Secondary Units are All the Rage 

Backyard manufactured homes – also known as granny flats, mother-in-law units and guesthouses to most and as accessory dwelling units or ADUs to urban planners – are all the rage in California and throughout expensive to live metropolitan areas across the United States, as with accessory dwelling unit permits up 78% in California.

“The economy has driven that pattern,” said Orange County chief building inspector, Bill Tarin. “People are talking about guesthouses, ADUs. I think it’s because of the high building costs.”

The economy, yes. But also a set of new California state laws that took effect in 2017, removing barriers to building secondary homes on a single lot. Those new laws specifically allowed new HUD Code manufactured homes to be utilized as accessory dwelling units. Those laws are already having an impact, according to a report by Southern California News Group.

In 2017, California municipalities issued 4,529 permits, up 60 percent from 2016, according to an Attom Data Solutions analysis of numbers from property data firm BuildFax.

In Los Angeles and Orange counties collectively saw permits jump 122 percent to 1,466 units. Numbers for 2018 so far show the trend continuing. California permits through July were up 78 percent compared with the same period in 2017. In the LA.-Orange County area, permits are up 125 percent so far this year. California state Sen. Bob Wieckowski, D.-Fremont, author of two ADU bills has projected that secondary units will put a dent in the state’s housing shortage providing as many as one million new units in the near future – meeting nearly a third of the state’s projected housing shortfall by 2025.


Manufactured homes are the only form of housing built in the U.S. subject to a national building health and safety code and are equal or superior to a comparably located site built home – the HUD Code – and will have a construction cost of up to 50 percent less than a site built without sacrificing quality, amenities or appearance. Most housing jurisdictions will not accept accessory dwelling units not built in compliance with the HUD Code – such as  “tiny” homes, or recreational vehicles (RVs). Utilizing a manufactured home as an accessory unit has many advantages for the main homeowner, as well as the resident of the ADU:

  • Who doesn’t want a “legal” second unit on their property? It increases their value.
  • Building the ADU in a factory reduces move-in time frame by many weeks compared to onsite construction.
  • A manufactured home ADU as a rental unit is an income source for many homeowners.
  • Others are adding living space for family members. In many cases, homeowners are moving into the granny flat and turning the main house into a rental home or living space for their children’s families.
  • Manufactured homes are available from a minimum of 400 square foot of living space up to 1200 square foot in California subject to the available space at the main home site.
  • Most manufactured home builders, including Kit Custom Homebuilders, Fleetwood Homes, Sunshine Homes, Deer Valley Homebuilders will allow home buyers to customize, even the smallest size homes, to meet their personal needs and desires – such as modifications for the handicapped and or specific requirements in fixtures, appliances, floor plan changes, exterior elevations, and much more.

California is not the only state or housing jurisdiction that is experiencing the manufactured home ADU phenomenon. Many are beginning to realize that manufactured housing is a key solution to the high cost of homes that have created a severe housing shortage across the country.

To learn more about backyard manufactured homes or dual residences on one parcel of land in Corvallis, Oregon, click our earlier post, Manufactured Home Accessory Dwelling Units Ease a Growing Shortage of Affordable Housing.”

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