How much does a garage conversion ADU cost in San Diego?

Most two-car garage conversions fall between about $80,000 and $200,000, or roughly $200 to $400 per square foot, depending on finishes, utilities, and structural work.

How much does a detached ADU cost in San Diego?

Detached new construction typically runs about $350 to $550 per square foot. A studio or one-bedroom is often about $220,000–$300,000; a two-bedroom about $300,000–$420,000 before unusual site conditions.

When is a garage conversion the better financial choice?

It usually wins when you have a large enough garage slab, need the fastest path to rent, want to stay under about $200,000, or lack rear yard space for a detached structure after setbacks.

When is a detached ADU worth the higher cost?

Detached builds make more sense when you need a larger two-bedroom unit for rent, have enough rear yard after setbacks, plan a long hold for appreciation, or want maximum privacy and resale appeal.

What should I verify before choosing garage conversion vs. detached?

Measure your garage's usable square footage. Confirm setbacks and lot coverage for your parcel. Pull rental comps within about a half mile. Check how an ADU may change your assessed value. Then model financing at current construction loan rates.

ADU Garage Conversion vs. Detached: San Diego Cost Guide

The right choice depends on your lot, your garage, your budget, and how long you plan to hold. This guide puts the numbers side by side so you can run the math before a contractor walks the property. For where permits cluster by community, pair this with San Diego ADU permits by neighborhood.

Cost snapshot

The three buckets most owners pick from

Three cost ranges define the ADU decision for most San Diego homeowners.

$80K-$200K

Garage Conversion

$200-$400/sqft | 4-8 yr payoff

$220K-$300K

Detached Studio/1BR

$350-$550/sqft | 8-12 yr payoff

$300K-$420K

Detached 2BR

$350-$550/sqft | 10-14 yr payoff

Garage Conversion: The Numbers

Why $/sqft is still a range

Garage conversions in San Diego run $200 to $400 per square foot. The range reflects a real split. A basic studio with builder-grade finishes sits near $200/sqft. Add a full kitchen, separate bathroom, and upgraded electrical, and you are closer to $350 to $400/sqft.

Total cost for most two-car garage conversions (400 to 500 square feet of usable space) falls between $80,000 and $200,000. That typically covers insulation, drywall, flooring, kitchen, bathroom, HVAC, electrical panel upgrade, and basic plumbing.

The part that surprises people: the foundation and framing are already there, but the slab still needs a moisture barrier and sometimes leveling. Garage doors get swapped for a framed wall and window. Running utilities from the main house can add $5,000 to $15,000. And most San Diego garages built before 1990 need a panel upgrade for the extra load.

Permit and plan-check fees run $3,000 to $8,000. Units under 750 square feet skip impact fees under current state law, saving you $10,000 to $20,000 compared to five years ago.

A two-car garage conversion in San Diego typically yields 400-500 sqft of livable space at $200-$400/sqft. Total: $80K-$200K.

Detached ADU: The Numbers

New construction from the ground up

Detached new construction runs $350 to $550 per square foot in San Diego. The higher cost per sqft reflects building from dirt: foundation, framing, roofing, full mechanical, electrical, plumbing, and exterior finishes.

A studio or one-bedroom (400 to 600 sqft) typically costs $220,000 to $300,000. A two-bedroom (600 to 800 sqft) runs $300,000 to $420,000. These ranges assume mid-range finishes and a flat or near-flat lot.

Site prep is the cost most homeowners miss. Grading, utility trenching, and equipment access can add $15,000 to $40,000. A sloped yard, tree removal, or tight alley access pushes every estimate toward the top.

The upside: tenants pay more for a detached unit because they value privacy. A detached one-bedroom rents for $1,800 to $2,400 per month. A two-bedroom pulls $2,200 to $3,000. Coastal ZIPs (92107, 92109, 92037) push the upper end. Inland neighborhoods like Clairemont or Mira Mesa sit near the midpoints.

Detached ADU cost: $350-$550/sqft. A 600sqft one-bedroom runs roughly $250K all-in with site prep.

Side-by-Side Comparison

One table, three paths

This table puts the three most common ADU paths next to each other on the metrics that drive the investment decision.

Type	Cost Range	$/SqFt	Rent Range	Payoff (Cash)	Best For
Garage Conversion	$80K-$200K	$200-$400	$1,600-$2,200/mo	4-8 years	Fast ROI, limited yard
Detached Studio/1BR	$220K-$300K	$350-$550	$1,800-$2,400/mo	8-12 years	Privacy, higher rent
Detached 2BR	$300K-$420K	$350-$550	$2,200-$3,000/mo	10-14 years	Max rent, long hold

Cost ranges in context

Cost bands at a glance

Build cost ranges for the three most common paths we see locally, based on mid-range construction quality and recent contractor bids.

ADU Build Cost by Type (San Diego, 2026)

When a Garage Conversion Wins

Clear wins for the garage path

Garage conversions are not always the right call, but they win clearly in these situations:

You have a two-car garage with 400-plus sqft and a slab in decent shape.
Your rear yard is too small for detached construction after setbacks. Many San Diego lots under 5,000 sqft fall here.
You want the fastest path to rent. Garage conversions take 3 to 5 months versus 8 to 14 for new construction.
Your budget is under $200,000 and you want to skip construction financing.
You live in the main house and want a lower-risk first rental investment.
Your garage is detached with its own utility access, which cuts conversion costs by $10,000 to $20,000.

When Detached Wins

When new build is worth the ticket

Detached new construction makes more financial sense in these scenarios:

Your lot is 6,000-plus sqft with enough rear yard for a 600 to 800 sqft structure after setbacks.
You want a two-bedroom unit to hit the $2,200 to $3,000/mo rent tier. No garage conversion delivers that.
Your garage is undersized (single-car, under 250 sqft) or has structural problems that make conversion too expensive.
You plan to hold for 10-plus years and want to build long-term equity. Detached units appraise higher and add more assessed value.
You are in a coastal or high-rent area where rents justify the bigger build cost.
You want to sell the ADU separately under AB 1033. Detached units are far more attractive to buyers than converted garages.

5 Questions to Answer Before You Decide

Parcel-level due diligence

Skip the contractor calls until you can answer these with actual data, not guesses:

What is your garage's usable square footage? Measure the interior. A standard San Diego two-car garage is 400 to 440 sqft. Single-car garages under 250 sqft rarely convert into a unit that justifies the cost.
What are the setback and lot coverage rules for your parcel? A 5,500 sqft lot with a 1,400 sqft house and 400 sqft garage may have almost no room for a detached unit. Check zoning data on the SANDAG portal before you spend a dime.
What do comparable ADUs rent for within a half-mile? Not citywide averages. Your micro-market. A converted garage in North Park rents differently than the same unit in Mira Mesa.
What is your property's assessed value, and how does an ADU change it? Garage conversions typically add $50K to $120K. Detached units add $150K to $300K. That gap hits your tax bill and your equity.
Are you paying cash or financing? At 6.5% to 7% construction loan rates, a $300K detached build costs about $2,000/mo in debt service. If expected rent is $2,400, the margin is thin after vacancy, maintenance, and insurance.

A Note on Financing

Rates change the winner

Construction loan rates in San Diego run 6.5% to 7% as of early 2026. That rate changes the math for each ADU type differently.

Garage conversion at $150,000: debt service is about $1,000/mo. Rent at $1,800/mo leaves you cash-flow positive from month one, even after 5% vacancy and $200/mo for maintenance and insurance.

Detached two-bedroom at $350,000: debt service is about $2,300/mo. Rent at $2,600/mo barely breaks even. The investment still builds equity, but you are not seeing real cash flow until rates drop or rents climb.

This is why garage conversions dominate San Diego's ADU market right now. The cash-flow math works at today's rates. Detached builds bet on appreciation and future rent growth. A reasonable bet in San Diego, but a different risk profile.

Illustrative payback: cumulative cash position

Illustrative, not a promise

Cash-only model: $150K garage conversion at $1,800/mo rent versus a $280K detached one-bedroom at $2,400/mo. Net rent after a rough operating haircut. Not a forecast. Your taxes, insurance, and financing will shift these lines.

Cumulative net position after rent (illustrative)

What This Means for Your Property

Your lot breaks the tie

City-level cost ranges are a starting point. They show the shape of the decision. But the real answer depends on your parcel: lot size, garage footprint, zoning, setbacks, flood zone, and what comparable units rent for on your block.

Two homes on the same street can have completely different ADU economics. One sits on a 7,000 sqft lot with a detached two-car garage and alley access. The one next door has a 4,800 sqft lot, an attached single-car garage, and a steep rear slope. Same neighborhood, different math.

CasitaScore builds parcel-level ADU reports with real data, not rules of thumb. Run your address for a free score and breakdown. For citywide permit context, see ADU permits by neighborhood.