[ArchitectAnon]

This article is talking about prefabricated single family homes i.e trailers. For environmental reasons you don’t want massive trailer parks because they generate huge transport carbon emissions from intensive vehicle use; cities need denser housing than these can provide. In a trailer park fire safety is achieved by having a space all around each trailer as a fire break. You can’t stack lightweight traileresque pods easily because they don’t contain enough materials with the thermal properties to resist fire spread between apartments because these materials are typically heavy and brittle. The most efficient and cost effective of these materials is drywall which is not well suited to construction where you transport and then lift the finished item into position.

Fully welded sheet steel mineral wool sandwich panels could work but they are a lot more expensive than drywall and need to be carefully designed to avoid corrosion issues from condensation. Lightweight fire resistance can be acheived with intumescent coatings but these are expensive and designed for structural fire protection not for preventing fire spread.

[luckylion]

Might be different in the US, but in Germany a prefab house isn't a trailer, and it's not a movable house either.

You pour a foundation / base plate, and then place concrete wall elements (which are fabricated in the factory and delivered to the site, that's the pre-fabricated part) and connect them to assemble the structure. You then add insulation and do the electrical work, plumbing and dry-wall etc the same way you would for a newly created brick-building, though they'll also pre-fabricate many of these parts or have a few generic alternatives to choose between (e.g. on stairs).

[alistairSH]

In the US, manufactured housing typically refers to homes built to be towed to location fully complete. Sometimes in two halves (double wide). While these homes have an axle, they typically get installed once - they aren’t campers/RVs.

What you describe exists, but is usually called prefab housing.

In the US there are two different sets of building codes that apply. Manufactured housing falls under federal rules. Prefab is all local rules - same as traditional built in place housing.

[luckylion]

Ah, thanks for the explainer! Makes sense that manufactured housing is its own special category then. We do have those, but it's super rare (likely because they'd still need to comply with lots of local regulation, and it becomes more complicated, not less).

[alistairSH]

No problem, it's pretty different that what's typically done in Europe (and I have no idea how standardized that is - though there are definitely lots of home/building shows in the UK where they by prefab from central Europe, etc).

We basically have the following... - RV (camper van and larger bus-based) - true mobile homes, follow a distinct set of federal rules. Generally not allowed permanently anywhere (most parks have a limit on number of weeks/months you can stay), though there are exceptions. Don't have permanent plumbing or electric supply (plug in with extension cord, black water tank that needs dumped periodically).

- "Mobile homes" (old name)/manufactured housing - "one piece" homes designed to roll to location, be dropped in place, and generally not moved again. Once on site, permanently plumbed and electrified. Older homes tend to be rotten nasty cheap things. Newer ones can be quite nice, but they still carry a bad reputation. Follow their own federal rules. In theory can be moved again, but rarely happens.

- Prefab (sometime also called modular) - factory built homes, but usually not delivered complete. Instead usually delivered as components (sometimes whole rooms, sometimes just walls and roof). Generally must adhere to local building regs. Built on a normal foundation. Truly permanent once installed.

- Normal construction on site. Local rules.

And because prefab has to follow local rules, which can vary substantially by region (CA with earthquakes/fires vs east coast without much in the way of natural disasters), the cost savings often isn't there.