Change orders on commercial HVAC projects usually come from five sources: concealed conditions, owner-requested changes, code or inspection findings, equipment substitutions caused by lead times, and unclear demarcation between trades. A specific scope, a walked site and early written notice reduce them. Every change should be described, scheduled and approved in writing before the extra work begins.
- Change orders are normal on mechanical projects. The goal is fewer surprises, not zero changes.
- Concealed conditions and demarcation gaps are the two most preventable triggers.
- A change needs a written description, a schedule effect, and an approval signature before work proceeds.
- Early notice protects everyone. A problem reported the day it is found is easier to solve than one found at closeout.
- Photos and readings from the original site walk are the best defense against later disagreement.
What a change order is, and is not
A change order is a written agreement that adjusts the work, the price, the schedule, or all three, after the original agreement is in place. It is not an accusation. Mechanical projects touch old buildings, hidden spaces and long supply chains, so some change is built in.
What separates smooth projects from painful ones is not the number of changes. It is whether each one was found early, described plainly and approved before the work was done. Pricing is discussed in the contract documents and is outside the scope of this page.
The five common triggers
| Trigger | Typical example | How a good scope helps |
|---|---|---|
| Concealed conditions | A duct run, gas line or support found to be different from the drawing once a ceiling or curb is opened | Site walk with photos, a stated process for discovery and a notice requirement |
| Owner changes | A tenant asks for a different zone layout or added equipment after award | A stated process for requests and a decision-maker named in the scope |
| Code and inspection findings | An inspector asks for a safety device, access clearance or documentation not shown originally | Permit responsibility and code basis stated up front |
| Lead-time substitutions | The specified unit is delayed, so an equivalent model is proposed | Lead times confirmed before award and substitution rules defined |
| Unclear demarcation | Both parties assumed the other would furnish the disconnect, curb adapter or control wire | A responsibility matrix naming a party for every task |
Concealed conditions and owner-requested changes
Concealed conditions
Older commercial buildings hold surprises. Rooftop supports that do not match the as-built drawings, abandoned piping, previously patched ductwork and corroded fittings are common. A scope cannot predict them, but it can set the rules: how a discovery is reported, who inspects it and whether work stops in that area until approval.
The cheapest protection is a documented walk before bids. When the contractor and owner both have the same photographs and measurements, a later disagreement becomes a comparison instead of an argument.
Owner-requested changes
Owners legitimately change their minds. A tenant moves a wall, a kitchen adds equipment, a school changes the room use. The cleanest approach is a request in writing, a short review of the effect on the work and schedule, and a signed approval before anyone proceeds. Verbal go-ahead in a hallway is the habit that causes the most disagreement later.
Code surprises, lead times and demarcation gaps
Code and inspection findings
Inspectors interpret requirements, and requirements change. A scope should say which edition or basis the design follows, and who communicates with the authority having jurisdiction. Confirm current requirements for items such as California Title 24 documentation and the California Mechanical Code before award. The Title 24 and permits guide explains the common documentation points.
Lead-time substitutions
When a specified model is delayed, someone proposes an equivalent. That is a change, even when it saves time. The substitute may have different dimensions, electrical needs or refrigerant, which affects the curb, the disconnect and the controls. A good scope sets a rule: substitutions require written submittal and owner approval, with the effects stated.
Unclear demarcation
Where mechanical work ends and electrical, roofing or structural work begins is the most preventable source of change. Davinci performs mechanical, refrigeration and controls work with its own crew. Other trades are not part of that, so the scope should name the licensed party responsible for each, and the owner or GC should confirm them. See the responsibility matrix method.
How to document and approve a change
A usable change record has the same parts every time. Using a consistent format makes review faster for everyone.
- Notice: report the condition or request in writing the day it is identified, with photos and the location.
- Description: state what changed in plain language and reference the scope line it affects.
- Cause: record whether it is a concealed condition, owner request, code finding, substitution or other.
- Effect on work: list added, removed or altered tasks and who performs each.
- Effect on schedule: state the days added or removed, or confirm no effect.
- Cost: attach the contractor's proposal in the form the contract requires.
- Approval: the named decision-maker signs before the work begins.
- Update: the master scope and drawings are revised, and the change is added to the log.
If Contractor encounters a condition that differs from the information provided or from what a reasonable site walk would show, Contractor shall notify Owner in writing with photographs before disturbing the condition. Work affected by the condition shall proceed only after Owner approves the change in writing, except where needed to protect life or property.
How a scope reduces change orders
- An equipment inventory prevents arguments about what was included.
- A responsibility matrix closes demarcation gaps.
- A clarifications round surfaces access, utility and permit questions early. Use the clarifications and exclusions checklist.
- Alternates and allowances give a controlled path for items not yet decided, covered in alternates, allowances and unit pricing.
- Defined closeout items stop late requests for documents and training that were never priced.
For public and school projects, change procedures are usually set by the agency. Review them in the public agency and school HVAC procurement guide and confirm current requirements before bidding.