Planning your ADU
What does an ADU cost?
Compare seven Lot2Build layouts from 400 to 1,200 square feet. These budgets keep the factory package and listed field work together, with foundation and utility assumptions made explicit.
Pricing basis updated October 28, 2026. Guide updated October 29, 2026. Planning allowances subject to site review and supplier/trade quotes.
Explore plans and customize your budget →ADU prices by size
Collection models assume slab foundations; Icon assumes crawlspace. Each includes existing utility connections at 50 feet per service. Price per square foot uses nominal total new floor area. Crane: TBD — paid by owner plus 10%. Excluded from dwelling price and price per SF.
| Layout | Beds / baths | Budget | Price / SF |
|---|---|---|---|
| 400 SF Single Story | 1 / 1 | $129,428 | $323.57 |
| 500 SF Single Story | 1 / 1 | $146,075 | $292.15 |
| 600 SF Single Story | 2 / 1 | $165,332 | $275.55 |
| 800 SF Two Story | 1 / 1.5 | $202,839 | $253.55 |
| 1,000 SF Two Story | 2 / 1.5 | $234,888 | $234.89 |
| 1,200 SF Two Story | 2 / 1.5 | $266,019 | $221.68 |
| Icon Legacy 600 | 1 / 1 | $172,523 | $287.54 |
The 1,200 SF model is $266,019 with the stated assumptions. Smaller layouts have higher costs per square foot because delivery, design and utility work are spread over less floor area. Collection home packages use the Icon benchmark and require design-specific supplier confirmation.
Slab versus crawlspace
The foundation choice depends on elevations, soil conditions, structural loads and manufacturer requirements. Slab compatibility must be confirmed for the factory floor system; the lower allowance alone does not establish suitability.
| Layout | Footprint | Slab allowance | Crawlspace allowance |
|---|---|---|---|
| 400 SF Single Story | 400 SF | $9,100 | $16,250 |
| 500 SF Single Story | 500 SF | $10,530 | $18,330 |
| 600 SF Single Story | 600 SF | $11,856 | $20,150 |
| 800 SF Two Story | 400 SF | $11,050 | $16,250 |
| 1,000 SF Two Story | 500 SF | $12,480 | $18,330 |
| 1,200 SF Two Story | 600 SF | $13,806 | $20,150 |
| Icon Legacy 600 | 600 SF | $11,960 | $20,410 |
Existing services, well and septic
Standard existing connections total $9,750: water $2,730, sewer $3,640 and electricity $3,380. Separate utility authority and approval allowances total $1,950. Ordinary 50-foot runs and adequate existing capacity are assumed.
A new well has a $34,667 installation allowance; a new septic system has a $21,667 allowance. Each replaces its existing connection option, with appropriate approval reserves carried separately. These are budget options, not site-specific bids. Exceptional drilling, alternative septic treatment and capacity upgrades require review.
ADU budgeting questions
What does the ADU budget include?
The dwelling budget includes the factory package, foundation, delivery, setting and closure, listed site work, finishes, building systems, and permit, tax and utility approval allowances. Customer prices include contractor overhead and profit. Final scope and pricing require site review and current supplier and trade quotes.
Are utility connections included?
The standard budget includes $9,750 for water, sewer and electrical connections, assuming ordinary 50-foot runs to existing services with adequate capacity. A separate $1,950 allowance covers utility authority charges and approvals. Longer runs, service upgrades, new wells and new septic systems change the budget.
Is the crane included in the price per square foot?
No. Crane cost is TBD and paid by the owner at actual cost plus 10%. It is excluded from the dwelling total and price per square foot. Setting labor and module closure remain included.
Does a two-story ADU need a larger foundation?
Foundation pricing uses the ground footprint, not the combined area of both floors. The 1,200-square-foot model has a 600-square-foot footprint. Structural supports, soil conditions and engineered details still affect the foundation price.
Can I use these prices as a final construction quote?
These are planning allowances, not a final contract price. Confirm zoning, permitted use, survey, soils, foundation compatibility, service capacity, selections and supplier scope first. Land and financing are excluded. The Icon layout is an attached in-law addition with a wet bar, not a full cooking kitchen.
Start with your property
Confirm the buildable area, permitted use, access, foundation and utility routes before committing to a layout.