Prefab Home Regulations & Safety Standards in the United States

Thinking of importing or manufacturing prefabricated homes for the US market? Although a unifying building code standard for prefabricated homes does not exist yet, there are regulations and safety standards that should be observed.

Construction products that are commonly referred to as “prefabricated” include:

• Kit homes
• Modular homes
• Stick-built homes
• Prefabricated panels
• Manufactured homes

However, from a legal point of view, there are two types of prefabricated homes:

• Those that follow federal laws (legally known as “manufactured homes”)
• Those that follow local state laws and codes (legally known as “modular homes”).

In this article, we present various legislation, codes, and safety standards that are relevant to the prefabricated housing market in the United States.

National Manufactured Housing Construction and Safety Standards Act

The National Manufactured Housing Construction and Safety Standards Act is a federal law that regulates manufactured homes and ensures that they are built in a manner that is safe for occupants to dwell in.

It enables the Department of Housing and Urban Development to develop safety requirements related to the construction of such homes through the codified version of the Act, 24 CFR Part 3280.

Product scope

“Manufactured homes” is a legal term of art as it is given its own definition under the legislation.

Manufactured homes

A manufactured home refers to a structure that for the most part is built off-site and assembled on-site. Equipment and installations used in manufactured homes are also regulated.

Looking at the above meaning, one might think that it refers to all prefabricated homes as they may be constructed in the same manner as described in the act. However, a distinction is made between manufactured homes and modular homes.

Modular homes

24 CFR Part 3280 sets the standards for manufactured homes and their equipment and installations, but it explicitly excludes modular homes. No definition is provided for a modular home. Instead, it provides a procedure whereby the manufacturer has the choice to exclude the construction product from the ambit of the act.

What is the difference between manufactured homes and modular homes?

Thus, a modular home is a construction product that is not subject to the National Manufactured Housing Construction and Safety Standards Act, and a manufactured home is a construction product that follows the Act. The manufacturer decides if the product is a manufactured home or a modular home.

Standards

In relation to manufactured homes, codes and standards from other organizations are also incorporated by reference in 24 CFR Part 3280, including:

a. ANSI/ARI Standard 210/240-89 – Unitary Air-Conditioning and Air-Source Heat Pump Equipment

b. AAMA 1503.1-88 – Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors, and Glazed Wall Sections

c. ANSI/AITC A190.1-1992 – For wood products – Structural Glued Laminated Timber

d. ASTM E1333-14 – Standard Test Method for Determining Formaldehyde Concentrations in Air and Emission Rates from Wood Products Using a Large Air Chamber

Incorporated standards copies may be obtained from the Office of Manufactured Housing Programs and are available for inspection at the National Archives and Records Administration.

Requirements for manufactured homes

In relation to manufactured homes, the following are some requirements:

a. Affixing the data plate on the manufactured home as per 24 CFR Part 3280.5

b. Stamping of the manufactured home serial number into the foremost cross member as per 24 CFR Part 3280.6

c. Affixing a permanent label to each transportable section of the manufactured homes as per 24 Part 3280.11

Requirements for other prefab homes (excluding manufactured homes)

In relation to prefab homes that are not defined as manufactured homes (e.g. modular homes), the essential difference between it and manufactured homes under the legislation boils down to whether the manufacturer elects to exclude his product from the ambit of the act.

Building codes

If the manner in which the construction product is built fits the definition of a manufactured home and the manufacturer elects to exclude his product, the manufacturer should either follow:

a. One of the nationally recognized building codes listed in 24 CFR Part 3282.12(b)(3)(i)

b. Any local code or State or local modular building code accepted as generally equivalent to the above-referenced codes, see 24 CFR Part 3282.12(b)(3)(ii)

Certification

If the manufacturer decides to exclude his product, then certification following 24 CFR Part 3282.12(c) must be provided.

It should state all of the following:

a. The manufacturer’s name and address

b. Serial number of the structure and affirm that the structure “is not a manufactured home subject to the provisions of the National Manufactured Housing Construction and Safety Standards Act”

c. The structure is “designed only for erection or installation on a site-built permanent foundation”

d. The structure is “not designed to be moved once so erected or installed”

e. The structure is designed and manufactured to adhere to the relevant codes prescribed in 24 CFR Part 3282.12(b)(3)

f. The manufacturer affirms that the structure “ is not intended to be used other than on a site-built permanent foundation” to the best of his/her knowledge

This certification should be permanently affixed in close proximity to the electrical panel, on the inside of a kitchen cabinet door, or in some other readily accessible and visible location.

Is there a Modular Home Building Code Standard?

A modular home-specific building code standard does not exist yet, however as previously-explained manufacturers may need to adhere to the applicable state and local building codes.

Most states do not write their own codes from scratch. Instead, most states adopt and customize published codes and standards from organizations like the International Code Council (ICC).

International Code Council®

The ICC develops international codes and standards and building safety solutions. States often adopt and customize the ICC standards and model codes instead of drafting their own codes and standards.

ICC Model Codes

Examples of the published model codes include the International Building Code (IBC) and the International Residential Code (IRC). The IBC and IRC are explained in subsequent sections.

Note that the published model codes go through updates and that different versions exist. However, not every state will make use of the same published version, let alone follow it strictly.

Thus, a construction project that is compliant in one state would not necessarily be compliant in another, and importers and manufacturers should observe such differences between the states carefully.

In relation to modular homes, as mentioned in a previous section, a modular home-specific building code does not exist yet.

ICC Standards on Modular Homes

The ICC and the Modular Building Institute have been recently working on standards specifically for modular homes. The following are examples:

a. ICC/MBI Standard 1200 – Standard for Off-Site Construction: Planning, Design, Fabrication, and Assembly

b. ICC/MBI 1205 – Standard for Off-Site Construction: Inspection and Regulatory Compliance

The two organizations are said to be coming up with one more modular home-related standard:

a. ICC/MBI Standard 1210: Standard for Mechanical, Electrical, Plumbing Systems, Energy Efficiency and Water Conservation in Off-site Construction

The purpose of the above standards is to provide minimum safety requirements and to address the challenges relating to the inspection and regulatory compliance of off-site construction works.

However, these standards are relatively new as they were just published last year, September 2021; and most states have not adopted them. Thus, importers and manufacturers opting for the modular home regulatory route may have to look to the IBC or IRC adopted state regulations (keeping in mind that some states have wholly adopted IBC and IRC, and some have adopted them with amendments).

International Building Code (IBC)

Two decades ago, the Uniform Building Code was one such set of codes that many states adopted to create local building standards. The UBC was published by the International Conference of Building Officials.

However, the ICBO was not the only organization setting standards and codes. The Building Officials and Code Administrators International (BOCA) published the BOCA National Building Code, and the Southern Building Code Congress International (SBCCI) had the Standard Building Code.

Currently, they have all merged to form the ICC. The ICC replaced the UBC with its own publication, the IBC. IBC’s aim is to ensure that the construction work is safe for occupants.

It is important to note that there are different versions of the code. For the purposes of this section, the 2018 version of the IBC will be referenced to explain the basics of the code.

Here are some of the States and their corresponding state legislations that have adopted the IBC 2018:

• Illinois – Building Code 2018 of Illinois
• Minnesota – 2020 Minnesota Building Code (with amendments)
• Mississippi – Building Code 2018 of Mississippi
• New York State – 2020 Building Code of New York State (with amendments)
• Portland – 2019 Oregon Structural Specialty Code (OSSC)

Product scope

With regards to the 2018 version, the IBC applies to most buildings, structures, or their connecting or attached appurtenances. The only exception being that if a building or structure falls under the scope of the IRC (explained in the subsequent section), the manufacturer must comply with it.

Examples of construction products that would fall under the ambit of this model code include:

• Commercial buildings
• Detached three-family dwellings
• Townhouses exceeding three stories above grade plane in height

Standards

The IBC may reference other codes and standards from other organizations to satisfy its safety requirements. However, the provisions of the IBC take precedence over other referenced codes and standards; and where conflicts exist, the IBC provisions apply. Referenced items are treated as part of the IBC.

Examples of IBC standards and reference standards and codes include:

a. IBC 803.15 – Application of interior finish materials to fire-resistance-rated or noncombustible building elements

b. IBC 1202.2.1 Ventilated attics and rafter spaces

c. ANSI A13.1 (referenced) – Scheme for the Identification of Piping Systems

d. BHMA A 156.19 (referenced) – Standard for Power Assist and Low Energy Power Operated Doors

e. ASTM C406/C406M (referenced) – Specification for Roofing Slate

Requirements

The requirements under this model code generally include:

a. Making an application to the building official from the Department of Building Safety (DOBS) and acquiring the required permit(s) before commencing on the construction project. The permit should be placed on the work site until the completion of the construction project

b. Each application in a. should be accompanied by the construction documents and other information as per Section 107. The construction documents will contain information about the construction project and present detailed information about how it will comply with the relevant parts of the IBC and the relevant legislations and regulations

c. The construction documents in b. should be accompanied by the manufacturer’s installation instructions

d. Ensure that the construction site is available for required inspections, and in each successive inspection approval is obtained from the building official

e. Submitting lab test reports to the building official when required

When the building official determines post-inspection that the construction work is compliant with the relevant legislation, codes, and standards, the building official should issue a certificate of occupancy to enable the construction project to be used.

International Residential Code (IRC)

Another model code published by the ICC that may be complied with is the IRC. Before proceeding with the applicable regulations, it is important to ensure that your project is within the code’s scope.

Again, there are different versions of the code. For the purposes of this section, the 2018 version of the IRC will be referenced to explain the basics of the code.

Here are some of the States and their corresponding state legislations that have adopted the IRC 2018:

• Kansas – Residential Code 2018 of Kansas
• Minnesota – 2020 Minnesota Residential Code (with amendments)
• Mississippi – Residential Code 2018 of Mississippi (with amendments)
• New York State – 2020 Residential Code of New York State (with amendments)
• Portland – 2021 Oregon Residential Specialty Code (ORSC)

Product scope

Referencing the 2018 version, the model code applies to most construction products that are:

“[D]etached one-and-two family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress and their accessory structures not more than three stories above grade plane in height.”

Examples of construction products include:

• One family dwelling homes
• Two family dwelling homes
• Accessory structures
• Townhouses not more than three stories above grade plane in height with a separate means of egress

Additionally, it regulates the inclusion of other components in residential properties like:

• Structural components
• Fireplaces and chimneys
• Thermal insulation
• Mechanical systems
• Fuel gas systems
• Plumbing systems
• Electrical systems

Standards

The IRC may reference other codes and standards from other organizations to satisfy its safety requirements. However, the provisions of the IRC take precedence over other referenced codes and standards; and where conflicts exist, the IRC provisions apply. Referenced items are treated as part of the IRC.

Examples of IRC standards and referenced standards and codes include:

a. IRC R403.1.3.1 – Concrete stem walls with concrete footings

b. IRC R702.3.6 Horizontal gypsum board diaphragm ceilings

c. IRC R1001.5.1 – Steel fireplace units

d. ANSI A108.1A-16 (referenced) – Installation of Ceramic Tile in the Wet-set Method, with Portland Cement Mortar

e. APA E30-15 (referenced) – Engineered Wood Construction Guide

f. DASMA 105 (referenced) – Test Method for Thermal Transmittance and Air Infiltration of Garage Doors and Rolling Doors

g. ASTM C1167-11(referenced) – Specification for Clay Roof Tiles

h. ANSI/AWC PWF (referenced) – Permanent Wood Foundation Design Specification

Requirements

The requirements under this model code generally include:

a. Making an application to the building official from DOBS and acquiring the required permit(s) before commencing the construction project. The permit should be placed on the work site until the completion of the construction project

b. Each application in a. should be accompanied by the construction documents and other information as per Section R106.1. The construction documents will contain information about the construction project and present detailed information about how it will comply with the relevant parts of the IRC and the relevant legislations and regulations

c. Making available the manufacturer’s installation instructions on the work site for inspection

d. Ensure that the construction site is available for required inspections, and in each successive inspection approval is obtained from the building official

d. Submitting lab test reports to the building official when required

When the building official determines post-inspection that the construction work is compliant with the relevant legislation, codes, and standards, the building official should issue a certificate of occupancy to enable the construction project to be used.