Automate accounts payable in construction: billing milestones, subcontractors and materials

Construction is a peculiar accounts payable case: each project is a business unit with its own budget, team and subcontractors. Central administration does not see the site; it sees invoices arriving in waves that have to be assigned to the right cost centre before the site manager either approves them blindly or rejects them because "they do not ring a bell".

Tools built for distribution or professional services do not contemplate partial billing milestones, retentions for performance bond, variable aggregate weight per truck or machine timesheet entries. Thesis: touchless AP does work in construction, but only if the system understands billing milestones, framework contracts with subcontractors and simultaneous multi-project operations.

Why construction is different from the rest of AP

According to the National Confederation of Construction (CNC) and the Construction Economic Survey by INE, the sector keeps a relevant weight on Spanish GDP and employs several hundred thousand people. What matters for AP is the cost composition: a very large share is subcontracting and materials with daily delivery frequency.

The five traits that make this case different:

• High and dispersed volume per project. 300-600 invoices/project per month is not exceptional. With three live projects, administration receives between 900 and 1,800 monthly documents that must be allocated to the correct cost centre before being touched.
• Subcontractors invoicing per partial milestone. The subcontractor bills 30% of the chapter this month, 25% the next, until liquidation. Each invoice goes against a milestone signed by the site manager that must reconcile with the original contract.
• Materials with daily delivery notes and agreed prices. Cement by tank, steel by truckload, aggregates by volume. The supplier delivers each day, the delivery note is signed by whoever receives on site, and at month-end the invoice arrives bundling 30 delivery notes.
• Equipment rentals with variable hours. A backhoe works 7 hours Monday, 3 Tuesday and 0 Wednesday. The renter bills the hours their record says; the site manager has their own record. When they do not match, someone overpays.
• Multi-project with duplicates and cost centres. The same supplier delivers to two projects and issues one invoice. Or worse: issues two invoices for the same delivery arriving at different inboxes. Without a project tag, everything goes to the same account.

The result is that an admin team of two or three people spends 100-150 hours a month just classifying invoices by project, chasing milestones and disputing differences. And a significant percentage of discrepancies still slip through: the typical avoidable overrun sits between 5% and 8% of project cost when there is no systematic cross-checking.

Classic problems in construction AP

The following table summarises the six most frequent blockages seen by construction companies arriving at ininvoice. None is solved by a classic OCR or a generic approval workflow.

Problem	Typical frequency	Impact
Subcontractor bills more than certified	10-20% of subcontractor invoices	Advance payment without matching bond
Materials at a price different from agreed	15-25% of fresh-material lines	Direct undetected overcost
Duplicates across projects from the same supplier	3-5% of invoices	Double payment without a project tag
Partial milestones with no linked contract	Common when the contract lives on paper	Impossible to audit real project progress
Equipment rental with mis-billed hours	20-30% of monthly timesheets	Inflated hour cost vs real timesheet
Transport with inflated mileage and surcharges	10-15% of logistics invoices	Margin eroded in logistics chapter

Subcontractors and partial milestones

Matching the subcontractor invoice is the most sector-specific and where the biggest savings live. The logic differs from classic three-way matching: here the "delivery" is a milestone, a percentage of executed work signed by the site manager. The invoice must reconcile with the milestone and with the framework contract signed at the start.

• Original contract. Defines chapters, measurements, unit prices and bond retentions.
• Partial milestone. Each month, the site manager signs what percentage of each chapter has been executed.
• Subcontractor invoice. Must reflect exactly what was certified, applying contract prices and discounting the retention.

Without a system, someone opens three documents in parallel and signs because "they have seen it before". Touchless AP cross-checks the three automatically, withholds the correct bond and only raises an exception when the invoice does not reconcile with the milestone or the price has drifted from the contract.

Materials and multiple delivery notes

The second large chapter is materials: cement, steel, aggregates, brick, prefab, fittings. The usual dynamic:

• Framework order. The site manager agrees estimated volume and unit prices (cement bag, steel ton, concrete m³).
• Daily delivery note. Each delivery generates a note signed by the foreman. Sometimes paper, sometimes digital.
• Monthly invoice. The supplier bundles the period's notes. If not cross-checked line by line, anything from the road to the invoice slips through unfiltered.

The universal line-by-line variance rule applies as-is here: never compare header totals. You must check unit price and quantity of each line against agreed price and the accumulated quantity from the period's delivery notes. Only this way do silent overcosts surface.

Equipment rental and timesheets

Rented equipment (backhoes, cranes, dumpers, platforms) is billed by effective hours or days. The recurring conflict: the renter sends their hours record, the site manager has their own, and between them there is usually a 5-15% difference nobody claims.

Automation cross-checks the renter's invoice against the signed site timesheet, line by line (machine, date, hours). When the system detects hours billed above the timesheet, it raises an exception directly to the site manager.

The touchless flow adapted to construction

A generic touchless flow does not work here. Six phases must be adapted:

1. Multi-project ingestion. Each project has its own inbox or alias. The invoice arrives tagged with the destination project without anyone forwarding anything. If the supplier sends a bundled invoice, the system splits by project using the delivery note or invoice line.
2. OCR/IDP with document typology. A subcontractor invoice, a material invoice and an equipment rental invoice are three different documents. The extractor identifies the type and applies the matching line model.
3. Adapted three-way matching. For subcontractor: contract vs milestone vs invoice. For material: PO vs delivery note vs invoice. For rental: contract vs site timesheet vs invoice. Three patterns coexisting in the same flow.
4. Risk scoring per supplier and project. The subcontractor who overbilled on the previous project carries more control weight. The aggregate supplier with recurring deviations is reviewed line by line. The rest passes automatically.
5. Routing to the site manager. A milestone deviation goes to the site manager who signed. A material price deviation goes to procurement or HQ. A cross-project duplicate goes to administration. Each exception reaches the person who decides.
6. Export to accounting and project cost control. Clean data flows into the ERP or project management software and feeds the actual-vs-budget cost control. Administration stops generating reports by hand.

This flow leaves humans where they add value: the site manager validates milestones, procurement renegotiates material prices, administration only reviews exceptions the system could not close.

Late payment and legal payment term

The construction sector is especially exposed to operational late payment. Law 9/2017 on Public Sector Contracts and general B2B late-payment regulation set typical payment terms around 60 days from invoice date for private commercial operations, with specific conditions for public administrations. [VERIFY WITH LEGAL ADVISER] the applicable term according to your contract and client type.

Manual AP delays invoice recognition: if it takes 9-14 days to enter the ledger because someone had it in a tray, the legal payment term starts running against you. Touchless AP cuts invoice → ledger time to under 48 hours, giving real margin to meet deadlines without paying early or incurring late-payment interest.

Integration with construction ERP

AP does not live in isolation. The invoice arrives, gets reconciled, and clean data feeds the project cost control that cross-checks real milestones with budget. Construction companies with a mature stack typically combine:

• Budget and quantity survey software with products like Presto, Menfis, Cype Arquimedes or equivalents. They provide the original contract with chapters and unit prices.
• ERP and accounting like A3 ERP, Sage Construction, Datisa or vertical packages. They receive clean entries from AP.
• AP automation layer between the supplier inbox and the ERP. ininvoice lives here: ingestion, reading, adapted three-way matching, export.

The idea is not to duplicate masters. Projects and cost centres remain in the ERP, ininvoice reads them. Subcontractor contracts live in project management software or the ERP, not in AP. The AP layer only cleans and matches.

Verifactu and construction

When obliged material suppliers and subcontractors progressively migrate to Verifactu and B2B e-invoicing, construction companies will receive invoices with signed structured data. This changes AP's input quality: less by-eye OCR, more QR and XML reading.

For a construction company, the practical effect is twofold: the invoice it receives is easier to process automatically, and at the same time the AEAT receives the same data from the supplier in real time. Any divergence between what your books show and what the subcontractor or material supplier has declared becomes detectable. [VERIFY WITH TAX ADVISER] the timetable applicable to your suppliers.

Estimated case: construction company with 3 concurrent projects

Indicative figures for a construction company with 3 open projects, 1,200 aggregated invoices/month and two admin people.

Metric	Manual AP	Touchless with ininvoice
Hours/month on capture, sorting and reconciliation	~120 h	~35 h (exceptions only)
Average invoice → ledger time	9-14 days	<48 h
% discrepancies detected	~40%	>95%
Imputable AP staff cost	~EUR 2,400/month	~EUR 700/month
AP software cost	EUR 0	EUR 249/month
Estimated monthly net saving	—	~EUR 1,450-1,620

This does not include recovered project overruns. If the company cuts half a point of the 5-8% avoidable overrun on EUR 6M/year of execution, that is an additional EUR 30,000 typically lost in the "we do not know exactly where the margin goes". The AP productivity figures are aligned with sector benchmarks from IOFM.

Checklist for the admin manager

Ten concrete actions an admin manager can kick off this quarter without slowing the site:

1. Inventory the real volume: how many invoices/month each project receives and from how many different suppliers and subcontractors.
2. Identify the top 10 subcontractors by amount and the top 10 material suppliers by volume. They usually do not overlap.
3. Measure how much time administration spends classifying by project vs resolving discrepancies.
4. Audit a real month of milestones: how many are linked to a contract and how many the site manager signs "because they have seen them before".
5. Compute real-cost vs budget deviation by project and chapter. The dispersion between chapters is usually telling.
6. List suppliers with variable weight (aggregates, concrete) vs fixed unit price (steel per kg, prefab per unit). Decide tolerances per family.
7. Confirm with procurement which contracted prices exist by framework and how they are kept up to date.
8. Confirm with the accounting team or firm how clean data flows into the ERP (A3, Sage, Datisa) and the project management software.
9. Define exception routing: what goes to the site manager, what to procurement, what to administration.
10. Pilot with one project before rolling out. Measure KPIs for 4-6 weeks.

Frequently asked questions

Does this work if my subcontractors still send milestones in Excel?

Yes. The system reads the Excel milestone signed by the site manager, extracts chapters and percentages, and compares them against the framework contract and the invoice. You do not need project software to start.

What about bundled invoices mixing several projects?

The system splits by project using the delivery note or the project reference on the line. If the supplier does not differentiate, ask them to; without a project tag, there is no cost control per centre.

How are bond retentions handled in subcontractor invoices?

The system stores the contract retention percentage and applies it on each milestone. If the invoice does not deduct the correct retention, it raises an exception. It is one of the points where advance payment slips through most.

Do I need a formal contract with each subcontractor?

To audit the matching well, yes. The framework contract with measurements, unit prices and retention is the only way to validate milestones automatically.

What integrations does it have with construction ERP?

ininvoice exports via CSV/API to your ERP. Native integration with A3, Sage, Datisa, Presto, Menfis or Cype depends on the specific product.

How long does it take to go live in a construction company?

It starts when you connect the inbox. Rolling out depends on volume and subcontractor heterogeneity. Most are fully covered in 4-6 weeks.

Does it replace the ERP or the project management software?

No. ininvoice is pure AP automation. It sits between the supplier inbox and your ERP or project software. Clean entries are exported to A3, Sage or Datisa.

Three things to remember

Construction is not just another AP case. It is one of the hardest there is and, for the same reason, where there is most room for good automation.

1. Manual AP at construction companies with 3+ projects silently eats whole points of margin. Cutting half a point of avoidable overrun on EUR 6M/year pays for touchless AP more than ten times.
2. Generic touchless will not do. You must match contract vs milestone vs invoice for subcontractor, PO vs delivery note vs invoice for material and contract vs timesheet vs invoice for machinery. Three patterns in the same flow.
3. The stack that works is light: supplier inbox → AP automation layer → construction ERP. The budget and survey software feeds contracts in parallel. No big projects.

If you want to see how your flow looks with one real project, try ininvoice with your own invoices. You can also check pricing and features in detail.

Related content

• Three-way matching: cross-checking invoice, PO and delivery note line by line
• Touchless accounts payable: what it means and how to measure it
• Managing invoices in construction: base guide by supplier
• Invoice automation rate: how to measure the touchless rate
• IDP vs OCR: why the difference matters in AP