ADU Planning Checklist for California Homeowners

Planning an ADU is different from planning a simple room update. An accessory dwelling unit may involve design, permits, utilities, plumbing, electrical, sewer connection, insulation, heating and cooling, windows, fire separation, structural details, site access, and finish work.

This ADU planning checklist is designed for California homeowners who are considering a garage conversion ADU, attached ADU, detached ADU, backyard cottage, in-law unit, or small independent living space. It will help you organize the information a contractor needs before reviewing the project or preparing an estimate.

If your project is in the Bay Area, Forge Construction Services provides ADU construction, garage conversion, interior build-outs, drywall, flooring, tile, finish work, and residential remodeling services.

Why an ADU Planning Checklist Matters

ADU projects can look simple at first, especially when the project starts with an existing garage or unused space. However, creating a legal and functional living unit usually requires more than adding drywall, flooring, and a bathroom. The project may involve structural review, insulation, plumbing, electrical upgrades, ventilation, heating and cooling, windows, egress, fire separation, sound control, and finish details.

A checklist helps separate a basic conversion idea from a real construction scope. It also helps avoid incomplete estimates. One contractor may price only interior finishes, while another may include design coordination, utility work, framing, insulation, drywall, flooring, bathroom work, kitchenette setup, and finish details.

The goal is to prepare enough information so the contractor can understand the existing conditions, intended use, and likely construction requirements.

1. Decide What Type of ADU You Are Planning

The first step is to define the ADU type. A garage conversion ADU, attached ADU, detached ADU, and interior conversion can all involve very different work.

Before asking for an estimate, describe the ADU type as clearly as possible. A simple “garage conversion” may mean a finished flex space to one homeowner and a legal rental-ready ADU to another.

2. Understand ADU vs Garage Conversion vs Flex Space

Not every finished garage is an ADU. A garage can become a bedroom, office, gym, studio, family room, flex space, or legal ADU depending on the intended use, layout, permits, utilities, and required features.

A legal ADU usually needs to function as an independent dwelling unit. That may include a bathroom, cooking area, separate entrance, heating and cooling, ventilation, insulation, electrical, and other requirements depending on the project and local jurisdiction.

A non-ADU garage conversion may still require planning and permits, but the scope can be different if the space is not intended to function as an independent dwelling.

For more detail, see our garage conversion services.

3. Take Clear Photos of the Existing Space

Photos help a contractor understand the existing structure before visiting the property. For ADU projects, photos should show both the interior and exterior conditions.

For a garage conversion ADU, take photos of:

• The full garage from each corner
• The garage door wall
• The ceiling and framing
• The concrete slab and floor condition
• Existing electrical outlets, lights, and panel location
• Any water heater, furnace, laundry, storage, or mechanical equipment in the garage
• Exterior garage walls
• Driveway, side access, and entry points
• Any cracks, moisture, rot, damage, or uneven areas

For a detached or backyard ADU, take photos of:

• The proposed yard location
• Side yard access
• Fence lines and neighboring structures
• Existing concrete, slope, drainage, trees, or obstacles
• Distance to the main house
• Possible utility routes
• Street, driveway, and parking access

Wide photos show layout and access. Close-up photos show problems and construction constraints.

4. Measure the Existing Garage, Room, or Proposed Footprint

Basic measurements help estimate layout options, bathroom placement, kitchenette size, flooring area, wall area, and general feasibility.

Rough measurements are useful for early planning. Final measurements should be confirmed before design, ordering materials, or starting construction.

5. Check Existing Structure and Site Conditions

Existing conditions can strongly affect ADU scope and cost. A clean-looking garage may still need slab review, wall framing updates, insulation, moisture control, electrical upgrades, plumbing, or structural corrections.

Before requesting an estimate, look for:

• Cracks in the slab or walls
• Sloped or uneven garage floor
• Moisture, stains, leaks, or drainage issues
• Old framing or damaged studs
• Low ceiling height
• Unfinished or poorly insulated walls
• Existing mechanical equipment that may need relocation
• Limited side access for workers and materials
• Tree roots, fences, retaining walls, or drainage problems near a proposed detached ADU

For garage conversion ADUs, the existing slab and garage door wall often deserve special attention. These areas can affect insulation, exterior finish, floor height, moisture protection, and final comfort.

6. Review Utility Access Early

Utilities are one of the biggest planning factors in an ADU project. Bathrooms, kitchenettes, laundry, heating, cooling, and electrical load can all affect the construction scope.

Utility planning should happen early. It is common for an ADU idea to change once plumbing, sewer, electrical, or HVAC constraints are reviewed.

7. Plan Bathroom and Kitchenette Needs

An ADU usually needs a bathroom and some form of cooking or kitchenette area. These areas are often the most expensive parts of a small ADU because they involve plumbing, electrical, ventilation, cabinetry, fixtures, waterproofing, tile, and finish details.

For the bathroom, prepare notes about:

• Shower or tub
• Toilet location
• Vanity size
• Tile or prefabricated shower walls
• Exhaust fan
• Lighting and outlets
• Waterproofing and flooring

For the kitchenette, prepare notes about:

• Sink location
• Cabinet length
• Countertop space
• Refrigerator size
• Cooktop or cooking appliance plan
• Microwave or hood/ventilation needs
• Garbage disposal if planned
• Outlet and lighting needs

Small ADUs need careful layout planning. Every inch matters, especially when bathroom, kitchenette, storage, bed area, sitting area, and access all need to fit into a compact footprint.

8. Think About Windows, Entry, Privacy, and Natural Light

An ADU should feel like a real living space, not a storage area with drywall. Windows, doors, natural light, privacy, and access are important parts of the design.

Before requesting an estimate, think about:

• Where will the main entrance be?
• Will the ADU have a separate exterior entrance?
• Are new windows needed?
• Is there enough natural light?
• Will windows face neighbors, fences, or the main house?
• Is privacy needed between the ADU and the main home?
• Is the walking path to the ADU clear and practical?
• Will the existing garage driveway remain usable?

For garage conversion ADUs, replacing or rebuilding the garage door wall is often a major design decision. That wall can affect exterior appearance, insulation, windows, entry, and how finished the space feels.

9. Prepare Finish and Material Preferences

Finish choices can change both the look and cost of an ADU. Flooring, cabinets, countertops, tile, doors, trim, paint, fixtures, lighting, and hardware should be discussed before the estimate is finalized.

If you already selected materials, send product links or screenshots. This helps clarify what is owner-supplied and what should be included in the contractor’s scope.

10. Understand Design, Engineering, and Permit Questions

ADU projects often require design, drawings, permit review, and sometimes engineering. Requirements vary by city, property, existing structure, utility conditions, and project type.

Before requesting an estimate, prepare these questions:

• Do I already have plans or drawings?
• Is this a legal ADU or a non-ADU garage conversion?
• Will the project need structural engineering?
• Will the existing garage slab or foundation need review?
• Will electrical panel capacity need to be checked?
• Will plumbing and sewer routing need design review?
• Will the city require inspections?
• Will the ADU affect parking, access, or exterior appearance?
• Who is responsible for plans, permits, and inspections?

For California ADU projects, avoid assuming that one property’s solution applies to every property. The same garage conversion idea can have different requirements depending on the city, structure, lot, utilities, and intended use.

ADU Estimate Checklist

Use this checklist before sending your ADU construction or garage conversion ADU request.

Common ADU Planning Mistakes

Many ADU problems start during early planning. The biggest mistake is treating an ADU like a simple room remodel. ADUs often involve more systems, more coordination, and more code-related decisions than a standard interior update.

Assuming the Existing Garage Is Ready to Convert

Some garages are easier to convert than others. Slab condition, moisture, ceiling height, framing, garage door opening, utilities, and insulation can all affect the project.

Ignoring Utility Routes

A bathroom or kitchenette location may look good on paper, but plumbing and sewer access can change the cost and complexity. Utility planning should happen early.

Not Planning the Garage Door Wall

In garage conversions, the garage door wall can make or break the final look. Poor planning can leave the converted space feeling like a closed-in garage instead of a finished living unit.

Choosing Finishes Before Confirming Layout

Finishes are important, but layout, plumbing, electrical, windows, access, and permits should be reviewed first. Material selections should support the final plan, not force the plan.

Comparing Estimates Without Matching Scope

One ADU estimate may include only interior finish work. Another may include utility work, insulation, framing, drywall, bathroom, kitchenette, flooring, design coordination, and exterior modifications. Compare the included scope, not only the final number.

Questions to Ask Before Hiring an ADU Contractor

Before approving an ADU or garage conversion estimate, ask clear questions about responsibility, scope, design, utilities, and finish work.

• What exactly is included in the estimate?
• What is excluded?
• Is this priced as a legal ADU, garage conversion, or interior remodel?
• Who handles plans, design, engineering, permits, and inspections?
• Are plumbing, sewer, electrical, and HVAC included?
• Is drywall, insulation, flooring, tile, cabinetry, and finish work included?
• Are owner-supplied materials allowed?
• Who orders fixtures, cabinets, appliances, tile, and finishes?
• How are change orders handled?
• What existing conditions could change the price?
• What needs to be confirmed before the project starts?

When to Request an ADU Estimate

You do not need complete architectural plans before having an initial project conversation. However, you should have photos, basic measurements, a general idea of the ADU type, utility notes, and a list of major features such as bathroom, kitchenette, laundry, separate entrance, windows, and finish expectations.

If you already have drawings, surveys, city notes, or permit comments, include them in your estimate request. If you do not have plans yet, a contractor can still help you understand the likely construction questions and next steps.

Need Help Planning an ADU or Garage Conversion?

Forge Construction Services helps Bay Area homeowners with ADU construction, garage conversions, interior build-outs, drywall, flooring, tile, cabinetry coordination, and finish details.

If you are planning an ADU, send photos of the existing space, approximate measurements, utility notes, layout ideas, and a short description of what you want to build.

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