An addition is the most permit-heavy project a homeowner takes on. Most of the delays we see happen before a single nail goes in. Work through this list first.
Confirm what you're allowed to build
Check zoning, lot coverage, and setbacks with the city or county before you pay for drawings.
- Property setbacks on all sides
- Maximum lot coverage percentage
- HOA architectural review, if applicable
- Easements shown on the parcel map
Get plans and structural calcs
Architectural drawings plus engineering typically take 3–5 weeks and are required for plan check. Title 24 energy compliance is required in California.
Budget for the invisible costs
Foundation, utility upgrades, and roof tie-in are where addition budgets grow.
- Electrical panel upgrade if the service is undersized
- HVAC extension or a separate mini-split
- Sewer or septic capacity
- Roof tie-in and matching existing exterior finishes
Plan the timeline honestly
A typical 400–600 sq ft addition runs 14–20 weeks from permit issuance, with plan check adding 4–8 weeks before that.
Bottom line
Spend the first two months on paperwork and planning. Projects that skip that stage lose the time later, with more disruption.
