Invoice-based vs. sensor-based A4-A5 documentation

When BR18 requires documentation of A4-A5 emissions on your construction project, there are fundamentally two ways to collect the necessary data: invoice-based documentation and sensor-based documentation. Both approaches can in principle satisfy BR18 requirements — but they differ significantly in setup, cost, and practical feasibility.

Invoice-based documentation builds on the business documents that already exist in your workflow — invoices, delivery notes, weigh slips, and fuel receipts. Sensor-based documentation installs physical measurement equipment on-site to record consumption in real time.

This comparison covers both methods in detail so you can choose the approach that fits your project. See also our introduction to BR18 A4-A5 and the article on data collection on the construction site for the broader context.

Invoice-based documentation starts from the documents that already flow through your business: supplier invoices, delivery notes, weigh slips, and fuel receipts. These documents contain the information BR18 requires — material types, weight, transport distances, vehicle type, and energy consumption.

AI technology can now extract the relevant data automatically from uploaded documents. An invoice from a concrete supplier contains material type, quantity, and delivery address — enough to calculate A4 emissions from transport. A fuel receipt from a plant hire company shows litres of diesel consumed — enough to calculate A5 emissions from machinery.

What does the method cover?

• A4 (transport): Distances and vehicle types from supplier invoices and delivery notes. Material weights from weigh slips. Full A4 coverage without additional data collection.
• A5 energy: Actual kWh from energy bills, litres of diesel from fuel receipts, litres of heating oil from invoices. Real consumption data — not estimates.
• A5 waste: Quantities and waste types from disposal invoices and weigh slips from recycling facilities.

The key point of this method is that the data already exists. It just isn't structured and calculated yet. See also the article on standard values vs. measured data for a walkthrough of which method produces the lowest results for your project.

Sensor-based documentation installs physical measurement equipment directly on the construction site. Typically this means IoT sensors monitoring electricity consumption at the distribution board, flow meters on fuel tanks, and in some cases GPS-based tracking on machinery.

The sensors continuously send data to a cloud platform that aggregates and visualises consumption in real time. This gives a detailed picture of when during the day energy is used and which processes draw the most.

Strengths

• Granular real-time data — hour-by-hour energy consumption rather than a monthly bill total.
• Opportunity for energy optimisation during construction — not just compliance documentation.
• Automatic data capture without manual document processing.

Limitations

• Hardware and installation: Sensors, gateways, and network infrastructure must be purchased, installed, and calibrated. Construction sites are harsh environments — equipment can fail.
• A4 (transport) is not covered: Sensors measure on-site energy consumption — but they cannot tell you how many kilometres the concrete travelled or what vehicle type was used. The A4 calculation still requires invoices and delivery notes.
• A5 waste is not covered: Quantities and types of construction waste come from disposal documents — not sensors.
• Ongoing maintenance: Equipment must be serviced, batteries changed, and software updates handled throughout the entire construction period.

The cost profile of the two methods is very different, and the difference is greatest on shorter projects and projects with limited budgets.

Invoice-based

• Subscription from 199 DKK per project per month — no hardware.
• Zero upfront cost beyond the subscription.
• Scales to all project sizes without additional cost per m².
• No logistics: you upload existing documents, the platform does the rest.

Sensor-based

• Hardware purchase or rental: sensors, gateways, and network connections. Price depends on site size and complexity.
• Installation and calibration: typically carried out by the supplier, but takes time and costs either technician hours or travel.
• Monthly platform and monitoring cost on top of hardware.
• Maintenance throughout the entire construction period — batteries, troubleshooting, possible replacement equipment.

When does sensor break-even?

Sensor-based solutions can justify the higher cost on very large, long-duration projects — typically over 50 months of construction — or on projects where real-time energy optimisation is a goal in its own right beyond BR18 compliance. If the goal is documentation alone, invoice-based is almost always cheaper.

An important and often misunderstood point: BR18 does not require real-time measurements. The law requires documented calculations with traceability from data source to calculation result. That is not the same as continuous monitoring.

BR18 accepts three official methods for establishing emissions data:

• Measured data: Actual consumption measurements — including invoices for actual fuel consumed and actual kWh delivered. This qualifies as measured data.
• EPD data: Environmental declarations for specific products (EN 15804).
• Standard values: Table values from BR18 Annex 2, when better data is not available.

Invoices for actual diesel consumed or actual electricity delivered are fully valid as measured data under BR18. They document actual consumption — just as a sensor would. The difference is only that a sensor updates every minute while an invoice summarises a month. For BR18 compliance, monthly granularity is sufficient.

What matters is traceability, not measurement frequency. If you can draw a direct line from a specific data source to a calculation result, the requirement is met. See standard values vs. measured data and the BR18 A4-A5 guide for details on which method produces the lowest result for your project.

There are scenarios where sensor-based monitoring delivers real added value — and scenarios where the extra complexity and cost simply are not worth it.

Sensors make sense for:

• Very large, long-duration projects (typically over 50 months), where ongoing energy optimisation can save more than the hardware costs.
• Projects with a standalone energy optimisation goal — for example demonstration projects or projects that need to show investors or building owners that real-time reduction is being actively pursued.
• Research and development construction projects, where granular data has independent scientific value.

Invoices are sufficient (and more practical) for:

• Most standard construction projects in Denmark — regardless of size.
• Projects with multiple subcontractors, where coordinating sensor data would add logistical complexity.
• Projects with tight timelines, where weeks of hardware procurement and installation are not realistic.
• Projects where cost efficiency is the priority — and compliance is the goal, not real-time optimisation.

A practical point: even sensor-based solutions need invoice-based data for A4 transport and A5 waste. Invoices cannot be avoided — sensors can.

For the vast majority of Danish construction projects, invoice-based documentation covers all BR18 requirements at a fraction of the cost of sensor-based solutions. The sensor approach adds real value in specific scenarios — but it is not required by law, and it does not replace the need for invoice data.

The choice should be driven by three factors: the project's size and duration, the budget for documentation, and whether real-time energy optimisation — beyond pure compliance — is a goal in itself.

If you are unsure which approach fits your project, invoice-based documentation is the safe starting point: low setup cost, no hardware risk, full BR18 coverage from day one.

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