Trusted ADU Site Prep & Utilities for Pomona Homeowners
ADU site prep and utilities in Pomona typically runs $35,000-$85,000 depending on scope, with foundation and grading work starting around $18,000 and full utility packages including electrical, plumbing, and gas reaching the upper range for hillside lots or aging infrastructure. Most Pomona projects move from site evaluation to permit-ready plans in 4-8 weeks, with utility connections coordinated through the city’s Development Services Department and Southern California Edison. Call (657) 286-7915 to schedule your free estimate - every project receives a written price before any work begins, per Haven Standard Clause 1.
We’ve designed, permitted, and built over 900 ADUs since 2015, the year California’s ADU laws fundamentally shifted. Pomona’s mix of postwar flat lots in the north and hillside terrain in Phillips Ranch and south Pomona means no two site prep packages are identical. The same slab that works in Lincoln Park may need full replacement in the Ganesha Hills area where expansive clay soils and steeper grades dominate. Our crews document every site condition with dated photos - you’ll receive the evidence, not a summary of how it felt.
Nadia Ellery leads every site evaluation personally or through her directly assigned project leads. Background-checked, uniformed crews carry the studio’s license number on every vehicle and document. The 365-Day Done Right Promise applies to site prep and utilities exactly as it does to the finished ADU: if the finished work does not match the permitted drawings and written scope, we make it right - in writing, before your project starts.
What Our ADU Site Prep & Utilities Service Includes
Foundation & Grading
Foundation and grading is the physical platform your ADU sits on - literally. In Pomona, we regularly encounter two conditions: older flat lots with 4-inch garage slabs that won’t carry a habitable structure, and hillside parcels where cut-and-fill grading triggers geotechnical requirements under the city’s hillside development ordinance. We evaluate soil bearing capacity, drainage patterns, and the proximity of existing trees whose root systems affect excavation. For a typical Pomona garage conversion, we’ll specify either a thickened edge foundation or full stem-wall system depending on the existing slab’s condition and the conversion’s structural load. Every foundation proposal includes a geotechnical referral when needed, with the report incorporated directly into your permit set.
Electrical Panel Upgrade
An electrical panel upgrade replaces or expands your service entrance equipment to handle the additional load of a full kitchen, laundry, HVAC, and EV-ready outlet. Pomona’s older housing stock - particularly in the Mayfair and Westmont neighborhoods built in the 1950s and 1960s - often carries 100-amp panels that max out with modern ADU loads. We coordinate directly with Southern California Edison for service size confirmation and temporary power during construction. Our permit set includes the single-line diagram, load calculations per NEC Article 220, and panel schedule - documentation the city requires and most contractors draft only after permit submittal. For projects specifying prefab systems from Boxabl or Plant Prefab, we match the manufacturer’s electrical specifications to your site conditions before any trenching begins.
Plumbing Lateral
The plumbing lateral connects your ADU’s waste and water lines to the city main, often requiring trenching through established Pomona landscaping or beneath existing driveways. Pomona’s clay soils shift seasonally, so we specify expansion joints and proper bedding per UPC Chapter 3 to prevent future separation. Many properties near downtown Pomona connect to older cast-iron or clay sewer laterals that fail under camera inspection - we include the video evidence in your project file and price replacement transparently if needed. For Montclair-adjacent properties on septic systems, we coordinate with San Bernardino County for percolation testing and leach field expansion. The lateral’s depth, length, and number of cleanouts are dimensioned on your permit set, not left to field interpretation.
Gas Line Extension
Gas line extension runs a properly sized branch from your existing meter or main line to serve the ADU’s water heater, furnace, dryer, and cooking appliances. Southern California Gas Company requires a meter capacity check for any addition over 100,000 BTU/hr cumulative - we submit this inquiry before your permit application so sizing surprises don’t delay inspection. In Pomona’s hillside areas, gas lines often require pressure regulation at the branch point and corrosion protection where soils are aggressive. We specify black iron or CSST (corrugated stainless steel tubing) based on the route’s accessibility and the city’s current amendment to the California Plumbing Code. Every gas line proposal includes a leak-down test protocol and the final pressure test documentation for your inspector.
Landscaping & Hardscape
Landscaping and hardscape restoration completes the site after utility trenches are backfilled and foundations poured. Pomona’s water conservation requirements - the city operates under Stage 2 Water Supply Shortage contingency - mean we specify drought-tolerant plantings and permeable surfaces where code allows. For San Dimas-area clients and others in our service territory, we coordinate with the Pomona Valley Municipal Water District for any irrigation system modifications. Hardscape includes the ADU’s required walkways, patio slabs per the city’s Zoning Code Section 17.58, and parking surface restoration where trenching disrupted existing concrete. Our scope specifies material depths, compaction requirements, and drainage slopes - the documentation that prevents callback disputes six months after move-in.
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
Ellery ADU Studio specifies and coordinates prefab and modular systems where the manufacturer’s site prep requirements differ from conventional stick-built construction. For Boxabl Casita installations, we verify crane access and the compacted aggregate pad specification - typically 6 inches of Class 2 base over native soil - then coordinate the utility stub locations to match the unit’s pre-plumbed and pre-wired chassis connections. The pad’s dimensional tolerance is ±1/4 inch, which sounds tight until you’ve seen a 375-square-foot module set on an out-of-level base. We document the pad survey with photos and a written certification.
For Plant Prefab and Tuff Shed structures, site prep varies by foundation type. Plant Prefab’s LivingHome series typically requires a conventional stem-wall or raised floor foundation with utility rough-ins stubbed to the exterior wall line. Tuff Shed’s installed buildings need either a gravel pad or concrete pier system depending on the city’s habitable-structure classification. We’ve coordinated dozens of each in Los Angeles County and understand where Pomona’s building official will accept a pier foundation versus where a full perimeter system is mandatory. For James Hardie siding systems on site-built ADUs, we specify the drainage plane and fastening pattern during framing - not as an afterthought when the siding crew arrives. Whether your project uses these brands or any other make, we can help.
Signs You Need ADU Site Prep & Utilities Right Now
- Your garage slab has visible cracks wider than 1/4 inch or differential settlement. These conditions indicate the existing foundation won’t support a conversion’s habitable load, and Pomona’s building official will flag them at the first inspection. We assess slab condition during initial site documentation and specify replacement or reinforcement before permit submittal, not after a failed inspection adds six weeks to your timeline.
- Your electrical panel still uses fuses or lacks open breaker spaces. Fuse panels haven’t met code for new habitable space in decades, and a full panel with tandem breakers already installed has no room for ADU circuits. We verify available amperage and breaker positions during our first visit, then coordinate the SCE service upgrade timeline with your construction schedule.
- Your property has mature trees within 20 feet of the proposed ADU footprint. Pomona’s tree preservation ordinance protects certain species and trunk diameters, and root zones affect both foundation depth and utility routing. We identify protected trees early, adjust the ADU placement if needed, and specify root barrier installation where trenching is unavoidable.
- Your water pressure drops noticeably when multiple fixtures run. Low dynamic pressure at the hose bib often means the existing lateral is undersized or partially obstructed for an additional dwelling unit. We pressure-test during evaluation and specify lateral replacement if static pressure falls below 40 PSI or flow rate can’t support the ADU’s fixture count.
- Your sewer has backed up or drains slowly even after cleaning. Recurring blockage suggests a collapsed or bellied lateral, conditions that camera inspection confirms. We include the video in your project documentation and price full replacement - not another band-aid cleaning - so your ADU’s plumbing starts on a functional system, not a failing one.
Our ADU Site Prep & Utilities Process - Step by Step
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Site Evaluation & Documentation - Nadia Ellery or a designated project lead walks your Pomona property with a tablet, documenting existing conditions with timestamped photos and measurements. We note soil type, slope, utility locations from visible markers, and any access constraints. You receive this photo record within 24 hours, before any pricing discussion begins.
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Utility Research & Coordination - We contact Southern California Edison, SoCalGas, and the Pomona Water Department to confirm service capacity, main locations, and any known infrastructure conflicts. For properties near the 10 Freeway corridor or in the industrial transition zones, we verify whether municipal sewer or septic applies. This research prevents the “surprise easement” that derails projects after permit approval.
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Permit-Ready Plans & Written Price - Our in-house drafters produce the site plan, utility plan, and structural details required for Pomona’s Development Services submission. Every line item - excavation, concrete, electrical service upgrade, lateral replacement, gas line, restoration - carries a fixed price. Haven Standard Clause 1: the written price is locked before any work starts. No change orders for scope we’ve already identified.
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Permit Submittal & Approval - We submit complete plans through Pomona’s online permitting portal and track review status weekly. Our familiarity with the city’s typical plan-check comments - foundation depth in expansive soils, electrical load letter format, gas line pressure test requirements - means first-round approvals on most site prep packages. We attend correction meetings in person when needed.
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Construction, Inspection & Handoff - Background-checked crews execute the scope with a superintendent on site for critical inspections: foundation footing, underground plumbing, gas pressure test, and final utility activation. Every inspection receives photo documentation. Upon completion, you receive the signed inspection cards, as-built utility locations, and the 365-Day Done Right Promise in writing.
How Much Does ADU Site Prep & Utilities Cost in Pomona?
A typical foundation and grading package in Pomona runs $18,000-$42,000 depending on square footage, soil conditions, and whether the existing slab is salvageable. Electrical panel upgrades with SCE coordination add $4,500-$12,000 for 200-amp service; full service replacement from the pole or underground transformer runs higher. Plumbing lateral work - trenching, pipe, bedding, and restoration - typically falls between $8,000 and $22,000 depending on length and whether the existing line requires replacement. Gas line extension adds $3,500-$8,500 for most Pomona lots under 8,000 square feet. Landscaping and hardscape restoration closes the range at $5,000-$15,000 depending on surface area and material selection.
Combined site prep and utilities for a standard Pomona garage conversion typically total $35,000-$55,000. New detached ADUs on flat lots with full utility packages run $55,000-$85,000. Hillside properties in Phillips Ranch, Ganesha Hills, or south Pomona’s steeper terrain can exceed this range when retaining walls, engineered fill, or extended utility runs enter the scope.
Several factors move these numbers. Expansive clay soils - common in the Pomona Valley - require deeper footings and possibly pier foundations. Properties with alley access simplify utility trenching; front-yard-only access may require pavement cutting and restoration. Older homes with original galvanized plumbing or fuse panels need full replacement, not extension. We identify these conditions during evaluation and price them explicitly - no “allowance” line items that balloon later.
How to avoid overpaying: get a second opinion on any estimate already in hand. Our Free Second Opinion service reviews competitor quotes against your actual site conditions and the permit set they’d produce. We’ve found $15,000+ discrepancies where a contractor priced a slab replacement as “repair” or omitted the electrical service upgrade entirely. Every Ellery estimate includes the full permit set, all utility coordination, and the documented photo record - scope items that separate professional site prep from hand-waving.
What’s included in your free estimate: a site visit with photo documentation, utility capacity research, a preliminary site plan showing foundation location and utility routes, and a written line-item price valid for 30 days. No deposit required. No “design fee” that applies only if you hire us. Call (657) 286-7915 to schedule.
ADU Site Prep & Utilities Near Pomona - Our Service Area
Ellery ADU Studio serves Pomona and the surrounding San Gabriel and Pomona Valley cities including Montclair, San Dimas, Diamond Bar, Upland, Covina, Glendora, Chino, Chino Hills, West Covina, Ontario, and Rowland Heights. Response time for initial site evaluation is typically 2-3 business days in Pomona proper and 3-5 days for outlying cities. We maintain active permit relationships with each city’s building department, so your site prep package moves through plan check without the delays of a contractor learning local requirements for the first time. For Montclair’s ADU site prep or San Dimas utility coordination, the same single-contract, written-price structure applies.
Serving Pomona, CA - Our Local Coverage Area
We’re based in the Pomona 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 Pomona
ADU site prep and utilities is the physical and mechanical groundwork that makes your property ready for construction: foundation excavation and concrete, electrical service sizing and panel upgrades, water and sewer lateral installation, gas line extension, and final landscape restoration. It needs its own scope because these trades require separate permits, separate inspections, and separate utility company coordination - work that many design-only firms omit and many contractors underestimate. At Ellery, site prep is specified in the same contract as your ADU’s design and build, so no one can claim “that wasn’t in my scope” when underground work runs into unexpected conditions.
From signed contract to final utility activation, most Pomona site prep packages take 6-12 weeks depending on permit review time and utility company schedules. Foundation work typically requires 2-3 weeks including cure time; electrical, plumbing, and gas trades add another 3-5 weeks with inspections; landscaping restoration closes the sequence. Southern California Edison’s service upgrade timeline is the most common variable - we’ve seen 3-week approvals and 8-week waits depending on their workload. We build this uncertainty into our project schedule and communicate updates weekly, not when you call asking.
Most Pomona homeowners invest $35,000-$85,000 for complete site prep and utilities, with garage conversions at the lower end and new detached ADUs on challenging lots at the upper. Foundation and grading typically represents 40-50% of this total; utilities split the remainder. Every Ellery project receives a written line-item price before any work begins - Haven Standard Clause 1 - with no change orders for conditions we identified during evaluation. Call (657) 286-7915 for an exact quote on your property; estimates are free and include the full photo documentation.
Yes. We specify and coordinate Boxabl, Plant Prefab, Tuff Shed, and James Hardie systems within the same single contract that covers your site prep and utilities. Each manufacturer publishes foundation and utility stub specifications that differ from conventional construction - Boxabl’s crane-set modules require a precisely leveled aggregate pad, while Plant Prefab’s units need conventional stem walls with rough-ins stubbed to exact dimensions. We verify these requirements during evaluation and warranty that our site prep matches the manufacturer’s tolerances. If the module doesn’t set properly due to our foundation work, the 365-Day Done Right Promise applies.
We don’t manufacture urgency, and we don’t promise impossible timelines. What we do offer: a live person answers calls 24/7, project schedules with realistic contingencies built in, and direct relationships with Pomona’s permit staff that move routine applications faster than contractors who submit incomplete plans. If your financing or lease-back agreement has a firm date, we build the schedule backward from that date with buffer weeks for utility company delays. The written price and scope don’t change because the timeline tightened - Haven Standard Clause 5 prohibits surprise surcharges for scheduling pressure.
The 365-Day Done Right Promise covers all site prep and utilities work: if the finished foundation, electrical, plumbing, or gas installation does not match the permitted drawings and written scope, we correct it at no additional cost. This is backed in writing before your project starts, not offered verbally after a complaint. Structural concrete carries the standard California contractor warranty period; utility workmanship is warranted against leaks, failures, and code violations for the full 365 days. We don’t subcontract site prep to avoid responsibility - our crews, our license, our promise.
Clear access to your electrical panel, gas meter, water main shutoff, and the proposed ADU location - our project lead needs to photograph and measure each. Locate any existing survey pins or property markers if you have them; if not, we’ll note where a boundary survey may be needed. Have your most recent utility bills available for account numbers and service addresses. If you’ve received a previous estimate, bring it for our Free Second Opinion review. The visit takes 60-90 minutes, produces 40-60 documented photos, and carries no obligation. Call (657) 286-7915 to schedule.
Schedule Your ADU Site Prep & Utilities Service in Pomona Today
Call (657) 286-7915 to schedule your free site evaluation and written estimate. A live person answers 24/7 - no voicemail queue, no callback that doesn’t materialize. Every project receives a documented photo record, a permit-ready plan set, and a fixed written price before any work begins. Nadia Ellery and the team at Ellery ADU Studio Pomona have delivered 900+ ADUs since 2015 under the Haven Standard: one contract, one written price, and the 365-Day Done Right Promise. Your property’s conditions are specific. Your estimate should be too.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Pomona since 2015.