Factory-Built ADU Prices Compared: San Mateo County

11/2/2026

If you own a home in San Mateo County and you're pricing a backyard ADU, the first number you want is simple: what does the unit itself cost? This post lays out the listed price ranges for factory-built homes from Green Galaxy Homes in Santa Clara, sorted by size, so you can see how cost changes as you add square footage and bedrooms. We'll also cover what those ranges don't show and who sets the rules for your lot.

How to read these prices

Green Galaxy Homes lists each home on its site with a price range rather than a single figure. The ranges below are copied from the public site as of this week. They're the listed range for the home; your full project budget will also depend on your site, foundation, utility connections, delivery and permit fees. Prices can change, so treat these as a starting point and confirm a current quote with Green Galaxy before you plan around a number.

Many of the most-viewed homes on the site are built by Champion Redman, including the CM-6622L, CM-7604B and CM-1482D.

Compact single-section homes: about $84K–$115K

These are the narrowest homes in the lineup, roughly 11 to 14 feet wide, which can help where backyard space is tight.

• CM-1482D — 2 bed / 1 bath, 560 sq ft, 11'8" x 48' — listed at $84K–$93K
• CM-2602B — 2 bed / 2 bath, 800 sq ft, 13'4" x 60' — listed at $103K–$113K
• CM-6563B — 3 bed / 2 bath, 803 sq ft, 14'4" x 56' — listed at $102K–$112K
• CM-6622L — 3 bed / 2 bath, 889 sq ft, 14'4" x 62' — listed at $104K–$115K

What stands out: moving from the 560-square-foot CM-1482D to the 800-square-foot CM-2602B adds a second bathroom and about $19K–$20K at the listed range. The CM-6563B and CM-6622L fit three bedrooms into under 900 square feet for about the same range as the two-bedroom CM-2602B.

Wider homes: about $145K–$178K

The homes in the lineup that are 20 feet wide or more carry a noticeably higher listed price. Square footage doesn't always rise as fast as price, so compare carefully.

The CM-8402D is 2 bed / 2 bath and 800 square feet at 20' x 40', listed at $145K–$161K. That's the same square footage as the CM-2602B but in a wider, shorter footprint, and the listed range is about $42K–$48K higher. If your lot is deep and narrow, a long single-section home may stretch your budget further. If it's short and wide, the wider plan may be the only one that fits.

Moving up in size, the CM-3443R (3 bed / 2 bath, 1,027 sq ft) is listed at $152K–$168K, the CM-3483B (3 bed / 2 bath, 1,120 sq ft) at $153K–$169K, the CM-3523L (3 bed / 2 bath, 1,213 sq ft) at $159K–$175K, and the CM- 4483B (3 bed / 2 bath, 1,280 sq ft) at $161K–$178K. Across those four, roughly 250 extra square feet adds only about $9K–$10K at the listed range.

Larger homes: about $169K–$300K

For homeowners with room for a bigger second home, or building a primary residence, the site also lists the CM-4563S (3 bed / 2 bath, 1,494 sq ft) at $169K–$187K, the CM-4663A (3 bed / 2 bath, 1,760 sq ft) at $188K–$208K, and the CM-7604B (4 bed / 3 bath, 2,289 sq ft, 40' x 60') at $272K–$300K. Whether a home that size can go on your lot as an ADU is a question for your local planning department.

Who sets the rules on your lot

Where your property sits matters. San Mateo County's Planning page says the County regulates second units in the unincorporated areas of the County only. If you live inside a city such as San Mateo, Redwood City or Daly City, your city's planning department handles ADU permits. The County page also notes separate rules for the Coastal Zone, and links to an ADU Resource Center.

State ADU law applies everywhere in California. The California Department of Housing and Community Development keeps an ADU Handbook and says it added an addendum in December 2025 summarizing changes to state ADU law in effect on January 1, 2026. It's worth a read before you talk to your city.

What the price range doesn't cover

Green Galaxy's building process runs through four steps: planning, designing, permits and construction. The company says it contacts the local building and planning departments about rules for your address, designs around your property access, and has a project coordinator gather the plans and documents needed for a building permit. It also says construction contracting, management, scheduling and coordination are included in its services, and that initial consultations are free.

What the listed home range doesn't spell out is your site cost: foundation, utility trenching, crane or delivery access and city fees. Those vary from lot to lot, which is why a site-specific quote is the only reliable total.

Get a quote for your property

Green Galaxy Homes is at Parkway Plaza, 4655 Old Ironsides Dr, Santa Clara, CA 95054 (Dealer License DL1256278). Call (408) 741-9008, see the ADUs and backyard homes page, browse every plan at greengalaxyhomes.com/homes, or reach out through the contact page.