Home Additions in Walnut Creek, CA
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What Triggers Discretionary Design Review
Additions in Walnut Creek need design review. Under the single-family design review rules, a project loses its exemption and gets fuller review when any of these apply:
- The lot was created on or after June 15, 1973.
- Total floor area on the lot exceeds 4,500 sq ft.
- In R-8 to R-10 districts: floor area ratio over 0.42, more than 40% of the floor area on the second floor, or a second story set back less than 10 feet from a side lot line.
- The addition is 50% or more of the existing house, subject to district floor-area cutoffs.
We check these before design so the addition fits the path you want.
Addition Work
Hillside Lots Below Mount Diablo
Walnut Creek sits at the foot of Mount Diablo, surrounded by the Shell Ridge, Lime Ridge, Acalanes Ridge and Sugarloaf open spaces. On residential lots averaging 15% slope or more, outside the Core Area and Rossmoor, the Hillside Performance Standards apply:
- No buildings where the true slope exceeds 30%.
- Geotechnical analysis against hazard maps.
- No structures within 50 feet of a fault line or the top of a creek bank.
- Ridgeline limits.
Additions of 10% or less are exempt from the hillside standards.
Trees and Permits
A tree permit is needed to remove any tree with a single trunk of 28 inches or more in circumference at 4½ feet, or 40 inches combined for multi-stem trees. Native oaks, madrone, buckeye, black walnut and grey pine are highly protected. File the tree application with the first development application; three or more trees require an arborist report.
Walnut Creek issues its own permits. Unlike Lafayette, Orinda or Moraga, Walnut Creek has its own Building Division that reviews plans, issues building permits and inspects the work. Plan check is electronic. The City’s published maximum for a first review of new residential work is 23 business days, with 18 for rechecks, and its goal is to approve most residential alterations and ADUs within two review rounds.
City Hall, 1666 North Main Street, 2nd Floor, Walnut Creek, CA 94596
Building permit technicians (925) 943-5834 · Duty planner (925) 256-3558 · Inspections (925) 943-5833
In person Monday to Thursday by appointment, with walk-ins taken as available; Fridays are remote service. All permit applications are filed through the City’s online Accela portal; paper and emailed applications are not accepted.
Inspections are scheduled through Accela or by phone before midnight for next-day service. Construction on Saturdays and City holidays needs an after-hours permit.
Explore More
Other Walnut Creek services: ADUs · Bathrooms · Kitchens · New Homes · Walnut Creek overview
Same service nearby: Lafayette · Alamo · Danville · Orinda
See home additions and second stories.
Walnut Creek Home Additions FAQ
Does a home addition need design review in Walnut Creek?
Yes. Exterior changes need design review, and certain additions, such as those of 50% or more of the house or on lots over 4,500 sq ft of floor area, get fuller review.
Do hillside rules apply to my addition?
On lots averaging 15% slope or more outside the Core Area and Rossmoor, unless the addition is 10% or less of the house.
Who issues the building permit?
The City of Walnut Creek, through its online Accela portal.
Is part of Walnut Creek unincorporated?
Some areas, such as parts of Saranap, are unincorporated and permitted by Contra Costa County. We confirm jurisdiction for your address.