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ADU contractors: what licenses to look for

By Contractor Lookout · Updated November 3, 2026

To build an accessory dwelling unit (ADU) in California, hire a contractor with a B General Building license. If your ADU is a manufactured home built off site, a C-47 General Manufactured Housing contractor can install it.

That’s the guidance in CSLB’s Fast Facts sheet “Tips for Building a Residential ADU” (revised November 2025). CSLB also notes that other C specialty contractors generally can’t manage a full ADU build.

Which license fits your ADU

Type of ADU project License to look for
ADU built on site B General Building
Manufactured home built off site and installed as an ADU C-47 General Manufactured Housing
One trade within the ADU, such as electrical or plumbing The C specialty for that trade, working under or alongside the main contractor

In CSLB’s current file, 107,757 licenses hold the B class and 459 hold the C-47.

A specialty contractor still has a place on an ADU job. Your B contractor may subcontract the electrical work to a C-10 or the plumbing to a C-36. What CSLB’s sheet rules out, generally, is a single-trade specialty contractor managing the whole build.

Why the B fits

Under BPC 7057, a B contractor can take a prime contract that involves at least two unrelated trades besides framing or carpentry. An ADU involves many trades, so it fits the B. Our A vs B vs C guide explains the rule in more detail.

ADU work is home improvement

CSLB treats building an ADU as a home improvement project. That brings in the home improvement contract rules:

One exception: a contractor with a qualifying blanket performance and payment bond on file can lawfully take more up front. The license record shows this as a secondary note. See our down payment guide and the status hub.

Permits

Your city or county issues building permits for an ADU. For a manufactured ADU, CSLB notes that the state Department of Housing and Community Development (HCD) may issue the permits instead.

Before work starts:

  1. Ask the contractor who will apply for the permits.
  2. Get copies of the issued permits.
  3. Make sure inspections are scheduled at the stages your permit requires.

A licensed contractor is needed for an ADU regardless of price. The minor work exemption only covers jobs under $1,000 that need no building permit. See the minor work exemption.

How to check an ADU contractor

  1. Get the license number and look it up with our search, then confirm the live record on CSLB’s Instant License Check. Our data is a weekly file, so the live record is the one to trust.
  2. Confirm the class. Look for B, or C-47 for a manufactured unit.
  3. Check the primary status is Clear and read any secondary notes. Our status guide explains each one.
  4. Confirm the $25,000 contractor’s bond with the surety. See contractor bonds explained.
  5. Check workers’ comp. If the license shows “Exempt,” ask who will do the work. An exemption is only for contractors with no employees. See how to check workers’ comp.
  6. Check the expiration date. A license runs for two years from the last day of the month it was issued, so make sure it won’t lapse mid-project without renewal.
  7. Check the salesperson’s HIS registration if someone other than the contractor sold you the job.

To compare general contractors in one city, start with a page such as general contractors in Los Angeles, or browse the counties and cities index.

For every step before you sign, see our hiring checklist.

This is general information, not legal advice.

Sources

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