What is a "Manufactured" Home?
Manufactured homes are pre-built in a factory and then moved to their final location. This differs from conventional home construction, where materials are assembled on-site to create a finished building. There are two categories: Mobile Homes and Prefab Homes. In this post we will discuss Mobile Homes, which have their own building code. Prefab homes follow the BC Building Code and have a different certification standard.
Mobile Homes
1950-1971: Early Days
Mobile homes first appear in the 1950s in the USA. They are designed to provide cheap mobile housing as the post-WWII population grew. The first mobile homes are small enough to be pulled behind a consumer vehicle, which is where the nickname "trailer" comes from. They are more like RVs than houses. They are generally built in compliance with the American Mobile Home Standards, and in Canada, they are governed by the Mobile Home Act. They are at most 12' wide, and under 600 square feet.
1972-1976: Growing Pains
In 1972, the CSA Z240-MH standard becomes available. This is a standalone building code specifically for mobile homes. Since the standard is not yet mandatory, construction standards of homes from this era varies greatly. The 14' wide standard is introduced, increasing the average size to around 950 square feet.
1977-1992: Standardization and Evolution
In 1977, the CSA Z240-MH standard becomes mandatory. All new mobile homes are built to this standard. In 1978, the Mobile Home Act is updated and changed to the Manufactured Home Act to reflect the changing market. Every several years CSA Z240-MH is updated, steadily increasing build quality and energy efficiency. Homes increase steadily in size to16' wide and around 1250 square feet.
1993-Present: Not Exactly Mobile
Around 1993, CSA Z240-MH standards become aligned with the standards of the BC Building Code. Homes built after 1993 are, in many ways, identical in construction to conventional homes, with a few important exceptions. The industry drops the term "mobile" in favor of "manufactured". The homes require heavy equipment and special permits to transport. Homes are now up to 20' wide and 1500 square feet.
How Are Mobile Homes Different?
The first thing you need to know about a mobile home: it is not a regular house.
No Foundation
The CSA Z240-MH standard does not require a conventional foundation. Homes can be placed on piers constructed from wood cribbing, masonry blocks, or poured concrete. Since they are not attached to a permanent foundation they are often required to be anchored to the ground in case of high winds.
Lightweight Construction (Older Models)
Since the homes were originally intended to be mobile, they were built with weight savings in mind. On older homes, exterior walls were often 2x3 instead of 2x4. Exterior walls and roofs often did not have plywood sheathing, they used a thin aluminum skin instead. Interior walls had thin pressboard panels instead of drywall. This meant that mobile homes were often significantly weaker than conventional homes. This is the main reason why so many older mobile homes in BC have a "snow shed" roof constructed over top of them: they were simply not designed for the local snow load.
An Engineered System
Mobile homes are designed and engineered for their required loads (like people, furniture, snow, and wind) as a self-contained system. Since emphasis is put on weight savings, the bare minimum of materials is typically used to achieve these values. Mobile home layouts cannot be changed or customized when they are purchased from the factory (even with most new homes), since doing so would require the updated plans to be re-approved by an engineer, adding time, hassle, and cost. For this reason, mobile homes cannot be altered or added onto without the proper permits and engineering.
Common Problems
Because of the strict rules around mobile homes, people (including contractors) often get themselves into trouble when doing home improvements. Here are some of the most common problems that we come across:
Roof-Over
Remember what we said about local snow load? A lot of people try to beef up their roof assembly by adding trusses, or building a steeper roof. This is allowed only if the new roof assembly is self-supporting, it cannot be held up by the home. If you thought the snow load was heavy, imagine that PLUS a few thousand pounds of trusses, plywood, and shingles, all held up by a structure that was designed to be as light as possible, rather than as strong as possible.
Additions, Decks, and Carports
Because these homes are not designed to support any additional weight, any additions, decks, or carports cannot be attached to the house. They must be self supporting, and totally independent of the home.
Crawlspaces
The bottom of mobile homes is covered with a black tarp-like product called a belly wrap. This acts as an air and moisture barrier, and protects the floor insulation. When the house is installed on site, this wrap is often cut open to provide access to hook up the plumbing. If insulation is not reinstalled and the belly wrap is not carefully repaired once the work is complete, there can be large gaps. Gaps can cause air leakage, condensation and rot, heat loss, and access for rodents.
Interior Renovations
While it may be tempting to remove a wall, rearrange the layout, or move the bathroom, doing so can compromise the structure. Remember, mobile homes are an engineered system, and any change to the layout needs to be approved by an engineer or local building authority. The BC Government website states that "(a mobile home) must not be compromised from its original specifications without proper permits to do so".
Drywall and Siding
The most common cosmetic change, that can cause big issues, is adding drywall or new siding. Many mobile homes use lightweight pressboard panels, or 1/4" drywall instead of standard 1/2" drywall, and thin aluminum or vinyl siding to save weight. Adding heavier siding, like Hardie-Plank, on a single wide mobile home could add upwards of 5,000 lbs, which is likely well beyond the design specifications.
Just adding standard 1/2" drywall to the interior of a typical single-wide mobile home, would add over 3,500 lbs.
Why Weight Matters
You may have noticed a theme here: you can't add any extra weight. Why not? We discussed how older homes were built to a lower standard. What about newer homes that are more similar to conventional houses?
The weight a mobile home can support depends entirely upon the original design specifications. Since each model is designed and engineered individually, there is no 'one-size-fits-all' approach to determining how much weight is OK.
Conventional homes have a concrete foundation that supports the exterior walls, floor, and roof, but mobile homes do not. They are built on a steel frame consisting of two beams that run the length of the home. These beams are designed to sit on the truck bed while in transit, and then support the weight of the home once it is installed. Because homes are wider than flatbed trucks, the frame is narrower than the home. This means that the frame is not able to directly support the load of the roof and walls.
Specification Sheets
All mobile homes are fitted with a specification sheet when they are manufactured. This is most often located on the inside the kitchen cupboard above the stove (sometimes they are by the electrical panel). The sheet will provide information on the home including framing size, insulation values, and design snow load.
Buying, Selling, and Transporting
There are a few extra steps to consider with mobile homes.
Certification Labels
When a home leaves a factory, it is given a CSA label. This indicates that it passed inspection at the facility where it was built. In order to list a manufactured home for sale in BC, there must be an intact CSA label for the electrical system. If any additional electrical work has been done, there must be a new inspection performed. This is typically done by Technical Safety BC, and the inspector can issue a "Silver Label" showing that the changes have been approved.
Transporting a Mobile Home
Most mobile homes are placed on a site and never moved again. However, it is possible to purchase one and move it to a different location. In order to do this, you must fill out an Application to Transport a Manufactured Home through the BC Government.
Buyer beware: some municipalities do not accept mobile homes older than a certain year of manufacture.
Always check with the appropriate regional authority before you try to move a home!
Prefab Homes
Around 1980 a separate standard, called CSA-A277 was created. This standard is not a standalone building code; it is a standard used to certify factories that are building in compliance with the National Building Code. Homes built in a factory to the National Building Code are considered prefabricated, or "Prefab". They are typically designed to be placed on a permanent foundation. Sometimes they look like mobile homes, and consist of only one or two sections. Others consist of many sections, or modules, and are commonly referred to as "Modular" homes. Modular homes often look just like conventional homes.
What Does it Mean For Me?
Mobile homes can be a great housing option for many buyers, but it's important to know what you're getting, and what the limitations are. We encourage anyone looking at a mobile home to get an inspection, which will help identify any changes or renovations, as well as any defects in harder-to-reach areas such as the crawlspace.
Key Points
Mobile homes have their own building code.
Older mobile homes were built to a much lower standard, newer ones are more similar to conventional houses.
They cannot be added onto or modified without proper permits.
There are special rules regarding buying and selling them in BC.
If a mobile home you are looking at buying looks like it was modified in any way, start asking questions.
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