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Garage Conversion ADU vs. Detached ADU in Pasadena: Which is the Best Investment?
For Pasadena property owners, the decision to build an Accessory Dwelling Unit (ADU) is often driven by two competing desires: maximizing rental income vs. minimizing upfront costs. The fork in the road appears immediately: Do you repurpose your existing garage or build new?
While the garage conversion ADU Pasadena is marketed as the "budget" option, the reality of local building codes—particularly regarding 1920s-era foundations and seismic requirements—often narrows the price gap. This guide provides a forensic comparison of these two development paths.
Option 1: The Garage Conversion ADU
The Strategy: Transforming an existing shell (typically 350–450 sq. ft.) into habitable space.
The "Existing Shell" Myth
In the eyes of the Pasadena Building Division, a garage is a "Utility" structure. Converting it triggers a "Change of Use," requiring full upgrades to 2025 residential standards.
⚠️ The Foundation Trap
Most pre-1980 Pasadena garages sit on a thin slab-on-grade without footings or moisture barriers.
The Reality: You cannot simply lay flooring over this. Moisture will wick through, ruining the interior. You will likely need to demolish the floor and pour a new foundation with proper footings.
Cost Impact: This remediation often adds $10,000 – $25,000 to the budget.
Fire Safety & Setbacks
Many garages are "grandfathered" on the property line. While you don't have to move the structure, any wall within 3 feet of the line becomes a fire wall. No windows or doors are allowed on these walls, which can make the unit feel dark without skylights.
Estimated Cost: $125,000 – $160,000
Option 2: Detached New Construction
The Strategy: Building a ground-up detached ADU Pasadena in the backyard, preserving the garage for parking.
The "Standard Plans" Advantage
This is the biggest differentiator. Pasadena offers Pre-Approved Standard Plans exclusively for new detached construction.
The Incentive: If you use these plans, the City waives the General Plan & Technology Fees and reduces Plan Check fees by 50%. Garage conversions do not get these waivers.
Design Value
Unlike garages with low 7-foot ceilings, a new build can feature vaulted ceilings (up to 16 feet), making a small unit feel massive and commanding higher rent.
Estimated Cost: $190,000 – $320,000+
Head-to-Head Comparison
| Feature | Garage Conversion | Detached New Build |
|---|---|---|
| Average Cost | Lower ($125k – $160k) | Higher ($190k+) |
| Permit Timeline | Slower (Custom Engineering) | Fast (Standard Plans) |
| City Fee Waivers | Limited | Extensive |
| Garage Utility | Lost Forever | Retained (Storage/Parking) |
| Appraisal Value | Moderate | Premium (1+1=3 Effect) |
Critical Decision FAQs
Need a site feasibility check? Call (747) 609-6912 to schedule yours.
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