How to Price an ADU Build: Real Numbers, Real Margin

If you want to know how to price an ADU build without leaving money on the table, you're in the right place. I've built accessory dwelling units across New Hampshire for years. Detached units, garage conversions, in-law additions, the works. And I've watched good contractors underbid these jobs into the ground. ADUs look small. They're not simple. Every trade shows up, but the volume is low, so your overhead per square foot goes way up. Price it like a scaled-down house and you'll lose your shirt.

This post is the real breakdown. No theory. Actual line items, actual markup, and the traps that eat your margin. Let's get into it.

Why ADUs Are Harder to Price Than a Full House

An ADU is a full house in miniature. You still have a foundation, framing, roofing, plumbing, electrical, HVAC, insulation, drywall, cabinets, and finishes. You still pull permits. You still coordinate every trade. The problem is scale. On a 3,000 square foot custom home, your fixed costs spread out. On a 600 square foot ADU, those same costs land on a tiny footprint.

Here's the math that burns people. Mobilization for a plumber is the same whether the job is big or small. That truck roll, that setup time, that minimum charge, it doesn't shrink because the job is small. So your per-square-foot cost on an ADU is almost always higher than your last big house. If you price ADUs at your house rate, you're already underwater.

The Real Cost Breakdown for an ADU Build

Let me give you rough numbers for 2026. These are New Hampshire figures for a detached 600 to 800 square foot unit with a kitchen and full bath. Adjust for your market, but the ratios hold up almost everywhere.

Hard Costs

• Site work and utilities: $15,000 to $40,000. This is the wild card. Trenching for water and sewer, running electrical from the main house or a new panel, grading, and any tree or ledge removal. In New Hampshire, ledge alone can add $10,000 fast.
• Foundation: $12,000 to $25,000 depending on slab, crawlspace, or full basement.
• Framing and sheathing: $25,000 to $45,000 including labor and lumber.
• Roofing: $8,000 to $15,000.
• Windows and exterior doors: $8,000 to $18,000.
• Siding and exterior finish: $12,000 to $22,000.
• Plumbing rough and finish: $15,000 to $28,000. A full kitchen and bath in a small box is expensive per fixture.
• Electrical: $12,000 to $22,000. New panel or subpanel adds cost.
• HVAC: $10,000 to $20,000. Mini-splits are common for ADUs and they price well.
• Insulation, drywall, and paint: $15,000 to $28,000.
• Interior finishes, cabinets, counters, flooring, trim: $25,000 to $50,000. This swings hard on selections.

Add it up and you're looking at rough hard costs of $180,000 to $330,000 for a modest detached ADU. Garage conversions run cheaper because the shell exists. Attached units save on some site work but complicate the tie-in to the existing structure.

Soft Costs You Cannot Skip

• Permits and impact fees: $2,000 to $15,000 depending on the town.
• Architectural and engineering: $4,000 to $12,000.
• Survey and site plan: $1,500 to $5,000.
• Utility connection fees: highly variable, sometimes $5,000 or more.
• Insurance and bonding allocation for the job.

Contractors forget soft costs constantly. They quote the build and eat the permits. Don't. Every one of these belongs in your number.

How to Set Your Markup on an ADU

Now the part that actually decides if you make money. Your markup. There's a difference between markup and margin and you need to know it cold. If you want 25 percent margin, you don't add 25 percent to your costs. You divide your costs by 0.75. Add 25 percent and your real margin is only 20 percent. That gap is where profit disappears.

For ADUs, I run higher markup than on large custom homes. The complexity per dollar is greater, the coordination is dense, and the risk of a nasty site surprise is real. Here's how I think about it.

1. 1Total your hard costs and soft costs. Every line. No shortcuts.
2. 2Add a contingency of 8 to 12 percent. ADUs surprise you. Ledge, old utilities, code updates on the main house.
3. 3Add your overhead recovery. This is your office, trucks, software, and salary. If you don't know your overhead percentage, you're guessing at pricing.
4. 4Apply your target margin by dividing, not adding. For a 30 percent margin, divide your loaded cost by 0.70.
5. 5Compare the final number to your local market. If it's too high, find real cost savings. Never cut margin to win the bid.

On most ADUs I aim for 28 to 35 percent gross margin. That covers overhead and leaves real net profit. Anything under 20 percent on a job this complex and you're working for free the second something goes wrong.

Estimate Faster and Stop Guessing

Here's where a lot of good builders get stuck. The pricing itself takes forever. Every ADU is a little different, and building the estimate line by line every time kills your evenings. That's exactly why I built EstimAI Pro. It takes your plans and your own pricing history and produces a full, detailed estimate you can trust. Not a generic national average. Your numbers.

The core of it is what we call Pricing DNA. It learns how you price. Your labor rates, your subs, your markup rules, your regional costs. Every estimate you build makes the next one sharper. So when the next ADU inquiry lands, you're not starting from a blank sheet. You're starting from the way you actually run your business. Check it out at estimaipro.com.

The ADU Pricing Mistakes That Cost Real Money

I've made some of these myself. Learn them cheap.

• Underpricing site work. The dirt is where jobs go bad. Get a real site evaluation before you commit to a number.
• Forgetting the utility tie-in. Running new water, sewer, and power to a detached unit is expensive and easy to underestimate.
• Assuming small means fast. ADUs take almost as long as they take because every trade still cycles through. Your schedule and your carrying costs are longer than you think.
• Skipping contingency. Small jobs have thin margins. One surprise wipes out your profit if you didn't plan for it.
• Copying your last house's per-foot price. Already said it. Saying it again because it's the number one killer.
• Not documenting your pricing. If your numbers live in your head, they die when you get busy. Systematize them.

That last point matters more than people think. The contractors who win consistently are the ones with a repeatable pricing system. When your Pricing DNA is captured and working for you inside EstimAI Pro, you quote faster, you quote more accurately, and you stop the slow bleed of underbidding. Head to estimaipro.com and put your pricing to work.

A Simple ADU Pricing Framework to Take With You

Boil it all down and it's this. Build your cost from real line items, not a per-foot shortcut. Load in soft costs and contingency. Apply overhead recovery. Set margin by dividing, not adding. Then sanity check against your market. Do that every time and ADUs become one of the most profitable jobs on your board instead of the one that keeps you up at night.

ADUs are booming in 2026. Zoning is loosening in a lot of states, homeowners want rental income and space for family, and demand isn't slowing down. The builders who price these right are going to own that market. Price them wrong and you'll be busy and broke at the same time.