---
title: "ADU Builders in San Jose | Detached, Attached & Garage ADUs | QA Builders"
description: "ADU builders in San Jose for detached, attached and two-story ADUs and garage conversions: design, City permits and construction by one licensed contractor."
url: "https://qabuilders.com/adu-builders/"
updated: "2026-10-03"
---

Accessory dwelling units

# ADU Builders in San Jose

As ADU builders in San Jose, QA Builders builds detached and attached units, two-story ADUs and garage conversions (JADUs), handling design, permits and construction as one licensed general contractor (CSLB #1073096). Call [(669) 213-8077](tel:+16692138077) and we will tell you which ADU your lot allows.

We've completed dozens of ADU projects across San Jose and the Bay Area, from garage conversions to ground-up custom builds. This page sets out the San Jose rules that shape an ADU, the permit steps, the timeline and what drives the cost.

## ADU types and which fits your lot

An ADU is a second home on the same lot, with its own living, sleeping, cooking, eating and bathroom facilities. San Jose allows ADUs on any lot with a legally built, permitted main house, whether single-family, duplex or multifamily. The type you choose depends on the space you have and how independent the unit needs to be.

### Detached ADUs

Standalone structures built from the ground up with full kitchens, bathrooms, and living areas. Under the City's standards the siting rule for a detached ADU reads "Behind main home or 45 ft front setback of zoning district" (Bulletin #210). In plain terms, [Municipal Code 20.80.175](https://library.municode.com/ca/san_jose/codes/code_of_ordinances?nodeId=TIT20ZO_CH20.80SPUSRE_PT2.75ACDWUN_20.80.175GE) puts a detached ADU in the rear yard, or lets a new one sit 45 feet back from the front property line if it keeps at least 4 feet from the interior side line. The unit also stays 6 feet from other buildings and, with any other structures, covers no more than 40 percent of the rear yard.

### Attached ADUs

Extensions to your existing home with separate entrances and self-contained living spaces. Under the City's standards an attached ADU can be up to half the living area of the main house (capped at 1,000 or 1,200 square feet depending on lot size), and its front door must be on a different side of the house from the main entrance.

### Garage Conversions (JADU)

Transform your existing garage into a livable unit, one of the most cost-effective ADU options. The label depends on the result. A junior ADU (JADU) is limited to 500 square feet and sits inside the footprint of the house, and can include an attached garage; if it shares a bathroom with the main house, the owner must live on the property. A converted garage with its own full facilities is an ADU. Our [garage conversion](https://qabuilders.com/garage-conversion-san-jose/) page compares the two.

### Two-Story ADUs

Maximize a small footprint with a two-story design that provides ample living space. San Jose's own standards allow a detached ADU up to 25 feet for a second story, while the state standards cap a new detached ADU at 16 feet, so a two-story detached unit is normally designed under the City's standards.

## San Jose ADU rules: City standards or state standards

San Jose lets you design an ADU under either its own standards (Municipal Code 20.80.175) or the state standards (20.80.176). You must pick one set for the whole design; the two cannot be mixed. The main limits for a single-family lot, from the City's ADU Universal Checklist (Bulletin #210, updated 09/16/2026):

| Limit | City standards, new detached ADU | State standards, new ADU |
| --- | --- | --- |
| Maximum size | 1,000 sq ft on lots under 9,000 sq ft; 1,200 sq ft on larger lots | 800 sq ft |
| Side and rear setbacks | 4 ft; for the first story a zero setback is allowed if building and fire requirements are met | 4 ft |
| Maximum height | 18 ft for one story; 25 ft for two stories | 16 ft detached (up to 2 ft more for a pitched roof near major transit); 25 ft attached |
| Where it sits | "Behind main home or 45 ft front setback of zoning district": in the rear yard, or 45 ft from the front property line with a 4 ft interior side setback (Municipal Code 20.80.175) | May use the front setback only if nothing else fits an 800 sq ft ADU |
| Rear yard coverage | All structures together, 40 percent at most, a limit that may not block an 800 sq ft ADU with 4 ft side and rear setbacks | No coverage limit |

The City standards allow a larger unit; the state standards drop the siting and coverage rules. Which set wins depends on your lot, and it is the first design decision we make with you. The minimum size is 150 square feet either way, and neither set limits the number of bedrooms or bathrooms beyond building and fire codes.

### Site conditions that change the design

- **Hazard zones:** flood zones A, AE, AH or AO bring flood design rules; a landslide or geologic hazard zone requires a Geologic Hazard Clearance; a Wildland-Urban Interface zone brings fire-resistant construction rules.
- **Historic properties:** on a listed property, the City standards come with simplified design standards; the state standards do not.
- **Easements and old pools:** you usually cannot build in an easement, and building over a filled-in pool needs demolition records or a geotechnical report.
- **Trees:** removing an ordinance-size tree for an ADU needs no separate permit but the tree must be replaced; a heritage tree has its own process.

### Fire access and utilities

- Both addresses must be visible from the street, and the ADU gets its own unit number.
- Every side of the ADU should be within 150 feet of the street curb along a clear path at least 4 feet wide, and within 600 feet of a fire hydrant; otherwise a fire variance with extra safety measures may be needed.
- Your water company must provide a letter showing the hydrant flow. The City names a missing letter as a common cause of permit delays, so we request it at the start.
- If the main house has fire sprinklers, the ADU needs them too; an attached ADU over 500 square feet on a property with more than 3,600 square feet in total means sprinklers for the whole house.
- PG&E now requires an ADU to have its own meter; a JADU does not need a separate one.

Sources: City of San Jose [ADU program pages](https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus), ADU FAQs and Bulletin #210, read October 2026.

## How an ADU gets permitted in San Jose

1. **Site Assessment.** We evaluate your property, review zoning regulations, and determine the best ADU type and placement for your lot, working through the City's Universal Checklist.
2. **Design & Architecture.** Custom designs that complement your main home's style and maximize the available space on your lot, drawn to the City's ADU plan requirements, with Title 24 energy calculations and a geotechnical report where required. The City also offers preapproved ADU plans, which lower review cost if one suits your lot.
3. **Permitting.** We handle all permit applications, plan checks, and utility coordination with the city of San Jose. The application is filed on SJPermits.org and the plans are reviewed in SJePlans; the first round of building review typically takes 20 business days unless the plans need more review, and complete, accurate plans keep it to one or two rounds.
4. **Fees and issuance.** Plan review, inspection and permit fees are paid before issuance. An ADU of 750 square feet or less pays no school or parkland impact fees; at 751 square feet and above, both apply.
5. **Foundation & Construction.** Expert construction from foundation to roofline, with the City's inspections at each stage.
6. **Inspection & Handover.** Final city inspection, certificate of occupancy, and a thorough walk-through before we hand you the keys.

From permits to completion, most ADUs take 6-12 months. Garage conversions can be faster (4-6 months), while custom detached units may take up to a year.

## What drives the cost of an ADU

- **Type:** converting a garage reuses a slab, walls and roof; a new detached unit needs all of them.
- **Size:** crossing from 750 to 751 square feet adds school and parkland impact fees.
- **Utilities:** the distance to the sewer line, water service and electrical panel, plus the separate PG&E meter.
- **Fire requirements:** sprinklers or a fire variance when the lot fails the access or hydrant tests.
- **Site:** hazard zones, soil reports, trees and easements.
- **Height and finishes:** a second story, and the level of kitchen and bathroom finishes.

ADU costs typically range from $150,000 to $350,000+ depending on size, type, and finishes. Garage conversions are generally the most affordable option.

An ADU also raises your property tax, based on the value of the new unit. Our [ADU cost guide](https://qabuilders.com/adu-cost-san-jose/) explains each factor in more depth.

## Rental income or family housing

A well-designed ADU in San Jose can generate $2,000-$4,000+ per month in rental income, often covering your mortgage. ADUs can increase your property value by 20-30%, making them one of the best ROI home improvements.

You can rent the house and the ADU to different parties, and the City notes that state law sets a minimum rental term of 30 days, including on short-term rental platforms, and that fair housing rules apply to how you advertise and choose tenants. The ADU cannot be sold separately from the house unless the property goes through a condominium conversion.

Multi-generational living is the other common reason to build: provide independent living space for parents or adult children while keeping family close. For more on both uses, read [the benefits of building an ADU](https://qabuilders.com/benefits-of-building-an-adu/).

## Why choose QA Builders for your ADU

ADU construction requires specialized knowledge of California's unique regulations, local zoning codes, and utility requirements. QA Builders has built dozens of ADUs and knows exactly how to navigate the process efficiently. We handle everything in-house: design, permits, construction, and finishing, so you have one point of contact and one team accountable for your project's success.

Our ADUs are built with the same quality and attention to detail as our full home remodels, ensuring your investment looks great and lasts for decades.

When you compare ADU contractors in San Jose, ask who draws the plans, who answers the City's plan-check comments, whether the water-flow letter, utility work and any fire requirements are in the price, and who you call during construction.

## ADU questions

### Do ADUs need a building permit?

Yes, ADUs require building permits. However, California law has streamlined the process significantly. We handle all permitting for you.

### Can I rent out my ADU in San Jose?

Yes! San Jose allows ADU rentals. A well-designed ADU can generate significant monthly rental income, often $2,000-$4,000+ in the Bay Area. The minimum rental term is 30 days.

### Is a guest house the same as an ADU?

A detached guest house with its own kitchen and bathroom is an ADU in San Jose and follows the ADU rules above. A detached room without a kitchen is an accessory building; it needs a permit if it is larger than 120 square feet or has any electricity or plumbing.

### Do you build ADUs outside San Jose, for example in Saratoga?

Yes. Saratoga, Campbell, Los Gatos, Cupertino and the other cities we work in each set their own ADU rules within state law and run their own permit office, so the limits on this page are San Jose's; we check your city's rules at the first visit.

## Find out what you can build

Contact us today for a free consultation and detailed estimate for your ADU construction project: call [(669) 213-8077](tel:+16692138077) or use our [contact page](https://qabuilders.com/contact/).