Accessory Dwelling Units, also known as Auxiliary Dwelling Units, Granny Flats, Second Units, or Garage Conversions, have become more prominent since the state of California endorsed bills AB2299 & SB1069, fostering the development of rentable units in single-family vicinities. The common question surrounding this is, “What does an ADU garage conversion cost?” This article is set to demystify ADU expenses, including permitting charges, blueprint costs, and the overall sum of money required for an ADU garage conversion.
ADU TYPES & THEIR APPLICATIONS
The escalating deficit of budget-friendly housing in California sparked the need for more homes in typically single-family neighborhoods. “Auxiliary Dwelling Unit” is a state-coined term for garage conversions and second units. There are three main kinds of ADUs: the increasingly popular garage conversion, an Attached ADU, and a Detached ADU.
INQUIRING MINDS SEEKING ANSWERS
People are most interested in understanding the cost implications of an ADU garage conversion. In the construction realm, the cost is directly tied to the scope of work. Augmenting the range of work naturally results in a higher total expense. Here’s a rundown of the three primary ADU types and a snapshot of the work required to bring them to fruition:
- Garage Conversion ADU (can be attached or detached) – Rehabilitation/Remodeling
- Attached ADU (akin to an extension) – New Development
- Detached ADU (ground-up design) – New Development
TRANSFORMING AN EXISTING GARAGE INTO AN ADU: 400SF – 500 SF
Of all ADU types, a garage conversion is the most cost-effective, given the existing framing. However, even these may require some renovation. Construction expenses are minimal if the garage is at the forefront of the lot with straightforward access to the sewer system. Typically, the ceiling may need reframing, the addition of wall insulation, and an electrical upgrade.
Construction Documents Requirement $15,000 – $18,500
– Architectural Blueprints & Site Layouts
– Engineering Blueprints (for wall, roof, and ceiling framing)
– Title 24 Report (energy computations mandated by law)
– Electrical Layout (for service panel & electrical wiring)
Construction Costs $100,000 – $120,000
For those contemplating a garage conversion ADU, anticipate paying between $15,000 and $18,500 in pre-construction charges. Your local municipality requires these documents to approve and permit your project. A decent quality garage conversion will range between $100,000 and $120,000, resulting in a studio-style ADU complete with a compact kitchen & bathroom, all fashioned with high-grade materials and finishes.
ATTACHED ADU (NEW DEVELOPMENT): 300 SF – 700 SF
An attached ADU is akin to a home extension as it is interconnected with the main structure but remains separate. These ADU types are slightly invasive during construction since they often utilize the main sewer line and electrical system. An electrical service panel upgrade to a minimum of 200 Amp is necessary to accommodate the increased load. Some municipalities might necessitate a double-meter electrical panel.
Required Construction Documents for Attached ADU $17,000 – $22,000
- Architectural Floor Designs and Site Layout
- Engineering Plans (for wall, roof, and ceiling framing)
- Title 24 Report (energy computations mandated by law)
- Electrical Layout (for service panel & electrical wiring)
- Soil Report
- Property Survey
Construction Costs $180,000 – $220,000
For an attached ADU, expect pre-construction expenses between $17,000 to $22,000. All these reports and plans are necessary for your local zoning department’s approval. You’ll need a full set of blueprints for city review and plan check; once approved, you can procure a permit for construction.
DETACHED ADU (NEW DEVELOPMENT): 350 SF – 1200 SF
Constructing a Detached ADU provides an opportunity to dream big. Starting from scratch allows for building a larger ADU that could yield higher rent (location-dependent). If the lot size permits, a detached ADU of up to 1,200 SF or 50% of the existing home’s footprint can be built. Detached ADUs offer the luxury of new construction, with the added benefits of new insulation, air conditioning, noise-reducing double-pane windows, and private access. You could even construct a two-story ADU in certain cities featuring ground-floor parking.
Required Construction Documents for Detached ADU: $18,500 – $24,500
- Architectural Flooring and Site-Plan
- Engineering Plans (for wall, roof, and ceiling framing)
- Title 24 Report (energy computations are required by law)
- Electrical Plan
- Lot Survey
- Soil Report
Construction Costs $280,000 – $320,000
For a detached ADU, the total cost will be between $280,000 and $300,000+, yielding a comfortable and luxurious dwelling. This modern amenity-filled large detached ADU will be a hit with both tenants and family members.
