Stacked Duplex Plans
The same two units stacked rather than spread — roughly half the ground footprint, which is the entire point on a narrow or shallow lot.
Half the footprint of side-by-side, on a lot that cannot spare the width.
A stacked duplex trades height for land. Where a side-by-side asks for 32 feet of width and roughly 830 square feet of ground, this one puts one unit above the other on a 32-by-13-foot footprint — about half the land for nearly the same living area, and your rear yard back. The two units have identical layouts: a one-bedroom of 361 square feet with its own kitchen, full bath, in-unit laundry and private exterior entrance. The catch is the height allowance. Two stories generally needs 18 feet, and 18 feet is conditional — you get it if your existing multifamily building is multistory, or if the property is within a half-mile walking distance of a major transit stop or high-quality transit corridor. If neither applies, you are held to 16 feet and this plan is not available to you.
- Configuration
- 2 × 1BR / 1BA
- Size
- 361 sqft per unit · 722 sqft total
- Footprint
- 32' × 12'-11"
- Height allowance needed
- 18–20 ft
Who this is for. Owners on narrow or shallow lots who qualify for 18 feet — either because the existing building is two or more stories, or because the property sits near qualifying transit.
361 sqft per unit · 722 sqft total
Each side is a complete home.
What makes it work.
Half the footprint, same living area
A 32-by-13-foot footprint — roughly 415 square feet of ground for 722 square feet of living area. The side-by-side needs about twice the land for a comparable result.
Both units well under the fee line
At 361 square feet each, both units sit far below the 750 sqft interior-livable-space threshold where impact fees begin — and on a multi-unit project that exemption applies per ADU.
Still a two-unit building
Like the side-by-side, it stays in the simpler Group R-3 building-code category. The sprinkler and accessibility step-up attaches at three units, not two.
Identical layouts, private entries
Both floors are the same one-bedroom plan, each with its own kitchen, full bath, in-unit laundry and private exterior entrance. No shared interior circulation, no common corridor.
Fixed plan fee, estimated build.
Construction estimate by an independent licensed general contractor. Not a CALI ADU price. City plan-check and permit fees are paid directly by you at cost.
What the plan fee includes
- Floor plans and elevations designed in-house by expert ADU designers
- Structural engineering and Title 24 energy compliance coordination
- Your interior and exterior finish selections, specified in the plans
- Entitlement documentation citing § 66323(a)(4) and the HCD Handbook
- Done-for-you permit processing and expediting with your city
- Unlimited plan-check corrections until your permit is issued
- A builder-ready set any licensed contractor can price and build
Why the build cost varies
Utility capacity
Adding two to four units can exceed the existing electrical service, sewer lateral, or water meter sizing. On multi-unit projects this is routinely the largest unbudgeted line item — and it is knowable early.
Your height allowance
Sixteen, eighteen or twenty feet. It decides whether a stacked configuration is even available to you, and it changes the structure, the stair, and the foundation.
Unit count and occupancy class
A detached two-unit building is generally Group R-3. Three or more is generally Group R-2, which brings sprinklers, accessibility provisions and stricter assemblies. The step from two units to three is larger than one to two.
Site access and existing conditions
Rear-yard access for equipment, grading, existing hardscape and the condition of what is already on the lot. Tenanted properties add sequencing constraints.
Multifamily ADU plans are designed in-house by our ADU design team and carry the same curated finishes as our detached Signature Homes. Your plan fee is fixed. Because multi-unit projects vary more than single ADUs — utility capacity, site access, grading, and the condition of your existing building — the cost to build is an estimate that starts at the figure shown and is confirmed for your specific property; it is not a single guaranteed price. Construction is performed by an independent licensed general contractor.
Confirm what your lot is entitled to.
Every plan on this page depends on two facts about your property: whether your existing building qualifies as a multifamily dwelling under state ADU law, and what height allowance you have. A duplex in an R1 zone qualifies — zoning is not the test, your structure is. And the difference between 16 and 18 feet is the difference between a single-story and a stacked building.
The full rules — unit counts, height tiers, setbacks, impact fees, what a city cannot require and what actually blocks these projects — are laid out on our multifamily ADU guide.
Questions owners ask.
How do I know if I qualify for 18 feet?
Two independent pathways. Your existing multifamily building is multistory (Gov. Code § 66321(b)(4)(C)), or the property is within a half-mile walking distance of a major transit stop or high-quality transit corridor (§ 66321(b)(4)(B)). Either one gets you to 18 feet. It is the first thing we check on a feasibility assessment, because it changes the answer more than anything else.
Can I get to 20 feet?
Only through the transit pathway. The extra two feet for a roof pitch matching your primary building appears in § 66321(b)(4)(B) — the transit provision — and nowhere else. The multistory provision is a hard 18 feet with no pitch bonus. This distinction is widely misread, including in some city guidance.
Is a two-story ADU allowed if my zoning caps buildings at one story?
Generally yes. If the project fits inside the height allowance, a local agency cannot deny it for being two stories, even where the underlying zoning restricts primary dwellings to one story. HCD made findings against the City of Los Angeles on exactly this point. Height governs, not a story count.
Other multifamily plans.
Side-by-Side Duplex
Two mirrored units under one roof, each with its own entrance.
16 ft 3 units · One or twoTriplex
Three units in a bar or stacked, depending on what your height allows.
16–20 ft 4 units · One or twoFourplex
The strongest per-square-foot economics in the line — with a real code caveat.
16–20 ftSee what your lot supports. Before anything gets drawn.
A written determination of your entitlement, height allowance, buildable envelope, and which configurations actually fit.
Designed in-house · Transparent pricing · Your choice of builder