Purchase Orders, Subcontracts, and Change Order Administration

Purchase Orders, Subcontracts, and Change Order Administration

Procurement documents are the legal foundation of every construction project. A purchase order (PO) and a subcontract define what is being bought, at what price, under what conditions, and when delivery is expected. Managing these documents accurately protects the project budget, the schedule, and every party involved.

The Purchase Order

A purchase order is a written commercial document issued by the buyer (the general contractor or owner) to a vendor or supplier, authorizing the purchase of specific goods or services at an agreed price and on agreed terms. Once the vendor signs or formally acknowledges it, the PO becomes a binding contract.

Every PO must include the following fields—leaving any one blank creates risk:

• Vendor name and address — identifies the legal party being engaged
• PO number — unique identifier used in the procurement log and in accounting
• Scope reference — cites the applicable specification section, drawing set, or bid package (e.g., "Structural Steel Package per Drawing Set S-100 through S-210")
• Unit prices and total price — itemized where possible so change orders can reference agreed unit rates
• Delivery date and location — states where material must arrive and by what date; ties to the project schedule
• Payment terms — for example, net 30 days after receipt of invoice and approved delivery ticket
• Insurance requirements — minimum coverage types and limits the vendor must carry (general liability, workers' compensation, automobile); certificates must be on file before work begins
• Submittal requirements — shop drawings, product data, or mill certifications that must be approved before fabrication starts

For a structural steel package, submittal requirements are especially important. Shop drawings must typically be approved by the structural engineer of record before the fabricator cuts any steel. Issuing the PO before that approval chain is in place is a common source of costly rework.

Subcontracts vs. Purchase Orders

A subcontract covers labor and materials together—a trade contractor who both supplies materials and performs installation on site. A PO typically covers a supplier who delivers goods only. Subcontracts are longer documents and include additional provisions: schedule adherence, site safety compliance, indemnification, and dispute resolution. Both documents must reflect the same scope, price, and insurance requirements written into the prime contract, so review the prime contract before finalizing either document.

Change Order Administration

A change order (CO) is a formal written amendment to an existing PO or subcontract. Changes happen on every project—material prices shift, scope is added or deleted, delivery dates move. The key discipline is that no change is valid until it is documented and signed by both parties.

When a vendor submits a change-order request, evaluate it in three steps:

1. Verify entitlement — does the contract actually allow this change? A material price escalation clause in the PO permits cost adjustments within defined limits; without such a clause, the vendor assumed that risk.

2. Check the numbers — compare the requested price change to the unit prices in the original PO. If the PO includes a unit rate for steel (dollars per ton), apply that rate to the revised quantity before accepting a lump-sum claim.

3. Assess schedule impact — a revised delivery date must be evaluated against the project schedule's critical path. If the new date pushes a milestone, document the impact and notify the owner or project manager immediately.

Your written rationale for approving or rejecting a CO becomes part of the project record. Be specific: cite the contract clause, the unit price, or the schedule float. Vague rationale creates disputes.

If you approve the CO, issue a revised PO or a numbered change order document that references the original PO number and clearly states the change in price, delivery date, and scope. The vendor must acknowledge it in writing.

Procurement Tracking Log

Every PO and CO must be entered into the project's procurement tracking log—typically a spreadsheet maintained by the project engineer or estimator. The log is the single source of truth for committed costs and delivery commitments. Key columns include:

• PO number and vendor
• Original committed cost
• Approved change order amounts (cumulative)
• Revised total committed cost
• Original and revised delivery dates
• Status (pending, approved, delivered, invoiced, paid)

The sum of all revised committed costs in the log must reconcile to the project budget line for that scope. If the log total and the budget line disagree by even one dollar, there is an error somewhere—find it before submitting a cost report to the owner or lender.

Safety and Record-Keeping Requirements

Procurement documents have a direct connection to site safety. Insurance certificates from vendors must be verified before any vendor personnel arrive on site—this is not optional. Workers' compensation coverage protects against liability if a delivery driver or fabricator employee is injured during unloading. Confirm that the vendor's safety plan, if required by the subcontract, is on file.

For steel erection specifically, OSHA standards govern the activities of the erection crew on site. While the PO covers supply, the erection subcontract must address fall protection, connecting work, and the steel erector's safety plan. Always ensure procurement documents align with site safety responsibilities so no gap exists between the supplier's obligations and the erector's obligations.

All signed POs, COs, insurance certificates, and acknowledgments must be filed in the project's document control system and retained for the period required by the contract and applicable law. Losing a signed document is the same as losing your legal protection.