The existing property changes the amount of work
A new detached ADU on an open site is a different assignment from converting an older garage or working around a slope and tight clearances. Before the rooms can be worked out, someone needs to understand the existing building and the site.
The amount and quality of available information also matters. A current survey, reliable drawings of the existing building, clear photographs, and confirmed utility information reduce assumptions. Missing or conflicting records can require additional field work, research, or help from an engineer or other specialist.
Be clear about what you want to build
New construction, additions, and conversions each bring different questions about foundations, structure, fire separation, energy documentation, utilities, and the existing use. Developing a custom layout is also different work from adapting a plan that has already been developed.
The proposal should name the project type and intended rooms or use. If the homeowner has not chosen an ADU idea, early design or an ADU review may need to come before a fixed permit-plan price.
- New detached structure
- Garage or accessory-building conversion
- Addition or attached ADU
- Interior conversion or junior ADU
- Custom design or adapting an existing design
Check who coordinates the separate consultants
Structural, civil, energy, survey, soils, septic, fire-sprinkler, solar, utility, or other consultant work may be required depending on the property and reviewing agency. The client selects, contracts with, and pays each required consultant directly.
A proposal should still state who requests proposals, exchanges project information, tracks listed deliverables, and assembles the permit package. A lower drafting fee may include less administrative coordination.
Revisions and permit follow-up need to be priced too
A proposal should state the included homeowner design rounds and separate them from city or county corrections. It should also explain who prepares the application, submits the drawings, tracks status, responds to agency questions, coordinates specialist revisions, and resubmits the package.
You may handle some of that work yourself, or the proposal may assign it to the team preparing the drawings. Either way, it needs to be clear. Preparing plans and following them through review are related tasks, but they are not the same amount of work.
- Number and timing of owner design revisions
- Included drawing and specialist coordination
- Submission and application responsibilities
- Status updates and agency communication
- Number of included plan-check response rounds
- Treatment of owner changes after approval
Keep drawing fees separate from the rest of the budget
Plan-review, permit, school, utility, impact, and other agency fees may apply. Separate specialist, survey, testing, and construction costs can also be significant. A permit-plan proposal should state which fees are included, which are estimates, and which the homeowner pays directly.
California law limits or regulates some ADU fees in certain circumstances, while local agencies maintain their own current schedules and procedures. A general internet estimate is not a substitute for checking the current city or county fees and project facts.
Put the proposals side by side
When two fees differ, place the proposals side by side and compare what each one includes. Look for the drawing list, design rounds, specialist tasks, submission work, correction support, site verification, extra expenses, schedule assumptions, and conditions that trigger additional fees.
A lower quote may be a good fit if you are comfortable handling more of the coordination. A higher quote may include work you would otherwise need to arrange yourself. Ask about those differences before assuming the two prices cover the same service.
- What will I receive?
- Which existing conditions are confirmed or assumed?
- Who identifies, retains, pays, and coordinates each required consultant?
- Who submits and follows up?
- How many owner revisions and correction rounds are included?
- Which agency, specialist, and construction costs remain separate?
Compare the drawing list, revisions, consultant coordination, and permit follow-up before comparing the price. Make sure you know which costs remain separate.
Official sources and useful references
Links checked September 8, 2026. Confirm that the current guidance applies to your property when you use it.
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This article provides general educational information. Property records, site conditions, required specialists, and city or county review may change the answer for a specific project.