Preapproved ADU Plans: What Still Has to Be Designed for Your Lot?

Distinguish the building design from the property

A catalog plan answers questions about a standard building. Your application must also explain where it goes and how it works on your property. Before paying for a design, compare its dimensions and assumptions with your site, access, existing structures and proposed utility routes. A floor plan that fits your needs may still need substantial coordination.

Ask the provider for a written list of what the plan purchase includes. Separate the right to use the design, site-specific adaptation, application preparation, review responses and construction services. Do not assume a vendor's statement that plans are preapproved covers every one of those services.

Read the official site-specific pathway

San José's San José: Preapproved ADU and Site-Specific Application distinguishes master-file plans from a site-specific application. Its instructions describe project documents and identify fire-related water information among the preparation items. Use the current checklist rather than an old screenshot from a vendor's brochure.

If the property is not in San José, ask the actual authority whether and how it accepts the selected design. Alameda County's Alameda County: Permit Forms and Resources includes its own ADU checklists and preapproved resources. Approval in one program is not evidence that a different jurisdiction has accepted the same package for your parcel.

Check code version and permitted variations

Ask which adopted code cycle the master design addresses and whether the provider has completed any required update. San José's published process requires updates when code, policy or zoning changes affect plans. A previously marketed approval should therefore be checked against current program records.

Also ask which changes remain within the approved design and which require additional review. Moving a window, changing square footage or altering structural assumptions should not be treated as a finish selection without confirmation. Keep a revision list so the site-specific drawings and the plan you priced remain consistent.

Budget the site work explicitly

Request separate scope for survey or site information, utility coordination, foundation assumptions, drainage and any project-specific professional work identified by the team. The appropriate items depend on the parcel; the point is to reveal assumptions rather than attach every possible study to every project.

In a hypothetical comparison, two providers sell a similar small ADU. One price includes site adaptation and review responses; the other covers only a standard drawing package. The second is not necessarily worse, but the prices do not describe the same deliverable. Compare total documented scope before deciding that preapproval has eliminated design cost.

A purchase-before-design checklist

Obtain the master plan identification, accepted code version, allowed variations, site-specific deliverable list, applicant responsibility, review-response scope and a list of excluded services. Ask who corrects a conflict between the standard plan and actual site conditions. Confirm whether the proposed construction contract uses the same plan version.

Your next step should be a feasibility check using those documents, not ordering a building solely because the interior layout looks suitable. Preapproval is most useful when it removes duplicated work while leaving site-specific responsibilities clear. It becomes disappointing when everyone assumes someone else has handled the property conditions that the standard design never addressed.

A vendor comparison worksheet

Compare providers across the same deliverables: standard-plan license, current version, site layout, required engineering coordination, application forms, outside information, comment responses and approved-document handover. Ask each provider to mark included, excluded or conditional. A conditional item needs the condition stated, such as a site assumption that must first be checked.

Next, identify who owns the unresolved site questions. If the designer expects the builder to confirm a connection route, make sure the builder's proposal includes that task. If both exclude it, arrange the missing service before calling the package complete. This is often more important than small differences in the standard-plan purchase price.

Finally, compare the plan's constraints with your priorities. A standard design may work well if you can accept its dimensions and documented variations. If you want extensive changes, ask the provider to explain the extra review and design scope before paying for a preapproval benefit that the customized version may no longer retain in the way you expect.

Before choosing the vendor, ask for a sample deliverable index rather than a customer's private plans. The index can show the categories of work included without exposing another owner's information. Compare that sample with the official checklist and ask who supplies any missing category. This provides a practical test of completeness while keeping the final assessment focused on your own site, chosen design and application pathway. It is more informative than a generic claim that the vendor handles everything.