Every contractor has had the job where the customer agreed to $6,800, the crew found rotted framing behind the old unit, someone said "go ahead" in the driveway, and the final invoice of $8,150 turned into a two-week argument. Change orders exist to make sure that conversation happens before the extra work, in writing.
Change orders in plain English
An electrician is installing an EV charger circuit for an agreed $1,450 (example numbers). When the panel cover comes off, there's no room for a new breaker without replacing two breakers with tandem units, or adding a subpanel. The electrician stops, photographs the panel, and writes a change order: "Add subpanel to provide space for EV circuit. Add $780. New total $2,230. Adds half a day; completion moves from Tuesday to Wednesday." The homeowner signs on the tablet, and work continues.
What should a change order include?
Change order contents
- Reference to the original estimate, contract or job number
- A change order number (CO-1, CO-2) so changes stay in sequence
- Plain description of the work added or removed
- Why the change is needed, with photos where possible
- Price added or subtracted, and the new contract total
- Effect on the completion date and any progress payments
- Customer signature and date, collected before the changed work starts
Worked example: a job with two changes
| Item (example) | Amount | Running total |
|---|---|---|
| Original contract: 3-ton heat pump replacement | $11,400 | $11,400 |
| CO-1: replace damaged return plenum found at tear-out | +$640 | $12,040 |
| CO-2: customer keeps existing thermostat (remove smart thermostat) | −$385 | $11,655 |
| Final invoice | $11,655 |
The final invoice should tie to the original contract plus every signed change order. If it doesn't, something was done without one.
When is a change order legally required?
Rules vary by state and type of work. California's home improvement law is one of the most specific. It says changes to a home improvement contract must be in writing and signed by the parties before the work covered by the change begins, and that extra work or a change order isn't enforceable against the buyer unless it states, in writing and before work starts, the scope of the work, the amount added or subtracted, and the effect on progress payments or the completion date.1
In U.S. federal contracting, a change order has a narrower meaning: a written order, signed by the contracting officer, directing the contractor to make a change that the contract's Changes clause allows without the contractor's consent.2 Residential and light commercial work usually works the other way round, with the customer agreeing to the change.
What causes change orders, and how to reduce surprises
| Cause | Example | How to reduce it |
|---|---|---|
| Hidden conditions | Rotted subfloor, undersized wiring, failed flue | Inspect and photograph before quoting; state exclusions |
| Customer changes their mind | Different unit, extra outlet, keep old fixture | Confirm selections in writing before ordering |
| Code or inspector requirements | Inspector requires an added disconnect | Note known code items in the original estimate |
| Equipment availability | Specified model unavailable | Name an approved alternate in the contract |
A clear original estimate prevents more disputes than a good change order fixes. State what's included, what's excluded and what happens if hidden conditions turn up. Our HVAC estimate template has a layout to start from.
Change order vs related terms
| What it is | When it's used | |
|---|---|---|
| Change order | Signed change to agreed scope or price | After the original agreement, before the changed work |
| New estimate | A proposal for separate work | New job, nothing agreed yet |
| Progress billing | Invoicing a large job in stages | Installs and projects with milestones |
| Not-to-exceed amount | A cap on a time-and-materials bill | Unknown-scope work |
Change orders also matter for job costing: the added revenue and the added labor and materials belong to the same job, or the job's margin looks wrong. On staged projects, each signed change also changes what's left to bill under progress billing.
Making change orders fast in the field
- 1
Stop before the extra work
Make it a rule: no added work on a verbal yes.
- 2
Photograph the reason
A photo of the rotted plenum or the full panel ends most arguments before they start.
- 3
Price it from the price book
Use the same task prices as the original estimate so the change looks consistent.
- 4
Get the signature on the spot
On the tech's phone or tablet, or by a link the customer can approve from wherever they are.
- 5
Tie it to the job
The change should land on the same job and invoice, numbered in sequence.
How change orders work in TradesWork
TradesWork doesn't have a dedicated change-order document or progress billing today. The shipped workflow that covers most service and replacement changes is to build the extra work as a new priced proposal on the same job, attach proof photos of what was found, and get approval: a drawn signature on the tech's phone, or a typed-name approval from the job's One Link. A sold option goes onto that job's invoice, so the final bill reflects what the customer approved.
Footnotes
-
California Business and Professions Code § 7159, subsections (c)(5), (d) and (e)(3)(B), text via California Public Law, accessed October 15, 2026. ↩
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FAR 2.101, Definitions, Federal Acquisition Regulation, Acquisition.gov, accessed October 15, 2026. ↩
