The Difference Between an ADU and a JADU

The terminology matters here because the two types of units follow different rules, have different size limits, and involve different construction approaches. Getting clear on which one applies to your property is the first step.

An ADU — Accessory Dwelling Unit — is a fully independent unit with its own entrance, kitchen, bathroom, and living space. It can be detached from the main house (a backyard cottage, for example) or attached (a converted garage, or a new addition that’s connected to the main structure). In California, ADUs can be rented to anyone — they’re not restricted to family members.

A JADU — Junior Accessory Dwelling Unit — is smaller (capped at 500 square feet), is typically created from existing space within the main house or an attached garage, and must share a wall with the primary residence. JADUs require an owner-occupancy condition in most jurisdictions, meaning you or a family member must live on the property.

We work on both in Los Altos, Sunnyvale, Mountain View, and Saratoga regularly. The right choice depends on your lot, your goals, and what the city will allow in your specific zone.

What SB-9 Actually Means for Peninsula Homeowners

California’s SB-9, which took effect in 2022, made it easier in theory to split single-family lots and add additional units. In practice, the implementation varies significantly by city, and the permitting path is not always straightforward.

The core benefit of SB-9 for Peninsula homeowners is that it limits the ability of cities to use zoning restrictions to block lot splits and new unit construction in single-family zones. But it doesn’t eliminate all local discretion, and the process still requires working through city planning departments that each have their own procedures and timelines.

If you’re thinking about SB-9 as a path to adding a second unit or splitting your lot, the first thing we do is a feasibility assessment of your specific parcel. Setback requirements, lot coverage limits, the size of the existing structure relative to the lot — all of these factors affect what’s actually buildable. We’ve done enough of these assessments that we can tell you quickly whether a project is realistic and what the likely path looks like.

Garage Conversions: The Most Common Path We See

On the Peninsula, the most common ADU we build is a garage conversion. The reason is practical: most lots don’t have enough room for a fully detached structure, but an attached or detached garage has the footprint and the existing structure to work from.

A proper garage conversion isn’t just closing off the garage door opening and adding a bathroom. It involves proper insulation (garages built in the 60s and 70s were not insulated to residential standards), upgrading the electrical panel or adding a subpanel, adding plumbing if the garage doesn’t already have it, addressing floor transitions and ceiling heights, and meeting current energy code requirements.

We’ve converted a lot of garages on the Peninsula. The ones that come out well are the ones where the structural and mechanical work was done right, not cut. A converted garage that’s cold in winter, has inadequate electrical capacity, or has a floor that was never properly sealed is going to be a problem for whoever lives in it.

Permitting an ADU in Santa Clara County

Permitting timelines vary across the Peninsula. The cities we work in most — Los Altos, Saratoga, Sunnyvale, Mountain View, and others in Santa Clara and San Mateo counties — have each developed their own ADU permitting processes, and the timelines differ.

Some cities have streamlined ADU approval to a few months for straightforward projects. Others still have longer review cycles, particularly for detached ADUs or projects that involve lot splits. State law has pushed cities to expedite ADU permits, but “expedited” is relative.

We handle permitting completely. You don’t interact with the building department — we do. We know what each city requires, how their forms are structured, what inspectors look for, and how to respond to comments. For clients who have tried to navigate permitting on their own before working with us, the difference is significant.

One Crew, Start to Finish

ADU projects are long. Depending on scope and permitting timelines, a garage conversion might take four to six months from permit approval to move-in ready. A detached ADU with full foundation work can take longer. Over that time, you need a team that’s consistent, communicative, and accountable.

The way we work — same crew, no subcontractors, daily project manager presence — is especially important on ADU projects. There are too many moving parts and too many sequential decisions for a rotating cast of unfamiliar faces to handle well. When the same people are on site every day, they know the project, they know the plan, and they flag issues before those issues become expensive.

If you’re thinking about an ADU on your Peninsula property, we’re happy to come out for a free feasibility visit. We’ll look at your lot, talk through what’s realistic given the local regulations, and give you a straight picture of scope and timeline. No obligation. CA Lic #1063024.