Site Preparation
Before any construction begins, your site needs proper preparation. This includes locating and marking underground utilities, removing obstacles, protecting valuable landscaping, and ensuring safe access for construction equipment. Skipping these steps can lead to costly utility strikes, damaged trees, or construction delays.
Quick Summary
Time needed
1-2 weeks
Cost
$2,000-8,000
Key contact
811 & site contractor
Why Site Preparation Matters
Proper site preparation sets the foundation for a smooth construction process. Rushing or skipping steps here can lead to expensive problems that delay your entire project:
- Hitting a gas line costs $10,000-50,000+ in repairs and fines
- Killing a mature tree can violate permits and cost $5,000-25,000 in fines
- Poor drainage planning leads to foundation problems later
- Inadequate access routes delay material deliveries and add costs
Site Preparation Step-by-Step
Call 811 to Mark Utility Lines
This is legally required before any digging. Call 811 at least 2-3 business days before excavation. Utility companies will come out FREE of charge to mark:
- • Red: Electric power lines
- • Yellow: Gas, oil, petroleum
- • Orange: Communications, cable TV
- • Blue: Water lines
- • Green: Sewer and drain lines
- • Pink: Temporary survey markings
- • Purple: Reclaimed water, irrigation
Critical: Markings are only valid for 14-30 days depending on your state. If construction is delayed, you must call 811 again.
Survey and Stake the Building Site
If not already done during permitting, have a surveyor precisely mark:
- • Property corners and boundaries
- • Exact ADU footprint location
- • Required setback distances
- • Utility easements
- • Elevation benchmarks for grading
Cost: $300-800 for staking; often included if you had a full survey done earlier.
Install Tree and Landscape Protection
Protect trees and plants you want to keep BEFORE any equipment arrives:
- • Install tree protection fencing at the drip line (not just around trunk)
- • Lay plywood over root zones if equipment must cross them
- • Wrap trunk bark with protective boards to prevent scrapes
- • Mark irrigation lines and sprinkler heads
- • Consider transplanting valuable shrubs before construction
Note: Many cities require tree protection during construction. Check your permit conditions—violations can result in stop-work orders.
Clear the Construction Zone
Remove obstacles from the building footprint plus a 10-15 foot work area:
- • Remove trees, stumps, and roots within the work zone
- • Clear brush, debris, and old structures
- • Remove or relocate sheds, fences, and garden features
- • Strip topsoil (save it for later landscaping)
- • Demo any existing concrete or pavement
Costs vary widely: $500-2,000 for basic clearing; $2,000-5,000+ if removing large trees or concrete demo is needed.
Establish Construction Access
Plan how equipment and materials will reach your site:
- • Create a stable access path (gravel or temporary road plates)
- • Ensure path is wide enough for concrete trucks (10-12 feet minimum)
- • Check overhead clearance for delivery trucks
- • Identify material staging and storage areas
- • Coordinate with neighbors if using shared driveways
Pro tip: Lay down geotextile fabric and gravel on access routes to prevent mud during wet weather. This small investment ($500-1,000) prevents major headaches.
Set Up Erosion and Sediment Control
Required by most jurisdictions to prevent runoff during construction:
- • Install silt fencing around disturbed areas
- • Place straw wattles or gravel bags at drainage points
- • Protect storm drains with inlet protection
- • Create a stabilized construction entrance
- • Stock erosion control materials for emergency repairs
Basic erosion control: $300-800. Required as a permit condition and inspected.
Site Preparation Cost Breakdown
Common Site Preparation Problems
Hidden Underground Obstacles
Old septic tanks, buried debris, or abandoned utility lines are common surprises. Budget 10-15% contingency for unexpected underground finds.
Poor Soil Conditions
If geotechnical testing reveals poor soil, you may need over-excavation and engineered fill. This can add $5,000-15,000 to foundation costs.
Drainage Issues Discovered
High water table or poor drainage may require French drains, sump pumps, or retaining walls not included in original plans.
Neighbor Conflicts
Notify neighbors before work begins. Dust, noise, and equipment blocking streets cause complaints. Good communication prevents problems.
Frequently Asked Questions
How far in advance should I call 811?
Call at least 2-3 business days before digging. Some states require more notice. Utility companies have 2-3 days to respond, and markings expire after 14-30 days depending on state law.
Can I do site preparation myself?
Some tasks like clearing brush, removing small shrubs, and protecting trees can be DIY. However, tree removal, grading, and operating heavy equipment typically requires professionals with insurance and proper equipment.
What if I need to remove a protected tree?
Many cities protect trees over certain sizes. You may need a separate tree removal permit, often requiring an arborist report. Some cities require replacement trees. Plan for $500-2,000+ in additional permit fees if removal is allowed.
Should I save the topsoil?
Yes! Have your contractor strip and stockpile the top 6-12 inches of topsoil. It can be spread around the ADU for landscaping later. Buying replacement topsoil costs $25-50 per cubic yard delivered.
Ready for the Next Step?
With your site prepared and utilities marked, you're ready to choose the right foundation type for your ADU based on your site conditions and budget.