One contract. One accountable party. From the structural drawings on the architect's desk to the certificate of occupancy at your back door.
Engineering, steel supply, and installation under a single contract. One contractor accountable for the whole steel frame ADU, start to finish.
Structural engineering for the steel frame ADU is performed in-house, by engineers who understand both California code AND how the structure will actually be built.
We source and prefabricate the light gauge steel, wall panels, floor joists, roof tracks, to the exact specification we engineered, from our established supply chain.
Our trained crew erects the frame on your site, the same crew, the same standards, every project. Frame-up is approximately one to two days for a typical ADU.
One contract. One contractor. One throat to choke.
An ADU is a small structure on a tight lot, often near the main house, often near a property line. The structural and durability stakes are higher per square foot than a custom home. Steel frame quietly resolves most of them.
An ADU 5–10 feet from the main house, or near a property line, faces real fire-spread exposure. Steel frame is non-combustible, it doesn't ignite, doesn't contribute fuel, doesn't spread fire to or from neighboring structures.
Steel is 30% lighter than wood. On a small lot where every cubic yard of concrete and every foot of excavation matters, the foundation savings are disproportionate. Real cost reduction at the slab.
Prefab steel panels arrive on the job site fabricated. The frame for a 1,000 SF ADU goes up in 1–2 days. Schedule compression matters when you're paying construction-loan interest.
An ADU often shares plumbing or sits on a damper part of the lot. Wood-frame ADUs are vulnerable to termite and mold issues from year one. Steel doesn't host either, for the life of the structure.
Non-combustible classification can reduce homeowner insurance premiums by up to 50% in California fire zones. For ADUs in Pacific Palisades, Malibu, hillside Bel Air, or Altadena, this is no longer optional, it's the difference between coverage and the FAIR Plan.
If your ADU is a rental, steel frame produces a structurally stable, low-maintenance, mold-free unit. Higher-quality rental, lower lifetime maintenance, fewer tenant headaches.
A separate structure on the lot, typically 400–1,200 SF. The most common type and where steel frame shines: structural simplicity, fast frame-up, fire separation from the main house. Up to two stories in most CA jurisdictions.
An ADU sharing one or more walls with the existing residence, often a garage conversion or addition. Steel frame integrates with existing wood-frame structures using engineered transition details. Particularly useful for fire-zone retrofits.
Up to 500 SF within the existing footprint of the main residence. Steel frame is used here primarily for non-combustible internal partition walls, particularly when adding a JADU to a wood-frame home in a fire zone.
Every steel frame ADU project is scoped specifically, site conditions, finish level, permit jurisdiction, and lot access all matter. Typical schedules from signed contract to certificate of occupancy:
| ADU Type | Size | Timeline (contract → CO) |
|---|---|---|
| Detached• single story | 400–800 SF | 5–7 months |
| Detached• two-story | 800–1,200 SF | 7–10 months |
| Attached / addition | 400–1,200 SF | 6–9 months |
| JADU• within footprint | up to 500 SF | 3–5 months |
The steel frame itself goes up in 1–2 days using prefab panels. Permit timelines depend on jurisdiction (LADBS, OC Public Works, individual cities) and whether the project qualifies for California's expedited 60-day ADU review.
For a project-specific budget, schedule, and feasibility review, request a free pre-construction consultation. Every ADU is scoped on its own merits, site, code, finish level, lot access. Begin a project →
California's ADU laws, SB 9, AB 68, AB 881, AB 1033• apply to all ADUs regardless of structural system. Steel frame ADUs benefit from the same expedited permitting, owner-occupancy waivers, and lot-coverage provisions as wood frame ADUs.
Most California jurisdictions, including LA County, City of Los Angeles, Orange County, City of Newport Beach, are required to issue ADU permits within 60 days of a complete application. ESRL handles the entire permit process: structural drawings, calcs, CBC/CRC compliance documentation, Title 24 energy compliance, and Chapter 7A (WUI) compliance where applicable.
Jurisdictions where ESRL has built steel frame projects:
If you're an architect specifying an ADU in Los Angeles or Orange County, particularly in a fire zone, a coastal lot, or a project where the ADU sits inches from the property line, steel frame is the structural answer the building inspector, the insurance carrier, and the long-term performance data all increasingly point to.
The hard part for architects is finding a contractor who can actually execute it. Most California GCs will say they "can do steel frame", but won't have an established supply chain, won't have a trained crew, won't carry their own structural engineer in-house. The result: cost overruns and schedule problems that get blamed on "steel" but are really contractor inexperience problems.
ESRL is the one-stop steel frame ADU contractor. Engineering, steel supply, and installation under one contract. You design the ADU. We make sure it gets built, without you having to coordinate three vendors.
For architects working with us regularly, ESRL maintains a preferred-architect program: priority scheduling, free constructability reviews on every project, and a co-marketing arrangement on completed projects (your firm credited prominently in all photography and case studies). More on our architect collaboration model →
A steel-frame ADU is an accessory dwelling unit whose structural shell, wall studs, floor joists, and roof tracks, is built from light gauge cold-formed steel (typically 14–18 gauge, galvanized to ASTM A653) instead of wood. The structure is engineered and lab-tested to AISI S100 specifications. Steel-frame ADUs are non-combustible, termite-proof, mold-proof, dimensionally stable, and conventionally permitted under California ADU law (SB 9, AB 68, AB 881, AB 1033).
Yes, and it's often the better structural choice. Steel is roughly 30% lighter than wood, which reduces foundation size, concrete volume, and excavation requirements, all material savings on a small or sloped lot. The prefabricated, panelized nature of light gauge steel also makes it easier to maneuver components onto restricted sites where wood-frame deliveries struggle. Long clear spans (40+ ft) allow design solutions that wood-frame ADUs cannot.
Yes. Light gauge steel framing is non-combustible at the framing line and meets California Building Code (CBC) Chapter 7A requirements for Wildland-Urban Interface (WUI) Fire Areas. For ADUs in Pacific Palisades, Malibu, hillside Bel Air, Altadena, or any other CalFire-designated High or Very High Fire Hazard Severity Zone, a steel-frame ADU qualifies for non-combustible classification and can deliver up to 50% lower fire-zone insurance premiums.
From signed contract to certificate of occupancy, a typical 800–1,200 SF steel-frame ADU in LA or OC takes 6–9 months: 2–4 months for design and permits, 3–5 months for construction. The steel frame itself goes up in 1–2 days using prefab panels. Permit timelines depend on jurisdiction (LADBS, OC Public Works, etc.) and whether the project qualifies for California's expedited 60-day ADU review.
Yes, completely. Steel framing is a structural system, not a finish. The exterior cladding (stucco, board-and-batten, stone veneer, brick, fiber cement, wood siding), interior drywall, doors, windows, roof type, and all visual elements can match the main residence exactly. A finished steel-frame ADU is visually indistinguishable from a wood-frame ADU, but with non-combustible structure, no termite or mold risk, and a 50-year structural warranty.
Free 30-minute pre-construction consultation. Site review, code feasibility, project-specific cost estimate. No obligation.
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