ADU in Diamond Bar - One Fixed Price, Permits Handled
We handle the design, the engineering, and the city permit, then build it. One contract, one crew, one accountable point of contact. Free feasibility check on your lot before you commit.
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Our ADU Services
From garage conversions and junior ADUs to fully custom detached units, we handle every phase of your ADU project under one trusted roof.
ADU Design & Permitting
Professional adu design & permitting service. Licensed & insured with a satisfaction guarantee on every job.
ExploreGarage Conversion ADU
Professional garage conversion adu service. Licensed & insured with a satisfaction guarantee on every job.
ExploreNew Detached ADU
Professional new detached adu service. Licensed & insured with a satisfaction guarantee on every job.
ExploreJunior ADU & Interior Conversion
Professional junior adu & interior conversion service. Licensed & insured with a satisfaction guarantee on every job.
ExploreADU Site Prep & Utilities
Professional adu site prep & utilities service. Licensed & insured with a satisfaction guarantee on every job.
ExploreOur Work in Diamond Bar
A look at recent adu projects across Diamond Bar and surrounding areas.
ADUs Built With the Care of a Custom Home
We believe an accessory dwelling unit should feel like a real home - not an afterthought tacked onto your property. Every ADU we build in Diamond Bar is framed, finished, and furnished with the same attention to detail we'd give a full custom residence. Our craftspeople take genuine pride in their work, and it shows in every corner, every connection, and every coat of paint.
Relationships matter more to us than volume. When you work with us, you'll have a dedicated project manager you can actually reach - someone who knows your name, knows your project, and keeps you informed at every milestone. That personal accountability is the foundation of every ADU we deliver.
Start Your ADU Project
Fast Permits, Fewer Surprises, On-Time Delivery
Permitting is where most ADU projects stall - but not ours. Our team has deep experience with Diamond Bar's building department and Los Angeles County's ADU ordinances, which means we submit complete packages, respond to plan-check comments fast, and keep your project on the calendar you were promised.
From the day you sign to the day you receive your certificate of occupancy, we track every deadline, every inspection, and every subcontractor schedule so nothing falls through the cracks. Speed without shortcuts - that's the promise we keep for every Diamond Bar homeowner we serve.
See How Fast We Move
What Homeowners Say
Projects across Diamond Bar and surrounding communities.
"Garage conversion finished on the drawings and close to the schedule. They were honest that the sewer connection was the unknown, and it was."
"The permit set and the build were one contract with one number. Our neighbours used two firms and spent a year watching them blame each other."
"They walked us through setbacks and utility capacity before we paid anything, and told us one of our two options was not going to get approved."
"Every allowance was itemised at the start, so the finish selections did not turn into a surprise at the end."
"The rental income has covered the payment since the second month. They were realistic about the numbers rather than optimistic."
Your ADU Journey, Made Simple
We've refined every step of the ADU process so you always know what's happening, what's next, and exactly who to call.
Free Discovery Call
We start with a friendly, no-pressure conversation about your goals, your property, and your timeline. You'll leave with clarity - not a sales pitch.
Site Assessment & Feasibility
Our team visits your Diamond Bar property to evaluate setbacks, utility access, soil conditions, and zoning rules so we can tell you exactly what's buildable before you spend a dime.
Custom ADU Design
Our designers craft floor plans tailored to your lifestyle and lot - whether that's a cozy junior ADU or a full detached cottage - with 3D renderings so you can see it before we build it.
Permit Package Preparation
We prepare a complete, code-compliant permit submittal for the City of Diamond Bar, handling all drawings, Title 24 energy reports, and supporting documents so your application sails through.
City Submission & Approval
We submit directly to the city and track your permit status daily, responding to plan-check comments swiftly to keep your timeline on track.
Site Prep & Utility Connections
Before a single wall goes up, we handle grading, drainage, electrical panel upgrades, and sewer or water connections - all coordinated to avoid costly delays.
Construction & Quality Checks
Our skilled craftspeople build your ADU with care and precision, conducting milestone inspections at every stage so quality is never an afterthought.
Final Inspection & Move-In
We walk the city inspector through your completed ADU, obtain your certificate of occupancy, and hand you the keys - ready for family, guests, or a rental tenant.
The Craftsmanship Standard You Deserve
Every ADU we deliver in Diamond Bar is measured against six quality benchmarks that define what premium construction really means.
Structural Integrity
We build to California's strict seismic standards with engineered framing and properly anchored foundations, so your ADU stands strong for decades.
Thoughtful Space Planning
Every square foot is designed intentionally - smart layouts that feel open and livable, never cramped, no matter the unit size.
Permit-Ready Documentation
Our in-house drafters produce complete, accurate plan sets that satisfy Diamond Bar building officials, reducing back-and-forth and keeping your project moving.
Plumbing & Utility Precision
From new sewer laterals to tankless water heaters, our plumbing installations are clean, code-compliant, and built for long-term reliability.
Schedule Reliability
We publish a detailed construction calendar and update you weekly - because your time matters as much as the finished product.
Finish Quality
Smooth drywall, solid cabinetry, and durable flooring - our finish crews treat every ADU with the same pride they'd bring to their own home.
Why Diamond Bar Builds With Us
Here's what sets us apart from the dozens of ADU contractors competing for your project in Diamond Bar.
Turnkey, One-Team Delivery
Design, permits, site prep, and construction all flow through a single coordinated team - eliminating the miscommunication and delays that come from hiring separate contractors for each phase.
Transparent, Fixed-Price Proposals
We scope your project thoroughly before we price it, then stand behind that number. No vague allowances or surprise change orders waiting to inflate your final invoice.
Genuine Local Relationships
Our project managers are based in the San Gabriel Valley and personally oversee every build. You'll always have a real person to call - and they'll actually pick up.
Craftsmanship Backed by Warranty
We stand behind the quality of our work with a written workmanship warranty, because a great ADU should give you confidence long after move-in day.
Frequently Asked Questions
Real answers to the questions Diamond Bar homeowners ask us most before starting their ADU journey.
Ready to Add an ADU to Your Diamond Bar Home?
Let's talk about your property, your goals, and how quickly we can get your ADU project moving. A free, no-obligation consultation is just one call away - and we promise to make it worth your time.
(657) 239-4865Get Your Free ADU Quote
Tell us a little about your property and project goals, and a local Diamond Bar ADU specialist will follow up within one business day.
ADU Service Across the Diamond Bar Area
We Are the Diamond Bar Team for Ellery.
Ellery was founded in 2015, the year California's ADU law changed and the permitting queue became the actual product. It is a design-build studio rather than a contractor: the drawings, the permit set and the build are one contract with one price, because the ADU projects that go wrong are almost always the ones where the designer and the builder can each blame the other.
Same training, same parts, same pricing practice, and the same 365-Day Done Right Promise - delivered by people who live here.
Visit Ellery →Part of the Haven Family.
Haven is a family of home-service brands held to one written standard, and Ellery is the adu company in it. One promise stands behind every trade, in every town.