Remodeling
Home Extension Cost Calculator
Prices an extension, where opening the existing wall into it is the structural part.
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 extension differs from an addition mainly in that it usually involves opening up a substantial part of the existing exterior wall to connect the spaces, and that wall is load-bearing by definition. Removing it means a beam sized for the roof and floor loads above, posts carrying that load down, and a foundation under those posts capable of taking a concentrated load it was not designed for. That sequence is the work, and it is engineered rather than estimated.
What moves the number
- Width of the opening into the existing house, which drives the beam size and the point loads.
- What the removed wall was carrying, including floors above as well as roof.
- Whether the existing foundation can take the new concentrated loads.
- Temporary support during the work, which has to carry the house while the wall is out.
Where this one goes wrong
The beam and its load path are the job. A wide opening in a bearing wall concentrates what was spread along that wall into two points, and those points need posts and foundations beneath them, which commonly means breaking the existing slab or footing and pouring a pad. Skipping that transfers the load onto whatever happens to be there, and the symptom is a sagging floor or a cracking wall later. Temporary support while the wall is removed is also real engineering rather than props put where they fit, because it is holding the structure up during the operation. This is work for an engineered design and an inspection, not a judgement call.
Before you quote
- Get the beam and its load path engineered, including the foundations under the posts.
- Confirm what the wall carries, floors as well as roof.
- Plan temporary support as part of the engineered design.
Where the rules come from
Questions
About this calculator
Can I open up a wall between my house and an extension?
Yes, with an engineered beam and a load path. An exterior wall is load-bearing, so removing a section means a beam sized for what it carried, posts taking that load down, and foundations under the posts able to take a concentrated load. That chain is the real work in an extension.
Why do the posts need new foundations?
Because a wide opening concentrates load that was previously spread along the whole wall into two points. The existing footing was designed for the distributed load, not the concentrated one, so pads under the posts are usually needed. Omitting them shows up later as settlement and cracking.
Does an extension need an engineer?
For any bearing wall removal, effectively yes, and the permit will normally require the calculations. Beam sizing depends on span, the loads above and the material, and it is not something to judge by eye. The design also has to specify the temporary support used while the wall is out.
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.