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HUD Code, IRC, IBC, ANSI A119.5: The 2026 Construction Standards Guide
Every factory-built dwelling in the US is built to one of four governing construction standards. The standard determines what jurisdiction can permit it, what lender can finance it, and what it can legally be used for.
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Every factory-built dwelling in the US is constructed to one of four governing standards. The HUD Code governs manufactured homes; the International Residential Code governs site-built and most modular single-family construction; the International Building Code governs commercial and larger multi-family construction; the ANSI A119.5 standard governs park model recreational vehicles. The standard a unit is built to determines what permitting office can sign off on it, what lender can finance it, what insurance products apply, and what it can legally be used for. This is the 2026 reference.
HUD Code
The HUD Code — formally the Federal Manufactured Home Construction and Safety Standards — was adopted in 1976 and governs all manufactured homes built for primary residence use in the US. The code preempts state and local building codes for the unit itself, meaning a HUD-Code manufactured home built to federal standards in one state can be legally placed in any other state without additional construction-standard review.
The code covers structural systems, plumbing, electrical, mechanical, energy efficiency, transportation, and installation. HUD-certified inspectors monitor factory production. Each unit ships with a HUD data plate and a HUD certification label permanently affixed to the exterior.
Buyers identify a HUD-Code unit by the red HUD label on the exterior and the HUD data plate inside (typically near the electrical panel or kitchen cabinetry).
International Residential Code (IRC)
The IRC is the model residential building code published by the International Code Council and adopted, with variations, by nearly all US states and many local jurisdictions. It governs single-family detached construction up to three stories. Both site-built and modular single-family homes are typically built to the locally-adopted version of the IRC.
Modular homes built to the IRC are inspected by state-certified third-party agencies during factory production. Each unit ships with a state modular certification label documenting the IRC version and any state-specific amendments the unit meets.
The IRC is updated on a three-year cycle. The 2024 IRC is the current published edition in 2026, with adoption by individual jurisdictions varying — many jurisdictions are still operating under the 2021 or earlier editions.
International Building Code (IBC)
The IBC is the broader model building code published by the International Code Council, governing commercial construction, multi-family residential above three stories, and structures that do not fit the IRC's single-family residential scope.
Modular construction for multi-family, commercial, and institutional use typically falls under the IBC rather than the IRC. The construction standards, inspection requirements, and certification pathways are similar in structure but differ in specifics from the IRC.
ANSI A119.5
The ANSI A119.5 standard governs park model recreational vehicles — the fixed-trailer units typically 400 square feet that combine RV mobility with semi-permanent residential layout. The standard is maintained by the American National Standards Institute and is the construction reference for park model manufacturers.
ANSI A119.5 units are legally classified as RVs in most US jurisdictions. They follow RV titling, RV financing, and RV permitting pathways — meaning they generally cannot be placed as a primary residence outside RV-zoned campgrounds and RV parks.
How to Identify Which Standard a Specific Unit Was Built To
Five signals identify the construction standard.
First, the data plate or certification label. HUD-Code units have a HUD data plate and red HUD certification label. IRC modular units have a state modular certification label. ANSI A119.5 units have an ANSI compliance label.
Second, the title status. HUD-Code manufactured homes have a separate title that may be cancelled upon permanent installation. IRC modular homes have no separate title and convey with the land. ANSI A119.5 units are titled as RVs through the state DMV.
Third, the chassis. HUD-Code units are built on a chassis that may be removed at permanent installation. IRC modular units are typically built without a chassis. ANSI A119.5 units are built on a fixed trailer chassis.
Fourth, the financing pathway. HUD-Code units finance through manufactured-home specialty lenders; IRC modular units finance through conventional mortgage products; ANSI A119.5 units finance through RV lenders.
Fifth, the permitting pathway. HUD-Code units permit through the local building department with reference to the HUD installation manual. IRC modular units permit through the local building department with reference to the IRC. ANSI A119.5 units permit through whatever framework the local jurisdiction applies to RV placement.
Where PERCH Fits
PERCH was built specifically to compress the operator-and-process work this guide describes. The verified ADU and small-home builder directory covers operators in each US region with documented installation history, real references, and traceable post-sale support. The marketplace surfaces verified inventory for buyers comparing options across configurations.
Ready to apply this to your specific project? Join the PERCH waitlist → for early access to verified operator inventory and concierge buyer support.
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