Unit prices and change orders on a tree contract
A unit-price contract fixes the price and leaves the quantity open. Payment runs on measured quantity at the bid unit price. Caltrans reopens a price when a bid item moves more than 25 percent; FAR 52.211-18 reopens it at 15 percent. Municipal tree contracts usually carry neither clause, so the unit price holds at any quantity.
A unit-price contract fixes the price and leaves the quantity open. The buyer writes an estimated quantity beside each item. The bidder writes a price. The two are multiplied to make a number that decides the award, and then the work is paid on what gets measured.
Two California tree contracts are the worked examples here. The City of San Bruno released a tree pruning and removal RFP on August 3, 2022 for an anticipated four-year contract, priced across nineteen per-tree line items. The City of Healdsburg opened bids on IFB-05-026 for electric line clearance on April 28, 2026, with a lump sum base and an hourly table for everything beyond it. Neither package contains a clause that reopens a price when the quantity moves.
Nineteen line items, and four of them carry the bid
San Bruno's Proposal Form runs nineteen numbered items with a quantity column. The first four carry real numbers. The remaining fifteen carry a quantity of one apiece.
Item | Description | Quantity |
1 | Street Tree Pollarding | 300 |
2 | Street Tree Pruning - Medium | 100 |
3 | Street Tree Pruning - Large | 150 |
4 | Street Tree Pruning - Very Large | 50 |
5 to 10 | Street tree removal and stump grinding, three sizes each | 1 each |
11 to 19 | Parks tree pruning, removal and stump grinding, three sizes each | 1 each |
The arithmetic checks against the scope. Section III.B asks the contractor to pollard "approximately three hundred (300) sycamore and mulberry street trees annually" and to prune "approximately three hundred (300) street trees annually." Items 2, 3 and 4 add to exactly 300.
Adding 300, 100, 150 and 50 gives 600 units carrying the extended bid total, against fifteen items contributing one unit each. Every removal price and every stump grinding price on that form is weighted at one. Section VI makes cost 30 percent of the evaluation.
A bidder that doubles its price for a very large park tree removal moves its scored total by the price of one tree, on a form dominated by 600 pruning units. It then performs every removal of that size at the doubled price for four years.
The estimate only exists to compare bids
Both cities say so in the package. San Bruno puts it in section III.A.2:
The tree quantities for the contract will vary. The City does not guarantee that the actual amount of work will correspond to the services described in these specifications, but reserves the right to increase or decrease the amount of any class or portion of the work or to omit items or portion of the work that may be deemed necessary by the Parks Services Manager.
Healdsburg puts it in section 1 of Exhibit E to its draft contract:
The estimate of the quantities of Work to be done is approximate only, being as a basis for the comparison of bids, and the City does not expressly or by implication agree that the actual amount of work will correspond therewith, but reserves the right to increase or decrease the amount or any portion of the work as directed by the City Representative.
What actually sizes the year is the appropriation. San Bruno says it plainly: "The Parks Services Manager will identify work requirements within the funding appropriated annually for the duration of the contract." A crew plan built against 300 pruning units is a crew plan built against a budget line the city adopts one year at a time. The same gap between an authorized figure and a spent figure runs through master agreements.
Two thresholds reopen a unit price, and neither is standard
A quantity-variation clause is a printed threshold past which the unit price is no longer the answer. Two of them govern California work, and they sit at different numbers.
Contract | Source | Trigger | What the adjustment covers | Who has to ask |
Caltrans and agencies adopting its specifications | Standard Specifications 9-1.06B and 9-1.06C, applied through the Construction Manual | Bid item quantity varies more than 25 percent | Units above 125 percent of the bid item list quantity | Overrun below $15,000 in value adjusts only on the contractor's written request |
Federal fixed-price construction | FAR 52.211-18 | Actual quantity varies more than 15 percent above or below the estimate | Costs due solely to the variation above 115 percent or below 85 percent | Either party, on demand |
The federal clause is one sentence:
If the quantity of a unit-priced item in this contract is an estimated quantity and the actual quantity of the unit-priced item varies more than 15 percent above or below the estimated quantity, an equitable adjustment in the contract price shall be made upon demand of either party.
FAR 11.703(c) directs the contracting officer to insert it whenever a fixed-price construction contract authorizes a variation in the estimated quantity of unit-priced items. Caltrans runs the mirror image on the downside. Where a bid item underruns by more than 25 percent, the engineer informs the contractor in writing as soon as work on that item is complete. That notice is what starts the conversation about mobilization costs spread over units that never arrived.
Neither San Bruno's package nor Healdsburg's carries anything of the kind. If item 3 turns into 400 large prunes, the price is the bid price for all 400. If it turns into 40, there is no adjustment to ask for. That is the ordinary condition of a municipal tree contract, and it is the first thing to check in a solicitation, because its absence is silent.
The size class is the unit, and two sections disagree
On a per-tree contract the classification decides the price, so the definition is the unit of measure. San Bruno prints two definitions.
Section III.H prices single pruning by height alone: medium under 40 feet, large from 40 to 65 feet, very large above 65 feet. Section III.I prices removals by height and diameter together:
2. Large Size Tree - Pruning/Removals - Trees between forty (40) and sixty-five (65) feet tall with a DBH greater than fifteen (15) and less than thirty (30) inches in diameter. 3. Very Large Size Tree - Pruning/Removals - Trees greater than sixty-five (65) feet with a DBH greater than thirty (30) inches in diameter.
A tree measuring exactly 30 inches DBH is outside both, because large stops below 30 and very large starts above it. A 70-foot tree with an 18-inch DBH meets the very large height and the large diameter. The Proposal Form carries one set of three size labels, so both definitions have to resolve into the same three prices.
Who decides is answered in the same document. The Parks Services Manager directs all pruning and progression of work, and the one case the RFP names is handled outside the schedule entirely:
If required, extraordinary trees with massive multiple trunks shall require a change order with a specific price quotation and approval by the Parks Services Manager.
The measurement that settles the argument is the contractor's own. San Bruno requires a site record update of "DBH and Height for each tree site worked" in the city's Arbor Access inventory, at no additional cost. A crew that enters 29 inches has priced the tree.
The contract picks among five ways to price a change
Caltrans's Local Assistance Module 8, Payment, dated January 2026, lists the methods available for change order work under section 9-1.03 of the Standard Specifications:
1. Bid prices 2. Bid prices with adjustment 3. Agreed price, as a lump sum or by unit 4. Force account 5. Specialist billing
Force account is time and materials with printed markups. The same deck summarizes them under section 9-1.04.
Cost | Markup |
Labor | Labor surcharge, then 35 percent |
Equipment | 15 percent on the rental rate |
Material | 15 percent on purchase price plus delivery |
Subcontractor | 10 percent on force account costs |
Healdsburg took that mechanism out. Section 10 of Exhibit E makes Caltrans Section 15 part of the contract and then deletes the references to "9-1.03, 'Force Account Payment,' 15-3.03, 'Measurement,' 15-3.04, 'Payment,' and 16-1.07, 'Adjustment of Lump Sum Item.'" A contractor looking in the incorporated text for a time-and-materials route will not find one. Note also that current Caltrans practice cites force account at 9-1.04 rather than 9-1.03, so it is worth confirming which edition of the Standard Specifications a contract incorporates before relying on a section number in it.
The rate nobody scored is the rate that governs the change
Healdsburg's Cost Bid Form is two tables. The first is the base bid: one item, "ELECTRIC LINE CLEARANCE SERVICES (MINIMUM REQUIRED WORK)," quantity 1, unit LS. The second collects hourly rates for four additional-work items, each priced three times over at straight time, time and a half, and double time.
Item | Unit |
Arborist report generation | HR |
Stump grinding | HR |
Two-man crew with aerial device (bucket truck) and chipper | HR |
Three-man crew with aerial device (bucket truck) and chipper | HR |
Twelve rate cells per bidder, and the form says what they are worth in the competition:
The undersigned Bidder understands that the decision to utilize its services for additional work beyond that awarded under the lump sum portions of this Contract is solely at the City's discretion and that the quoted unit prices for additional work have no effect on the award of a Contract.
Three bids opened on April 28, 2026: $166,699.00 from Mountain F Enterprises, Inc., $174,899.00 from Arbor Pros, LLC, and $225,000.00 from West Coast Arborists. The gap between the low bid and the high bid is $58,301.00, and it was settled on one lump sum line while twelve rate cells per bid went unweighted. Those unweighted rates then govern every change the city orders for the life of the contract.
Section 2 of the agreement closes the other side of it: "The City will not pay for rates not listed in Exhibit G." A two-man crew and a three-man crew have prices. A four-man crew, a crane, a traffic control truck and a night shift do not. The form is the complete price list, and a blank on it is a rate the contractor negotiates from nothing after the award.
Work before the change order is a gift
San Bruno states the rule twice, in sections IV.D and IV.E:
Contractor shall perform no extra work from the services specified in this RFP unless agreed to in writing by City. City shall not compensate Contractor for extra work that City did not agree to in advance in writing.
City shall have the right to revoke, amend, or modify the General Services Agreement at any time by issuance of a written amendment in the form of a change order. No verbal revocations, changes, or modifications shall be binding on City, and City is not required to compensate Contractor for services not authorized in advance by written amendment to the General Services Agreement.
Healdsburg sets the form the proposal has to take, in section 20 of Exhibit E:
All change order proposals must be submitted on completed City Change Order forms. All such change order proposals must itemize all cost impacts of the proposed change order and include a total price for that change order and the amended Contract Price that would become effective upon execution of the change order.
Two things in that sentence are easy to miss. The proposal carries the amended contract price, not just the delta, so a contractor has to reconcile to the ceiling every time. And the amendment takes effect on execution, which is a signature by somebody with authority to bind the city.
Section 22 of the same exhibit names the City Representative as the person who decides questions of quality, acceptability and interpretation of the specifications. On a utility purchase order the same two-step runs through a field change order and then a change order issued by the procurement agent, which the master agreement sets out.
What closes a unit is a record
The invoice is paid against documentation, and each contract names the document.
San Bruno requires a log daily and a written record delivered to the Parks Services Manager every Monday, carrying date, address, type of tree care performed and species. Acceptance is monthly and it is a person:
For purposes of this contract, the work for each monthly billing period shall be inspected and approved by the Parks Services Manager. This shall constitute final acceptance.
Identified deficiencies must be remedied within 30 days of discovery, and the city withholds payment for them until they are rectified. Healdsburg bills on a different geometry. Invoices indicate the number of hours worked, which Grid Maps were completed, and the dates. Payment is made on five separate invoices at completion of 20, 40, 60, 80 and 100 percent of the awarded work area.
Section 6 of Exhibit B adds a gate that has nothing to do with trees: "Receipt of certified payroll records by the City of Healdsburg is a prerequisite to payment." What those records contain and when they are due is covered in certified payroll in XML. On an investor-owned utility program the closing record is a quality control sample rather than an inspection, and what an enhanced program counts as a unit sets out how that sampling works.
A firm price runs four years, and the wage moves
San Bruno's section IV.C is one sentence long:
All proposal pricing is firm for the term of the original contract and is subject to all applicable California sales and use taxes and not subject to escalation.
The Proposal Form in the same package carries three blank lines under the heading "INCREASE OF CONTRACT OVER TERM OF CONTRACT," asking for a not-to-exceed percentage increase for fiscal years 2023/24, 2024/25 and 2025/26. Those blanks are the whole of the escalation a bidder will ever get on that contract, and they are filled in before any of the three years has happened.
The work is prevailing wage. Section II.R subjects it to the Department of Industrial Relations rates for San Mateo County, which are republished on a schedule the contractor does not control. Whether a determination's rate moves during a contract term turns on the asterisk printed on it, and the prevailing wage determination is where that mark is read. A firm per-tree price carries every increase the determination prints over four years, and the percentage in those three blanks is the only offset.
When the change order is refused, three clocks start
A rejected change order becomes a claim, and California runs more than one statute at it.
Statute | Applies to | Deadline on the agency | Consequence |
Public entity contracts entered into on or after January 1, 2017 | 45 days for a written statement of disputed and undisputed portions; 30 days to schedule a meet and confer on written demand; 10 business days after it concludes | Claim deemed rejected in its entirety; unpaid amounts bear interest at 7 percent per annum | |
Local agency claims of $375,000 or less | 45 days on a claim of $50,000 or less; 60 days above that; 30 days to schedule a meet and confer | Claimant has 15 days to demand the conference; the dispute then goes to the statutory procedures | |
Progress payments by a local agency | 30 days from an undisputed and properly submitted payment request; 7 days to return an improper one | Interest at the legal rate, 10 percent per annum |
Section 9204(d)(3) makes the silence itself an event:
Failure by the public entity to respond to a claim from a contractor within the time periods described in this subdivision or to otherwise meet the time requirements of this section shall result in the claim being deemed rejected in its entirety.
The San Bruno package is where this gets interesting to read. Section 3 of its General Services Agreement says the city "shall endeavor to pay each invoice within thirty (30) calendar days, but shall not be responsible to Contractor for additional charges, interest, or penalties due to failure to pay within that period." Section 20104.50 requires each local agency to set forth that article, or a summary of it, in the terms of any contract subject to it.
Which sentence governs a late progress payment on that contract is a question for the agency's counsel and the contractor's, and it is cheaper to ask during the solicitation than after the first late invoice. A second-tier subcontractor reaching the agency at all runs through the prime, which flow-down clauses covers.
Where this lands on a contract
What a unit-price tree contract is worth turns on five things, and four of them are settled before a price is submitted.
The quantity column, and whether the items that carry the extension are the items the crew will actually spend its year on
The presence or absence of a quantity-variation clause, and its threshold if there is one
The size class definitions, tested against a real tree that sits on a boundary
The rate table for additional work, and every crew configuration, piece of equipment and shift premium missing from it
The escalation blank, filled in against a wage determination that will move whether the price does or not
The contractor signs one document. The agency reads the invoice against another. When those two are the same document, the change order is paperwork. When they are not, it is a claim.
Further reading
How a utility MSA is structured, and what a sub sees of it: The release that authorizes the work, the ceiling it carries, and the change order that amends it.
Flow-down clauses: what a prime passes to a sub: How a subcontractor's claim on a change order reaches the agency, and the seven-day payment clock underneath it.
DIR prevailing wage on public works vegetation contracts: The determination that sets the wage floor a firm unit price has to absorb for the life of the contract.
Frequently asked questions
If a bid schedule estimates 150 trees and the agency orders 400, does the unit price change?
On most municipal tree contracts, no. The City of San Bruno's 2022 tree pruning RFP reserves the right to increase or decrease the amount of any class or portion of the work and attaches no adjustment mechanism. The City of Healdsburg's 2026 line clearance package says the estimate of quantities is approximate only and reserves the same right. A Caltrans contract is different: section 9-1.06B of the Standard Specifications adjusts payment for units above 125 percent of the bid item list quantity. A federal fixed-price construction contract carrying FAR 52.211-18 reopens the price at a 15 percent variation on demand of either party.
Who decides which size class a tree falls into when the definitions overlap?
The agency's named representative. San Bruno's RFP prices single pruning by height alone and prices removals by height and diameter at breast height together, and the two schemes do not produce the same answer for every tree. A tree measuring exactly 30 inches DBH falls outside the large category, which stops below 30 inches, and outside the very large category, which starts above it. The Parks Services Manager directs all pruning and progression of work, and the contractor's own Arbor Access entry of DBH and height for each tree site worked is the record the question gets settled against.
Can a crew perform extra work on a verbal instruction and bill for it afterward?
Not on either contract examined here. San Bruno's terms state that the City will not compensate a contractor for extra work it did not agree to in advance in writing, and that no verbal revocations, changes, or modifications are binding on the City. Healdsburg requires every change order proposal on a completed City Change Order form, itemizing all cost impacts and stating the amended Contract Price. On a utility purchase order the equivalent step is a change order issued by the procurement agent.
Do the hourly rates on a bid form affect who wins the contract?
Not at Healdsburg. Its Cost Bid Form states that the decision to use a contractor for additional work is solely at the City's discretion and that the quoted unit prices for additional work have no effect on the award of a contract. The three base bids opened on April 28, 2026 were $166,699.00, $174,899.00 and $225,000.00, and the award turned on that single lump sum line. Those unscored rates govern every change afterward, and section 2 of the draft agreement adds that the City will not pay for rates not listed in the cost bid form.
What happens when an agency refuses a change order on a California public works contract?
Public Contract Code section 9204 gives the public entity 45 days to provide a written statement identifying the disputed and undisputed portions of a claim. Missing that deadline results in the claim being deemed rejected in its entirety, which opens the next step rather than ending it. A written demand obliges the entity to schedule a meet and confer conference within 30 days. Amounts not paid in a timely manner bear interest at 7 percent per annum. For claims of $375,000 or less against a local agency, section 20104.2 runs a parallel schedule of 45 or 60 days depending on the amount.
