Fast, Reliable ADU Builders Across Highgrove
ADU construction in Highgrove runs $220 – $380 per square foot for a detached unit, with most homeowners in the 92313 zip code budgeting $140,000 – $340,000 depending on whether they go prefab, modular, or fully custom site-built. That’s a wide range, and the spread exists because Highgrove isn’t a typical tract-home suburb. We work on half-acre and larger lots with older homes, private wells, and septic systems that shape what gets built and where. Call (855) 617-6356 to talk through your lot with someone who knows this area.
Highgrove sits in unincorporated Riverside County. That one fact changes everything about how ADUs get permitted, designed, and priced here. We’ve spent enough time navigating the county’s ADU ordinance that we can tell you before you spend a dime whether your septic system, not your lot size, will be the thing that dictates your ADU footprint.
Why Holloway ADU Builders Is Highgrove’s Preferred ADU Builders Company
Homeowners in Highgrove call us because we’re ADU-first. This isn’t a side service bolted onto a general contracting business. ADU Builders is what we do, day in and day out, across prefab, modular, and site-built construction. Neil Trescott leads our team, and he’s built the company around one question: what’s actually the right ADU for this specific lot, this budget, and this family’s timeline.
That question matters more in Highgrove than almost anywhere else in the Inland Empire. The answer here often hinges on a percolation test result. We’ve walked enough Highgrove properties to know that a half-acre lot off Center Street can look perfect on paper and still need the ADU sited forty feet from where the homeowner assumed it would go, because the leach field runs exactly where the original sketch placed the structure.
Our Highgrove clients also get something most ADU contractors can’t offer: real optionality. We’re authorized to work with six major prefab and modular brands, including Cover, Dvele, Mighty Buildings, and Boxabl. If a factory-built shell makes sense for your site, we’ll tell you. If site-built is the better call, we’ll tell you that too. We don’t have a dealer margin pushing us toward one answer.
JADU in Highgrove
A JADU in Highgrove is a conversion of existing space inside or attached to your primary home, typically a garage, spare bedroom, or underused bonus room, into a self-contained junior accessory dwelling unit under 500 square feet. For older Highgrove homes, especially the mid-century ranches that fill much of the 92313 zip code, a JADU is often the fastest and least expensive path to rental income or a home for an aging parent, because it doesn’t require a new foundation, a separate septic connection, or a detached structure subject to setback and leach-field constraints.
When a JADU Makes Sense
The septic issue that constrains detached ADUs in Highgrove mostly disappears with a JADU. Since the unit lives inside your existing building envelope and ties into your current plumbing, you’re not adding a new connection to a leach field that may already be at capacity. That’s why we tell Highgrove homeowners with smaller lots or older septic systems to look hard at the JADU path before committing to a detached build.
What a Highgrove JADU Costs
A JADU conversion in Highgrove typically runs $70,000 – $150,000, depending on whether the space already has plumbing rough-ins, what level of kitchen and bath finish you choose, and whether you’re working within an existing garage slab or carving out interior square footage. The low end assumes a straightforward garage conversion with a modest kitchenette and bath. The high end reflects full custom millwork, relocated plumbing, and higher-end fixtures. Since Holloway also handles bathroom and kitchen remodeling, you won’t need a second contractor to make the JADU livable.
ADU Plans in Highgrove
ADU Plans in Highgrove mean more than architectural drawings. They’re the site plan, structural calculations, Title 24 energy compliance, and septic system evaluation that Riverside County’s building department will actually review. Because Highgrove is unincorporated, every detached ADU plan set runs through the county’s site-plan review process, which looks at lot coverage, setbacks, well and septic capacity, and fire access before anyone considers the structure itself.
Septic-First Site Planning
This is where most Highgrove ADU projects get delayed or derailed. A percolation test and leach-field capacity check needs to happen before you finalize any footprint. If the existing septic can’t absorb another bedroom’s worth of wastewater, you’re looking at either a smaller ADU, an engineered septic upgrade, or a JADU instead. We order that test early, so you’re not paying for drawings that can’t get permitted.
Working with Your Designer or Architect
If you already have a designer or architect, we coordinate directly with them. Our role is to reconcile their vision with the county’s septic, setback, and wind-load requirements specific to Highgrove. If you don’t have plans yet, we’ll connect you with professionals who understand Riverside County’s unincorporated ADU ordinance. Either way, you get a plan set that passes review the first time, not a third or fourth resubmittal.
Trusted Brands We Service in Highgrove
We’re authorized to work with six major prefab and modular ADU manufacturers, and that matters for Highgrove homeowners because the right brand can cut months off your timeline. Dvele’s panelized shells arrive with a level of precision that works well on the expansive, heat-exposed sites common in the 92313 zip code. Cover and Mighty Buildings offer factory-built units that reduce on-site construction time, which matters when Santa Ana winds and triple-digit summer heat compress your practical building window. Boxabl rounds out the portfolio for smaller, ADU-scale structures. We also handle Tuff Shed conversions for homeowners who want a lower-cost entry point. One team from foundation to finished kitchen.
Common ADU Builders Problems We See in Highgrove Homes
- Drawing the ADU before the perc test. In Highgrove, a detached ADU’s site plan can be blocked by a percolation test and leach-field capacity long before Riverside County ever sees a drawing. Septic, not square footage, is frequently the binding constraint on placement and size.
- Long-lead items priced on a verbal estimate. Custom cabinetry and architectural glass can carry 8 – 20 week lead times. When a contractor quotes those verbally and then the supplier raises prices, the homeowner absorbs it. We fix the price in writing before anything goes to the shop.
- Coastal wind assumptions on a Highgrove site. Detailing a roof and western exposure for a mild coastal breeze instead of Highgrove’s Santa Ana gusts and intense summer cooling loads produces a structure that underperforms. We specify wind-resistant attachments and deep overhangs from the start.
- Septic capacity ignored until plan review. An existing leach field sized for a three-bedroom house can’t always absorb a one-bedroom ADU. We flag this in week one, not when the county sends back your submittal.
Pricing for ADU Builders in Highgrove, CA
Detached ADUs in Highgrove run $220 – $380 per square foot, putting most projects between $140,000 and $340,000 all-in. JADU conversions land at $70,000 – $150,000. Prefab and modular shells from Dvele, Cover, or Boxabl often reduce on-site labor costs, but factory pricing plus foundation, site work, and interior finishing typically mirrors site-built on a square-foot basis. What actually moves your number is millwork, glass, and finish level. Custom white-oak cabinetry, a full quartz or stone kitchen, and architectural glazing can add $40,000 – $70,000 to a Highgrove ADU versus builder-grade finishes. Call (855) 617-6356 for a free estimate with a written, line-item price you can hold us to.
We Also Serve Cities Near Highgrove
Holloway ADU Builders works throughout the Inland Empire, including Grand Terrace, Colton, Rubidoux, and Bloomington. If your property sits near the Highgrove boundary or you own a rental in a neighboring community, we can carry the same septic-first, county-permitted approach across city lines. Call (855) 617-6356 and we’ll tell you whether your property falls under Riverside County or a city jurisdiction.
Serving Highgrove, CA — Our Local Coverage Area
We’re based in the Highgrove area and know this community well. Use the map below to see our service coverage — if you’re nearby, we can almost certainly help.
FAQs About ADU Builders in Highgrove
Yes. Most of Highgrove runs on private septic systems, and your leach field’s capacity is often the single biggest constraint on ADU size and placement. A percolation test tells us what the soil can absorb. If the existing system is maxed out, you’ll either size the ADU down, upgrade the septic, or pivot to a JADU inside your current footprint. Call (855) 617-6356 and we’ll order the perc test before you spend money on plans.
Because on a custom ADU in Highgrove, framing is the fast part. Custom millwork runs 8 – 16 weeks and architectural glass 10 – 20 weeks, depending on the manufacturer. The schedule is set by when those long-lead items clear the shop, not by how fast a framing crew works. We lock the order schedule and the price in writing before anything is fabricated, so lead-time shifts don’t become change orders.
Riverside County. Highgrove is unincorporated, so there’s no city building department. Your ADU permit runs through Riverside County’s building and safety office, plus the county’s site-plan review for setbacks, septic, wells, and fire access. It’s a different process than a city like Colton or Grand Terrace would use. We handle that paperwork for you.
Yes, and for many older Highgrove homes it’s the smarter play. A JADU converts existing space inside your home or attached garage, so it doesn’t add a new septic connection or trigger the setbacks and site-plan review a detached ADU requires. If your leach field is at capacity or your lot is tighter than you’d like, a JADU gets you a rentable unit without the septic headache. Call (855) 617-6356 to talk through which path fits your property.
We fix the price in writing before anything goes to the shop. On a recent Highgrove project off Spring Street, the leach field forced the ADU footprint 14 feet off the original stake line. We re-detailed the western glazing with deep overhangs and shaded glass to handle Santa Ana wind and summer heat, re-coordinated a custom white-oak millwork package and a Dvele shell order in the same locked schedule, then held that price fixed in writing before either went to fabrication. That’s the standard on every Highgrove project we take.
Written by Neil Trescott, Owner at Holloway ADU Builders, serving Highgrove and the Inland Empire.