A Photo Guide to Modular Home Construction Identification & Inspection
MODULAR HOME CONSTRUCTION - CONTENTS: Definition and description of modular construction - how can we identify a factory-built modular home?Definitions and description of modular construction & factory built homes. Examples of how a modular home set crew operates on site. What modular home components are built on site: foundations, garages, decks, etc. What building codes regulate the construction of modular homes. What is the difference between a mobile home, a manufactured home, a modular home, and panelized construction?
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Guide to modular home construction, inspection, troubleshooting, diagnosis, repair: how are modular homes recognized? How is a modular home built, brought to a homesite, and assembled? What portions of a modular home were not made in a factory? What is the quality of modular homes? What are their features, common defects, problems, solutions.
This series of articles describes the history and
characteristics of these different types of factory-built structures. Our page top photo shows a four-section modular home after the set-crew has finished placing the four individual sections of the building and the roof has been lifted and enclosed.
Modular homes, earlier in their conception, 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 (photo above left) and lifted by a crane to be set upon a foundation which has been prepared ahead of time (photo above right).
can be quite large, involving four or quite a few more individual sections which are lifted and "set" into place
at the site (photo at left)
Contemporary modular construction of homes have these attributes:
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
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).
How to Identify a Modular or factory built home after construction has been completed
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 (photos above). 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.
The modular home basement girder members should be touching. IF you see a gap at the center of this structure the building sections may not have been properly set on the foundation. Conversely, if there is to be any gap it should be at the top of the modular sections (visible in the attic, for example) - which assures that the bottom mating members are tight.
In the living area, if the building is a two-story 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 kitchen look under the kitchen sink base cabinet for the modular home manufacturers' labels (these labels may also be placed in a basement or by an electrical panel or at other locations) (Photos above).
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:
There may be hinged roof rafters (Photo at above left and sketch, below). Many modular homes have roof slopes which would be much too high
for the upper roof-bearing sections to travel up the highway.
Modular home uppermost sections that will include a roof 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.
As the dimensions of a sloped roof will cover more area than the flat top section of the building, the roof of a modular or factory built home will often include an additional section that must be set in place, usually near the ridge (photo at above right) - you will see this separately framed structure in the attic of these homes.
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.
There will also be a mating joint at the ridge where instead of a single ridge board you may see up to four horizontal "ridge boards" - the roof sections need to be framed as stable sections that can be lifted into place. (Photo at left).
Just how Strong are Factory Built Homes? Stronger than Stick Built Wood Framed Houses?
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.
Factory built homes are constructed so that each section can withstand being lifted onto a trailer, driven up the highway at 65 mph, pushed or pulled over an uneven, often sloped site, lifted into the air by the site crane, and set into place on the foundation.
Often factory built homes combine glue as well as conventional framing fasteners, extensive use of truss joists, girders, and additional framing of individual building sections so that each can be manipulated into place.
Question: Double-wide mobile home with no insulation?
Do these come pre trimmed in the inside? Or do I have to pull them off and insulate underneath them? Im renting and its costing me 600 a month to heat. I don't think the renters insulated it at all. I pull a piece of trim from around the slider door and no insulation there. The pipes, no caulk or anything. I can throw a penny down to the ground from the bath pipes. It is a double wide. The house has a gap in the floor where it looks like the house is coming apart. I can stick a long needle rite threw it to the ground. - Kevin 8/13/12
Do Double wide Mobile come pre trimmed to the sellers in the inside? Or do the businesses that sell them have to have to pull them off and insulate underneath them? I'm renting a 2004 and its costing me $500-$600 a month to heat. I don't think the renters insulated it at all. I pulled a piece of trim from around the slider door and no insulation there. I put my hand underneath the cement foundation and the floor. No insulation there as well.
The heat comes out semi cold. It only has a 56000 BTU heater and is new. But.. This seems low for a 40X60 or 40X70 Im not sure which one this is. But it runs for house trying to get the house warm. The dishwasher water freezes in the inside of it during the winter. I tried pulling it out to see why. But its hooked in. Cold air rushes from the light sockets to where it blows a lighter out. I came from a 3 story victory. So I know little about pre-manufactured homes. The pipes, no caulk or anything. I can throw a penny down to the ground from the bath pipes. I have caulked around it now.
The house has now formed a gap in the floor where it looks like the house is coming apart. I can stick a long needle rite threw the carpet it to the ground. Is the house just settling? Also the electric is $300-to $400 a month. The light bulbs flash like a strobe light all the time. They had a 12,000 volt cow fence hooked and water for their 50 head of cows in when we got here. After paying for that (unknowingly) for 6-8 months I realized that it was hooked in.
When I turn off the electric to the house. The fence and water would turned off. So they put in a separate pole. But the lights still flicker and the fuse box blows fuses all the time (for no reason) like if I have the washer on. I have two small girls. The renters say this is all normal. - Computer Geekz - 8/13/12
In order to sort out the question of what are common construction practices and what is usually included or not with a manufactured home, we first need to get a couple of confusing terms straightened out.
You have posted a question about double-wide mobile home construction here in an article on modular construction
(MODULAR HOME CONSTRUCTION) .
There in the Mobile Homes FAQs section we include your original question along with detailed answers.
Question: What building codes regulate the construction of modular homes
Does a modular home or factory built home made in another state or province have to meet local state, provincial or other building codes?
A modular home is built using conventional 2x4 or 2x6 wood framing much like a stick built house, but it is constructed in several sections that are then trailered to a building site, set upon a conventional building foundation or slab, and fastened together there. The floor of each section is built strong enough to be placed on a temporary trailer for transport to the building site where the trailer chassis is removed prior to assembly of each section.
Building codes and standards for modulars are essentially the same as for a stick-built residential home. Even when the modular home is built in a different state from which it is to be assembled, the home must comply with state building codes.
In fact because modular home manufacturers want to be able to ship their models to multiple states or provinces, often the units are constructed to meet the most stringent code requirements of the various states/provinces served - a condition that means a modular home might exceed local building code requirements.
Question: modular home roof ventilation plus plumbing not vented outside SNAFU leads to mold contamination
9/12/2014 Dan said:
We bought a used 1995 modular home in 2005 that consists of one middle pod (10 ft ceilings) and two side pods (8 foot ceilings). The roofline is 4/12 pitch. When you enter the attic space up to the middle pod (which is overlaid with metal sheeting) you can see all the way to the other end. However, in order to get from the middle pod to the side pods, you have to crawl through a small opening that was cut out by one of the workers. Everywhere else there is a wall of plywood that separates the lower section (side pods) from the upper (middle pod). I did not think much of it until we found out that the lower sections now have mold growing on the underside of the plywood for the roof. A mold inspector told us that this plywood was preventing air from circulating. In short, he said that the eave vents have no way of circulating air with the middle pod's roof vents. My question: What is the purpose of the plywood? Should it have been removed?
During this discovery, we found out that a sewer vent, and two other air vents were never vented out through the roof. In other words, the vents were exhausting warm air into the attic. The mold inspector commented that the combination of these two failures brought on the mold which is now making my family sick. 2nd question: What can I do about this huge problem we now face?
What a mess. Under a 4/12 roof the accessible area under the lower slopes is very limited - too limited to think about adequate cleaning & insulation replacement from inside the attic space.
That leaves two approaches: tear off all of the roof, remove all insulation, clean and seal all surfaces, re-insulate, re-roof,
Tear down ceilings indoors and do the same job from inside.
The second approach is more disruptive to the occupied interior and increases the risk of cross contamination and thus the need for still more indoor HEPA vacuum cleaning and wiping.
Normally I oppose heroic, expensive roof tearoffs to address attic mold as not being justified. But I would not want to leave a large problematic mold reservoir in a building: indeed air movement can move "backwards" down into a structure in some conditions.
I would first do some careful sampling of the molds present: on plywood, in insulation (by vacuum testing) and on the attic side of ceiling drywall. If none of the molds found are highly mobile - highly harmful (e.g. if it's just some simple Cladosporium) I might do nothing except fix the venting. Otherwise, I'd consider the remediation I outlined above.
The plywood was doubtless in place to enclose and protect the structure during transport.
Leaving it in place indeed blocks the proper roof ventilation.
Failure to vent plumbing vents to outdoors is a site set-crew SNAFU which is another example of why modular companies often want their own crews to set the house. Modulars encourage construction by builders who don't know enough about building.
Tell me the state where you are located and the brand and model of your home and I can research this further.
Kudos to your home inspector.
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 Section 184 Indian Home Loan Guarantee Program, U.S. Department of Housing & Urban Development, web search 1/5/2012, original source: portal.hud.gov/hudportal/HUD?src=/program_offices/public_indian_housing/ih/homeownership/184 - Quoting:
The Section 184 Indian Home Loan Guarantee Program is a home mortgage specifically designed for American Indian and Alaska Native families, Alaska Villages, Tribes, or Tribally Designated Housing Entities. Section 184 loans can be used, both on and off native lands, for new construction, rehabilitation, purchase of an existing home, or refinance.
Also see Freddie Mac & Fannie Mae
 Native American Housing Loan Guarantee Program HUD Section 184 Loans At A Glance, FannieMae, web search 1/5/12, original source: efanniemae.com/sf/mortgageproducts/pdf/section184aag.pdf
 "Modular Home Construction, special defects and inspection methods" Dan Friedman, NY Metro ASHI Seminar, Holiday Inn, Crowne Plaza, White Plains NY, October 4, 1996
 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
 Thanks to home inspector Peter Bennett for eagle-eye editing assistance regarding spelling at this web article series. Little Silver, NJ 07739 Office 732-758-9887 Fax 732-758-8993 Cell 732-245-9817 email@example.com
 Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative. - Entry on Mobile Homes, original source: http://en.wikipedia.org/wiki/Mobile_home#Regulation, retrieved 8/14/2012
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328
This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.