Guest houses & detached ADUs · San Jose & the Bay Area
Guest House Builder in San Jose, CA
A backyard guest house is a small home built from the ground up: foundation, framing, utilities and a permit. We build them as detached accessory dwelling units (ADUs), so they can be lived in by family, guests or tenants.
- CSLB Lic. #1003436
- Free estimates
- (650) 749-7436
Is a guest house the same as an ADU?
Industry Resources & Standards:
A guest house with its own kitchen and bathroom is an accessory dwelling unit (ADU). A backyard structure without them, such as a studio, office or pool house, is a different kind of building with different rules. This page is about the first kind: a detached, livable unit.
California state law sets the baseline for detached ADUs: four-foot side and rear setbacks, and a city must allow at least an 800-square-foot unit. Your lot, your city’s standards and utility connections decide what actually fits.
What state law says about detached ADUs
These points come from the California Department of Housing and Community Development (HCD) ADU Handbook. State law was renumbered in 2024, so the section numbers below are the current ones.
| Topic | What the state says | Gov. Code |
|---|---|---|
| Side and rear setbacks | A city cannot apply standards that block an ADU of at least 800 sq ft with four-foot side and rear setbacks | § 66321(b)(3) |
| Maximum size | Where a city has no compliant ADU ordinance, a new detached ADU can be up to 1,200 sq ft of interior living space | § 66314(d)(4) |
| Height | A base height limit of 16 feet for detached ADUs, with higher limits near major transit | § 66321(b)(4) |
| Owner occupancy | A city cannot require the owner to live on the property | § 66315 |
| Impact fees | No impact fees for an ADU of 750 sq ft of interior living space or less | § 66311.5(c) |
| Review time | A completed ADU application must be approved or denied within 60 days when the lot has an existing home | § 66317(a)(3) |
Source: California HCD, Accessory Dwelling Units and its ADU Handbook. Cities can adopt their own, less restrictive standards, and the rules change. Confirm the current requirements for your address with the City of San Jose or your city’s permit office before you commit to a plan.
Six things that decide a backyard guest house
These are the usual constraints. They are easier to settle on paper than after the slab is poured.
Site and setbacks
Where the unit can sit depends on the lot shape, the main house, easements and any trees or utilities in the way.
Next step: Get a site plan and survey before design.
Foundation
A guest house needs a proper foundation sized to the soil and the structure, usually a reinforced concrete slab or footings.
Next step: Plan for grading, forms, rebar and inspections before the pour.
Utilities
Water, sewer, electrical and gas connections have to run from the main house or the street to the back of the lot. Distance and depth drive the work.
Next step: Locate the sewer lateral, water line and panel first.
Access during construction
Materials and equipment have to reach the backyard. A tight side yard changes how the slab is poured and how the framing is delivered.
Next step: Walk the access route with your contractor.
Design and energy code
A new ADU must meet current energy and building codes, and newly built ADUs are subject to the California Energy Code solar requirement.
Next step: Ask for the energy and solar plan during design.
Privacy and fit
Window placement, entry location and height affect your neighbors and how the unit feels from the main house.
Next step: Review window and door layout on the drawings.
How a guest house build typically runs
Feasibility
Check the lot, setbacks, utilities and what the city allows, and agree the size and layout.
Design and permit
Prepare the drawings and the energy documents, submit the application and respond to plan-check comments.
Site work and foundation
Grade the site, set the forms and rebar, and pour and inspect the slab or footings.
Framing and weather-tight shell
Frame the walls and roof, then add the wrap, windows, doors and siding.
Utilities and interior
Run plumbing, electrical and mechanical, pass the inspections, then insulate and close the walls.
Finish and final inspection
Fixtures, flooring, paint and trim, followed by the city’s final inspection.
A backyard unit, from slab to siding
These photos are from one of our San Jose backyard projects, in the order the work happens.
Guest house questions
Do I need a permit to build a guest house?
Yes. A new detached unit needs a building permit, with inspections for the foundation, framing, electrical, plumbing and energy work. We prepare the plans and handle the application.
How big can a backyard guest house be?
It depends on your city and lot. As a baseline, California law says a city must allow an ADU of at least 800 square feet, and where a city has no compliant ordinance a new detached ADU can be up to 1,200 square feet (Gov. Code § 66314(d)(4)). Your city may allow more or set its own limits.
How close to the property line can it be?
State law sets four-foot side and rear setbacks as the standard for an ADU of at least 800 square feet (Gov. Code § 66321(b)(3)). Front setbacks and other local standards can still apply, so confirm your lot with your city.
Does the owner have to live on the property?
No. California law prohibits owner-occupancy requirements for ADUs (Gov. Code § 66315). Rental terms and other rules are set separately, so check your city before planning around a tenant.
How long does the permit take?
For an ADU on a lot with an existing home, state law requires the city to approve or deny a completed application within 60 days (Gov. Code § 66317(a)(3)). Plan-check comments and the city’s workload can affect the overall schedule.
What is the difference between a guest house and a garage conversion?
A guest house is a new, detached building. A garage conversion turns an existing garage into living space. Both can be ADUs. See our garage conversion page for the garage option.
How much does a guest house cost?
It depends on the size, the foundation, the utility runs and the finishes. We give a written estimate after seeing the lot. Call (650) 749-7436 to schedule one.
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Licensed • CSLB#1003436 • Serving San Jose & Bay Area
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Quartz is a construction and remodeling company serving San Jose and the nearby areas. Our firm offers a wide range of services, including full-home renovations, kitchen remodeling, bathroom renovations, window replacement, deck building and repair, patio construction, and more.
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Address: 1777 Hamilton Avenue #1080, San Jose, 95125 California, USA.
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