ADUs in Diamond Bar
Backyard homes for Diamond Bar, priced before you sign.
We design, permit and build standard ADU models in Diamond Bar and across Los Angeles County. You pick a model, we assess your lot, and you get one all-in price before you sign.
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The models
Four standard homes, each with a price up front.
Starting prices include design, permitting and construction with standard finishes. Site work and utilities generally run $15,000 to $35,000 and are priced after we see your lot, and city permit fees are billed at cost. All four fit the City's detached ADU limits for their bedroom count. See what's included.
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Diamond Bar ADU rules in plain English
What you can build in the City of Diamond Bar.
The basics for a single-family lot in Diamond Bar. Where the City's code and current state law differ, we show state law and confirm the City's approach for your address before we price anything.
How many
An ADU, a junior ADU and a detached ADU
State law lets a single-family lot have one ADU and one junior ADU inside the house, or the ADU in an existing accessory building, plus one new detached ADU of up to 800 sq ft. We confirm with the City which combination fits your lot.
Gov. Code 66323(a)Size
850 or 1,000 sq ft detached
A detached ADU can be up to 850 sq ft as a studio or one bedroom, or 1,000 sq ft with two or more bedrooms, and 800 sq ft when the lot also gets a junior ADU. An attached ADU is tied to the size of your house, and we confirm that limit for your lot. Every ADU needs at least 220 sq ft.
DBDC 22.42.120(7)(g)-(h)Height
16 ft detached, 25 ft attached
A detached ADU can be 16 ft tall, or 18 ft within a half-mile walk of a major transit stop, with up to two more feet to match the house's roof pitch. An attached ADU can be 25 ft or the house's height limit, whichever is lower, and two stories at most. A conversion has no height limit.
DBDC 22.42.120(7)(i)Setbacks
4 ft from the side and rear
That applies to a new attached or detached ADU. A conversion needs no new setback, as long as the existing setbacks are enough for fire and safety.
DBDC 22.42.120(7)(e)Parking
One space, with exceptions
A new attached or detached ADU needs one space, unless it's within a half-mile walk of public transit, part of the house or an accessory building, a detached ADU of 800 sq ft or less, in a historic district, or within a block of a car share vehicle, among other exceptions.
DBDC 22.42.120(7)(l)Owning and renting
Rent for 30 days or longer
You don't have to live on the property to have an ADU. Rentals must be 30 days or longer, and an ADU can't be sold separately from the house except as state law provides.
DBDC 22.42.120(9)(a)-(c)Worth knowing in Diamond Bar
A junior ADU can be up to 500 sq ft, inside the house or an existing attached garage. Under state law it needs the owner living on site only when it shares a bathroom with the house, and we confirm how the City applies that to your plan.
A conversion that adds no floor area has no size cap, and an existing accessory building can grow by up to 150 sq ft for an entry.
On a lot with an existing apartment building, state law allows converting non-living space into at least one ADU and up to a quarter of the unit count, plus up to eight detached ADUs, never more than the units already there. We confirm the City's numbers for your lot.
Changing on January 1, 2027
SB 1117 limits the impact fee on an ADU over 750 sq ft to the area above 750 sq ft, in proportion to the main house, for up to two ADUs on a lot. ADUs of 750 sq ft or less still pay no impact fee.
AB 956 lets you build two new detached ADUs on a single-family lot through the state's approval path. On that path a city can cap each one at 800 sq ft.
Sources: Diamond Bar Development Code Section 22.42.120, as amended by Ordinance No. 03(2024); California Government Code sections 66310 to 66342; SB 1117 and AB 956 (2026). Checked November 2026.
How it works
From your lot to move-in.
Step 1
Pick a model
Choose a model and finishes online, or book a free consultation to talk it through.
Step 2
Site assessment
We visit your lot, check utilities, access and the City's rules, and give you one all-in price before you sign.
Step 3
Design and permits
We finish the plans and run the permit with the City of Diamond Bar from submittal to approval.
Step 4
Build and move in
We build on site and manage the job through final inspection and your certificate of occupancy.
Typical timeline: 8 to 12 months from start to finish. About 1 month of design, 2 to 4 months of permits and 3 to 5 months of construction. Your lot and the City's review times can move it.
Diamond Bar ADU questions
What Diamond Bar homeowners ask us.
Our models start at $165,000 for Model S, $195,000 for Model 1, $270,000 for Model 2, $360,000 for Model 3. Those are all-in starting prices for design, permitting and construction. Site work and utilities generally run $15,000 to $35,000, and we price yours after the site assessment, before you sign. City permit fees are separate: your city sets them and we bill them at cost. You start with $1,000, credited in full to your contract, and many of our clients finance the whole build through our lending partners, subject to credit approval. See what's included in the price.
A detached ADU can be up to 850 sq ft as a studio or one bedroom, or 1,000 sq ft with two or more bedrooms, and 800 sq ft when the lot also gets a junior ADU. An attached ADU is tied to the size of your house, and we confirm that limit for your lot. All four of our models fit the detached limits for their bedroom count, and Model S, Model 1 and Model 2 are 800 sq ft or less.
Our typical timeline is 8 to 12 months from start to finish: about 1 month of design, 2 to 4 months of permits and 3 to 5 months of construction. Your lot and the City's review times can move it either way, and we give you a schedule for your address after the site assessment.
A new attached or detached ADU needs one off-street space, which can be in a setback area or tandem on the driveway. No space is needed if the ADU is within a half-mile walk of public transit, part of the house or an accessory building, a detached ADU of 800 sq ft or less, in a historic district, within one block of a car share vehicle, on a lot with apartment buildings, or where on-street permits are required but not offered to the occupant.
Under state law, yes: a single-family lot can have one ADU and one junior ADU inside the house, or the ADU in an existing accessory building, plus one new detached ADU of up to 800 sq ft. A junior ADU can be up to 500 sq ft, inside the house or an existing attached garage. We confirm with the City which combination fits your lot.
Yes. We build across Los Angeles County, as well as Orange County, San Diego and the Inland Empire. Each city has its own ADU rules and plan check, and we confirm them for your address. Enter your address in our quote tool to check that you're in our service area.
Where we build
We also build in these cities.
Each city page covers that city's ADU rules and who issues the permit. All cities.
Los Angeles County
Orange County
San Diego County
Inland Empire
See your price for a Diamond Bar ADU.
Pick a model and tell us your address. After the site assessment you get one all-in number, before you sign.