The costs between land purchase and construction start that most custom home budgets do not include — and should.
What site costs should I budget for before construction starts on a custom home in Idaho?
Site costs are the expenses between closing on your land and breaking ground — costs that are separate from both your land purchase price and your builder’s construction contract. Specifically, they include utility connection fees (water, sewer, power, gas), grading and earthwork, driveway installation, retaining walls if the lot has slope, well drilling and septic installation if not on city utilities, and soil remediation if geotech reveals problem conditions. On a typical Ada County buildable lot, site costs range from $30,000 to $150,000 depending on parcel conditions. However, on a rural acreage parcel with no utilities, site costs can reach $200,000 or more.
Dennis Fomin — Founder, Fomin & Company. Site costs are the most commonly underbudgeted line in a custom home project. Buyers see the land price and the builder’s price, so they assume that covers it. However, the costs in between — connection fees, grading, utilities — are often $50,000-$100,000 and are not in either number.
The Site Cost Categories — What to Budget
Utility Connection Fees
Water and sewer connection fees in Ada County cities range from $10,000 to $30,000+ per connection. These are one-time impact fees charged by the city before service is activated. Also, Meridian, Eagle, and Boise all have different fee schedules — request the current fee schedule from the city before you close on the land.Water Service Extension
If the city water main does not currently run adjacent to your parcel, the city may require you to extend the main to serve your lot — at your cost. Generally, extension costs depend on the distance from the nearest main and the capacity of the existing system.Driveway and Access Road
A basic concrete driveway on a standard lot: $8,000-$20,000. A gravel access road on a rural acreage parcel to reach the build site: $15,000-$60,000+ depending on distance and grade. Also, these costs are almost never in the builder’s contract.Grading and Earthwork
Generally, flat lots require minimal grading. However, sloped lots may require significant cut-and-fill earthwork to create a buildable pad. In addition, extreme slope or rocky soil requires blasting or heavy equipment — $15,000 to $80,000+ depending on severity.Retaining Walls
Sloped lots with significant grade change often require retaining walls to stabilize the build pad and create usable yard space. A simple concrete block retaining wall: $40-$80 per linear foot. An engineered concrete retaining wall with drainage: $150-$300+ per linear foot.Well and Septic (if not on city utilities)
Well drilling in Ada and Canyon County: $8,000-$20,000 depending on depth to water. Septic system installation: $12,000-$25,000 for a standard system. Engineered septic on difficult perc soil: $25,000-$50,000+.Site Costs by Parcel Type — Rough Ranges
How to Get Site Cost Estimates Before You Close on Land
Request city fee schedule and connection cost estimate
Contact the city public works department. They can then tell you the current connection fee schedule and whether the water/sewer main is adjacent to the parcel.Hire a civil engineer for a site development estimate
A civil engineer can review the parcel’s topography, soil survey, and utility map and produce a site development cost estimate for $1,500-$3,000. In fact, this is the most reliable pre-purchase site cost estimate available.Ask your builder for a site assessment
Also, an experienced builder who has worked in your target area can give you a rough site cost estimate based on a site visit. This is less precise than a civil engineer’s estimate but is a useful sanity check.Build a contingency
Even with a civil engineer’s estimate, unexpected site conditions — underground obstructions, water table issues, soil bearing problems — can add cost. That is why you should budget 15-20% above the civil engineer’s estimate as contingency.Frequently Asked Questions
Want a Site Cost Estimate for a Parcel You Are Evaluating?
Dennis Fomin — Founder, Fomin & Company. Associate Broker, GRI, RSPS. Free 2026 This Is Boise Area Guide.
- —Civil engineer referrals for pre-purchase site assessments
- —City fee schedule research for your target jurisdiction
- —Site cost budgeting incorporated into the full custom build budget model
- —Dennis surfaces site costs during land due diligence — before you close
Serving Boise, Meridian, Eagle, Nampa, Caldwell & the Treasure Valley.
Summary
Site costs are the line item that most frequently blows custom home budgets — not because they are unavoidable, but because they are not included in the land price or the builder’s contract and are therefore easy to overlook. In fact, a $120,000 site development budget on a rural parcel is not unusual and is not visible in either transaction until someone asks.
Budget site costs before you close on land. After all, the civil engineer’s estimate costs only $2,000. Discovering site costs after closing on a parcel you cannot build on economically costs far more.
Dennis Fomin
Founder, Fomin & Company · Associate Broker, GRI, RSPS · Equity Northwest Real Estate208-371-9099 · dennis@dennisfomin.com · Meet Dennis →
903 N Main Street, Meridian, ID 83642
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