Remodeling
ADU Construction Cost Calculator
Prices an accessory dwelling unit, where zoning and utilities decide feasibility before construction does.
Result
A planning estimate, not a quote. Access, the age of the equipment, what is found once it is opened up and local labour rates all move the real figure, sometimes a long way.
Get a Free Business AuditHow the calculation works
Hours times crew times rate, plus materials and the call-out. An ADU is a complete small dwelling: foundation, structure, envelope, a kitchen, a bathroom, heating and cooling, and its own electrical and plumbing. The cost per square foot is high because a kitchen and a bathroom are the two most expensive rooms in any house and a small unit has one of each over very little area. Converting existing space such as a garage or basement is cheaper than building new, with its own constraints.
What moves the number
- Whether zoning permits an ADU on the lot, and on what terms.
- Utility connections, since a separate water, sewer and electrical service is a major cost.
- Whether existing sewer and electrical capacity can take another dwelling.
- New build against conversion of existing space, which differ substantially.
Where this one goes wrong
Zoning is the gate and it varies enormously, including whether an ADU is permitted at all, maximum size, setbacks, height, owner-occupancy conditions and parking. Those rules have changed quickly in many places, so current local information matters more than general knowledge. Utilities are the cost that surprises: whether the unit shares the house's water, sewer and electrical service or needs its own changes the number substantially, and the existing sewer lateral and electrical panel may not have capacity for a second dwelling. Both are worth establishing before design, because either can make a project uneconomic.
Before you quote
- Confirm current local ADU rules, including size, setbacks and occupancy conditions.
- Establish whether utilities are shared or separate, and whether capacity exists.
- Compare new build against converting existing space on the same lot.
Where the rules come from
Questions
About this calculator
Can I build an ADU on my lot?
It depends on local zoning, which varies widely and has changed quickly in many places. Whether an ADU is permitted, how large it may be, how close to boundaries, how tall, and whether the owner must live on site are all local rules. Current local information is essential rather than general guidance.
Why is an ADU expensive per square foot?
Because it contains a kitchen and a bathroom, which are the two most expensive rooms in any dwelling, spread over a very small floor area. It also needs its own envelope, heating and services. The fixed cost of being a complete dwelling does not shrink with the footprint.
Does an ADU need separate utilities?
Sometimes it may share the main house's services and sometimes separate connections are required or desirable, and the difference is substantial. The existing sewer lateral and electrical panel may also lack capacity for a second dwelling. Both need checking before design rather than during construction.
The formula
total = hours x people x rate + parts + call-out, then sales tax
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How to use this calculator
- Hours on site (h). Enter your own figure; the page starts at 160 h.
- People needed. Enter your own figure; the page starts at 1.
- Labour rate charged ($). Enter your own figure; the page starts at $88.
- Parts and materials ($). Enter your own figure; the page starts at $11,000.
- Call-out or diagnostic fee ($). Enter your own figure; the page starts at $95.
- Sales tax (%). Leave at zero if you are quoting before tax.
The result updates as you type, so you can try a figure, see what it does to estimated total, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Hours on site | 160 h |
| People needed | 1 |
| Labour rate charged | $88 |
| Parts and materials | $11,000 |
| Call-out or diagnostic fee | $95 |
| Sales tax | 0% |
What comes out
| Result | Value |
|---|---|
| Estimated total main result | $25,175 |
| Labour | $14,080 |
| Before tax | $25,175 |
| Sales tax | $0 |
About $25,175: $14,080 of labour, $11,000 of parts and a $95 call-out.
How sensitive the answer is
Holding everything else steady and changing only labour rate charged, this is what happens to estimated total. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Labour rate charged ($) | Estimated total |
|---|---|
| $44 | $18,135 |
| $66 | $21,655 |
| $88 example above | $25,175 |
| $132 | $32,215 |
| $176 | $39,255 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Hours on site (h)
- Measured in h, between 0 and 400, starting at 160 h.
- People needed
- A number, between 0 and 40, starting at 1.
- Labour rate charged ($)
- A money amount, starting at $88.
- Parts and materials ($)
- A money amount, starting at $11,000.
- Call-out or diagnostic fee ($)
- A money amount, starting at $95.
- Sales tax (%)
- Leave at zero if you are quoting before tax.
What the results tell you
| Result | What it is |
|---|---|
| Estimated total | The headline result. A money figure. |
| Labour | A money figure. |
| Before tax | A money figure. |
| Sales tax | A money figure. |
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.