Accounts payable in commercial construction is structurally different from AP in any other industry. Tiered approval chains, lien-waiver coupling, three-way matching against the sub's pay app and the project's budget, retention math, and pay-when-paid statutory protections all live inside what would otherwise be a routine "pay the bill" workflow. This is a guide for mid-market GC accountants and controllers on how construction AP actually has to work, what most GCs run today, and how AOS automates the chain end-to-end.
If you're the controller at a mid-market commercial GC, you already know that "construction AP" is two words doing a lot of work. The sub's pay application is technically an AP document. So is the supplier invoice for the truckload of rebar that landed on site Tuesday. So is the consultant bill from the geotechnical engineer, and the field-purchase from the foreman who bought $400 of fittings at the local supply house. Each one has different approval logic, different supporting-document requirements, different GL coding, and different lien-waiver implications.
This post walks through what construction AP automation should actually look like for a mid-market commercial GC — the approval chain, the three-way matching, the lien-waiver coupling, the retention coupling, and where AOS automates each piece.
The four types of AP documents a commercial GC processes
Before getting into automation, it's worth being precise about what's actually flowing into AP. A typical mid-market GC processes four distinct types of payable documents, each with its own workflow.
1. Subcontractor pay applications (AIA G702/G703). The largest dollar volume in most GC AP. Submitted monthly per sub per project. Requires three-way matching against the sub's contract SOV, the budget, and the actual percent-complete certified by the project team. Triggers retention withholding and lien-waiver requirements.
2. Supplier invoices for materials. Concrete, rebar, lumber, mechanical equipment, electrical gear. Often delivered against a PO. Requires three-way matching against the PO, the receiving record, and the invoice. Some materials trigger lien-waiver requirements depending on state and supplier registration.
3. Consultant and service invoices. Geotechnical, environmental, surveying, IT services, legal. Typically don't have a PO; charged against project soft-costs budget or G&A. Approval logic is contract-based: who authorized this work?
4. Field purchases and reimbursements. The foreman who bought fittings; the PM who bought lunch for a client meeting; the superintendent who paid for an emergency rental. Smallest dollar amounts individually, often the highest count, and the hardest to control because they happen distributed across the field.
An AP automation that handles only one of these well (most legacy systems handle subcontractor pay apps and not much else) leaves the rest of the workload manual.
The tiered approval chain construction AP actually requires
The single biggest difference between construction AP and generalist AP is the approval chain. A standard SaaS AP automation system assumes one or two-tier approval — manager approves, finance pays. Construction AP requires more tiers, with the people doing the approving sitting in different functions and different physical locations.
The typical mid-market GC tiered chain looks like this:
- Tier 1: Field verification. For sub pay apps, the project superintendent or PM confirms the percent-complete numbers match what's actually been built. For supplier invoices against a PO, the receiving record confirms the material arrived. For field purchases, the foreman who made the purchase substantiates it.
- Tier 2: Project Manager review. The PM confirms the work was authorized, the contract terms are correct, the change-order chain is reflected, and the dollar amount fits the budget. They also catch SOV-line errors, retention rate mistakes, and CO-related discrepancies.
- Tier 3: Accounting review. The accountant confirms the GL coding, the cost coding, the retention withholding, the lien-waiver requirements (and that the waiver is attached), and the prompt-pay statutory deadline. They check for duplicate billing.
- Tier 4: Owner certification (where applicable). For some contract structures (cost-plus, GMP with open book), the owner reviews the underlying payable before approving the GC's master pay app. This tier doesn't always trigger but matters when it does.
- Tier 5: Payment release. Finance authorizes the actual disbursement, the lien waiver gets executed at the moment of payment, the AP record posts to the GL, and the sub's AR (if they're on AOS) sees the status change.
That's five tiers for a sub pay app. Some GCs collapse Tiers 2-3 by giving the PM accounting authority for the project. Others collapse 4-5 by having the GC finance lead and the owner's representative as the same person. The shape varies; the core requirement is that field verification, project authorization, accounting/compliance review, owner certification, and payment release are five distinct decisions that all need to happen with audit trail and timestamping.
Three-way matching: what most GCs actually have today
Three-way matching is the standard AP control: the PO, the receiving record, and the invoice all have to agree before payment authorizes. In generic AP systems this is straightforward. In construction it's complicated by the fact that the equivalent of the "PO" varies by document type.
For subcontractor pay apps, the three-way match is: the subcontract SOV (with approved change orders), the field-verified percent-complete, and the submitted G702/G703 amount. Most legacy construction-accounting systems handle this fine for the basic case but fall down on edge cases: variable retention rates by SOV line, materials-stored line items requiring photo evidence, change orders that hit some lines and not others.
For supplier invoices, the match is: the PO, the receiving record (a packing slip or a signed delivery ticket), and the invoice. Most mid-market GCs handle this with manual matching in their accounting system — a clerk pulls up the PO, pulls up the receiving record, compares to the invoice, and approves. Automation here matters because the volume is high (a single $50M project might have 500+ supplier invoices over its life) and the per-invoice value is low (most are under $5K), so manual handling is a real percentage of overhead.
For consultant invoices, there's no PO, so the "match" is against a contract or LOE. The PM authorizes; the accountant confirms the contract terms.
For field purchases, the match is usually a receipt against a foreman's expense limit and the project's authorized soft-costs budget. Most GCs handle this informally; AP automation here is genuinely an open problem at most mid-market firms.
The lien-waiver and retention couplings
Two specific complications make construction AP fundamentally different from generic AP.
Lien waivers couple the payment to the document. A GC cannot prudently pay a sub without receiving a lien waiver covering the dollar amount being paid. This means the payment release step in the AP automation has to be coupled to the lien-waiver workflow — the waiver must exist, be on the correct state's form, cover the correct amount, and be properly executed before payment authorizes. (Our state-by-state lien-waiver guide walks through the form-and-amount requirements in detail.)
For mid-market GCs working in multiple states, this means the AP system either has to know all 51 jurisdictions' statutory waiver forms or has to rely on a separate platform (Textura, GCPay) to handle it. Most GCs use a separate platform, with the integration cost showing up as duplicate data entry and reconciliation work.
Retention couples the payment math to the GL. Every sub pay app payment withholds retention, which is held as a liability on the GC's books until release. The AP automation has to apply the correct retention rate per contract per SOV line, track the running retention balance, identify statutory release triggers (50% completion in Florida, substantial completion in most states, etc.), and queue retention release in the appropriate cycle. (Our retention rollforward guide walks through the sub-side mechanics, which mirror the GC-side workflow.)
Most legacy construction-accounting systems do this OK for the basic case but treat retention as a project-level number, not an SOV-line number, which breaks at closeout when partial releases start happening.
What most mid-market GC AP automation looks like today
The typical mid-market GC AP workflow:
- Sub pay apps come in through a separate portal (Textura, GCPay) or by email PDF
- The GC's PM reviews and either certifies in the portal or emails approval to accounting
- Accounting re-enters the pay app into the GC's accounting system (Sage 300 CRE, Foundation, Viewpoint) to record the payable
- Lien waiver collection happens through the portal or by email, separately from the payable record
- Approval routing is by email — "approved, please pay" from PM to accountant; further approvals chase by Slack/Teams/email
- Payment release happens when accounting cuts checks (or ACH batches) on Friday, with the lien waiver finalized at that point
- Supplier invoices, consultant bills, and field purchases all come through completely separate workflows, often with different software and different approval logic
- At month-end, the controller reconciles all of the above against the GL, catches the discrepancies, and pushes corrections
This is a workflow with maybe 6-10 handoffs per sub pay app, multiple data re-entries, and a lot of email-based approval routing. It works, but it consumes office labor and creates the conditions for the kinds of errors that delay payment cycles. (We covered the broader stack patchwork problem in why the mid-market GC software stack is broken.)
How AOS handles construction AP end-to-end
In AOS, the AP workflow is built around the construction-specific approval chain and the document type. Specifically:
- All four AP document types live in one queue — sub pay apps, supplier invoices, consultant bills, field purchases. Each type carries its own approval logic, but the GC's accounting team works from one screen.
- Tiered approval is configurable per document type and per project — a $50K sub pay app might require PM → accounting → owner cert; a $400 field purchase might require foreman → PM only. The platform routes based on the rules.
- Three-way matching is automatic against the source records that already live in AOS: the subcontract SOV, the budget, the field-verified percent-complete for sub pay apps; the PO, the receiving record, the invoice for supplier invoices.
- Lien-waiver coupling is built in. The platform knows the controlling state for each project, generates the correct statutory waiver form, computes the exact released amount, and prevents payment release until the waiver is signed.
- Retention is tracked at the SOV-line level with state-statutory triggers. Retention release queues automatically when triggers fire.
- If the sub is on AOS, the entire AP cycle is cross-tenant. The sub's pay app appears in the GC's AP queue without document upload, the GC's approval state is visible to the sub in real time, and the payment status posts back to the sub's AR the moment it releases.
- Audit trail is field-level. Every approval decision, retention calculation, lien waiver execution, and payment release is timestamped and attached to the relevant project record, the relevant SOV line, the relevant GL entry. Defensible if a payment dispute or audit ever arises.
For the broader strategic story on what happens when both sides of the project run on AOS — including how the AP/AR cycle compresses from 60 days to 30 — see the both-sides-on-one-record post. For the pay-app form mechanics specifically, see our AIA G702/G703 working guide.
The AP readiness checklist for mid-market GCs
If you want to evaluate whether your current AP workflow is genuinely automated or just digitized-paper, the questions to ask are:
- Can your AP system route a sub pay app through PM → accounting → owner cert without anyone forwarding emails?
- Does it perform three-way matching automatically against the contract SOV and the field-verified percent-complete?
- When a pay app is approved, does the corresponding lien waiver auto-generate in the correct state's statutory form for the exact released amount?
- Is retention tracked at the SOV-line level, with state-statutory release triggers built in?
- Can the same system handle supplier invoices with PO matching, consultant invoices against contract authority, and field purchases against foreman expense limits?
- If the sub is on a connected platform, does the GC's AP status post back to the sub's AR in real time, without portal re-entry?
- Is the full audit trail of every approval decision, retention calculation, and waiver execution accessible in one report?
If most answers are "in some places, with workarounds" — that's the gap AOS closes.
If you'd like to see it
We're in private-beta design-partner mode for mid-market subs and GCs. If you want to walk through how AOS handles AP end-to-end on a real project of yours — particularly the multi-tier approval chain and the lien-waiver coupling — apply to the beta. The GC accounting role page walks through the full workflow from the controller's seat.