Thinking about adding living space or rental flexibility to a Cupertino home? You’re not alone. Many buyers weigh an ADU against a JADU, but the rules, costs, and timelines are not the same. This guide breaks down the key differences, Cupertino permitting basics, a quick feasibility checklist, and practical next steps so you can move forward with confidence. Let’s dive in.
ADU vs JADU: What they mean
Definitions and size limits
An accessory dwelling unit (ADU) is a self-contained home that’s secondary to the main residence. It can be detached, attached, or created by converting existing space like a garage.
A junior accessory dwelling unit (JADU) is created within the walls of the existing single-family home. It is smaller and not a full independent dwelling in the same way as an ADU.
Typical state caps: JADUs are up to 500 sq ft. ADUs commonly max at about 1,200 sq ft under state provisions, with some local flexibility within those limits.
Where each can be built
You can build ADUs as detached backyard cottages, attached additions, or conversions of interior or garage space. JADUs must be carved out from space already inside the primary home, often from an existing bedroom or a portion of the house.
How many units you may add
On most single-family lots, state law allows one ADU and one JADU, subject to local objective standards. Local cities still apply zoning rules, but they must follow state statutes and use a streamlined, ministerial review process when you meet the standards.
Cupertino permitting basics
Who approves your project
If the property sits inside Cupertino city limits, the City of Cupertino Planning and Building Divisions are your primary permit authorities. If the parcel is in unincorporated Santa Clara County, the County’s Planning and Development team handles ADU/JADU permits.
What standards shape your design
Your parcel’s zoning, setbacks, height limits, and lot coverage or floor area ratio (FAR) drive what is feasible. Historic status or conservation areas can add rules. Utilities and meter requirements vary, and local agencies for water, sewer, electricity, and fire safety set connection standards. Detached ADUs must meet California Building Codes for egress, fire separation, and may trigger sprinklers depending on size and local fire code.
Parking and fees
Parking rules are limited by state law and may be waived in some scenarios, including certain conversions or proximity to transit. Expect possible utility connection and impact fees, though state law restricts how fees are applied to ADUs and JADUs. Always confirm current fee schedules with the city or county.
Owner-occupancy and rentals
JADUs often carry owner-occupancy implications. ADU owner-occupancy rules have evolved under state law. Long-term rentals are generally allowed, while short-term rentals may be restricted in some cities. Check Cupertino’s latest policies before you plan rental use.
Quick feasibility checklist
A. Parcel-level technical checks
- Confirm zoning and permitted uses for the parcel.
- Measure lot size, current coverage, and buildable area based on setbacks and any easements.
- Note existing house square footage to evaluate interior or garage conversions.
- Assess garage conversion potential and current parking layout.
- Identify utility connection points and whether separate meters are required or allowed.
- Check for easements, slopes, soils issues, and any floodplain or creek setbacks.
B. Regulatory and fees
- Review objective standards for setbacks, height, and lot coverage.
- Verify parking requirements or waiver eligibility, including transit proximity.
- Request fee estimates for water, sewer, and potential impact fees.
- Ask about permit timelines and what a complete submittal must include.
C. Practical and market factors
- Consider construction access, especially on narrow or sloped lots.
- Review HOA or CC&R limitations if applicable.
- Think through rental goals in Cupertino’s high-demand market and any short-term rental rules.
- Talk with your lender, insurer, and the assessor about financing, insurance, and tax implications.
Popular ADU/JADU paths in Cupertino
Garage conversion ADU
- Pros: Often lower cost, no added lot coverage, and fewer site impacts.
- Cons: Potential loss of covered parking and storage; confirm your parking strategy.
JADU within the main home
- Pros: Minimal exterior change, smaller scope, and typically faster/cheaper than a new build.
- Cons: Limited to 500 sq ft and usually tied to owner-occupancy considerations.
Detached backyard ADU
- Pros: Maximum privacy and flexibility as an independent living space.
- Cons: Higher cost and more complex, with lot coverage, height, and utility connections to solve.
Attached ADU addition
- Pros: Can integrate with existing systems and architecture.
- Cons: May trigger broader code upgrades to the main house and a longer build timeline.
Cost and timeline expectations
Construction costs in the Bay Area are generally higher than the national average. Conversions, including garages and JADUs, tend to be the most cost-effective. Detached, ground-up ADUs often cost more and take longer due to site work and utilities.
Even with ministerial permits, expect several months from planning to permit, and additional months for construction. A straightforward conversion can move faster than a new detached ADU that needs full site work.
Parking strategies that work here
- Conversions: Turning a garage into living space can reduce parking needs under state rules in many scenarios.
- On-site solutions: Tandem or uncovered spaces may work, subject to driveway and curb regulations.
- Transit context: Cupertino is not as transit-dense as urban cores, so plan to provide a space unless a clear waiver applies.
Smart next steps for buyers
- Confirm the property’s jurisdiction and zoning category.
- Book a pre-application conversation with Cupertino Planning to surface lot-specific constraints early.
- Review CC&Rs or HOA rules for any private restrictions.
- Engage an architect or ADU-focused contractor for a feasibility sketch and rough budget.
- Verify utility connection points and capacity with local providers.
- Obtain multiple contractor bids and realistic permit/build timelines.
- Explore financing options such as HELOCs or construction loans.
- Contact the Santa Clara County Assessor to understand tax implications after construction.
If you want help targeting homes with ADU or JADU potential, or you need introductions to trusted local pros, reach out to Sunaina Arora for data-driven guidance and a smooth plan from search to close.
FAQs
What is the max size for ADUs and JADUs in Cupertino?
- State rules commonly cap ADUs around 1,200 sq ft and limit JADUs to 500 sq ft, with final feasibility shaped by local zoning, setbacks, and lot coverage.
How long does it take to build an ADU or JADU?
- A conversion can move in several months, while a detached new-build ADU typically takes longer due to design, permitting, utilities, and construction.
Do I need parking for an ADU in Cupertino?
- Parking may be required, but state law provides waivers in specific cases like certain conversions or proximity to transit; verify your parcel’s eligibility.
Can I use an ADU for short-term rentals?
- Short-term rentals can be restricted; check the City of Cupertino’s current rules before planning any short-term rental strategy.
Do JADUs require owner-occupancy?
- JADUs often include owner-occupancy implications under state and local interpretations; confirm Cupertino’s current policy before you proceed.
How do HOAs and CC&Rs affect ADUs and JADUs?
- Private rules can limit rentals, exterior changes, or ADU/JADU approvals and are separate from city zoning, so review them early in your process.
