ADU fees in Mountain View: $8,997–$51,548 for a 1,000 sq ft backyard unit
Mountain View publishes typical ADU building permit fees rather than a per-sq-ft formula: $7,000 to $13,000 for new construction. On top of that come a land use document fee and, above 750 sq ft, a transportation impact fee. Water and sewer capacity fees may also apply when a new connection is needed.
7 fee lines · 2 official sources · checked Oct 18, 2026 · Sources · Calculator
Modeled fees by ADU size
Detached ADU, 2,000 sq ft main home (example assumption), law in force today. Bars: solid = fees that apply, hatched = fees that may apply.
Most lots in Mountain View cap a detached ADU at 1,000 sq ft; larger sizes are shown for comparison.
Each fee with its official source (numbers link to the source list). Est. = computed by us from the official rate; May apply = high total only; Up to = statewide cap, district may charge less.
Fee
499 sq ft
750 sq ft
1,000 sq ft
1,200 sq ft
Planning & zoning
Land use document fee (0.24% of construction valuation)20.24% of construction valuation, shown for the City's typical $100,000–$300,000 range.
Est.$240–$720
Est.$240–$720
Est.$240–$720
Est.$240–$720
Building permit & plan check
Building permit, new construction ADU (City's typical range, incl. inspections)1The City's published typical range for a new construction ADU, not a per-project calculation. It depends on construction valuation ($100,000–$300,000 typical).
Est.$7,000–$13,000
Est.$7,000–$13,000
Est.$7,000–$13,000
Est.$7,000–$13,000
Excavation permit, if utility or right-of-way work is needed1Up to $12,000, only when utility or right-of-way work is needed. High total only.
May apply$12,000
May apply$12,000
May apply$12,000
May apply$12,000
Impact fees
Citywide transportation fee2Per net new unit. The schedule doesn't say which rate applies to an ADU, so we show the multi-family to single-family range, prorated by ADU size over the primary home's size.
Exempt
Exempt
Est.$1,757–$3,137
Est.$2,108–$3,764
School district fee
School impact fees (Mountain View Whisman / Los Altos & MVLA high school districts)3The City says new residential space over 500 sq ft pays school fees, collected by the districts. We show the statewide Level 1 maximum as an upper bound.
Exempt
Up to$4,035
Up to$5,380
Up to$6,456
Utility connections
Water capacity fee (if a new connection is required)2State law limits ADU capacity charges to a proportional share (Gov. Code 66311.5(e)) and bars new ones for most conversions. Which class the City uses for an ADU isn't stated. High total only.
May apply$9,389
May apply$9,389
May apply$9,389
May apply$9,389
Sewer capacity fee (if a new connection is required)2Same caveat as water. High total only.
May apply$7,923
May apply$7,923
May apply$7,923
May apply$7,923
Modeled total
$7,240–$43,032
$7,240–$47,067
$8,997–$51,548
$9,348–$53,252
Junior ADUs
The City's typical building permit fees for a JADU are $4,000 to $6,000 (construction valuation $25,000–$35,000). 1
Water & sewer
Conversions that fix a nonconforming condition, code violation or unpermitted structure pay no impact or connection/capacity fees unless new utility infrastructure is needed. 1
Rules
What you can build in Mountain View
Maximum size
Single-family lots: 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms); an attached ADU is capped at 50% of the main home. Multifamily lots: 1,200 sq ft detached. 1
Height
28 ft for a 1- or 2-story ADU (a basement counts as a story). 1
Setbacks
4 ft side and rear; front per the zoning district. 1
Parking
None for a studio; one space for 1+ bedrooms, with exceptions (City Code 36.12.95). None on multifamily lots. 1
Owner occupancy
Not required for an ADU. For a JADU, an owner must live in the house or the JADU. 1
Pre-approved plans
State law: every city must run a program to pre-approve ADU plans (Gov. Code 65852.27). Local rule not captured yet.4
Junior ADU (JADU)
Up to 500 sq ft, entirely within the walls of the house; a deed restriction is recorded. 1
State law
Why a 750 sq ft ADU pays no impact fees
California bars impact fees on ADUs of 750 sq ft or less of interior livable space. Above that, they must be proportional to the main home’s size; we assume 2,000 sq ft unless you enter yours. School fees start at 500 sq ft. From January 1, 2027, SB 1117 limits impact fees to the area over 750 sq ft. How the state rules work →
ADU permits issued
Mountain View issued 86 ADU building permits in 2025
356 from 2018 to 2025, as the jurisdiction reported to the state in its Housing Element Annual Progress Reports (Table A2, ADU rows; may include JADUs). “–” means no ADU rows were reported that year.
The Governor approved SB 1117 (Chapter 809, Statutes of 2026) on September 29, 2026. It amends Gov. Code 66311.5: on lots with up to two ADUs, impact fees on an ADU over 750 sq ft must still be proportional to the primary home, and may only be charged on the area over 750 sq ft. Regular 2026 statutes take effect January 1, 2027. Until then, fees on a larger ADU are figured on its full size. Our calculator has a 2027 setting that shows the difference.
Mountain View's development fee table, effective August 22, 2026, sets the citywide transportation fee at $6,273.15 per new single-family unit, along with updated water and sewer capacity fees.
The Department of Housing and Community Development updated its ADU Handbook to reflect the laws that took effect January 1, 2026. Its proportional-fee example: a 1,000 sq ft ADU next to a 2,000 sq ft home pays 50% of the fee a new home would pay. Our models use 2,000 sq ft as the example primary-home size unless you enter your own.
On January 28, 2026 the State Allocation Board raised the statewide maximum Level 1 developer fee for residential construction from $5.17 to $5.38 per sq ft (+4.06%). School districts collect it on ADUs of 500 sq ft or more, at their own adopted rate up to this cap (higher Level 2/3 fees need extra findings). Where we haven't confirmed a district's rate, we use $5.38 as the upper bound.
For a detached ADU with a 2,000 sq ft main home (an example assumption), our model of Mountain View’s official fee schedules comes to $7,240–$47,067 at 750 sq ft and $8,997–$51,548 at 1,000 sq ft. Ranges show fees that may or may not apply to your project.
Does Mountain View charge impact fees on a 750 sq ft ADU?
No. California Government Code section 66311.5 bars impact fees on an ADU of 750 sq ft of interior livable space or less (500 sq ft or less for a JADU). Above 750 sq ft, impact fees must be proportional to the size of the main home. At 1,000 sq ft, the impact fees we model for Mountain View come to at most $3,137.
Do school fees apply to an ADU?
Only at 500 sq ft or more. School districts charge their adopted developer fee per sq ft, capped at the State Allocation Board’s Level 1 maximum ($5.38 per sq ft since January 28, 2026) unless they qualify for higher levels.
How big can an ADU be in Mountain View?
Single-family lots: 850 sq ft (studio or 1 bedroom) or 1,000 sq ft (2+ bedrooms); an attached ADU is capped at 50% of the main home. Multifamily lots: 1,200 sq ft detached.
A local agency, special district, or water corporation shall not impose any impact fee upon the development of an accessory dwelling unit that has 750 square feet of interior livable space or less