ADUs
We're building an ADU for Mom or Dad. What should we build in now so it still works in ten years?
Most of what makes a unit work for an older parent is decided on the plans and in the framing. After drywall, the same features cost several times as much, and some cannot be added at all.
Build for the parent your parent will be in ten years, not the one who moves in. That means a zero-step entry, wide doors and halls, a bathroom with a five-foot turning circle and a curbless shower, and blocking in the walls for grab bars before anyone needs them. Almost all of it is cheap when it is on the plans and the framing is open, and very expensive once the unit is finished.
Which kind of ADU fits a parent
California law gives you four ways to add a unit, and each one lands differently for an older parent. The right answer turns on how much privacy both households want and on what the lot allows. How your parent gets around today matters too.
| Type | What it is | For a parent |
|---|---|---|
| Detached ADU | A new building in the yard. Under the Energy Code it is new construction. | The most privacy, and the cleanest place to build everything in this guide from the ground up. Usually the largest budget. |
| Attached ADU | A new unit that structurally connects to the house. State law caps it at half the existing house's floor area. | Close enough to hear a call for help. Shared walls need sound attention. Grading and the floor level of the house decide whether the entry can be zero-step. |
| Garage conversion | An ADU built inside an existing garage or accessory structure. | Often the lowest-cost full unit. The slab is usually below the house floor and close to the driveway, which can help a zero-step entry or fight it. |
| Junior ADU (JADU) | Up to 500 sq ft of interior space carved out of the existing house, including an attached garage. One per lot. | The least separation. Can share the house bathroom. Needs only an efficiency kitchen, and the owner usually has to live on the property. |
As a rule of thumb the cost order runs from the detached unit at the top down to the JADU, because each step down reuses more of a structure that already exists. Site conditions can reorder that, so treat it as a starting point. Our published ADU range is $300K–$360K for a good-quality build. A site visit is what turns that into a number for your lot.
The JADU kitchen rule, in plain terms
A JADU must have at least an efficiency kitchen: a cooking facility with appliances, a food preparation counter, and storage cabinets of reasonable size for the unit. HCD's handbook says a city cannot demand more than that, including a 240-volt circuit or a particular appliance. For a parent who cooks a little and eats with the family a lot, that can be enough. If the bathroom is shared, the JADU has to have an interior door to the main house.
Who lives where: the owner-occupancy rule
This is the question families ask most, and the state answer changed recently. Under Government Code section 66315, as quoted in HCD's ADU Handbook (March 2026 update), a city may not require the owner to live on the property as a condition of an ADU. The only exception is an ADU sold separately as a condominium under section 66341.
A JADU is different. Under section 66333(b), if the JADU shares a bathroom with the house, the owner must live either in the rest of the house or in the JADU. If it has its own bathroom, owner-occupancy is not required. Some city codes still print an older, broader version of this rule, so confirm the current wording with your city's planning counter before you choose a JADU.
If you might move out one day and rent the main house, a detached or attached ADU keeps that door open. A JADU with a shared bathroom ties the family to living there. Settle which future you are planning for before the plans are drawn.
What costs little in framing and a lot later
The features below come from AARP's lifelong-home guidance and from the accessible housing standards HUD publishes. None of them is required in a private ADU. Each one is a decision for the plans, and most cost very little while the walls are open.
Getting in the door
- Zero-step entry. AARP's recommendation is to build the entry into the landscape so the walk rises gently to the door, with a beveled threshold no higher than half an inch. This is decided at grading: the finished floor height and the slope of the yard are set before the foundation is poured. Change it later and you are building a ramp.
- A path from the car to the door. A firm, level, lit walkway wide enough for a walker, with a covered landing at the door and somewhere to set down a bag. Plan it with the site plan, not after the landscaping goes in.
- A 36-inch entry door. A standard 36-inch door gives roughly a 32-inch clear opening. That is the width that gets a wheelchair or a rolling walker through.
Moving around inside
- 36-inch interior doors and 42-inch halls. AARP and HUD both point to a 42-inch hall. AARP quotes one contractor who tells owners that widening a hallway later costs so much they are better off moving. In a new unit it costs a few inches of floor.
- Bedroom and full bath on one level. No stairs between the bed and the toilet, ever. In a two-story detached unit this means the parent's suite goes downstairs.
- Lever handles on every door and faucet. They work with a closed fist or an elbow, which a knob does not.
- Rocker light switches no higher than 48 inches and outlets at 18 inches or higher off the floor. Your electrician sets these heights at rough-in for nothing. Moving them after drywall means patching every box.
The bathroom
- A five-foot turning circle. A clear 60-inch circle (or the T-shaped alternative in the ICC A117.1 standard) lets a wheelchair turn around. It is the single dimension that decides the bathroom's size, so it goes on the first floor plan.
- A curbless shower. No lip to step over. The floor framing or slab has to be recessed for the shower pan before anything else happens, which is why it is a framing decision and not a tile decision.
- Blocking for grab bars at the right heights. Most standards mount a grab bar with its centerline 33 to 36 inches above the floor. Where California's accessible housing chapter applies, it calls for continuous wall reinforcement 32 to 38 inches up in the shower, and HUD suggests starting the backing as low as 30 inches. Solid backing around the toilet and inside the shower costs very little with the studs exposed.
- Non-slip flooring. AARP notes that smaller floor tiles are more slip resistant than large ones, and recommends porcelain over ceramic. Ask for a slip-resistance rating suited to a wet floor, and carry the same floor into the shower.
Light, air and the rest of the house
- Light the route from bed to bathroom. Motion-sensor night lights in the hall and the bathroom are on AARP's HomeFit list. Hardwired low-level lights on a sensor are cleaner than plug-ins, and the boxes go in at rough-in.
- More light overall. Older eyes need more of it. Plan for good general lighting plus task lights at the kitchen counter and the vanity, on switches that are easy to reach.
- A washer and dryer inside the unit. Carrying laundry across a yard is a fall risk. A stacked pair fits in a closet if the plans give it a drain and its own circuit, plus a vent unless you choose a heat pump dryer.
- A quiet heat pump. Under the 2025 Energy Code a new detached ADU is new construction, and the prescriptive baseline is a heat pump for heating and for hot water. Ask the mechanical designer about the indoor unit's sound level and where the outdoor unit sits relative to the bedroom window. Our heat pump guide explains the rule.
Room for help later
Plan the bedroom so a hospital bed could stand with clear floor on both sides, and so a caregiver can get around it. If a live-in caregiver is ever possible, a second small bedroom or a room that can become one is worth discussing with your designer now. A pocket door or an outswinging bathroom door keeps someone who falls from blocking the only way in.
What the ADA does and does not cover
The Americans with Disabilities Act does not apply to a private home used only as a residence. The Department of Justice's own Title III regulations say so in plain words. An ADU built for a family member is a private residence. So when someone says a unit is "ADA compliant," ask what they mean, because no inspector checks it against the ADA.
California's accessible housing rules for dwelling units sit in Chapter 11A of the Building Code. That chapter covers multifamily buildings, generally four or more condominium units or three or more apartment units. A house with one ADU behind it is not one of those. The national reference is ICC A117.1, the technical standard building codes point to for accessible and usable buildings.
That leaves the choice with you. The useful move is to borrow the dimensions from those standards and put them on your plans as your own requirements. Then they are in the contract, and the city's inspector will check that the work matches the approved plans.
The family conversation before the plans
The build is the easy part. The conversations that go badly are the ones nobody had before the permit was pulled. Talk through these with everyone who has a stake.
- Who owns the unit. An ADU is part of the property it sits on. If a parent is paying for it on a child's lot, or the reverse, get advice from an estate planning attorney on how that contribution is recorded. We are builders, so this is not our call.
- What happens later. A parent may need more care than a unit can give, or may pass. Decide now whether the unit becomes a rental or stays in the family, because that changes the layout you choose.
- Renting it. Under section 66315 a city may require that an ADU be rented for terms of 30 days or longer. A JADU cannot be a short-term rental at all and must be rented for longer than 30 days.
- Your city's own rules. San Jose's ADU FAQ states a 30-day minimum for any ADU rental, including Airbnb. Palo Alto's ADU code requires rental terms of 30 days or more. Every other city sets its own, so check before you count on short stays.
From permit to move-in in Santa Clara and San Mateo counties
State law puts two clocks on your city. Once an application arrives, the permitting agency has 15 business days to say in writing whether it is complete. Once it is complete, the agency has 60 days to approve or deny it when there is already a house on the lot (Gov. Code section 66317). A denial has to come with a written list of what to fix. If you ask the city for a delay, the clock pauses.
Plans
A designer or architect draws the unit, with the dimensions in this guide written on the plans. A Title 24 energy report and structural calculations go with them.
Plan check
The city reviews against the 15-day and 60-day clocks. Corrections are normal; a clean set comes back faster.
Build
Foundation, framing, rough-in and inspections. The blocking, the shower recess and the switch heights all get set in this phase.
Final and occupancy
No one may live in an ADU or JADU until the city issues a certificate of occupancy (Gov. Code section 66328).
How long the whole sequence takes depends mostly on the city and the site. Our ADU timeline guide walks through what moves it.
Paying for it
Families usually pay for a parent's unit from savings or by borrowing against the house: a HELOC, a renovation loan or an ADU lender. We do not quote rates or programs. A lender will tell you what you qualify for, and our guide to paying for an ADU covers the questions to ask.
How we run a parent ADU
We are the builder. If you already have plans, we price them and build them. If you need plans, we point you to a designer, and we will tell you which of the items in this guide to ask them to draw. A dimension on the plan is a promise we can price and an inspector can check. A wish in a conversation is neither.
The first step is a Project Discovery Call. Bring the lot address and your budget. Bring a plain answer about how your parent gets around today, too. Those settle which of the four unit types makes sense before anyone draws a line.
Common questions
Does a parent have to own the property to live in an ADU?
Does the ADA apply to an ADU built for my parent?
What kitchen does a junior ADU need?
Can I rent the ADU on Airbnb after my parent moves out?
How long does the city have to approve an ADU permit?
Where to go next
Written by the team at Elusive Construction, a licensed California general contractor (B #1112902) building in Santa Clara and San Mateo counties. General information about how residential construction works — not legal advice. For your specific contract, talk to an attorney.
Also Worth Reading
The rest of what we publish
Cost guides
What an ADU, an addition, a kitchen or a whole house actually costs here, and what moves each number.
Our own projects
Two jobs written up start to finish, including what we found once the walls were open.
Paying for it
Renovation lenders we work with. We take no referral fee, and we never quote you a rate.
Where we build
Sixteen cities across two counties, and what genuinely changes at each city line.
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