Yuna Drafting
A homeowner called our office last spring hoping to convert a spare bedroom into a rentable studio unit, expecting the permit process to involve a simple floor plan and a few dimension annotations. When our team confirmed the space qualified under California's JADU statutes, the scope of what the drawings needed to show expanded considerably — because junior ADU conversion drawings in Sunnyvale and Cupertino carry sheet-level documentation requirements that go well beyond a standard interior remodel permit set. Our architectural drafting and design studio has processed JADU permit sets across both cities, and the specifics of what each jurisdiction expects are distinct enough to warrant a thorough, city-by-city breakdown.
A junior ADU is defined under California Government Code §65852.22 as a unit of up to 500 square feet created entirely within the existing footprint of a single-family home, including attached garages. State law requires the property owner to occupy either the main dwelling or the JADU itself, and the unit must share at least one interior wall with the primary structure. These statutory constraints shape the drawing set from the site plan through the kitchen detail, which is why submittals assembled without city-specific knowledge rarely survive plan check in a single round.
Both Sunnyvale and Cupertino layer municipal amendments on top of state ADU law, and our team's experience preparing ADU permit sets across Santa Clara County has confirmed that city-specific details are what separate a clean first-pass approval from a multi-round correction cycle. Understanding precisely what each building department requires before the first sheet is drafted is what allows our studio to submit complete, accurate sets without unnecessary delays.
Contents
- When a JADU Conversion Is the Right Path — and When It Isn't
- Junior ADU Conversion Drawings in Sunnyvale and Cupertino: What Each City Requires
- Keeping a JADU Permit Set Accurate Through Plan Check
- JADU Conversions Our Team Has Prepared in Sunnyvale and Cupertino
- Drafting Strategies That Move JADU Sets Through Plan Check Quickly
- Frequently Asked Questions
- Key Takeaways
When a JADU Conversion Is the Right Path — and When It Isn't
The most common misconception our team encounters is that any room inside a single-family home can become a junior ADU with a basic permit set and a few cosmetic changes. California law defines qualifying spaces narrowly, and Sunnyvale and Cupertino have each added administrative conditions that tighten eligibility further. Getting clarity on qualification before a single sheet is drawn prevents wasted drafting hours and applicant disappointment well into the permitting process.
Spaces That Qualify Under California JADU Law
A JADU must be created entirely within the existing envelope of the primary residence — no additions, no detached structures, and no expansions beyond the 500-square-foot statutory cap are permitted. Attached garages qualify because they share at least one wall with the main dwelling and are physically connected to the primary structure, which is why our work with garage-to-ADU conversions in Sunnyvale follows the same drawing framework as interior room conversions. The qualifying space must accommodate an exterior-facing entrance independent of the main dwelling's primary entry point, a dedicated efficiency kitchen, and sanitation facilities that may be shared with the primary unit — a legal allowance that distinguishes JADUs from full ADUs under state law.
Conditions That Rule Out a JADU at Plan Check
Detached structures — regardless of how close they sit to the main house — do not qualify under §65852.22 and must be permitted as standard ADUs under a different regulatory framework. Any space that requires an addition to the existing footprint in order to reach a functional living area size falls outside JADU parameters entirely. Our team has also seen submittals rejected when the proposed unit shares only the front door with the main dwelling without a secondary exterior access point, or when the existing structure's floor-to-ceiling height falls below the 7-foot minimum required for habitable space under the California Building Code's residential occupancy provisions.
Watch for this: Sunnyvale plan checkers consistently flag JADU submittals where the proposed exterior door is shown without a header detail — always include the full framing callout on the wall section, not just a door symbol on the floor plan.
Junior ADU Conversion Drawings in Sunnyvale and Cupertino: What Each City Requires
When our team compares the two cities' submittal checklists directly, the similarities are substantial — but the differences are precisely the kind that trigger plan check corrections when overlooked. The table below outlines the key drawing and administrative requirements for JADU permit sets in both jurisdictions, organized to make city-specific distinctions immediately visible.
| Requirement | Sunnyvale | Cupertino |
|---|---|---|
| Maximum unit size | 500 sq ft | 500 sq ft |
| Submittal method | Accela online portal; OTC track available for simple conversions | Public counter or online; no OTC JADU track |
| Owner-occupancy covenant timing | Deed restriction recorded after permit issuance | Signed affidavit required at permit application |
| Separate exterior entrance | Required — shown on floor plan and elevation drawings | Required — shown on floor plan and elevation drawings |
| Efficiency kitchen detail | Required; countertop dims, sink, under-counter fridge | Required; same elements plus circuit notation |
| Electrical panel schedule | Not required unless panel modification is proposed | Required in all JADU submittals |
| Fire separation at shared wall | ½" Type X drywall minimum | ½" Type X drywall minimum |
| Title 24 Part 6 compliance | Required regardless of scope | Required regardless of scope |
| Structural engineering stamp | Required only if load-bearing elements are modified | Required only if load-bearing elements are modified |
| Typical plan check timeline | Same-day (OTC) to 2–4 weeks | 3–5 weeks |
Sunnyvale's JADU Drawing Package
Sunnyvale routes straightforward JADU conversions — those with no structural modifications to load-bearing walls or floor systems — through its over-the-counter review track, where approvals can come within the same appointment. The drawing package requires a complete site plan, a dimensioned existing and proposed floor plan with wall construction types annotated, ceiling height notes on every space involved, and a dimensioned efficiency kitchen detail that calls out the countertop footprint, single-basin sink, and under-counter refrigerator. Title 24 Part 6 compliance documentation is mandatory regardless of scope, and our team prepares it as an integrated part of the set rather than a separate standalone submittal submitted under a different routing number.
What Cupertino Adds to the Standard Checklist
Cupertino requires everything Sunnyvale does, plus a signed owner-occupancy affidavit submitted alongside the permit application — a step that Sunnyvale defers until after permit issuance through a recorded deed restriction. Cupertino also expects the existing electrical panel schedule to appear on the drawings, with a notation confirming whether the panel has adequate capacity to support the JADU's dedicated circuits for the kitchenette and bathroom. Our team adds a panel schedule sheet to every Cupertino JADU set as a standard practice, because submitting without it reliably generates a correction notice that adds several weeks to an otherwise straightforward timeline.
Keeping a JADU Permit Set Accurate Through Plan Check
A JADU permit set does not end at initial submission — plan check corrections are a predictable part of the process in both cities, and how a drawing set is organized from the start determines how quickly and cleanly those corrections can be addressed. Our team structures every set with resubmittal in mind, which means comments are resolved in a single revision round rather than a rolling series of partial fixes that extend the timeline by months.
Documentation Standards That Prevent Resubmittal
The most productive investment in any JADU set is complete annotation on the first submission, treating every callout as an opportunity to answer a plan checker's question before it becomes a formal correction notice. Every wall section should identify the existing framing, the new drywall assembly, and the fire separation rating with explicit material references. Every door and window on the floor plan should cross-reference a schedule with rough opening dimensions, frame material, and glazing type, because glazing in a new exterior opening triggers energy compliance review under Part 6. Our team labels all existing conditions distinctly from proposed work — typically with a screened line weight for existing and a bold line for proposed — because visual ambiguity between existing and new construction is the most consistent trigger for a plan check correction notice in both Sunnyvale and Cupertino.
Title 24 and Structural Notes in JADU Sets
Title 24 Part 6 compliance for a JADU conversion addresses the newly conditioned space specifically — the existing home's compliance is assumed from its original permit, and the JADU's compliance is calculated as a discrete scope. If the conversion involves adding a window or cutting a new exterior door into an existing wall, the glazing area, U-factor, and SHGC must all be tabulated against the performance budget for the addition. Structural review is triggered when a new exterior door is cut into a bearing wall, when garage door headers are removed to open up the interior, or when any alteration to the floor or roof framing becomes necessary. Our experience confirms that proactively flagging the structural scope — even when an engineer stamp may ultimately not be required — produces a measurably faster and more predictable plan check outcome.
Pro insight: Including a brief structural narrative note on the title sheet — describing which walls are non-load-bearing and how that determination was made — reduces plan checker questions significantly, even for projects that fall below the engineer-stamp threshold.
JADU Conversions Our Team Has Prepared in Sunnyvale and Cupertino
The clearest way to understand how these requirements play out is through the specifics of actual projects, because the variables that matter most — existing wall construction, ceiling heights, electrical panel capacity — are always site-specific and determine how many sheets the set ultimately requires. The two projects below represent the range of conditions our team most frequently encounters across both cities.
A Sunnyvale Attached Garage Conversion
One Sunnyvale project involved a two-car attached garage with an existing interior door connecting to the kitchen — a condition that initially seemed ideal for a JADU conversion. The garage floor sat 6 inches below the home's interior finish floor level, which required a floor build-up detail showing the new sleeper assembly, vapor barrier, and subfloor that added a dedicated sheet to the set. The new exterior entrance was cut through the rear garage wall, requiring a full wall section showing the new header, king stud assembly, trimmer configuration, and drywall fire separation on both the modified exterior wall and the shared wall with the main house. Our team submitted through Accela and received over-the-counter approval at the same appointment, largely because the set included a pre-completed Title 24 calculation and a clear materials schedule cross-referenced directly on the floor plan.
A Cupertino Bonus Room JADU
A Cupertino bonus room project presented a different set of conditions — the space was fully within the existing envelope, so no structural modifications were necessary, but the existing electrical panel was at capacity with no spare circuit breaker slots available. The drawings included a panel schedule showing the existing load distribution alongside the proposed JADU circuits, with a notation confirming that a 60-amp subpanel would be installed within the JADU space. Plan check flagged the subpanel location as too close to the efficiency kitchen counter, requiring a minor revision to the floor plan showing the panel relocated to the adjacent wall. Without the panel schedule in the original submittal, that correction would have arrived as an incomplete-submittal notice rather than a targeted dimensional revision, adding significant time to the overall permit timeline.
Drafting Strategies That Move JADU Sets Through Plan Check Quickly
Most JADU permit sets take longer to approve than they should, not because of inherent code complexity but because of avoidable omissions in the drawings that generate correction notices on otherwise approvable projects. Our team has developed a consistent set of practices that produce first-round approvals or minimal-correction submittals across both Sunnyvale and Cupertino building departments.
Pre-Submittal Coordination
For any JADU project with structural modifications or ambiguous space classification, our team schedules a pre-application meeting with the building department before finalizing the drawing set. Both Sunnyvale and Cupertino offer pre-application consultations that allow drafters to confirm the permit pathway, identify any zoning overlay conditions affecting the property, and resolve questions about owner-occupancy documentation timing and format. This step adds a few days to the preparation schedule but consistently saves three to six weeks of plan check corrections, making it among the highest-ROI investments available on any JADU project. Anyone considering a JADU conversion in either city should also confirm the current ADU checklist directly with the building counter, because both jurisdictions update their requirements periodically as state law continues to evolve.
Handling Correction Cycles Efficiently
When plan check corrections arrive, the most efficient response is addressing every comment in a single resubmittal rather than returning a partial revision that resolves only the most urgent items. Our team annotates each correction with a revision cloud and delta marker on the affected sheet, adds a revision block to the title sheet listing every change alongside its corresponding plan check comment number, and resubmits the complete set — not just the revised sheets — in the format each city's portal requires. This approach aligns precisely with what both Sunnyvale and Cupertino expect in a formal resubmittal package and eliminates the risk of secondary corrections triggered by a reviewer examining changes without full drawing context. The practices that help avoid initial rejections are documented in detail in our post on common reasons Bay Area permit sets get rejected at plan check, and many of those principles apply directly to JADU sets.
Frequently Asked Questions
A junior ADU is a unit of up to 500 square feet created entirely within the existing footprint of a single-family home, including attached garages. Unlike a full ADU, a JADU does not require a separate, fully self-contained bathroom — shared sanitation with the primary dwelling is permitted — and California law requires the property owner to occupy either the JADU or the main house. Full ADUs have no owner-occupancy requirement, can be detached, and can exceed 500 square feet depending on lot size and local zoning.
No. California Government Code §65852.22 requires that a JADU be created within the existing walls of the primary dwelling, including attached garages that share at least one interior wall with the main structure. A detached garage — even one located immediately adjacent to the house — must be permitted as a full ADU, which carries different setback, height, and permit set requirements than a JADU conversion.
State law requires an efficiency kitchen in every JADU, defined as a cooking facility with a food preparation counter, storage cabinets, and a sink. A gas or electric range is not permitted inside a JADU by most local interpretations, including in Sunnyvale and Cupertino, which means the drawings must show an under-counter refrigerator and countertop cooking appliance rather than a freestanding range. The kitchen detail on the floor plan must dimension the counter footprint and call out the sink and appliance locations explicitly.
Cupertino requires a signed owner-occupancy affidavit submitted as part of the permit application package, confirming that the property owner intends to occupy either the primary dwelling or the JADU. This differs from Sunnyvale, where the owner-occupancy requirement is documented through a deed restriction recorded after permit issuance. Missing the Cupertino affidavit at submittal results in an incomplete application notice that restarts the plan check clock.
Structural engineering review and an engineer stamp are required when the conversion involves modifications to load-bearing walls, floor framing, or roof framing — the most common trigger being the installation of a new exterior door through an existing bearing wall. Interior room conversions that involve only non-structural partition walls and new MEP rough-in typically do not require an engineer, but our team recommends including a structural narrative note on the drawings to pre-empt plan checker questions about wall classification.
A straightforward interior JADU conversion in Sunnyvale or Cupertino typically requires five to eight sheets: a cover and site plan, an existing and proposed floor plan, a reflected ceiling plan, at least one wall section through the shared and exterior walls, a window and door schedule, an efficiency kitchen detail, and Title 24 Part 6 compliance documentation. Cupertino sets add an electrical panel schedule sheet. Conversions involving structural modifications may require an additional structural plan and details, increasing the count to ten or more sheets.
Yes — shared bathroom facilities are explicitly permitted under California's JADU statutes, which is one of the primary distinctions between a JADU and a full ADU. The drawings must show the means of access to the shared bathroom from within the JADU and note that the bathroom is shared, since plan checkers verify that no separate full bath is being marketed as a self-contained unit without appropriate permitting. Most JADU projects our team has prepared in Sunnyvale and Cupertino use a shared bathroom accessed from a shared interior hallway.
Sunnyvale offers over-the-counter approval for straightforward JADU conversions without structural modifications, meaning approval can come at the same appointment — typically two to three hours. More complex submittals in Sunnyvale enter the standard plan check queue and typically take two to four weeks. Cupertino does not offer an OTC track for JADU permits, and our team's experience places standard plan check timelines at three to five weeks for a first submission, with resubmittals adding two to three weeks per round when corrections are required.
Key Takeaways
- Junior ADU conversion drawings in Sunnyvale and Cupertino require city-specific documentation beyond the state baseline — notably Cupertino's mandatory owner-occupancy affidavit and electrical panel schedule at the time of application.
- Sunnyvale's over-the-counter review track offers same-day approval for simple conversions, making complete, annotated first submissions especially valuable for reducing the overall project timeline.
- Structural engineering review is triggered specifically by load-bearing wall modifications, new exterior door openings through bearing walls, or framing alterations — not by JADU conversions as a category.
- Proactive pre-application coordination with the building department, combined with a fully annotated and cross-referenced drawing set on the first submission, consistently produces faster plan check outcomes than any reactive correction strategy.
