standardises the building, not the permit.

Still, it is the right complement. The ICC/MBI standards and CSA A277 attack the quality-assurance bottleneck: can an official trust what came out of the factory? The design catalogue attacks the approval bottleneck: has this building been seen before? An industry that wants to behave like manufacturing needs both, moving together. As of 2026 the US has moved further on the first and Canada on the second, and neither has closed the loop.

What to do with this

Manufacturers should treat jurisdictional approvals as a product catalogue decision, not an afterthought: pick the states or provinces you will serve, hold those approvals continuously, and decline the one-off project three borders away. Developers should ask, before signing, which third-party agency will inspect and whether the local official has accepted that agency before. Advocates should stop asking for "modular-friendly codes" — the codes are fine — and start asking for reciprocity compacts and for catalogue designs to be pre-engineered as modules. The standards were the easy part.