Triplex Plans
Three independent units in a single detached building, laid out as a long single-story bar or stacked across two floors.
Three units in a bar or stacked, depending on what your height allows.
A triplex owner is entitled to three detached ADUs, and they can share one structure. Which layout works comes down to the same two numbers as everything else on this site: your height allowance and your buildable width. A single-story bar clears 16 feet but wants real frontage. A stacked layout — two units down and one up, or the reverse — needs 18 feet but fits a narrower lot. Three units also crosses the building-code line into Group R-2, which is a real cost step and one we would rather discuss before you fall for a layout.
- Configuration
- 3 × 1BR / 1BA
- Size
- Unit sizing set against the 750 sqft fee line
- Footprint
- Bar or stacked
- Height allowance needed
- 16–20 ft
Who this is for. Owners of an existing triplex or fourplex who want to use more than two of their detached ADU entitlements in a single building.
What makes it work.
Three entitlements, one structure
A triplex is entitled to three detached ADUs. Because HCD confirms they need not be detached from each other, one building can carry all three — three foundations and three roofs become one.
Bar or stacked, decided by height
Single-story bar at 16 feet if you have the frontage; two-story stacked at 18 feet if you do not. We establish which is available before design starts.
Group R-2 begins here
Three or more dwelling units in one detached building generally moves you from Group R-3 into R-2 — sprinklers, accessibility provisions and stricter assemblies. The step from two units to three is larger than from one to two.
Unit sizing against the fee line
An ADU at 750 sqft of interior livable space or less pays no impact fees, and the exemption applies per unit. On a three-unit building that is three separate exemptions to design for or forfeit.
Pricing on request.
Triplex configurations are in active development for the Signature lineup. We are not publishing a plan fee until the lineup is final — we would rather quote your lot than post a number we intend to revise.
What is available today is the work that has to happen first regardless of which plan you land on: establishing what your property is actually entitled to. The multifamily feasibility assessment is $490, credited in full toward design.
What every 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.
Do I need a triplex to build a triplex ADU building?
You need at least three existing attached units on the lot. Gov. Code § 66323(a)(4)(A)(ii) caps detached ADUs at the number of existing units, up to eight — so a triplex gets three and a fourplex gets four. A duplex is capped at two and would not support this configuration.
Is a three-unit building much more expensive than a duplex?
Per unit, yes — more than most owners expect. The California Building Code generally treats a detached two-unit building as Group R-3 and three or more as R-2, which brings fire sprinklers, accessibility provisions and stricter assemblies. That is why paired structures — two separate two-unit buildings — are sometimes the better answer on a fourplex lot, and why we price both.
Are triplex plans available now?
Not yet as a stock plan. Triplex configurations are in active development for the Signature lineup. What is available today is a feasibility assessment that establishes what your specific property supports — entitlement, height allowance, buildable envelope and which layouts fit — which has to happen before any plan is selected anyway.
Other multifamily plans.
Side-by-Side Duplex
Two mirrored units under one roof, each with its own entrance.
16 ft 2 units · Two storiesStacked Duplex
Half the footprint of side-by-side, on a lot that cannot spare the width.
18–20 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