Trusted ADU Site Prep & Utilities for Los Angeles Homeowners
Los Angeles ADU Site Prep & Utilities typically runs $28,000 to $65,000 for a full new detached unit, depending on slope, soil, panel capacity, and how far your sewer lateral needs to travel. A garage conversion with existing utilities often lands between $12,000 and $22,000 for the site work portion. That’s the number most Los Angeles homeowners actually need before they can decide whether the project pencils out.
Ellery ADU Studio has handled this work since 2015, the year California’s ADU permitting landscape genuinely shifted. We’ve designed, permitted, and built more than 900 ADUs across Los Angeles since then, every one with a written price before work started, under Haven Standard Clause 1. No allowances, no “we’ll see when we dig.” If you want to talk through your specific lot now, call (971) 497-2402. A live person answers.
Nadia Ellery runs the studio and has built the practice around one idea: the permit set is the product. The dirt work, the trenching, the panel, the lateral replacement all flow from drawings that the city has already approved. When the drawings are right, the utilities are right. When they’re not, you find out at $900 a day for a crew standing idle. We’d rather you not learn that the expensive way.
What Our ADU Site Prep & Utilities Service Includes
Foundation & Grading
Foundation and grading is the part of the job you never see again, and it’s where a cheap line item becomes a $40,000 correction. Lots run from flat Mid-City 5,000-square-foot rectangles to hillside parcels in Silver Lake and Echo Park with 20 percent or more of cross-slope. For ADU Site Prep & Utilities - Huntington Park and similar flat areas, grading is simpler. Grading matters because the city’s maximum retaining wall height without an engineered design is 4 feet, and a poorly graded pad will route water toward the ADU rather than away from it, which is how you get a mold claim three years after occupancy.
We evaluate the geotech report (required by LADBS for most hillside and canyon ADUs), then establish the pad elevation, compaction, and drainage path before the first yard of concrete goes in. When the existing structure is a garage, we drill and test the slab thickness. A 4-inch slab with minimal cracking is often usable as a foundation with a curb and additional shear wall detail; a 3-inch slab with heaving corners means demolition and a new mat slab. We tell you which one you have in writing, with photos, before you commit.
Electrical Panel Upgrade
Your 1948-era 100-amp panel will not carry a new ADU with a mini-split, an induction cooktop, a washer-dryer stack, and an EV charger. It won’t even carry half of that. An ADU in Los Angeles needs either a dedicated 100-amp subpanel (minimum, under current LADBS and LADWP requirements for a detached unit) or a service upgrade to 200 amps, and the difference in price is roughly $4,000 to $9,500 depending on whether the utility drop is overhead or underground and how far your panel is from the meter.
We run the load calculation as part of the permit set, not as a surprise discovery during rough-in. If your panel is a Zinsco or Federal Pacific, we’ll flag it by brand name and photo in the site assessment. Those panels are uninsurable with several carriers, and no legitimate electrician will add a subpanel off one without replacing it first.
Plumbing Lateral
The sewer lateral is the pipe that runs from your house to the city main, and in pre-1960 Los Angeles neighborhoods like West Adams or Jefferson Park, it’s likely clay or cast iron with root intrusion every 4 feet. You can spend $18,000 renovating a garage ADU and then discover the lateral needs replacement and the city won’t sign off on the ADU connection until it’s done. ADU Site Prep & Utilities - South Gate follows the same LADBS rules, so we camera the lateral before we finalize the permit set. We camera the lateral before we finalize the permit set, so the line item is in the contract on day one, not in a change order on day forty.
Replacement typically runs $6,000 to $14,000 for a 40- to 80-foot run depending on depth, sidewalk cutting, and street restoration requirements, and that number appears in your written price under Clause 1. For an ADU, LADBS requires a separate cleanout at the property line and, in many cases, a backwater valve because the ADU is built lower than the main house’s finished floor. We spec both into the drawings, and the inspector sees them on the approved plans, so there’s no standoff at final inspection.
Gas Line Extension
A separate gas line to an ADU is no longer the default in Los Angeles. All-electric ADUs with heat-pump HVAC and induction cooking avoid the gas line entirely, which saves $3,000 to $7,000 in piping, trenching, and LADBS testing, and many Los Angeles neighborhoods now have building code paths that actively discourage extending gas to new detached units. But if you’re keeping the ADU on gas because you want a tankless water heater or you simply prefer a gas cooktop, the line gets sized from the meter, not from the existing house manifold, which half the bids we see get wrong.
The run matters. A 120-foot gas line from a meter on the opposite side of the property with two bends and a riser costs more than a 30-foot straight shot, and the difference is not small. We show you the route on the site plan and give you the fixed number per lineal foot before we trench. If we hit rock, which happens a lot in the foothills above Pasadena and in the Verdugo-adjacent pockets of the Valley, the rock clause in your contract tells you exactly what happens next. It’s written down, Clause 5, no surprises.
Landscaping & Hardscape
Site prep ends where the finished grade meets the property line, and that means drainage swales, retaining walls in some cases, and enough hardscape to make the ADU feel like it was always there rather than dropped onto the lot like a shipping container. We don’t design planting palettes, so know that we stop at the hardscape and rough grading, trees, irrigation, and planting design go to your landscape architect, and we coordinate with them on the drainage and grade calls.
What we do handle is the stuff the city cares about and the stuff that fails silently: compacted walkways with ADA-accessible path-of-travel if the ADU will be used for any kind of rental, retention or infiltration for stormwater (required for additions adding more than 500 square feet of impervious area under the city’s Low Impact Development ordinance), and the retaining wall, which needs an engineer’s stamp if it exceeds 4 feet. That’s not a fence. That’s a structure. We treat it like one.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Brands We Service for ADU Site Prep & Utilities
We specify and coordinate prefab and modular ADU systems from Abodu and Cover most often in Los Angeles, because both manufacturers have units that fit the city’s 1,200-square-foot maximum for a detached ADU and both require precise foundation, utility, and grading work before the module ever lands on a truck. With Abodu, the foundation tolerances are tighter than city code requires: the top of the concrete has to be level within an eighth of an inch across the pad, and we run a laser check the morning of the set. With Cover, we’ve managed the panel and trenching to support their all-electric mechanical packages, which pull 90 amps on the larger two-bedroom units, so the service upgrade is part of the initial design conversation, not a surprise after the unit arrives.
For Dvele and other high-performance modular brands, the utility rough-in demands a different level of coordination: Dvele units arrive with their electrical and plumbing stubbed into specific wall cavities, and the stub locations have to match the site utilities within half an inch. We’ve done it enough times to know that a half-inch is a real tolerance, not a head start. Whether your build is a site-built detached ADU, a garage conversion, or a prefab unit from any manufacturer, the point is the same: the drawings, the permit set, and the construction are one contract, so the foundation and utilities never become a dispute between two different companies.
Signs You Need ADU Site Prep & Utilities Right Now
- Your electrical panel is a Zinsco or Federal Pacific. These panels have documented failure-to-trip issues and several Los Angeles insurers won’t write a policy with one in place. If you’re planning an ADU of any kind, the panel gets replaced or upgraded as part of the permit, no exceptions, so finding out now saves you a three-week delay mid-project.
- You’re planning a garage conversion and notice the slab has a visible step crack. A step crack of more than a quarter inch in the slab or stem wall is often differential settlement, and if it’s still moving, the new ADU walls will move with it. You need a structural opinion on the slab, not just a fresh pour over the old crack.
- Tree roots have invaded your existing sewer line. If you’ve had Roto-Rooter out more than once in the past three years, the lateral is compromised, and the ADU connection only adds more flow to a pipe that’s already failing. Replace it while the trench is open for utility work; don’t pay to dig the same yard twice.
- Your water pressure drops noticeably when two fixtures run at once. A 3/4-inch main from the meter with a 1/2-inch branch to the house was fine for a 1958 bungalow. Add a full second dwelling with its own bathroom, kitchen, and irrigation, and you’ll be doing a dedicated water line replacement anyway. Better to size it during site prep than after the ADU is occupied and the shower goes cold mid-rinse.
- The lot slopes more than 6 feet from back to front. Anything beyond a 6-foot fall across the buildable area means retaining walls, stepped footings, or both, and the cost to bring that hillside into code compliance can equal the cost of the ADU structure itself. You want that number before you buy the prefab unit and find out the pad work is $70,000.
Our ADU Site Prep & Utilities Process - Step by Step
Site prep is the least forgiving part of any ADU project, because the mistakes are buried. Here’s the sequence we follow in Los Angeles, unchanged since Nadia Ellery formalized the studio’s process in 2015, and documented in writing at every milestone.
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Site assessment and documentation. We walk the lot and the existing structure, drill the slab, camera the lateral, inspect the panel, and map the grading. You receive a written assessment with photos, measurements, and the findings tied to your specific situation. If the slab is 4 inches, we say so. If the lateral is collapsed at 22 feet, we show you the camera still. This assessment is yours to keep, whether or not we build the project.
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Permit set and fixed scope. The drawings, the structural engineering, the grading plan, the panel schedule, and the utility routing all go into a permit set that we submit to LADBS and, where required, LADWP. The site work scope is written line by line, with a fixed price attached. There is no allowance line item that can balloon later. Clause 5 locks the scope at signing; no door-side upsells.
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Demolition and rough grading. We clear the build area, demolish any slab sections that can’t be repurposed, and cut the pad to the elevations on the approved grading plan. Laser-leveling on every pad, not eyeballing from stakes. For hillside lots, we install temporary silt fencing and erosion control before any dirt moves; LADBS and the Regional Water Board both check for that.
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Utilities rough-in. Panel upgrade or subpanel, trenching for water and sewer, gas line if the ADU is staying on gas, plus the conduit runs for low-voltage and communications. Every trench is photographed at depth before backfill, and you get those photos: documented evidence of what was installed and where it sits, which matters in ten years when you’re trying to remember where the line runs.
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Foundation pour and backfill. Forms set to plan, rebar per the structural drawings, concrete placed and finished. For prefab units from Abodu, Cover, or Dvele, we verify slab flatness to the manufacturer’s spec before the set date. Then we backfill, compact in lifts, and rough-grade the site to drain. The inspector signs off, the photo record closes out, and the 365-Day Done Right Promise runs from the day the work completes.
How Much Does ADU Site Prep & Utilities Cost in Los Angeles?
For a new detached ADU on a reasonably flat Los Angeles lot, site prep and utilities typically run $28,000 to $65,000 all in, from demolition and pad grading through panel upgrade, sewer lateral, water service, and final rough grade. ADU Site Prep & Utilities in Bell follows the same pricing structure for flat lots. A garage conversion where the slab, panel, and lateral all pass inspection comes in lower, usually $12,000 to $22,000, because the structure exists and the utilities are partially in place. Hillside lots above a 2:1 slope ratio can push the site work line past $80,000 fast, because retaining walls and engineered footings are priced by the lineal foot and the cubic yard, not by the project.
What moves the number most: slope and retaining needs, the condition and age of the sewer lateral, the panel capacity and service upgrade requirements, and the distance from the meter to the ADU. A 160-foot gas line with three bends costs more than a 25-foot straight shot, and we’ll show you both routes on the plan before we sign anything. Avoid overpaying the way you’d expect: get the geotech report early, camera the lateral before final bids, and don’t accept a contract with an allowance line item for “site conditions.” That allowance is where the price goes to die. Every Ellery ADU Studio contract has a fixed written price before work starts, per Haven Standard Clause 1. No allowances, no change orders, no door-side surprises.
If you already have a written estimate from another company, bring it to us. We’ll go through it line by line and tell you what’s missing, what’s padded, and what’s priced correctly. A free second opinion. If you’d rather start from zero, call (971) 497-2402 and we’ll schedule the site assessment. The estimate is free, the written price is fixed, and the assessment is yours either way.
ADU Site Prep & Utilities Near Los Angeles - Our Service Area
We work across Los Angeles proper, from the Mid-City flatlands to the hills of Mount Washington, and out through the San Fernando Valley and the San Gabriel Valley into Pasadena and Burbank. Typical lead time for a site assessment is one to two weeks, depending on where you are in the city and how quickly LADBS can pull the existing permit history on your lot. For context on how we approach this work in other markets, see our ADU Site Prep & Utilities in Houston and ADU Site Prep & Utilities in San Antonio pages. The site conditions change; the written-price standard doesn’t.
Serving Los Angeles, CA - Our Local Coverage Area
We’re based in the Los Angeles area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions - ADU Site Prep & Utilities in Los Angeles
ADU site prep and utilities is the underground and structural work that makes a new ADU buildable: clearing and grading the pad, building or reusing the foundation, upgrading the electrical panel, connecting water and sewer, extending gas if needed, and rough-grading the finished site so it drains. It’s the part of the project that doesn’t show in photos but determines whether the ADU lasts 50 years or 15. In Los Angeles specifically, it also includes the LADBS inspection sequence, the title 24 energy compliance path, and the stormwater infiltration requirements that kick in for any ADU adding significant impervious area.
For a new detached ADU, the site prep and utilities phase runs four to eight weeks from first day of demolition to the foundation inspection, depending on slope, retaining walls, and how much utility trenching is required. Garage conversions with an existing foundation and working utilities can be through site prep in two to three weeks. The real scheduling variable in Los Angeles is LADBS inspection lead times and utility coordination with LADWP, which is why the permit set is submitted as early as possible, so the site work isn’t waiting on plan check.
A new detached ADU on a typical flat Los Angeles lot runs $28,000 to $65,000 for full site prep and utilities. A garage conversion usually runs $12,000 to $22,000 for the site work portion, assuming the slab, lateral, and panel are usable. Hillside lots can stretch past $80,000 because engineered retaining walls and stepped footings are priced by the lineal foot. Every project we take on has a fixed written price before work starts, under Haven Standard Clause 1, so the number you see at signing is the number you pay at final inspection. Call (971) 497-2402 for a free estimate with the actual numbers for your lot.
Yes, we coordinate site prep and utilities for Abodu, Cover, and Dvele prefab units throughout Los Angeles, and we’ve worked with all three brands long enough to know their foundation tolerances and utility stub requirements. Abodu requires a slab level within an eighth of an inch across the pad, which we laser-verify before set day. Cover’s all-electric units pull substantial amperage, so the panel upgrade is part of the initial design conversation, not an afterthought. Dvele’s stubs have to match the site utilities within half an inch, and we’ve coordinated enough Dvele sets to treat that as a hard spec. If you own a different prefab brand, the same single-contract coordination applies.
Yes, in almost every case. Site prep and utility work is noisy and will disrupt your parking for a few weeks depending on trenching locations, but the main house can stay fully occupied, with water, power, and gas remaining live except for short, scheduled outage windows when the panel is swapped or the water service is re-routed. We schedule those outages in writing and tell you the exact hours in advance. If you have a home office, plan a few days where jackhammering and backhoe work will be audible from inside.
Our 365-Day Done Right Promise covers every element of the site prep and utility work for a full year from final inspection: if anything is not built to the permitted drawings, we make it right, in writing, before the project starts. That includes foundation work, drainage, panel installation, sewer and water connections, and gas line installation. The promise is part of The Haven Standard and it’s stated in the contract, not in a brochure.
Gather your lot survey, any prior structural or inspection reports you have, and photos of the existing utility connections if they’re accessible, then walk the yard and note where the gas meter, water shutoff, and house panel sit relative to where you’d like the ADU to go. We’ll handle the rest: slab drilling, lateral camera, panel inspection, and grade mapping. The assessment takes about 90 minutes on site, and you’ll receive a written report with photos and measurements within a week. There’s no cost for the assessment, and the report is yours whether or not we build the project.
Schedule Your ADU Site Prep & Utilities Service in Los Angeles Today
If you’re weighing an ADU in Los Angeles, the site work is the foundation of the budget, and the number should be written down before you spend a dollar elsewhere. Ellery ADU Studio has done this work since 2015, with 900+ ADUs designed, permitted, and built, every one priced in writing before work started. Call (971) 497-2402 to schedule your free site assessment and written estimate. A live person answers, 24/7, and the price we give you is the price you pay.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Los Angeles since 2015.