Remodeling
Home Addition Cost Calculator
Prices an addition, where you are building a small house and tying it to an existing one.
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 addition carries every cost of new construction at small scale: foundation, framing, roof, envelope, windows, mechanical, electrical, plumbing and finishes, with none of the efficiency a larger build gets from repetition. On top of that it has to join an existing building, and that connection is its own work: tying new roof into old, matching or deliberately contrasting the exterior, and extending services from a house whose capacity was sized without it.
What moves the number
- Foundation type and site conditions, since excavation is the least predictable element.
- Roof tie-in, which is detail work and a common source of leaks if rushed.
- Whether existing services have capacity, as an electrical panel or heating system may not.
- Setbacks and lot coverage limits, which can constrain size or prevent the addition.
Where this one goes wrong
Check setbacks and lot coverage before designing anything. Zoning sets how close a structure may be to boundaries and how much of the lot may be built on, and an addition that breaches either needs a variance or does not happen. Service capacity is the other item that surprises: adding conditioned area may exceed the existing heating and cooling system and may exceed the electrical panel, and either can be a significant additional cost. The roof tie-in deserves attention beyond its cost, because a poorly flashed junction between new and old roof is the most likely place for the finished addition to leak.
Before you quote
- Confirm setbacks and lot coverage before design work.
- Assess existing heating, cooling and electrical capacity for the added area.
- Detail and flash the roof tie-in carefully rather than quickly.
Where the rules come from
Questions
About this calculator
Why does an addition cost so much per square foot?
Because it is new construction without the efficiency of scale. It needs its own foundation, roof, envelope and services, and a small footprint spreads those fixed elements over very little area. It also has to join an existing building, which is detail work that a standalone build does not need.
Can I add on anywhere on my lot?
No. Zoning sets minimum distances to boundaries and a maximum share of the lot that may be covered, and an addition breaching either needs a variance or cannot proceed. Those constraints are worth confirming before any design work, because they can change the whole concept.
Will my heating system and electrical panel cope?
Not necessarily. Adding conditioned space can exceed the capacity of an existing heating and cooling system, and the electrical panel may not have room or capacity for the new circuits. Both are significant costs if needed and both are assessable before committing to a scope.
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.