A single wide is a manufactured home that ships as one transportable section, commonly somewhere around 12 to 18 feet wide and 60 to 80 feet long, so it arrives whole on one truck and is set on piers or a foundation with no seam running down the middle of it.
The word describes the shipping, not the size. Everything a buyer notices about a single wide (the long narrow shape, the rooms in a line, the lower price) follows from the decision to build the home as one box that can be towed down a road in one piece. Once you know that, the rest of the category stops being arbitrary.
The federal code that governs these homes does not use the phrase at all. It counts sections. A single wide is what the industry calls a home the code would describe as single-section.
One section, and what the code actually requires
A manufactured home is defined in the HUD code at 24 CFR 3280.2 as a structure transportable in one or more sections which in the traveling mode is 8 body feet or more in width or 40 body feet or more in length, or 320 or more square feet when erected on site, built on a permanent chassis and designed to be lived in. Read that carefully: the numbers are minimums. There is no maximum width in the code, and there is no line in it separating a single wide from a double wide. The words are trade language for how many sections came down the road.
Everything the code does govern applies to a single wide exactly as it applies to a larger home: structure, fire safety, plumbing, wiring, insulation, the wind zone it was built for, and the ability to survive the tow. Homes finished on or after 15 June 1976 carry a red HUD certification label riveted to the outside of each section, so a single wide has one label. A double wide has two.
The shape it produces
Because the whole home has to fit inside one towable box, the plan runs end to end rather than side to side. Typical single wides are quoted at 12, 14, 16 or 18 feet nominal width and 60 to 80 feet long, which puts most of them between roughly 600 and 1,300 square feet with two or three bedrooms. Circulation is normally a hallway down one side or through the middle, with the kitchen and living room at one end and the bedrooms at the other. Older pre-1976 homes were narrower still, 8, 10 and 12 feet being common, which is one of the quick tells on an unlabelled home.
The nominal width is a market label rather than a measurement. The finished box on a home sold as a 16 wide is usually a few inches under that, and the number the assessor and the insurer care about is the exterior dimension at the largest horizontal projection when the home is erected on site, which is the measure the HUD code uses for floor area.
Where they end up
Single wides are the standard home in most manufactured home parks, because a park space is a fixed rectangle and a narrow home fits more of them. They also work on narrow infill lots and on rural parcels where the point is to get a legal dwelling on the ground quickly. What they do not usually do is sit in a subdivision governed by CC&Rs, because covenants that restrict factory-built housing are typically drafted around the HUD code and the permanent chassis and catch every manufactured home regardless of width.
The practical setup is the same either way. The home is levelled on piers, anchored with tie-downs sized for its wind zone, skirted, and connected to water, sewer or septic, power and gas. On land the owner holds, the same home can instead be put on a permanent foundation and converted to real property, which is the step that changes what it can be financed and insured with.
What the single section costs you later
A single wide is the cheapest way into a home that is genuinely yours, and that is the whole case for it. The costs are on the other side of the transaction. Several of the better-priced manufactured housing loan programmes are written for multi-section homes, so a single wide owner often has a shorter list of lenders. Appraisers value it against other single-section homes, and where those sales are thin the appraisal is the thing that holds a deal up. And on a rented space, a single wide is personal property depreciating on somebody else's appreciating land, which is the pattern the published figures keep showing.
None of that is an argument against buying one. It is an argument for knowing before you sign whether the ground under it will ever be yours.
Questions people ask
How many bedrooms does a single wide have?
Usually two or three, laid out along the length of the home rather than around a centre. A 16 or 18 foot wide plan can carry three bedrooms and two bathrooms comfortably; a 12 or 14 foot plan of the same length usually gives up either a bedroom or the second full bathroom.
Is a single wide the same as a trailer?
In conversation, yes; in the paperwork, not necessarily. Trailer is an old word for the pre-1976 homes built before the federal code existed. A single wide built on or after 15 June 1976 is a manufactured home with a HUD label, and lenders, insurers and parks treat the two very differently.
Can a single wide be put on a permanent foundation?
Yes, on land the owner holds. The home is set on an engineered foundation, the running gear is removed, the state title is surrendered and the home is recorded as part of the real estate, after which it is taxed and financed as a house rather than as personal property.