Factory-Built Housing

Introduction to Factory-Built or Off-Site Construction Building Standards

Off-site construction refers to structures or components built at a different location (a factory) than the location of use. Factory-built homes are also referred to as prefabs. Different building codes are used for the various kinds of housing built in factories. For instance, manufactured housing uses the HUD building code and modular homes use the International Building Code developed by ICC.

THIA Board Members David R. Tompos and Nick Mosley sit on the ICC-OSMC Committee—stands for Off-Site Modular Construction.  The goal of this committee is to create standards for housing, built "off-site" in factories (more on this below). These standards include transportation, inspection, design, plan approval, quality control, planning, definitions, etc. Everything from conception to delivery of a unit on a job site. They are primarily procedural standards that will then go under review by ICC (International Code Council). Learn more here.

Offsite Construction Expo

The Offsite Construction Expo offers focused presentations of the abilities of offsite construction across all markets and educational insights into offsite construction.

They have partnered with companies from across the offsite construction industry to share information about all aspects of offsite construction, all part of the Offsite Construction Alliance. THIA is honored to be a partner.


"I am the representative for the tiny house industry (on ICC-OSMC Committee) to make sure as new/upcoming industry, our voices are heard. During the meetings, there have been various discussions of tiny homes and how they fit into the much larger modular construction industry. Before this committee, they have generally been excluded.

The goal is to adopt tiny home building practices into the greater body of the standards vs. creating a separate space that would leave it up to the authority having jurisdiction (AHJ) to choose whether or not they want to allow tiny homes (this has been achieved for both foundation-based AND movable tiny houses!).

- Nick Mosley, California Tiny House CEO & National Builders' Commitee Co-Chair

Some also believe that Off-Site Construction Standards recently released by ICC, namely the ICC/MBI 1200 (Planning, Design, Fabrication, and Assembly) and ICC/MBI 1205 (Inspection and Regulatory Compliance), excluded MTHs. That is also inaccurate. These standards apply to all buildings built using off-site construction techniques. Please note that the ICC’s codes and standards are widely adopted in the United States, the District of Columbia, Guam, Puerto Rico, and the U.S. Virgin Islands.
The ICC provides model language for building movable tiny houses that can be added to any law covering the adoption of residential building codes. Further, they offer verbiage that can be added to any relevant law covering the regulation of off-site/industrial/pre-fabricated/factory-built/modular construction. The Modular Building Institute (MBI) and the ICC collaborated to capture best practices that can be used to enhance existing state off-site construction programs or establish new programs where they do not yet exist. Additionally, the standards can be used to support off-site construction in local jurisdictions where a statewide program does not exist.

Clarification on Building Tiny Homes to Off-Site Residential Building Standards:

"Becoming a THIA member helped me bring tiny houses to my town.  Now, I can live where I want and how I want, legally."

-Jessica B. San Jose, CA

"We entered the Tiny House on Wheels industry because we felt that this product is both of vital future importance, and also that the industry would benefit
from experienced professional construction and standards. THIA stands for exactly these things which are the reason we started building tiny homes in the first

With THIA I feel confident that we are moving towards a fair and correct set of national standards, and as this is an organization that has a real purpose, not just a name and a sticker, we will be a member moving forward. It's also fantastic to have somewhere to get some feedback or secure a referral."

- Jerry Terry, Decathlon Construction

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