ADU Builders in Highland — Design, Permits and Build Under One Contract

Fast, Reliable ADU Builders Across Highland

Adding an ADU to your Highland property means working with a builder who knows exactly what these foothill lots demand. We’ve built and converted units all over 92346, from the flat blocks near Baseline to the sloped streets off Boulder Avenue. Sapphire ADU Builders is an ADU-first company led by Nelson Avery, and we’ll match you to the right construction path, whether that’s a prefab unit from Abodu or Cover, or a fully site-built detached ADU. Call (855) 594-0655 and we’ll talk through your lot, your budget, and what actually makes sense for your property.

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Why Sapphire ADU Builders Is Highland’s Preferred ADU Builders Company

Most general contractors treat ADUs as a side job. We don’t. ADU is all we do, which means our team has already worked through the hillside grading questions, the setback interpretations, and the utility hookup realities that trip up contractors who only occasionally build backyard units in Highland. Nelson Avery built this company specifically around accessory dwelling units because the projects deserve better than a remodeler guessing at the permit process.

Our Highland customers consistently tell us the same thing: the estimate process felt different from the other bids they collected. We walk the lot, we look at the existing garage or outbuilding if there is one, and we point out the costs other builders skip in their quotes. That honesty, plus our access to six distinct prefab manufacturers including Dvele and Plant Prefab, means you’re getting brand-agnostic guidance instead of a sales pitch for whatever product a builder happens to carry.

We’re headquartered in Perris, but our crews are in Highland regularly enough that we know the city’s plan check rhythm and where the foothill soil transitions from stable to expansive. That local knowledge shows up in the quote, not in a vague promise.

ADU Construction in Highland

ADU Construction in Highland typically costs between $180,000 and $350,000 for a detached unit, depending on whether we’re converting an existing structure or building new from the foundation up. That range covers everything from a 400-square-foot studio to a two-bedroom unit with full kitchen and bath. The first question is always the same: what’s already on your lot?

Mid-century Highland homes often have detached garages or outbuildings sitting on generous lots. That’s a real advantage, but it’s also where inexperienced contractors miss costs. A garage built in 1962 has framing, electrical, and waterproofing that almost never meets what a permit will require once walls are open. We inspect first, write allowances into the contract for the upgrades we expect, and price anything unexpected in writing before we touch it.

Site-Built Units

When a Highland lot doesn’t suit a prefab module, either because of access constraints or the homeowner wants custom dimensions, we build on site. Our team owns the full scope, including the kitchen and bathroom finishes, so the unit is move-in ready when we hand over the keys.

James Hardie fiber cement siding is standard on our site-built ADUs. Highland summers are brutal on exteriors, and we’d rather build the exterior once with material that holds up for decades than slap on a budget product that fades and warps in three years.

Garage Conversions

Converting a detached garage in Highland is often the fastest path to a rentable unit, but only if the structure justifies the work. We’ve found that many older garages off Boulder Avenue and around the foothill neighborhoods need more than cosmetic updates. Expect the conversation to include foundation, electrical, and waterproofing corrections.

Detached ADU in Highland

Detached ADU construction in Highland generally runs $200,000 to $350,000 for a new build, while a conversion of an existing detached garage typically lands between $130,000 and $220,000 after structural and utility corrections. The spread comes down to what the existing structure gives you versus what it costs to bring it to code.

Highland’s housing stock works in your favor here. Those mid-century homes on large lots frequently have detached garages that already have a roof, slab, and basic framing. That’s a head start. But these structures were never built to be lived in, and the gap between “garage” and “dwelling unit” includes insulation, HVAC, plumbing, and seismic upgrades that can surprise a homeowner if the builder didn’t flag them upfront.

In the foothill blocks off Boulder Avenue, many detached garages sit on sloped lots, so converting one to an ADU usually means retaining walls or a pier-and-beam foundation before any interior work, a cost that flat-lot parts of San Bernardino never see. If your lot slopes more than a few feet across the garage footprint, we’ll account for that in the first quote, not a change order.

Pier-and-Beam Foundations

Sloped foothill lots often can’t support a conventional slab extension. Pier-and-beam keeps the new living space level while respecting the grade, and it allows access for plumbing and electrical routing beneath the floor. We’ve built these in Highland enough times that the engineering and inspection path is routine for us.

Prefab Detached Units

For flatter Highland lots with clear crane or roll-off access, a prefab detached ADU from Abodu, Cover, or Dvele can cut months off the construction timeline. We’re authorized to build and install all three, plus several other manufacturers, so we match you to the product that fits your lot and budget, not the only one we happen to carry.

Trusted Brands We Service in Highland

We’ve installed and serviced units from Abodu, Cover, and Dvele in Highland, and our crews are familiar with each manufacturer’s installation specs, warranty documentation, and finish packages. When you’re evaluating a prefab ADU, the brand matters less than whether the installer actually knows how that brand’s module ties into Highland’s utility and foundation requirements. We do. And because we’re authorized across multiple manufacturers, we can give you a straight comparison of what each one costs and delivers on your specific lot.

Common ADU Builders Problems We See in Highland Homes

• Cloth-wrapped wiring in mid-century garages. Homes built in the 1950s and 1960s often used cloth-insulated wiring that’s now brittle and unsafe. Opening the walls for an ADU conversion almost always triggers a full electrical update, and that’s a cost you want in the contract from day one.
• Failed waterproofing at old garage door thresholds. The slab edge where a garage door used to meet the ground is a classic leak point. We’ve seen conversions where a contractor simply framed over it and called it done. The first Highland rain season floods the unit. We correct it before any finish work begins.
• Sloped lot foundations off Boulder Avenue. A flat-lot bidder will miss the retaining wall or pier-and-beam requirement entirely. Then you’re hit with a five-figure change order after demo starts. We survey the grade first and price it upfront.
• Undersized cooling for 100°F summers. Highland regularly exceeds 100°F in July and August. An ADU needs insulation and HVAC sized for that reality. A window unit won’t hold a 400-square-foot space at a livable temperature, and the tenant will notice.

Pricing for ADU Builders in Highland, CA

We Also Serve Cities Near Highland

Our ADU Builders team works throughout the Inland Empire. We regularly build in San Bernardino, Muscoy, Redlands, and Loma Linda, which means our permits, our crews, and our material suppliers are already close to Highland. If you’re just outside the city line, call us anyway. We likely already have a project nearby.

FAQs About ADU Builders in Highland