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ADU SITEWORK & UTILITY COSTS: 10 HIDDEN COSTS
When planning an accessory dwelling unit (ADU), it’s important to know where the ADU will fit and how big it can be… but that is just the beginning. There are many factors to consider when determining the best location for your ADU to ensure optimal outcome and value. Does the ADU fit within required setbacks? How will it be accessed? Are there views or environmental factors to consider? Is there a better area to build due to slope, vegetation, or utilities?
SOMETIMES THE WORST INFORMATION IS THE BEST INFORMATION
Why is the worst info sometimes the best? You want to know about potential cost pitfalls before investing heavily in a project. It’s important to know the all-in costs to make an educated decision when comparing ADU bids.
You can easily estimate the vertical building cost for your ADU upfront since the structure and foundation are new. However, sitework costs can vary significantly, even for identical ADU plans, depending on property conditions. These variations could amount to tens of thousands of dollars. Identifying potential costs as early as possible is key to minimizing surprises.
A flat lot’s sitework typically costs about $25K, provided utility tie-ins are within your property bounds. We begin with a robust assessment of utilities on-site to determine their size, location, and serviceability before starting floor plans. This allows us to provide firm pricing for sitework early in your project.
Read on to understand the most common additional costs and whether they will likely apply to your property.
10 HIDDEN COSTS TO WATCH OUT FOR WHEN BUILDING YOUR ADU
1. Sewage & Long Utility Runs
• If your property uses a septic system, a separate one may be required for the ADU, costing $30-40K.
• Sewer access tie-in depends on location and gravity flow. If proper flow isn’t possible, a sewage pump might be needed ($5K).
• Long utility runs can cost up to $200/linear foot.
2. Slope
• Steep lots may require grading, terracing, or retaining walls, costing $20-30K or more.
• Foundation needs vary with elevation differences:
• Up to 2’: Deepened footings (~$4.5K).
• 2’-4’: Grading or raised foundations ($10-20K).
• Beyond 4’: Custom solutions.
3. Soils Export & Grading
• Grading may be required to prepare the lot, with export costs ranging from $5-10K if soil cannot remain on-site.
4. Survey
• A survey may be necessary to verify lot boundaries, especially for irregular or challenging lots, costing $4-10K.
5. Soils Report
• A soils report may be required, costing $3K. Over-excavation due to soil conditions can add $4-5K.
6. Sufficient Access
• Limited space for construction equipment can add $5-8K if digging must be done by hand or materials need to be craned in.
7. Structures & Surroundings
• Existing sheds, trees, or hardscaping in the building area may need removal or relocation, costing $2-4K for large trees.
8. Separate Electric Panel
• A separate meter for the ADU may be required, costing $10.5K. Additional electrical upgrades may also be necessary.
9. Solar
• Many projects require a solar system to meet energy guidelines, with installation costs ranging from $12-18K. A federal tax credit of 30% may apply.
10. Sprinklers
• If the main house has sprinklers, the ADU must also have them, costing $5-10K. This may also increase water line size requirements.
Plan ahead to avoid surprises and ensure a successful ADU project. Thorough preparation saves time, money, and stress!
