The Short Answer
All ADUs in Morgan Hill — detached, garage conversion, junior ADU — require a building permit, regardless of size. California Government Code 65852.2 (and 2024 amendments) override local zoning restrictions, but Morgan Hill still manages the permit review, setbacks, parking, and utility connections locally.
Morgan Hill, unlike some Santa Clara County neighbors, does NOT have a pre-approved ADU ordinance that fast-tracks permitting or auto-waives parking. This means your ADU application goes through the standard 60-day plan-check cycle (AB 671 shot clock), with local scrutiny on lot coverage, setbacks (typically 5–15 feet depending on type), utility metering, and egress windows. The City of Morgan Hill Building Department applies both state ADU law and local development standards — so your 800-square-foot detached ADU on a 7,500-square-foot lot in East Morgan Hill may clear state law but still need variance approval or parking-requirement demonstration. Neighboring cities (Gilroy, San Martin unincorporated) may have different local amendments or no formal ADU policy at all, making Morgan Hill's middle ground worth understanding. The key Morgan Hill difference: they require separate utility service (not just sub-metering) for detached ADUs, which adds $2,000–$5,000 to soft costs and extends the project timeline by 2–3 weeks for utility company coordination.
What happens if you skip the permit (and you needed one)
- Morgan Hill Building Enforcement can issue a Notice to Correct and assess fines of $500–$1,500 per violation per day, plus mandatory demolition or removal of the unpermitted structure.
- Your title insurance and future buyers' lenders will flag unpermitted ADU work on a property, making resale difficult and potentially blocking refinancing; California requires ADU disclosure on TDS (Transfer Disclosure Statement).
- If your tenant or a neighbor files a complaint, the City will impose a stop-work order, plus you'll owe double permit fees ($6,000–$15,000) and all retroactive plan-check costs when you finally pull permits.
- Property insurance may deny claims related to unpermitted work, leaving you liable for injury or damage claims in the ADU — a $300,000+ exposure.
Morgan Hill ADU permits — the key details
California Government Code 65852.2, expanded by AB 881 (2020) and further clarified in 2023, mandates that cities allow ADUs on single-family residential lots, overriding local zoning that might otherwise prohibit them. Morgan Hill adopted a local ADU ordinance in 2020 (aligned with state law) but has NOT eliminated all local restrictions — notably, the city still imposes a 50-foot setback for detached ADUs on corner lots, a 15-foot side-yard setback for detached units on interior lots, and a 5-foot front-yard setback for garage conversions. These setbacks are tighter than the state-law minimums in many cases, meaning your lot size and shape directly determine feasibility. Juniors ADUs (interior conversions within the primary dwelling, typically 375–500 square feet) have the most lenient setback rules (none apply, since it's interior) and are often the fastest path to approval. The IRC R310 egress requirement — two emergency exits, one operable window per bedroom minimum 10 square feet — applies to all ADU types; Morgan Hill's plan-review team will flag missing egress on first submittal if not clearly shown on floor plans.
Three Morgan Hill accessory dwelling unit (adu) scenarios
Scenario A
Detached ADU (900 sq ft), East Morgan Hill, 8,500-sq-ft lot, interior lot with 100-foot frontage
You own a 50-foot × 170-foot lot on Evergreen Avenue (interior lot, not a corner). You want to build a detached 900-square-foot, two-bedroom ADU in the rear yard, 25 feet from the rear property line and 20 feet from the side property line. Morgan Hill code requires a 15-foot side setback for interior-lot detached ADUs and 20-foot rear setback, so your 20-foot side placement FAILS — you must either move the ADU 5 feet closer to the home (or 10 feet further back), redesign to meet the 15-foot side setback, or request a variance. Assuming you adjust to 15-foot side and 20-foot rear, you proceed with a formal permit application. Separate utility service is mandatory: you'll coordinate with PG&E (4–6 week lead time for a new electrical service line from the street) and the Water Department for a separate sewer tap (2–3 weeks). The plan-check review takes 8–10 weeks with one correction cycle (typically egress-window clarification and fire-sprinkler waiver, since your lot is 8,500 sq ft and the ADU is 900 sq ft, totaling under 4,000 habitable units). Parking is satisfied with a 10-foot × 20-foot off-street pad beside the ADU. Total permit fees: $5,500 (base permit $2,200, plan review $1,800, utility inspection $800, impact fee $700). Utilities and site work: $4,000–$6,000. Construction timeline: 4–5 months from permit issuance to final. Total soft costs (permits + design + utilities coordination): $9,500–$11,500.
Permit required (detached, interior lot) | Setback adjustment or variance needed | 15-ft side, 20-ft rear minimum | PG&E + Water Dept. coordination required | Separate sewer tap $2,000–$3,000 | Electrical service extension $2,000–$3,000 | Parking pad required | Fire-sprinkler waiver likely | Plan review cycle: 8–10 weeks | Total permit fees: $5,500 | Total project cost estimate: $150,000–$220,000
Scenario B
Garage Conversion ADU (500 sq ft, Junior ADU), West Morgan Hill residential zone, 6,500-sq-ft corner lot
You own a corner lot on Cochrane Road with a detached single-car garage (approx. 12×20 feet, 240 sq ft). You want to convert it to a Junior ADU (interior addition to existing dwelling or standalone garage conversion) with a second sleeping area, kitchenette (sink, hot plate, microwave — no full stove), and a full bathroom. Because this is a garage conversion (not a brand-new detached structure), Morgan Hill's 50-foot corner-lot setback does NOT apply — the garage is already built and setbacks are pre-satisfied. However, Morgan Hill still requires separate utility service for this conversion-type ADU if it becomes 'habitable' (kitchen + bathroom + sleeping area). A kitchenette does NOT trigger full kitchen requirements (no range hood, no separate gas service required), so you may be able to use a sub-meter arrangement instead of a full separate service line; confirm this with the City during pre-submittal (a 20-minute phone call with the Plan Review technician). Parking is the main hurdle: you've removed the garage (one parking space), so the primary home now has zero off-street parking. Corner lots on Cochrane Road do NOT qualify for the transit-waiver (no bus service within 0.5 mile), so you must demonstrate either (a) a new carport or driveway pad for one car (4–6 weeks, $3,000–$5,000 site work), or (b) a Parking Variance request to the Planning Commission (4–8 weeks, $400 fee, hearing required). Most applicants choose the carport. Plan review: 6–8 weeks with one correction cycle (typically parking plan clarity and kitchenette-water-line detail). Separate utility: 2–3 weeks coordination, possibly waived if sub-meter approved (save $2,000–$3,000). Total permit fees: $4,200 (base permit $1,800, plan review $1,400, impact fee $600 — no separate utility inspection if sub-meter). Construction timeline: 3–4 months (simpler than new detached because foundation is existing). Total soft costs: $6,500–$9,000 (permits + design + carport construction).
Permit required (garage conversion) | No setback issues (existing structure) | Kitchenette acceptable, no range required | Sub-meter may be acceptable (confirm pre-submittal) | One off-street parking space must be provided | Carport addition: $3,000–$5,000 | OR parking variance + hearing: $400–$1,200 | Plan review cycle: 6–8 weeks | Total permit fees: $4,200 | Total project cost estimate: $80,000–$140,000
Scenario C
Above-Garage ADU (650 sq ft), East Morgan Hill, narrow lot (40-ft frontage, 7,000 sq ft total), single-story primary home with integral garage
Your 40-foot × 175-foot lot has a 1960s ranch home with an attached, integral garage (not a separate structure). You want to add a second story over the garage only (a 650-square-foot, one-bedroom above-garage ADU), with a separate exterior staircase and entrance on the side. This is NOT a full second story on the entire home — only the garage area. Morgan Hill's local code treats above-garage ADUs as a special type of 'attached ADU' with relaxed setback rules compared to fully detached units. The side-yard setback for above-garage ADUs is 10 feet (vs. 15 for detached), and front-yard is 5 feet (matching the primary home setback). Your 40-foot frontage means you have roughly 40 - 10 (existing house) - 10 (side setback) = 20 feet of lot width available; since the garage is 12 feet wide, an above-garage structure is feasible. Utility requirement: above-garage ADUs use the primary home's existing electrical panel and water line (sub-meter for metering), so no separate service trenching is required — saving $3,000–$5,000 and 4–6 weeks of utility coordination. However, you MUST show that the home's sewer main can handle the additional occupants (two occupants for one-bedroom ADU + existing home = typically 5–6 occupants total); Morgan Hill's Public Works may require a sewer-capacity letter from the property owner's plumber (cost: $300–$500, 1 week). Parking: your lot has a driveway with room for two cars (one for primary home, one for ADU), so parking is satisfied without variance. Plan review: 8–10 weeks with correction cycle (typically structural detail for the second-story connection to the existing roof, and sewer-capacity confirmation). Inspections: foundation/connection (new second story must be properly anchored to existing garage structure), framing, rough utilities (separate sub-meter for ADU, new HVAC if needed), drywall, final. Total permit fees: $5,000 (base permit $2,100, plan review $1,800, impact fee $700, structural review $400). Utilities and site: $1,500–$2,000 (sub-meter, sewer check, exterior staircase footings). Construction timeline: 4–5 months. Total soft costs: $7,500–$9,500.
Permit required (above-garage ADU) | Attached ADU with relaxed setbacks | 10-ft side, 5-ft front minimum | Sub-meter acceptable (no separate service line needed) | Sewer-capacity letter recommended | Parking satisfied (driveway two-space minimum) | No parking variance needed | Structural review required (roof connection) | Plan review cycle: 8–10 weeks | Total permit fees: $5,000 | Total project cost estimate: $120,000–$180,000
City of Morgan Hill Building Department
Contact city hall, Morgan Hill, CA
Phone: Search 'Morgan Hill CA building permit phone' to confirm
Typical: Mon-Fri 8 AM - 5 PM (verify locally)
Contact city hall, Morgan Hill, CA
Phone: Search 'Morgan Hill CA building permit phone' to confirm
Typical: Mon-Fri 8 AM - 5 PM (verify locally)
Disclaimer: This guide is based on research conducted in May 2026 using publicly available sources. Always verify current accessory dwelling unit (adu) permit requirements with the City of Morgan Hill Building Department before starting your project.