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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.
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Definitions: If you are not sure if your home is a mobile home, trailer, double-wide, caravan, or a modular or panelized-built or factory built home, please
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).
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 (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:
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:
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.
Continue reading at PANELIZED CONSTRUCTION or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
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
In a separate article that defines modulars, factory built homes, mobile homes, doublewides,
Double-wides, caravans, trailers and mobile homes are not built using the same structural materials, codes, standards as the modular homes discussed in the article above.
Details about double-wide homes and mobile homes are discussed separately
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,
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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