Quick Answer: An ADU permit in Milpitas takes 4 to 8 months from starting design to permit in hand, and costs $14,000 to $34,000 in city fees. Applications go to the Milpitas Building Division at 455 East Calaveras Boulevard. State law gives the city 60 days to approve or deny a complete ADU application, which is a real protection — but the clock only starts when the application is complete, so a thorough first submittal is worth more than any expediting.
ADUs are the most streamlined residential permit in California, and Milpitas processes them routinely. The delays that do happen are almost always caused by incomplete submittals or by discovering a site constraint after the design was drawn.
Step 1 · Confirm the unit is allowed and sized correctly
Before design, establish four things:
| Question | Why it matters |
|---|---|
| Maximum size for your lot | Typically 800 sq ft for one bedroom, up to 1,000 for two |
| Required setbacks | Four feet from side and rear property lines for a new detached unit |
| Height limit | Governs whether a two-storey or above-garage unit is possible |
| Where the utilities and sewer lateral run | Determines trenching cost and whether a lateral upgrade is needed |
The fourth is the one skipped most often and the one that costs most. Locating the sewer lateral and checking its size and material before choosing where the ADU goes can save tens of thousands.
Step 2 · Drawings and reports
| Document | Produced by |
|---|---|
| Site plan with setbacks, utilities and existing structures | Designer |
| Floor plan and elevations | Designer |
| Foundation and framing plans | Structural engineer |
| Structural calculations, stamped | Structural engineer |
| Title 24 energy compliance report | Energy consultant |
| Electrical load calculation for the whole property | Designer with electrician input |
| Soils report, where required | Geotechnical engineer |
Expect $8,000 to $20,000 for the set. The electrical load calculation deserves attention: it covers the existing house plus the new unit, and it is what determines whether you need a service upgrade. Doing it early rather than at submittal avoids a redesign of the panel and meter arrangement.
Step 3 · Submit and start the 60-day clock
Submittals go through the city portal. Intake screens for completeness, not correctness.
The 60-day rule is the most useful thing to understand here. Under state law the city must approve or deny a complete ADU application within 60 days. That is a genuine constraint on the city and it works.
What it does not do is start the clock on an incomplete package. A submittal missing the Title 24 report, the structural calculations or the load calculation gets returned, and the 60 days begins again when you resubmit. Every incomplete submittal is a wasted month.
Step 4 · Review
Your set goes to Building, Planning, Public Works for utilities and drainage, and Fire where access or sprinkler requirements apply.
The corrections that come back most often
- Electrical service capacity insufficient. The load calculation shows the existing panel cannot carry the house plus the ADU. Fix is a 200-amp upgrade at $5,000 to $10,000, and it changes the meter and panel drawings.
- Sewer lateral undersized or in poor condition. The city may require replacement before allowing a second connection. $8,000 to $25,000.
- Setback measured from the wrong line. Common where a fence does not sit on the actual property line. A survey resolves it and should precede design on tight lots.
- Fire access or sprinklers. Distance from the street and the presence of sprinklers in the main house both affect whether the ADU needs them.
- Drainage. The new roof adds runoff, and Public Works wants to see where it goes.
Step 5 · Fees and issuance
| Fee | Range |
|---|---|
| Building permit (valuation-based) | $3,500 – $9,000 |
| Plan check | $2,800 – $7,000 |
| School impact fees | ~$5.17 per sq ft over 500 sq ft only |
| Plumbing, electrical, mechanical | $700 – $1,800 |
| Utility connection and meter fees | $2,500 – $9,000 |
| Energy compliance review | $300 – $800 |
Two useful exemptions. School fees apply only to floor area above 500 square feet, so a 500 square foot unit pays none. And ADUs under 750 square feet are exempt from impact fees that larger units pay, which is why so many are built at 749 square feet.
Step 6 · Inspections
- Setback and form, before the foundation pour
- Foundation, after steel placement
- Underground utilities, before backfill
- Framing and shear
- Rough plumbing, electrical, mechanical
- Insulation
- Drywall nailing
- Final, including the separate utility connections
The underground utilities inspection before backfill matters more than it sounds. Covering a trench before it is inspected means digging it out again.
How long, realistically?
| Stage | Duration |
|---|---|
| Site and utility investigation | 2 – 3 weeks |
| Design and engineering | 8 – 14 weeks |
| Plan check under the 60-day rule | 8 – 12 weeks including one correction cycle |
| Permit issuance | 1 – 2 weeks |
| To permit in hand | 4 – 8 months |
| Construction | 7 – 12 months |
How to keep it on schedule
- Locate the sewer lateral and run the electrical load calculation before design. These are the two most common corrections and both are preventable.
- Get a boundary survey if any fence line is ambiguous. Setback corrections are avoidable.
- Submit genuinely complete. The 60-day clock is your best protection and an incomplete package forfeits it.
- Decide on 500 or 749 square feet deliberately if you are near either threshold, since both carry fee consequences.
- Respond to corrections in days. The only part of the timeline fully in your control.
Getting through it cleanly
An ADU in Milpitas is a well-defined process with two failure modes: incomplete submittals and site constraints found late. Both are addressed in the first month.
DevArt8 Builders builds ADUs throughout Milpitas, San Jose and Fremont and handles the permitting end to end, including the utility investigation before design. See our Milpitas service area page for project detail.
Frequently Asked Questions
How long does it take to get an ADU permit in Milpitas?
Four to eight months from starting design to permit in hand. State law requires the city to approve or deny a complete ADU application within 60 days, but that clock only starts when the application is complete, so an incomplete first submittal effectively costs you a month.
How much are ADU permit fees in Milpitas?
$14,000 to $34,000 in total city fees for a detached unit, including the building permit at $3,500 to $9,000, plan check at $2,800 to $7,000, and utility connection fees at $2,500 to $9,000. School impact fees of roughly $5.17 per square foot apply only to area above 500 square feet.
What is the most common reason an ADU submittal gets corrections in Milpitas?
Insufficient electrical service capacity. The load calculation covers the existing house plus the new unit, and many older Milpitas homes on 100 or 125-amp service cannot carry both. The fix is a 200-amp upgrade at $5,000 to $10,000, and it changes the panel and meter drawings. Running the calculation before design avoids the redesign.
Why do so many ADUs get built at 749 square feet?
Because units under 750 square feet are exempt from impact fees that larger units pay. There is a second threshold at 500 square feet, below which school impact fees do not apply at all. If your plan is near either number, the decision is worth making deliberately rather than by accident.
Do I need a survey?
If any fence line is ambiguous relative to the actual property line, yes. Setbacks for a detached ADU are measured from the property line, not the fence, and a setback correction after submittal means redrawing and restarting review. On tight lots a survey is cheap insurance.
Ready to build? Here is how we work as an ADU builder in Milpitas.