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Definition of: Modular Construction, Mobile Homes, Campers, Double-Wides, Panelized Construction
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Modular Construction, mobile homes, trailers, campers, doublewides, panelized construction - what are the differences and how are these structures recognized? This article describes the history and characteristics of these different types of factory-built structures. This set of definitions and identifying characteristics of these homes and construction methods is a supplement to my more detailed paper, Mobile Home Inspections. Use the links at page left to navigate this document or to go to Other Resources. The Green links at left show where you are in our document & website. © Copyright 2008 Daniel Friedman, New York State License # 16000005303 All Rights Reserved. Information Accuracy & Bias Pledge is at below-left.

Definitions: What is a Mobile Home, Trailer, Doublewide, Modular Home, Factory-Built Home, Panelized-Construction-Built Home?

The following is the opinion of the author and has not had a technical review by other industry experts. Various trailer, mobile home, and modular housing manufacturers may disagree with some of these views. Corrections and content suggestions are welcome.

Characteristics of Trailers as Living Space

Trailer traditionally describes a usually small, wheeled, home with a history and image of flimsy construction such as wooden 1x3 wall framing clad with aluminum siding, virtually no insulation, and low quality leaky windows. "Trailers" up until the 1970's (my estimate) included both campers which really were intended to be towed by a car or truck and moved often from site to site (though some were left parked for decades at campgrounds), and also lightweight factory-made homes which were intended to be towed once to a home site and then kept there. The little blue structure used as an addition to the left of the small house in the photo at the top of this page was undoubtedly a small camper.

No one building "trailers" calls them that any longer because of the "flimsy" image. The closest thing to a "trailer" in current products on the market are motor homes and campers. The least-costly campers (such as my pickup truck "slide-on camper") built after 2000 are probably considerably better constructed than the "trailers" of old. In current language (2006), a "trailer" is either a "mobile home" that is more than 20 years old (see below), or it is a camper designed to be moved easily and often from site to site. (Or in different usage, a "utility trailer" is a utility vehicle intended to haul goods or large items and designed to be fastened to the back of a car or truck, and a "tractor trailer" is of course a larger (typically 40 ft long) hauling system for moving goods by highway from city to city.)

Trailers may have had their wheels left on, but normally they'd be set on a masonry pier foundation and a skirt installed around to hide the under-trailer area.

Characteristics of Mobile Homes as Living Space

In the past few decades (to 2006), "trailer" manufacturers have considerably improved the quality of construction of such homes. The national manufacturing and building code standards for these structures have also been improved. Perhaps in part to escape the less than wholesome image of "trailer", manufacturers use the term "mobile home" to describe what is usually larger and better made home than "trailers" of old, though perhaps with similar materials.

Mobile homes are built in a factory and are designed to be moved (once and uncommonly, perhaps once again) on its own wheels attached to its own frame to a site where a foundation is prepared and connections to utilities are made. In the U.S., states have regulations about the siting, foundation, steps and entry, wiring, plumbing, tie-downs for wind and storm safety that apply to these homes. Some examples of mobile home regulations for New York State are this website. Individual state regulations will vary - you'll want to see what your state requires. Even within states regulations vary as wind and weather conditions do also.

Examples of mobile home improvements include stronger overall wall and roof construction, less leaky roof covering, and windows that are less notoriously leaky. In addition newer mobile homes have, for fire safety, bedroom windows that can be pushed out to a wide opening for emergency exit in case of fire - an important safety improvement. Usually building departments grandfather in older structures, but sometimes they will insist that certain life-safety improvements be made, for example if an older mobile home is being brought to a new site in a new community. If this is the case one or two windows may need to be replaced to provide this important safety improvement.

When there is a severe storm or hurricane, mobile home communities are among the worst damaged as a strong wind can completely turn over or demolish mobile homes. For this reason, mobile homes set up in high wind-risk zones have extra requirements for tie-downs to secure the building against upset during a storm.

Mobile homes may arrive on wheels but they will be jacked enough to be set on some type of approved building foundation, such as masonry piers or a masonry foundation.

In case these terms are not confusing enough, some mobile home makers like to call these "factory built homes". But that use of "factory-built homes" is confusing too since modular homes are also "factory built" but are quite different from trailers or mobile homes.

Characteristics of a "Doublewide" Mobile Home or Trailer

Some manufacturers provide mobile homes constructed to be joined together, side by side to form a double-width living unit. While a double-wide mobile home is basically constructed by the same materials and methods just described above, the tie-down and connection requirements for these living units may be different in some jurisdictions, since their risk of being blown away in high winds is different. Other installation and support requirements, such as connection of the two units and placement of foundation support will also have to accommodate this variation.

Characteristics of Modular Homes or Modular Housing

Modular homes, too, enjoyed a less than stellar reputation several decades ago, having the reputation of flimsy construction. That is certainly no longer the case. A modular home is constructed in a factory of one or more sections which are carried to the building site on a trailer and lifted by a crane to be set upon a foundation which has been prepared ahead of time. Modular homes can be quite large, involving four or quite a few more individual sections which are lifted and "set" into place at the site. Some manufacturers provide custom architectural services and can deliver unique, but factory-built homes in sections. Contemporary modular construction of homes have these attributes:

• The home is built indoors in a factory under controlled conditions, usually resulting in straight and square construction of walls, ceilings, roofs, and floors.
• Exterior wall sheathing and roof sheathing are glued as well as nailed to the surfaces of their respective studs or rafters. Interior sub flooring and drywall on walls and ceilings are also glued as well as nailed or screwed to their joists or studs. Some models by some manufacturers also install a double layer of interior drywall. These methods result in a very stiff and strong construction.
• The home is probably built to meet the building code requirements of all U.S. states, or at least all of the states within a manufacturer's shipping area. You'll find an identifying label for the home with this information, often on a kitchen sink cabinet wall.
• The home is built strong enough to be lifted at the factory by crane for setting atop a steel trailer for transport, then driven at 65 MPH down a highway, pushed or dragged on its trailer over an often hilly and rough construction site, and lifted again by crane for final "set" atop its foundation. Without falling apart. (Try this with a stick-built house.) At the Contempri factory in Pennsylvania on a modular home construction tour about a decade ago, suddenly all of the workers and managers dropped their tools, ran to their cars, and drove madly out of the factory parking lot. We followed to see what was happening. One of their modular sections was being towed on U.S. interstate I84 when the trailer disconnected from the towing tractor. The tractor drove ahead. The trailer ran off the highway at 65 MPH. The trailer ran head on into the end of a steel guard rail. The trailer stopped. The modular home section kept going, and impaled itself centered atop the guard rail. When we got to the accident, there was no debris anywhere except where the guardrail had punched out of the rear wall of the modular home section. You could look in windows into the kitchen where the cabinets and appliances were perfectly in place.
• When the modular home is transported to its site, it is moved by being lifted and set onto an independent steel frame which has its own independent wheels. At the destination the modular home or home section is lifted by crane and set onto an independent foundation, and the steel frame/wheel set returns to the factory for re-use.
• A modular home is normally set on a foundation which has already been placed at the building site.
• If the modular home is placed over a basement or if there is to be an attached or detached garage, often that construction is performed by a local building contractor rather than by the modular home manufacturer (sometimes resulting in different quality of workmanship).
• A modular home can be difficult to recognize once its construction has been completed. However these clues will work every time:
  • In the basement, if the ceiling is not fully enclosed, look at the main girder. Since most modular homes use at least two long sections that have to be built and transported to the site, there will be at least two completely independent floor framing systems, and at their mating point over the basement center, you'll see an unusually wide built-up girder with (if properly installed) through bolts connecting the two building sections.
  • In the living area, if the building is a two-storey unit, as you walk up the stairs from first to second level, notice that there are a few more steps than usual between floors? Since each of the four stacked sections in a four-section two-story modular home has been framed with a complete floor, wall, and ceiling structure, the "ceiling" between the first and second floors will be double the normal depth since it is comprised of both the first floor section ceiling framing and the second floor section floor framing. So if 2x10 joists were used, there will be about 20" of ceiling thickness between floor (a great place to run wires and ducts).
  • In the attic is the fail-safe way to always identify a modular-built home unless there is simply no attic access or all surfaces are covered. You'll find one, possibly two or even three features unique to modular home construction:
    (1) there will be a mating joint of the front and rear sections of the home visible as two girders in the attic floor, running along the long dimension of the building, usually with a small gap between them, hopefully with insulation or other fire blocking stuffed into the gap. The reason for the gap is that properly placed, the sections are set with their bottom girders touching tightly, which may leave the top sections slightly separated at their highest point.
    (2) there may be hinged roof rafters. Many modular homes have roof slopes which would be much too high for the upper roof-bearing sections to travel up the highway. They travel with the roof laid flat atop the upper floor module. The roof rafters are hinged, roughly 18-24" from the eaves of the home, and are lifted up at the site, then supported by an attic knee wall. So you'll see two knee walls, one supporting the front and one the back roof section. You may see the hinges on the rafters down near the eaves as well.
    (3) One modular home I inspected had fallen off of its trailer while being lifted by the crane. It rolled over on its face. Like the unit which had impaled itself on the guard rail, there was little damage other than broken windows. But there was a slight crease in all of the roof shingles about 24" up from the eaves. The rafter hinges had all been slightly bent when the section toppled. Outside, even on a modular section which has not fallen, you may see this telltale line of slight shingle anomaly, parallel to the eaves.

Characteristics of Panelized Construction

Panelized construction makes use of wall, floor, ceiling or roof "panels" which have been framed off-site and brought to the site by truck. Panels are lifted into place by crane and fastened together on a foundation, and possibly a framed-in floor which have been prepared before the panels arrive.

Some framing panels make use of special materials, such as plywood and foam roof panels for insulated cathedral ceilings.

More Reading

Information Sources for Mobile Home Inspection, Codes, Products, Manufacturers, Standards & More Information on Building Diagnostic Inspections and Repairs

"Modular Home Construction, special defects and inspection methods" Dan Friedman, NY Metro ASHI Seminar, Holiday Inn, Crowne Plaza, White Plains NY, October 4, 1996

Mobile Home Inspections

Trailer vs Mobile Home vs Modular vs Panelized Construction an explanation of terms and how to identify these structures.

New York State: "Manufactured Homes: an installation guide for the code enforcement official," undated. [Div. of Code Enforcement & Admin. - 518-474-4073, George E. Clark, Jr., Director] - this is a guide tool, not an enforcement code or standard.

HUD State Administrative Agency (for 36 states) (NY: 518-474-4073) - for complaints

Manufactured Housing Institute, 2101 Wilson Blvd. Ste. 610, Arlington VA 22201 703-558-0400 >www.mfghome.org

NYMHA, 35 Commerce Ave., Albany NY 12206-2015 518-435-9859 800-721-HOME (they want the Star Program to provide for separate assessment of manufactured homes)

Consumer Reports: www.consumerreports.org - special report 2/98

Mobile Home Inspection Checklist, Florida, Town of Lady Lake Building Department

InspectAPedia ^TM Home & Site Map - Building Inspection, Diagnosis, & Repair, Environmental Inspection & Testing - Research Website

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Home Inspection Construction Consulting Services & advice for home buyers

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Contact Daniel Friedman for website content suggestions or for fee-paid consulting

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