What an ADU actually costs, in Colorado terms.

National averages are a starting point, not an answer — Front Range labor, permitting, and lot conditions move the number more than most articles admit. Here’s both.

National cost ranges

Fully built, permit-to-keys, for a typical single-story unit.

ADU type	Typical size	Cost range	Cost per sq ft
Garage conversion	300–500 sq ft	$60,000 – $150,000	$150 – $300
Basement / interior conversion	400–700 sq ft	$75,000 – $175,000	$150 – $280
Attached ADU	500–800 sq ft	$120,000 – $280,000	$220 – $350
Detached ADU (site-built)	500–1,000 sq ft	$180,000 – $400,000+	$300 – $450
Detached ADU (prefab/modular)	500–900 sq ft	$150,000 – $320,000	$250 – $380

Ranges are directional, drawn from published national ADU cost data and Front Range builder patterns — not a quote. See the calculator below for a lot-specific estimate.

What moves the number on the Front Range

Ranges are directional, drawn from published national ADU cost data and Front Range builder patterns — not a quote. See the calculator below for a lot-specific estimate.

Rough it out

A directional starting point — not a bid. Full calculator with financing scenarios coming soon.

ADU type

Approximate size (sq ft)

Site conditions

Estimated range

$180,000 – $253,000

Based on 600 sq ft × $375/sq ft × site multiplier, ±15%. Every lot is different — this is a ballpark, not a bid.

Ranges are directional, drawn from published national ADU cost data and Front Range builder patterns — not a quote. See the calculator below for a lot-specific estimate.