#1 ADU Contractor in Montclair
Custom Builds by Horizon Remodeling
Need more space or searching for an ADU contractor near Montclair? Horizon specializes in seamless home additions and custom ADU construction in Montclair, from extra bedrooms to backyard cottages and detached units. As your trusted ADU contractor near Montclair, we manage design, budgeting, permits, and material selection—ensuring every project meets city codes and your vision. Our promise: safety, satisfaction, and a smooth build from start to finish. Let’s turn your ADU and home expansion dreams into reality.
SERVICES WE OFFER
Room Additions
Sunroom Additions
Garages & Conversions
Extensions
about the process
When it comes to enhancing your living space, room additions combined with Accessory Dwelling Unit (ADU) construction offer unparalleled versatility and value. These projects not only increase square footage but also provide additional living accommodations — whether for extended family, rental income, or work-from-home setups — making them a popular choice for homeowners seeking to maximize their property’s potential. According to California’s Department of Housing and Community Development, ADUs are a key solution to expanding housing options in urban and suburban neighborhoods.
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California moved its ADU law into Government Code sections 66310 through 66342 in 2024, and it changed again on January 1, 2026: square footage is now measured as interior livable space, and an agency has 15 business days to determine whether an application is complete and 60 days to approve or deny it. Approval is ministerial — no hearing, no discretionary design review.
For a property in Montclair, that application goes to the City of Montclair Building Division. One local factor worth knowing: no unusual local overlay applies, so the building code and the age of the house are what govern.
San Bernardino County adopted a new ADU chapter — Development Code Chapter 84.36 — at the Board of Supervisors on January 13, 2026, which makes it the most current county ADU ordinance of the four we serve. The county’s published standards allow an ADU from 200 up to 1,200 square feet, a junior ADU to 500 square feet, 25 feet of height attached and 18 feet detached with two more feet to match a roof pitch, and four-foot side and rear setbacks with five feet of separation between detached structures. Two provisions are genuinely unlike the coastal counties: two ADUs per lot are allowed, and three units on properties of five acres or more.
Sewer is the question that decides feasibility on a great many parcels here. Connection is required when a sewer line runs within 200 feet of the property line, with that distance increasing by 100 feet for each additional dwelling unit — otherwise the project is on septic or advanced treatment. We bring Environmental Health into the conversation before a plan is drawn rather than after.
The lot decides most of the rest. Housing here was built mostly in the postwar tract boom on land that had been citrus groves through the first half of the twentieth century, after incorporation as Monte Vista in April 1956 and the renaming to Montclair in 1958, and the typical home is a compact postwar single story house with an attached garage and a small kitchen walled off from the living room, which shapes where a detached unit can sit and how far the utilities have to run.
Other Remodeling Services We Offer
A modern kitchen adds functionality, comfort, and lasting value to your home. At Horizon Construction & Remodeling, our kitchen remodeling experts bring fresh ideas and professional project management tailored to your unique needs. From layout design to material selection, we prioritize delivering a high-standard kitchen that’s both beautiful and energy-efficient — enhancing the way you cook, gather, and live every day.
Whether you envision a classic Southern California pool or a fully customized backyard oasis, Horizon Construction & Remodeling delivers the highest level of quality and service. Our comprehensive pool design and remodeling services cover everything from layout and decking to built-in BBQs and final touches like landscaping. Let Horizon be your trusted partner in transforming your backyard into the perfect outdoor retreat.
If you are planning a complete bathroom remodel or simply want to change your tub, shower, update your plumbing fixtures, or make the space more efficient, our team at Horizon will help you through the process with expert advice, professional craftsmanship, and affordable options with beautiful results. Learn more about our bathroom remodeling services.
Transform your space with our expert interior work services. We offer a comprehensive range of solutions — from space planning and custom design to the selection of high-quality finishes and materials. Our team of experienced professionals works closely with you to create a space that’s both functional and stylish, tailored to your unique needs, goals, and budget. Whether you’re updating a single room or overhauling your entire interior, we bring precision, creativity, and craftsmanship to every project.
At Horizon, we believe your home is more than just four walls — it’s where life happens. It’s the place you relax, gather with family and friends, and create lasting memories. That’s why we offer a full range of exterior work services designed to elevate your outdoor living space. From patios and hardscaping to custom decks and exterior renovations, we help turn your vision into a dream yard that complements your lifestyle and enhances curb appeal.
At Horizon Construction & Remodeling, our expert team includes a dedicated design and planning division that works hand-in-hand with licensed architects and structural engineers. We take care of everything — from detailed plans and blueprints to securing city permits — so you don’t have to deal with delays or red tape. Our goal is to streamline the process and provide a fully approved set of documents that aligns with both your vision and city regulations, saving you time and stress.
Why Choose Horizon Remodeling As Your ADU Contractor In Montclair ?
Horizon Construction & Remodeling builds ADUs as a licensed Class B general building contractor, CSLB #938230, bonded and insured, with more than 15 years of design-build work behind us. One company draws the plan, runs it through the agency, and builds it.
In San Bernardino County the feasibility questions come before the design questions: sewer or septic, percolation, well, access, fire hazard zone, and which of the county’s three regions the parcel sits in. We answer those first. A 1,200 square foot ADU on the valley floor and the same unit in a mountain community are not the same build — snow load, frost depth and freeze protection change both the structure and the plumbing. The state protections travel with the parcel wherever it is: no owner-occupancy requirement for an ADU, no sprinkler retrofit of the main house triggered by building one, and no impact fees on a unit of 750 square feet or less of interior livable space.
Our ADU crews also work in Needles, Ontario and Rancho Cucamonga. Landmarks and neighborhoods we work around in Montclair include North Montclair, Downtown Montclair, the Holt Boulevard corridor, the Monte Vista Avenue corridor.
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ADU Contractor Services In Montclair
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ADU Contractor in Montclair FAQ
What is an ADU and why should I build one?
An ADU, or Accessory Dwelling Unit, is a secondary housing unit built on your property—like a backyard cottage, garage conversion, or in-law suite. Building an ADU with Horizon Remodeling allows you to expand your living space, create a rental income opportunity, or provide independent living space for family members.
How much does it cost to build an ADU in California?
The honest answer is that it depends on things we cannot know from a web page: the size and type of unit, whether it is a conversion or new detached construction, the site work and utility runs your lot needs, and the finish level you choose. What we can tell you is where the money goes and what the law protects you from. An ADU of 750 square feet or less of interior livable space is exempt from impact fees; school fees apply only above 500 square feet; and connection fees for a conversion or a junior ADU are limited, because the state does not treat those as a new residential use. Building an ADU also cannot trigger a fire sprinkler retrofit of your main house. Anyone quoting a firm price before seeing the parcel is guessing — we walk the property, confirm the utility and setback situation, and then give you a fixed scope and price you can hold us to.
One warning worth repeating: the CalHFA ADU grant program is closed, its funding fully allocated, and the agency itself warns that anyone offering to help you obtain an ADU grant is running a scam.
Do I need permits for an ADU in Montclair?
Yes. Every ADU needs a building permit. For a property in Montclair the application goes to the City of Montclair Building Division, and the county’s own guidance already reflects the current state timelines of 15 business days for a completeness determination and 60 days to approve or deny. Expect Environmental Health to be part of the review wherever septic or a well is involved, and expect the sewer proximity rule to be checked — connection is required when a sewer line is within 200 feet of the property line. Horizon manages the submittal, the corrections and the inspections.
How long does ADU construction take with Horizon Remodeling?
Most ADU construction projects take between 4 to 8 months from design to completion, depending on scope and permit approvals. Horizon Remodeling prioritizes efficient timelines while maintaining quality workmanship.
What types of ADUs can Horizon Remodeling build?
We specialize in building detached ADUs, attached ADUs, garage conversions, backyard cottages, and junior ADUs (JADUs). Our team can help you choose the right ADU style for your property and goals.
Can I build a detached ADU on my property in Montclair?
Yes, if your property meets California zoning and space requirements. Horizon Remodeling will assess your site, secure the necessary permits, and build a fully detached ADU tailored to your preferences.
Is Horizon Remodeling licensed to build ADUs in my area?
Yes, Horizon Remodeling is fully licensed, bonded, and insured to build ADUs throughout Orange County and surrounding areas. We have over 15 years of experience delivering high-quality ADU projects.
What are the benefits of hiring Horizon Remodeling for my ADU project?
By choosing Horizon Remodeling, you gain a partner with expertise in ADU design, permitting, and construction. We manage the entire process from start to finish, ensuring your ADU meets building codes, stays within budget, and is completed on schedule.
Does Horizon Remodeling handle ADU design and permitting?
Absolutely! Horizon Remodeling provides complete ADU design services, including architectural plans and 3D renderings. We also handle city permits and inspections, streamlining your project and reducing stress.
How do I get started on an ADU with Horizon Remodeling?
Contact Horizon Remodeling to schedule a free consultation. We’ll assess your property, discuss your goals, provide design recommendations, and deliver a detailed estimate. From there, our team guides you step-by-step through every phase of your ADU project.
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Horizon is a licensed Class B general building contractor serving Montclair and the surrounding Orange County communities. CSLB #938230.
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