Modular vs manufactured homes

Welcome. We’ll cover five parts of the construction process, and how they differ on HUD and IRC homes. By the end you’ll have a clear picture of what sets these two apart.

Manufactured housing is the HUD code. Modular housing is the IRC. From here we’ll call them manufactured and modular. The codes sit in the background, but the comparison is manufactured versus modular.

Start with the foundation. On a modular home we take the wheels off. Those wheels are only used on the production line. The home goes on a permanent foundation. A yard dolly moves the modules around the yard and out to the site, then comes back so we can use it again. A manufactured home has a chassis permanently attached. It is brought to the site and left there.

Because that chassis runs down the center and supports the home, manufactured floor joists are a 2×6 or a 2×8. A modular home sits on a permanent foundation from one side to the other, so the joists have to span the whole distance. We go to 2×10s. On our homes we use a full-length LVL, which adds rigidity. Most modular plants lap a double 2×10 all the way down. Either way, it bears on the permanent foundation.

Manufactured exterior walls are a 2×4, and lately some plants have moved to a 2×6, with a 1×6 bottom or top plate. They keep the plates thin. The IRC is prescriptive. It calls for a single bottom plate, a full 2×6, and a double top plate. You only see one plate on this side of the module because the other side is where the roof sections come together. We glue, screw, and nail that joint. Look at the wall construction if you are comparing a manufactured house.

Interior walls follow the same pattern. Modular is 2×4 studs at 16 inches on center, with full 2×4 plates, including two full 2×4 top plates. Manufactured is 24 inches on center with a 1×4 bottom plate. That is more wood, because the IRC spells it out. Manufactured housing stays as light as it can, to move more floors down the line.

Manufactured homes come in different widths, and as the home gets wider the roof has to get flatter so it can travel. Modular can be taller, steeper, or flatter, using folding hinge trusses. We usually keep our gable units around a 5/12. Shed roofs are flatter. Every modular plant builds that a little differently.

Snow load changes with the roof, too. Manufactured housing generally fits a 30 psf load. Modular is designed for the snow load the local jurisdiction requires. We start at 30 psf, go up to 70, and we have gone as high as 100. It depends on where the home is going.

Insulation is the next difference. Manufactured exterior walls run from about R-13 to R-19, and sometimes R-21. The IRC calls for R-21, so a modular 2×6 wall gets high-density R-21.

In the floor, a manufactured home has the chassis and thick blankets of R-38. Heat rises, so the IRC calls for R-30 in the floor. Modular is R-30. Manufactured is R-38.

The ceiling is the critical spot. Manufactured housing uses R-38. Under the 2021 IRC, modular is R-49. We use closed-cell spray foam and then a high-density R-21 batt, which meets or exceeds that R-49.

Subfloor: manufactured is 5/8 inch. Modular uses the 3/4 inch the code allows. At Wolf we glue, screw, and nail it. The glue holds the sheet, and the screws keep it from squeaking.

Headers carry the joists, and the joists carry the snow. Manufactured headers are a 2×4 or 2×6 on edge. The IRC calls for structural dimensional lumber, a 4×6 or a 4×8. At Wolf we run the header past the opening on both sides, which adds racking strength.

Heating and ventilation: manufactured housing still follows the older code as HUD adopted it. Modular is held to the current IRC. We use an ERV, an energy recovery ventilator, so the fresh air coming in trades energy with the stale air going out. The ducts run to the end of the house, pulling fresh air in and sending stale air out.

Lighting: a manufactured home can still use incandescent bulbs. Under the IRC, at least 75 percent of the lights have to be LED. Wolf uses 100 percent LED, and the appliances are Energy Star. Our water heaters meet the current insulation requirement, so the hot water stays hot longer.

Those are the main differences between HUD and IRC construction. If you want a video on modular tiny homes or the factory, leave a comment. Thanks for watching.