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ADU builders for backyard homes & garage conversions

An ADU is the best square footage most LA lots will ever add: housing for family, or rent that pays a mortgage's worth of bills. We build detached ADUs, attached units, and garage conversions from the first site check to the final inspection — plans, engineering, utilities, and construction under one roof.

Detached ADUsGarage conversionsAttached ADUsJunior ADUsGuest housesSite & utilitiesPlans & permits
ADUs & Garage Conversions — Guillen Construction

Because we self-perform concrete, framing, plumbing, electrical, drywall, and stucco, your unit isn't waiting on a parade of subcontractors. That's how ADUs finish on schedule.

ADUs & Garage Conversions

What's included

Detached new-build ADUs

A complete small home in your backyard — foundation, framing, systems, and finishes, up to 1,200 sq ft under state law.

Garage conversions

The fastest, most affordable path to a rentable unit: foundation checks, insulation, systems, and a finish that doesn't feel like a garage.

Attached ADUs & JADUs

Additions and junior units carved from existing space, with the required separate entrance and kitchen done to code.

Guest houses & casitas

Not every backyard building needs a full kitchen — we build casitas, studios, and offices to the same standard.

Site work & utilities

Trenching, sewer connections, panel upgrades, and meters — the part of ADU budgets everyone forgets. We price it up front.

Plans, engineering & permits

Architectural plans, structural engineering, Title 24, and city plan check — or we build from the plans you already have.

$100k–$180k
Typical garage conversion, turnkey
$250k–$400k+
Typical detached ADU, turnkey
$1,800–$2,800/mo
Typical SFV ADU rent today

Typical 2026 Los Angeles-area ranges including construction; plans, permits, and utility fees vary by city and site. Many owners see the unit pay for itself in 7–12 years of rent.

How it works

How we work

01

Walk the job

We meet at your property, listen, measure, and give you straight answers — including the ones you didn't ask for. Estimates are free.

02

Price & permits

A written, line-item scope with a milestone payment schedule that follows California law. Plans, engineering, and permits handled.

03

Build

Our own crews, a clean site, and a schedule we actually keep. You get one point of contact and updates you don't have to chase.

04

Walk-through & warranty

We punch the list to zero, pass final inspection, and stand behind the work after the trucks leave.

FAQ

Questions we hear a lot

How big can my ADU be?

California law generally allows a detached ADU up to 1,200 sq ft with 4-foot side and rear setbacks, and most lots also qualify for a junior ADU. We confirm exactly what your parcel allows before you spend a dollar on plans.

How long does an ADU take, start to finish?

Plan on 2–4 months for design and permits, then 4–8 months of construction depending on size — garage conversions land at the short end. We give you a written schedule with the contract.

Will an ADU raise my property taxes on the whole house?

No — the county reassesses only the value the ADU adds, not your existing home. Your current assessment stays where it is.

Can I rent it out?

Yes — long-term rentals (30+ days) are allowed essentially everywhere ADUs are. Short-term rental rules vary by city, so tell us your plan and we'll flag what applies.

Areas we serve

ADUs guides by city

Free estimate

Let's walk your project.

Free on-site estimates. Straight answers on price, permits, and timeline — no runaround.

(213) 858-9161 Call or text — English y español.

Tell us about your project

We reply within one business day — usually faster.

No spam, no pressure. A licensed contractor reads every message.