Should I Convert the Garage or Build a Detached ADU?
Converting an existing garage runs roughly $110k-$250k in Los Angeles; building a detached ADU from scratch runs roughly $425-$675 per square foot, which puts a typical 800 sq ft unit around $340k-$540k. We have no completed ADU or garage-conversion projects with published final costs, so every figure here is a Los Angeles market estimate rather than a summary of our own finished work. Conversion is cheaper and faster because the slab, walls and roof already exist. Detached wins on everything else — size, layout, natural light, privacy, and what a tenant or buyer will pay for it. The deciding question is usually whether you can afford to lose the yard.
The trade the money is actually buying
Conversion buys you a finished unit for less by inheriting a structure. Detached buys you a better unit by starting from nothing.
A garage conversion is constrained by what the garage already is. A standard two-car garage gives you roughly 400-500 sq ft, a footprint you cannot change, a slab that was poured for cars rather than habitation, and typically one wall that can carry windows. The result is usually a studio or a compact one-bedroom.
A detached ADU is constrained only by your lot and the setback rules. You choose the footprint, where the windows go, how high the ceilings are, and where the front door faces. For 2-3 times the money you get a unit that reads as a small house rather than a converted garage, and that difference shows up in every rent negotiation and every appraisal.
What conversion costs that the price does not show
Two things regularly push a garage conversion above its headline range.
The slab. Garage slabs are frequently poured thinner than habitable space requires, often slope toward the door for drainage, and rarely include a moisture barrier. Levelling, sealing or replacing it can add $8k-$25k, and it is not usually knowable until the finish floor comes up.
Utility separation. If the ADU needs its own electrical sub-panel, its own water connection or a separate meter, that work runs $10k-$35k depending on how far the runs travel and where the main service sits. Detached units carry the same cost, but nobody is surprised by it there.
The pattern worth understanding: conversion budgets go wrong on discoveries, detached budgets go wrong on scope creep. One is the building surprising you, the other is you changing your mind.
What you give up either way
Converting costs you the garage. In practice that means storage, and in a Los Angeles house with no basement and little loft, the garage is usually where everything lives. Households consistently underestimate this and end up paying for off-site storage indefinitely, which quietly erodes the saving.
Building detached costs you yard. On a typical Los Angeles lot a detached ADU consumes a large share of the usable outdoor space, and once it is built the garden you had is gone. If the yard is why you bought the house, that is a real loss and no rental income makes it back.
There is a third option people forget: an attached ADU built as an extension of the existing house, which takes less yard than a detached unit and is not limited to the garage footprint.
How to decide
Choose conversion if the budget is the binding constraint, the garage is genuinely surplus, you want the unit finished sooner, and a studio or compact one-bedroom serves the purpose — an office, a family member, a modest rental.
Choose detached if you want two bedrooms or more, you want it to feel like a home rather than a converted garage, you intend to rent at the top of the market, or you are protecting long-term resale value.
Choose neither yet if you have not checked your lot's setbacks. That single check, done before any design work, determines whether a detached unit of the size you want is even permissible, and it costs nothing to find out first.
Frequently asked follow-ups
Do I have to replace the parking I lose? +
Generally no. State ADU law bars cities from requiring replacement parking when an existing garage is converted into an ADU, and it also removes parking requirements for ADUs within half a mile walking distance of public transit. This is one of the most commonly misunderstood points in Los Angeles ADU planning, and it is worth confirming for your specific address before assuming either way.
Which one adds more value to the property? +
A detached ADU, in most cases, because it is larger, more flexible and reads as an independent dwelling to both appraisers and buyers. A garage conversion still adds value, but it also removes the garage, and in a market where covered parking and storage matter, that subtraction is real. The gap tends to be widest on larger lots and narrowest where the garage was already unusable.
Which is faster to build? +
Conversion, typically by 3-6 months door to door, because there is no foundation, no framing of a new shell and no roof. Permit review is usually simpler too. Detached construction takes longer at every stage, and a detached unit on a hillside or a constrained lot takes longer still because of the additional review those sites attract.
Can I convert only part of the garage? +
Yes, and it is a genuinely underused option. Converting two-thirds of a two-car garage into a studio while keeping a section for storage and utilities preserves some of what you would otherwise lose. The unit ends up smaller, but for an office or a guest space that is frequently the better trade.
Will my property taxes go up? +
Yes, but only on the new work. Under Proposition 13 the county adds the assessed value of the ADU to your existing basis rather than reassessing the whole property at current market value. Building an ADU does not reset the assessment on the house you already own, which is a common and expensive misconception.
Want the same answer applied to your specific project? Onn personally reviews every inquiry.
Written by Onn Cohen-Meguri, founder and designer at Design Onn Point. Onn has spent 20+ years designing and building in Los Angeles. CSLB #1133368.
Published .