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Construction Terms

Building Codes: Local and State

As opposed to the federally-mandated HUD Code, which is preemptive of local codes and creates uniformity of manufactured home construction across state lines. Manufactured homes installation and foundation systems are typically subject to state or local building codes.

Certificate of Occupancy (CO)

This is a document issued by the local or state building department inspector certifying that the manufactured home has been installed, the home is certified for occupancy, and the  conditions of the permit application have been fulfilled. In some states, the signed off permit is considered approval to occupy.

Consumer Complaints

HUD has entered into cooperative agreements with 38 state governments to respond to consumer complaints about the performance of manufactured homes. These state governments each designate a State Administrative Agency (SAA). If you have any complaints about the performance of your manufactured home that have not been resolved by the retailer or manufacturer, you should first contact the SAA in the state where you live.

Crawl Space

This is the area between the floor of the manufactured home and the ground. This area is enclosed by perimeter blocking or skirting. Foundation piers or blocks supporting the steel beams of the home are positioned per the manufacturer’s instruction manual. This area is not habitable.


Customer requested changes to existing manufacturer-approved floor plans.

Delivery and Installation

The transport of the home from the retailer or manufacturer location to the site and subsequent setup. See “Set-up” below.

DAPIA (Design Approval Primary Inspection Agency)

These are third-party independent agencies that approve manufactured home engineering and designs for compliance with the Federal Manufactured Home Construction and Safety Standards.

Engineer's Certification

A letter issued by a structural engineer certifying the acceptability of a foundation system, generally to meet the requirements of the HUD publication, Permanent Foundation Guide For Manufactured Homes. In the case of FHA loans, an engineer is usually required to certify the foundation.

Expansive Soils

Soils that change volume significantly as their moisture content changes.


The manufacturer that constructs the home in accordance with HUD Code and under HUD inspections. In other words, the builder.

Factory-Built Home

A dwelling unit fabricated in an off-site manufacturing facility to be installed at a building site. A modular home is considered factory-built, but unlike a manufactured home it is not built to the national preemptive HUD Code. Factory-built homes are constructed to comply with the local prescribed building codes.


The Federal Housing Administration within the U.S. Department of Housing and Urban Development.


A term referring to the individual sections of a home. For example, a double wide is two floors, a triple wide is three floors, etc.


The term “foundation” means all components of the support and anchoring systems, such as: piers, footings, slabs, walls, ties, anchoring equipment, and any other material that supports a home and secures it to the ground. The steel frame and chassis itself affords the manufactured home a solid foundation that supports the home during transport from factory to site. A permanent foundation is required by lenders and state building agencies to allow the manufactured home to be considered and taxed as real estate.

Foundation System

An engineered pre-fabricated assembly of materials designed to resist the effects of external forces once the manufactured home is installed upon it. Engineered foundation systems are required in California to resist the seismic effects of earthquakes.


The finished ground level adjoining the manufactured home at all exterior walls.


The U.S. Department of Housing and Urban Development. The agency of the federal government responsible for national building code enforcement in manufactured housing.

HUD Code

Manufactured homes are built to the Manufactured Home Construction and Safety Standards Act which was passed by the U.S. Congress and became law on June 15th, 1976. The HUD Code is administered by the U.S. Department of Housing and Urban Development. Hud regulates the design and construction of manufactured homes, formerly known as mobile homes, to a specific performance code. This is called a preemptive code because it preempts all local building codes for single family dwellings. The Federal program includes the monitoring of third parties involved in the design review and inspection process, but excludes the actual installation of the homes. Every HUD home has a special label affixed on the exterior of the home, indicating that the home has been designed, constructed, tested, and inspected to comply with the stringent federal standards set forth in the code. No manufactured home may be shipped from the factory unless it complies with the HUD Code and receives a certification label from an independent third party inspector.

HUD Label

This is a 2×4″ aluminum insignia plate that is attached to the lower rear corner of each transportable home section. The fist three alpha characters identify the third party independent inspection agency (IPIA) that inspected the home while it was under construction. A series of 6-7 numbers follow the IPIA. While the numbers are generally sequential on multi-section homes, this is not a requirement. The HUD label is essentially the Social Security Number of the manufactured home and will tell you the manufacturer, the date of manufacturing, and where the home was shipped to. Most lenders will require proof of the Hud Label number.

I-Beam or C-Beam

A steel beam with short flanges and a cross section formed like the letter I or C that traverses the length of the manufactured home. The beams are an integral part of the manufactured home chassis and is the location of where the pier or block support stanchions are placed at time of home installation.

Live Loads

These loads produced by the use and occupancy of the building or other structure and not including construction loads or environmental loads such as wind load, snow load, earthquake load, flood load, or deck load.

Manufactured Home

A home fabricated in a manufacturing facility for installation at the installation site, bearing a label certifying it is constructed in compliance wit the federal Manufactured Home Construction and Safety Standards, making it a HUD home.

Manufacturer's Statement of Origin (MSO)

A document prepared by the factory that is used to create a chain of ownership, which is used to legally create a static-h3 to home when first purchased by a consumer.

Marriage Line

The area where multi-section homes are joined.

Mobile Home

Predecessor of today’s manufactured home. Officially, the name changed following the implementation of the HUD Code requirements in the early 1980s. Many still use the term even though the mobile home of yesteryear bears little resemblance to the manufactured home of today.

Modular Home

Also called prefabricated homes, factory-built homes, or systems-built home. Modular homes do not have axles or frames, which means they are typically transported to their site on flatbed trucks (off-frame). Sometimes the modular home is transported to the site on their own chassis, which is removed upon arrival at the site (on-frame). Modular homes are not subject to the HUD Code, and instead subject to local siting jurisdictions.

Moisture Barrier

A technique for minimizing moisture accumulation under the home by placing a continuous polyethylene sheet of at least 6 mm thickness on the ground below the home. The barrier blocks moisture in the ground from entering the crawl space.


A manufactured home built in individual sections with their own frame and chassis that are joined together during delivery and installation at the site. Also known as a “double wide” (two sections), “triple wide” (three sections), “quad” (four sections), etc. A third section where one section is considerably shorter in length is often referred to as a “double-width with a ‘tag'”. 


Features and amenities offered by a manufacturer at the buyer’s discretion, for comfort, convenience, or ambiance.


An integral part of the chassis support system, the outrigger projects laterally from longitudinal steel frame members. Typically, the outriggers are about 8″ on centers and give strength to support the weight of the perimeter walls.


This is the footer on the ground upon which a pier sets atop. These are designed to spread the load bearing of that pier over a larger area, thereby providing a more stable base. The square pads/footers may be either poured or precast concrete, preservative wood, or other materials approved by the local building authority. The spacing of the piers are typically spaced 5 to 10 ft. apart, depending on the home design, local soil characteristic, and roof snow load. The spacing and load requirements are outlined in the manufacturer’s installation instructions.

Park Model

A park model is 14′ or narrower and 40′ or shorter and less than 400 square feet. Park models are not manufactured homes, nor modular homes, nor trailers. They are a breed of their own.


An instrument for measuring firmness or consistency of soil. The allowable bearing capacity of the soil is a measure of its strength and ability to carry the weight of the pier without settling or compressing. On new manufactured home installations, pads for piers should be set on compacted or undisturbed soil. Organic or loose matter, such as weeds, trash, and other objects must be cleared away. Then the area for the pad is scraped until solid, undisturbed soil is exposed. If this is not done, uneven settlement can occur.


A measure of the ability of the land to absorb water in determining provisions for a sanitation system and drainfield.

Permanently Affixed

With respect to real property, this term is understood to refer to a manufactured home that has been legally attached to the land, thus becoming a fixture.


City or county authorization to install homes, sewage disposal systems, electrical connections, outbuildings, etc.

Personal Property

A manufactured home is considered personal property unless the owner eliminates the home’s static-h3 and permanently affixes it to land owned by the owner of the manufactured home. At that point, it becomes real property.


Stanchions of masonry or steel that provide support between the footing pad and the main steel beams of the manufactured home.  The manufacturer’s installation manual stipulates the number and placement locations depending on size and weight-bearing capacity.

Plot Plan

Detailed scale drawing of the home site, showing the location of the home, outbuildings, and septic systems, as well as set-backs and dimensions. Usually required to obtain home placement permits.

Pit Set, Low Profile, Subterranean Set

Excavating a manufactured home site to allow the homes to have a residential low profile look where the appearance of the home is that it is sitting on a concrete foundation. This type of installation is more common in areas of the country that do not experience significant rain or snow, such as Southern California. A full perimeter foundation and moisture prevention measure are recommended for this type of installation.


Pounds per square foot.


Pounds per square inch.

Real Property

A term usually applied to real estate and homes and other structures that are permanently attached to land.


Homes installed using piers and pads sometimes will “settle” and become un-level after initial leveling at installation, as the weight of furniture and personal items are moved into the home. Often the retailer will return to re-level the home after a sufficient time is allowed for settling to occur. Homes installed on a foundation system and stable soil will not require re-leveling.

Retailer or Dealer

Considered one and the same. A company licensed and bonded with the appropriate local and state authorities, holding an agreement with manufacturer(s) to sell manufactured homes.

Residential Set

Sometimes referred to as pit set or low profile. Requires excavation of the site prior to construction of the foundation.

Rim Joist

The outermost joist around the perimeter of the floor framing.

Septic Design

A plan drawn by a licensed septic contractor and approved by the local health department that shows the type and location of a septic tank and drainfield on a piece of property.


Distances buildings must be located from property lines, as required by code or zoning regulations.


Also called home installation. These are the final stages of the construction of the home which must be completed on site; e.g. joining of sections, completion of roofing, tape and texture surfaces, painting of the exterior trim, carpet installation, leveling of floor and frame, and connecting utilities.

Shear Wall

A general term for walls that are designed and constructed to resist racking from seismic and wind forces with masonry, concrete, cold formed steel, or wood framing.

Single Section

Also known as a “single wide.” Built, delivered, and installed as one complete unit. Depending on individual state requirements, they can be in widths of 14, 16, or 18 feet. Available in multiple lengths with maximums also subject to highway permit restrictions.


The property location or address where the manufactured home is to be installed.

Site Preparations/Improvements

Construction necessary to prepare the site for the home and to complete it after home is set-up. Includes excavation, foundation, garage, well, septic tank, driveways, sidewalks, electrical poles, etc. Varies in each home installation situation.


Materials used to enclose the foundation and crawl space beneath a home. This parameter may be concrete block, pressure treated wood, matching wood siding, or other building products depending on the application needs and zoning codes.

Snow Load Roofs

Manufacturers usually offer a 30# load bearing roof as a standard specification, but upgrades are usually available in 60#, 90# or more per square foot, depending on climate area requirements.

Tag Section

See “multi-section” above.

Tape and Texture

The closing of seams on the interior walls of a manufactured home that has been sheetrocked, and applying material to the sheetrock to give a traditional surface suitable for painting.

Wind Zone Map

In 1994, HUD wind and storm regulations were amended, requiring manufactured home builders to comply with standards in pre-designated storm-susceptible regions of the country, based on the severity of expected winds. The more strict requirements are for homes built to be placed in Wind Zone 3, which includes the Gulf and Atlantic coast area of the country.