HVAC
HVAC change order management and scope control field guide
Stop giving away the extras: what a change order is, what triggers one, how to price it, getting it signed before the work, the scope baseline, the log, and billing the change so it never disappears into the final.
Direct answer
A change order is the written, priced, and approved record of any change to the agreed scope, price, or schedule of a job. The customer asks for extras, the field finds hidden conditions, the design shifts. Get the change signed before you do the work, or you eat it. Verbal handshakes never get paid.
Key takeaways
- A change order is the written, priced, and approved record of any change to a job's scope, price, or schedule, signed before the work happens.
- Get the change order signed before doing the work; verbal handshakes never get paid and many contracts deny payment for unauthorized changed work.
- Uncontrolled change and scope creep cost roughly 10 to 15 percent of a project, often the entire profit on a thin job.
- Price change orders as labor plus material plus markup; a combined overhead-and-profit markup around 15 percent is common, though the contract often caps it.
- State schedule impact in days on every change order, even when zero; a blank is read as no impact and hands the customer a free time extension.
What a change order is, and why working without one gives money away
A change order is the written, priced, and approved record of any change to the agreed scope, price, or schedule of a job. The original contract sets what you are doing, for how much, by when. Anything that moves one of those three needs a change order to move it on paper, signed by the person who can authorize the money, before the work happens.
The reason it exists is simple. Jobs change. The customer asks for a second zone while you are already in the attic. You open a chase and find ductwork that is nothing like the drawings. The engineer revises the equipment after you priced it. None of that was in the contract you signed, so none of it is work you owe for free. The change order is how you get paid for the work the contract never covered.
Here is the part that costs contractors real money. The one who does the extra on a handshake eats it. You finish the job, you add the extra to the final invoice, and the customer says they never agreed to that price, or that they thought it was included. Now it is your word against theirs, and you are the one who already spent the labor and the material. Get it in writing and signed before you touch it, or it becomes a fight you lose. The proposal guide covers selling the original job and the agreement guide covers the contract that frames it. This guide is about everything that changes after the ink is dry.
What change orders protect
Change orders protect four things, and they are the four things that quietly bleed a contractor dry. Margin first. The extras you eat come straight out of profit, because the labor and material are real whether you billed them or not. A job priced at a healthy margin can finish at break-even on nothing but unbilled extras, and the owner never sees why the good job made no money.
Scope creep is the slow version of the same problem. Not one big change, but a steady drip of small ones, each too minor to argue about, that add up to weeks of unbilled labor by the end. Industry estimates put the cost of uncontrolled change at roughly 10 to 15 percent of a project, and on a thin job that is the whole profit.
Then there are disputes. The change order is the document that ends the argument before it starts, because the price and the scope were agreed in writing when everyone was still friendly. And the schedule. Every change takes time, and a change order that does not claim that time hands the customer a free schedule extension while you still owe the original completion date. Money and time both leak through the same hole, and the change order is the patch.
What triggers a change order
Most changes come from one of a short list of sources, and knowing which one you are looking at tells you who pays and how to price it.
The customer request is the obvious one. While you are here, can you add a return in the back bedroom, run a line to the garage, bump the unit up a size. Anything the customer asks for that was not in the contract is a change order, even when it is small and even when they are standing right there nodding.
Hidden conditions are the field's contribution. You open the wall or the chase and find what the drawings did not show: rotted framing, asbestos on the old pipe, undersized or collapsed ductwork, a flue that does not meet code. These are differing site conditions, and under most standard contracts the owner pays for what could not have been seen at bid time.
Design changes come from the other direction. The engineer or the architect revises the drawings, the equipment schedule changes, a submittal comes back marked up with new scope. An RFI you sent comes back with an answer that quietly adds work, and that answer is a change even though it arrived as a clarification. And code upgrades. The inspector or the adopted code requires something the contract did not price, a larger flue, a combustion-air opening, a disconnect that was not there. Each of these is a change order waiting to be written, and the trap is treating the design and code ones as your problem to absorb.
Get it in writing and signed before the work
This is the rule the whole guide hangs on. The change order is written, priced, and signed before you do the work, not after. No verbal. No nod across the room. No we will settle up at the end. Later never comes, or it comes as an argument you are not holding the paper to win.
The reason is plain. Once the work is done, you have lost every piece of bargaining power you had. The customer already has what they wanted, your labor and material are already spent, and the only thing left to negotiate is whether they feel like paying. A verbal agreement is real, but proving it months later in front of a skeptical customer or a judge is a different thing entirely, and the burden is on you.
Get the signature first and the conversation is over before it starts. A signed change order supports a mechanics lien claim or a lawsuit if it comes to that, because it is a document, not a memory. The discipline is hard in the moment, because the customer is right there and the work is right there and stopping to write it up feels like friction. Stop anyway. The two minutes it takes to document the change and get the sign-off is the cheapest insurance on the job.
What goes on a change order
A change order has four parts, and leaving any of them vague is how a signed change order still turns into an argument. The description of the change, the price, the schedule impact, and the signature.
The description names exactly what is being added, removed, or modified, in enough detail that someone who was not there can read it and know what was done. Add a 6 inch insulated return run from the master bedroom to the existing trunk, including grille and balancing damper beats add return in bedroom every time. The price is the dollar figure, broken out enough that the customer can see it is real and not a number you pulled from the air. The schedule impact says how many days this adds to completion, even if the answer is zero, because a blank there is a claim you gave away. And the signature, dated, from the person who actually has authority to spend the money, not the tenant, not the spouse who happens to be home, not the site super who cannot bind the owner.
Number every change order in sequence so nothing falls through. CO-01, CO-02, and so on, each tied to the original contract. The number is what lets you track it later and what keeps two changes from quietly becoming one in the billing.
How do you price a change order?
Price a change order the same way you priced the original job: labor plus material plus markup. Figure the real hours the change takes, the material at your real cost, and add overhead and profit on top. A common combined markup for overhead and profit on change-order work is 15 percent, sometimes split into separate overhead and profit lines that add up to it, though the contract often sets or caps the number, so check it. The estimating and proposal guide covers building the underlying number.
Do not discount the change because it is small. This is the most expensive habit in the trade. A small change still has setup time, a trip to the supply house, the paperwork, and the same overhead burden as any other work, and often the per-hour cost of a small add is higher than the base job because there is no economy of scale. Price it at the real cost with the real markup. The customer who balks at the price of a small extra is telling you they expected it for free, which is exactly the conversation you want to have before the work, not after.
When the scope is genuinely unknown, do not guess at a fixed price. Price it time and material, with rates stated up front, or set a not-to-exceed cap so the customer has a ceiling. Guessing low on an unknown and eating the overage is the same mistake as the handshake, just with extra steps. If you cannot define it, tag it and track it instead of pretending you can price it.
Small changes add up
The little extras are where the margin goes, precisely because they feel too small to write up. While you are here, can you, is the most expensive sentence on the job. Each one is fifteen minutes, or a fitting, or a quick reroute, and each one feels churlish to charge for. Stack a dozen of them across a job and you have given away a day of labor and a parts run, unbilled, while feeling like a good guy the whole time.
Write them up too. Not necessarily a full formal change order for every grille, but they get captured, priced, and acknowledged, even if it is a single approved line on a running field-authorized list the customer initials. The point is that no extra work happens without somebody agreeing to pay for it, no matter how small. The cumulative number is what matters, and the only way to see the cumulative number is to capture every piece of it.
The field crew has to be trained on this, because they are the ones standing there when the customer asks. The instinct of a good tech is to say yes and help. The instinct you want is to say yes, that is easy, let me write it up real quick so it is on the record. Same answer, same helpfulness, but now it is documented.
The scope baseline: you cannot prove a change without it
You cannot prove something changed if you never wrote down what it was to begin with. The scope baseline is the clear, original definition of the work in the contract, and without it every change order is an argument about what was supposedly included. The customer's memory of the deal will always be more generous than yours, and with no written baseline, their memory wins.
The baseline lives in inclusions and exclusions. The inclusions say exactly what you are doing: the equipment, the tonnage, the linear feet of duct, the number of runs, the thermostats, the line set, the electrical you are providing and the electrical you are not. The exclusions are just as important and get skipped more often. State plainly what is not in the price: permits if the owner is pulling them, electrical beyond the disconnect, drywall repair, painting, anything you suspect the customer assumes is included but is not. The estimating and proposal guide is where the baseline gets built; the change order is where it gets defended.
A sharp exclusion list is what turns a future argument into a change order. When the customer says the drywall patching was supposed to be included, you point to the line that says drywall repair by others. Now the patching is a change order with a price, instead of free work you do to avoid a bad review. The exclusions are not you being difficult. They are you drawing the line that lets you charge for crossing it.
Framing the change to the customer
How you present a change order decides whether the customer signs it or fights it, and the difference is whether it lands as a gotcha or as you looking out for them. Nobody likes a surprise bill. Everybody appreciates being shown a problem and given a choice.
Frame it as here is what we found and here is the option. Not you owe me more money. Walk them to the condition, show them the photo or the actual rot, explain what it means for the system if it is left, and present the fix with a price. You are not springing a charge on them. You are bringing them a decision that is theirs to make, which is exactly what it is. The proposal guide covers presenting options and the value behind a price; the same skill carries straight into change orders.
Tie it back to what they care about, which is the result, not your labor. The customer does not want to pay for a new flue. They want their heat to work and their family safe, and the flue is how that happens. Present the change in those terms and the price is the cost of getting what they already wanted. Done right, a change order can raise trust instead of spending it, because you showed them the problem honestly instead of hiding it in the final number.
The commercial change order process
On commercial and institutional work the change order is a formal process with its own paperwork, and the names matter because they decide when you are allowed to get paid. It usually starts as a potential change order, the PCO, which is your notice and your priced proposal for a change. The PCO goes to the general contractor or the owner's representative for review and approval, and only once it is approved and executed does it become a change order that flows into a pay application.
On AIA jobs the executed change order is commonly the G701, signed by owner, contractor, and architect, which formally adjusts the contract sum and the contract time. Until that document is signed, the change is not contract money no matter how much everyone agrees it is coming. When the parties cannot agree on price or time but the work has to start, the mechanism is a construction change directive, a CCD, where the owner directs you to proceed and the price and schedule get settled afterward. A CCD is direction to proceed, which is what protects you; a verbal go-ahead is not.
The trap on commercial work is the notice clause. Many contracts require written notice of a change or a claim within a set number of days, and miss that window and you can forfeit the right to the money even when you were owed it. Read the change and claims provisions before the job starts, track the deadlines, and treat the paperwork as part of the work, because on these jobs it is. The specifics vary by contract, so confirm the process and the time limits against your actual documents and, where the money is real, your counsel.
Time and material, and the not-to-exceed cap
When you cannot define the scope tightly enough to fix-price it, time and material is the honest answer, and the discipline that makes it work is the signed daily ticket. Every day, the labor hours, the material, and the equipment for the changed work go on a ticket, and the customer or their representative signs it that day. The signed ticket is the contemporaneous record that the work happened and the hours were real. Unsigned T and M is a wish, not a bill.
The customer's worry with time and material is the open meter, that you will run hours forever with no ceiling. The not-to-exceed cap answers it. You bill actual T and M up to a stated maximum, and you cannot exceed the cap without another approval. The customer gets the protection of a ceiling, you get paid for the actual work under it, and the unknown scope stops being a reason not to start.
Run T and M tight or it turns on you. Tickets signed daily, not assembled at the end from memory. Rates agreed in writing before the work. The cap in writing. A pile of unsigned tickets reconstructed at billing time is exactly as weak as the handshake this whole guide is about.
Claim the time, not just the money
Every change order has two costs, and contractors reliably claim one and forget the other. They price the money and leave the schedule blank. A change adds work, the work takes days, and if the change order does not say so, you have just agreed to do extra work and still finish by the original date. That is a free schedule extension handed to the customer, and it is the one you pay for in liquidated damages or in the overtime to make up time you should have been given.
State the schedule impact on every change order, even when it is zero. Adds three working days to substantial completion. No impact to schedule. Either is fine; blank is not, because blank is read as no impact and you cannot claim it back later. On a job with liquidated damages for late completion, an unclaimed time extension is money out of your pocket the day the change is signed, whether you feel it then or not.
Time and money are linked, because a schedule that slips also runs your overhead longer: the supervision, the trailer, the general conditions that cost the same per day whether the delay was your fault or the change's. Claim the days when you claim the dollars, in the same document, so the record shows the change moved both.
The risk of working without a signed change order
Proceed without the signed change order and you may not get paid, full stop. This is the consequence that makes everything else in this guide matter. The work is done, the cost is real, and your right to collect it rests on a conversation the other side may not remember the way you do.
Many contracts go further and say it explicitly: no payment for changed work performed without prior written authorization. Do the work on a verbal and you may have waived the right to bill it under the terms you yourself signed. Even without that clause, you are now the one trying to prove an oral agreement, after the fact, with no document, against a customer who has every incentive to forget. That is a losing position before you start.
There is a real bind here, and pretending otherwise is dishonest. Sometimes the work genuinely cannot wait for the paperwork, an emergency, a safety issue, a condition that will get worse by the hour. In those cases get something in writing fast, even a text or an email confirming go ahead, fix it, we will paper it today, and then paper it the same day. A timestamped text is weaker than a signed change order and far stronger than nothing. The line you do not cross is doing the work on pure memory and hoping it works out. It usually does not, and where serious money or contract terms are at stake, have your counsel tell you where your specific contract draws the line.
The change order log: track them or lose them
Every change order on a job lives in one place: the log. Number, description, date submitted, status, amount, approved or pending, billed or unbilled. Without it, change orders go missing, and a missing change order is unbilled work, which is the same as free work. On a busy job with a dozen changes in flight, the log is the difference between collecting all of them and collecting the ones you happen to remember.
The log answers the questions that otherwise turn into write-offs. Which changes are approved but not yet billed. Which are submitted and waiting on a signature you need to chase. What the total of approved changes does to the contract sum. How much potential change is sitting unapproved that you should not be spending labor on yet. A change order you cannot find at billing time is one you will not bill.
This is where a field-service platform earns its place. FieldOS keeps the change order on the same job record as the work, so the number, the status, the price, and the sign-off are tracked together instead of scattered across a notebook, a phone, and somebody's memory. When the change is created in the field at the moment the customer agrees, with the photo and the price attached, it cannot quietly disappear before billing. The log stops being a thing somebody has to remember to update and becomes a byproduct of doing the work.
Bill the change order
An approved change order that never gets billed is the most painful loss on the list, because you did everything right up to the last step. You found the change, you priced it, you got it signed, you did the work, and then it never made it onto an invoice. The signed change order sitting in a folder is worth nothing until it is billed and collected.
The classic way it disappears is into the final. The change orders pile up during the job, the final invoice gets assembled in a hurry at closeout, and two or three approved changes never get added to it, or get folded into a lump sum that the customer then disputes because they cannot see what it covers. Bill each change order as its own line, tied to its number, so the customer sees exactly what they approved and you can prove what they signed.
On commercial work the approved change order flows into the next pay application as its own line in the schedule of values, and the same discipline applies: every executed change order shows up in the billing, none of them ride along invisibly in the base contract amount. Reconcile the log against what you have actually billed before you close the job. The change you forgot to bill is gone the day you mark the job complete.
Document the condition from the field
The proof of a change is captured where the change happens, which is in the field, by the person standing in front of it. A photo of the rotted chase, the collapsed duct, the asbestos tape, taken before anyone touches it, is worth more than any description written from memory at the truck. The condition is the evidence, and evidence has a short shelf life once the demo starts.
Train the crew to photograph first and cut second on anything that looks like a change. Wide shot to show where it is, close shot to show what it is, and a quick note of what it means. That packet, the photo plus the note plus the price, is what makes the change order easy for the customer to approve, because they are looking at the same thing you are looking at instead of taking your word for it.
FieldOS is built for exactly this capture: the tech photographs the condition on the phone, the images attach to the job and the change order at the moment they are taken, and the documented change travels straight into the log and the customer sign-off without anyone retyping it later. The change that gets photographed, priced, and signed off in the field is the change that gets paid. The one that lives only in somebody's memory is the one that turns into an argument at billing.
The numbers that tell you the system works
A change order process either works or it leaks, and a few numbers tell you which. Change order revenue as a percentage of contract value is the first one. On most jobs there will be legitimate change, and a shop that books almost none is usually not running a tight process, it is eating the extras. A healthy number is real changes captured, not changes invented.
Approval time is the second. How many days from when you submit a change order to when it is signed. A long lag means crews are either stalled waiting or, worse, working ahead of approval and exposed. Watch the average and chase the ones that sit. The third and most important is unbilled change orders: approved work that has not made it onto an invoice. That number should be near zero, and any time it is not, there is money sitting in a folder.
These numbers are only as good as the tracking under them, which is the case for keeping change orders in one system instead of across notebooks and phones. FieldOS rolls the change order log into the job and the billing, so the change order percentage, the approval lag, and the unbilled total are there to read instead of a number somebody has to assemble by hand at month end. You cannot manage what you cannot see, and the unbilled total is the one nobody sees until they go looking, usually too late.
The change order clause in the contract
The whole system rests on a clause in your contract that says changes are by written change order only, and no verbal change is binding. Put it in writing in the agreement, before the job starts, and you have set the rule everyone agreed to play by. Leave it out and you are improvising the rules in the middle of a dispute, which is when you have the least standing to set them.
The clause states a few things plainly. No change to the scope, price, or schedule is valid unless it is in a written change order signed by both parties. No payment is owed for changed work performed without that prior written authorization. And, where the contract allows it, a markup percentage for overhead and profit on change-order work, so the rate is settled before there is a change to argue about. The agreement guide covers building the contract this lives in.
Set this up with your attorney, not from a template you found online, because the enforceability of these provisions varies by state and by the type of contract, and consumer-protection rules on residential work can override what you wrote. A change order clause that is unenforceable in your jurisdiction is worse than none, because it gives you false confidence. Get it drafted right, then hold to it on every job, because a clause you waive whenever it is inconvenient trains your customers that it does not mean anything.
Common mistakes
- Doing the extra work on a handshake, then trying to collect for it after it is already done.
- Having no clear scope baseline, so there is nothing to prove the work actually changed.
- Discounting the change order because it is small, when small adds carry the same overhead and often a higher per-hour cost.
- Proceeding before the signature, which can waive your right to bill the work under your own contract.
- Claiming the money but leaving the schedule impact blank, handing over a free time extension.
- Pricing an unknown scope as a fixed number instead of tagging it time and material with a cap.
- Letting approved change orders disappear into the final invoice, or never billing them at all.
What to document on every change order
A change order is only as good as what is written on it, and a thin one is nearly as weak as no change order at all. Capture the elements below on every change, in writing, before the work starts. The reason for each is the same: it is what answers the question at billing time, or in a dispute, when the friendly conversation has been forgotten and only the document is left.
| Element to record | Why it matters |
|---|---|
| Sequential CO number tied to the contract | Lets you track and bill it without two changes merging into one |
| Plain description of what changed | Someone who was not there can tell exactly what was done |
| Trigger and source (customer, hidden condition, design, code) | Establishes who is responsible for paying it |
| Price, broken out into labor, material, and markup | Shows the customer it is real and supports the amount in a dispute |
| Schedule impact in days, even if zero | A blank is read as no impact and cannot be claimed back later |
| Photos of the condition, taken before disturbing it | The evidence that the condition existed and was not your doing |
| Dated signature of the person with authority to spend | Makes it binding and proves they agreed before the work |
| Status: submitted, approved, billed | The log that keeps an approved change from going uncollected |
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The change order is a creature of your contract, so the contract and its general conditions are the first reference. On commercial work the AIA documents are the common framework: the G701 is the executed change order that adjusts the contract sum and time, and the general conditions, the A201, define the change order, the construction change directive, and the notice requirements that go with them. ConsensusDocs provides a parallel set used on many projects. The specific forms and timelines vary by which documents your project actually uses, so read the ones you signed.
The right to extra payment for unforeseen conditions usually comes from a differing-site-conditions provision in the contract, which on standard forms places that risk on the owner, and from the law of extras where no such clause exists. Both are jurisdiction-specific and fact-specific, so treat the general rule here as the starting point and confirm your position against your contract and counsel before you rely on it.
Pricing and markup on changes follow your estimating practice and whatever the contract caps; a combined overhead-and-profit markup around 15 percent is common but not universal, and the contract controls. The themes that hold across all of it: get it in writing and signed before the work, define a clear scope baseline so you can prove the change, and price and bill every change order so the work you did is the work you collect. Where the money is significant or the contract terms are unusual, have your attorney review the change and claims provisions before the job, not after the dispute.
Terms and definitions
Change order paperwork carries its own vocabulary, and the same idea shows up under different names across residential and commercial work. The terms below are the ones that decide when you are allowed to get paid.
A change order, sometimes abbreviated CO, is the executed document that changes the contract scope, price, or time. A potential change order, the PCO, is the priced proposal for a change before it is approved. A construction change directive, the CCD, is the owner's direction to proceed when price or time is not yet agreed. Differing site conditions are physical conditions that materially differ from what the contract showed, and time and material, T and M, is billing by actual hours and cost rather than a fixed price, usually with a not-to-exceed ceiling.
- Change order (CO)
- The written, signed document that changes the contract scope, price, or schedule
- Potential change order (PCO)
- A priced proposal for a change, submitted for approval before it becomes a change order
- Construction change directive (CCD)
- The owner's written direction to proceed with a change before price or time is settled
- AIA G701
- The common executed change order form that adjusts the contract sum and contract time
- Differing site conditions
- Physical conditions that materially differ from what the contract documents represented
- Scope baseline
- The original contract scope with inclusions and exclusions, the reference a change is measured against
- Not-to-exceed (NTE)
- A cap on time-and-material billing that the contractor cannot pass without further approval
FAQ
What is a change order?
A change order is the written, priced, and approved record of a change to a contract's scope, price, or schedule, signed before the work happens. It documents extras the customer requests, hidden conditions the field finds, and design or code changes, so the contractor gets paid for work the original contract never covered.
Why do you need a change order in writing?
A verbal change is nearly impossible to prove once the work is done and the customer disputes it. A written, signed change order ends the argument before it starts and supports a lien or lawsuit if needed. Many contracts also deny payment for changed work performed without prior written authorization.
How do you price a change order?
Price it labor plus material plus markup, the same way you priced the original job. A combined overhead-and-profit markup around 15 percent is common, though the contract often caps it. Do not discount small changes, they carry the same overhead, and price genuinely unknown scope as time and material with a not-to-exceed cap.
What is scope creep?
Scope creep is the gradual, unauthorized expansion of work through many small changes, each too minor to argue about, that add up to significant unbilled labor by the end. Estimates put its cost around 10 to 15 percent of a project. A clear scope baseline and writing up every extra are what control it.
What happens if you do the work without a signed change order?
You may not get paid. The work and the cost are real, but your right to collect rests on proving an oral agreement after the fact, against a customer with every reason to forget. Many contracts explicitly deny payment for changes done without prior written authorization, so you can waive the money under terms you signed.
Who pays for hidden or differing site conditions?
Under most standard contracts the owner carries the risk of conditions that materially differ from what the documents showed and could not have been seen at bid, like rot, asbestos, or collapsed ductwork. You only collect if you stop, document, photograph, and price it as a change before proceeding, instead of swallowing the work.
What is an AIA G701 and when do you use it?
The AIA G701 is the executed change order form used on many commercial projects, signed by owner, contractor, and architect, that formally adjusts the contract sum and contract time. It comes after a potential change order is reviewed and approved. Until it is signed, the change is not contract money no matter who agrees it is coming.
Should a change order include a time extension?
Yes. State the schedule impact in days on every change order, even when it is zero. A change adds work and work takes time, and a blank schedule line is read as no impact, handing the customer a free time extension. On jobs with liquidated damages, an unclaimed extension costs you the day the change is signed.
How do you keep change orders from going unbilled?
Keep a change order log with every CO's number, amount, and status, and bill each one as its own line, not folded into the final. Reconcile the log against what you have actually billed before closing the job. A field tool like FieldOS ties the change order to the job so approved work cannot disappear before billing.