2. Utility Upgrades (The Budget Killer)
Electrical Panel: Does your main house have a 100-amp or 200-amp panel? If you add an all-electric ADU (which is encouraged or required depending on code cycles), you likely need to upgrade your main panel to 200 or 400 amps. This involves PG&E and can take months.
Solar Mandate: As of current California energy codes (Title 24), newly constructed detached ADUs generally require solar panels. This is an upfront cost you must budget for (roughly $3k–$6k depending on size).
Gas vs. Electric: Lafayette encourages electrification. Running a new gas line is expensive and increasingly restricted. Plan for an all-electric unit (heat pump HVAC, induction stove, heat pump water heater).
3. Construction Method: Prefab vs. Stick-Built
City geography dictates this choice more than other cities.
Prefab/Modular: Faster and less on-site mess. However, modules must be craned into the backyard. If you live on a narrow, winding road or have overhead wires, a crane might not be able to access your site.
Stick-Built (Custom): Takes longer (4–10 months) and is noisy/messy, but it is the only option for difficult terrain or custom shapes.
4. Budgeting "Soft Costs"
Many homeowners budget for the construction (hard costs) but forget the soft costs, which can eat up 20-25% of the budget.
Design Fees: Architect/Draftsperson.
Engineering: Structural engineer (mandatory) and Civil engineer (for grading/drainage).
Permit Fees: While impact fees are waived for units under 750 sq. ft., you still pay plan check fees, building permit fees, and school district fees (if over 500 sq. ft.).
Title 24 Report: An energy consultant must verify the unit meets efficiency standards.
5. Financing Strategy
You cannot get a standard mortgage for an ADU construction project. You need to secure funding before starting. Common options include:
HELOC (Home Equity Line of Credit): Most common method.
Cash-Out Refinance: Rates may be higher than your original mortgage.
Renovation Loan (Renofi, HomeStyle): Based on the future value of the home.
Note on ROI: In Lafayette, building costs are high ($350–$500+ per sq. ft.). Ensure the rental income or property value increase justifies the $250k–$400k spend.
6. Privacy and Neighbor Relations
Lafayette puts a premium on privacy. Even if the city allows you to build 4 feet from the fence:
Windows: If you put a large window facing your neighbor's bedroom, you create conflict. Plan for clerestory windows (high up) or skylights to get light without invasion of privacy.
Construction Fatigue: Your neighbors will deal with noise and dumpsters for months. Inform them early to maintain good relationships.
7. Property Tax Implications (Prop 13)
Assessment: Your existing home’s tax basis generally does not change.
The ADU: The ADU is assessed as "new construction." You will pay roughly 1.1% of the cost of construction (or market value of the addition) in additional annual property taxes.
Resale: While an ADU adds value, it rarely adds dollar-for-dollar construction cost value immediately. It adds immense value in marketability.
8. The End-User (Design for the Tenant)
Who is this for?
Aging Parents: You need 36-inch wide doors, curbless showers, and no steps (Universal Design).
Renters: They want privacy, separate entry paths, and durable finishes (LVP flooring, quartz counters).
Your Home Office: You need soundproofing and high-speed hardwired internet (don't rely on Wi-Fi from the main house).
Summary Checklist for Week 1:
Map it: Get your plot map and locate easements.
Inspect it: Check your electrical panel capacity and sewer line age.
Fund it: Talk to a lender to see how much cash you can access.
Ask them: Call the Lafayette Planning Department to verify your zone and fire requirements.
1. The "Hidden" Site Constraints
Before you dream up a floor plan, you need to know what lies beneath and above your soil.
Topography & Soil (Geotech): Lafayette has many hillsides. If your lot is sloped, your foundation costs will skyrocket. You may need a Geotechnical (Soils) Report to prove the ground can support the structure.
Sewer Lateral Compliance: In this area (EBMUD territory), you usually cannot obtain a building permit without certifying your sewer lateral. If your current sewer line is old or leaky, you may be forced to replace the entire line to the street, which costs thousands.
Septic Tanks: Some parts of Contra Costa County like portion of city of Lafayette are on septic. Expanding a septic system to handle an ADU is very difficult and expensive. You generally need to connect to the public sewer if possible.
Power Lines & Easements: Check your title report. You cannot build an ADU over a utility easement (PG&E, water, etc.). Also, look up—you cannot build directly under high-voltage power lines.
Make your ADU project easier
Note: Zoning laws in California are dynamic and subject to change due to new state legislation. As of the current date (November 26, 2025), the following details are based on the Municipal Code and overarching California State Laws (HCD). You must verify this information with your city Planning Department before starting construction. Let us know and we can give you more up to date information by confirming it with your city planning Department.