Aligning Quantities and Conversion Factors for Carbon Accuracy

A common source of error in carbon assessments is a mismatch between the quantity unit extracted from your BIM model and the unit expected by the emission factor database. This article explains how ORIS handles unit alignment, where to get the right density values for the most common infrastructure materials, and how to ensure your transport calculations stay consistent.

Aligning BIM Quantities with Database Units

Accelerating Setup with AI Mapping

Synchronising Logistics and Truck Loads

Where to Get the Right Density Value

Density Reference Table for Infrastructure Materials

Aligning BIM Quantities with Database Units

When creating your material table in the open BIM module, each material has two units in play: the dataset default unit (the unit ORIS uses to measure the material quantity) and the EF unit (the unit the emission factor is expressed in). ORIS pre-fills a conversion factor (CF) between these two dimensions. You should verify it, but in most cases you will not need to change it.

What you do need to check is whether the dataset default unit matches what your BIM model is actually extracting. If it does not, you must change the unit in the material row to match your BIM quantity unit, and then set the CF manually to convert from that unit to tonnes.

For example, consider concrete:

• If the dataset's default unit is m³ and you are also extracting concrete quantities in m³, the pre-filled CF applies automatically. Verify it reflects the correct density and move on.

• If you are extracting the quantities of a pavement layer in m² rather than m³, change the unit in the material row to m². The existing CF is deleted when you do this. Enter the correct CF manually: CF (t/m²) = layer thickness (m) × material density (t/m³).

Accelerating Setup with AI Mapping

The AI Mapping feature significantly accelerates the initial setup of a carbon assessment. The AI engine analyses the components extracted from your model, searches the selected carbon database for the most relevant materials, and automatically attempts to match quantity units, including proposing conversion factors where needed.

To use it effectively:

• Best use case: AI Mapping is ideal for the first analysis of a new model. It generates a comprehensive baseline mapping quickly, saving you from assigning every material from scratch.

• Review and refine: The AI provides suggestions, but you remain in full control. Review each mapping and accept, reject, or modify the proposals to ensure accuracy.

Synchronising Logistics and Truck Loads

Unit alignment must extend to your transport parameters, if you are using supplier-based calculations. When defining truck constraints during the site selection step of a Material Assessment, the truck load unit follows the material unit:

• If the material unit is tonnes, ORIS sets the truck load automatically to match the truck capacity.

• If the material unit is m³, m², or linear metres, ORIS does not provide a default truck load. Enter it manually in the same unit as the material. For example, a 20-tonne truck carrying crushed rock at 1.9 t/m³ has a capacity of approximately 10.5 m³.

Conversion Factor Calculator

Use the ORIS conversion factor calculator to estimate the correct CF between quantity units before entering it in the material table.

Where to Get the Right Density Value

The CF for most materials is a density value. Check these sources in order of preference:

• Project specification or mix design. Always the most accurate source. A concrete mix design gives you exact density. A pavement specification states the compacted layer density. A geotechnical report gives you site-specific soil and fill densities.

• National authority guidance. Many infrastructure authorities publish density assumptions as part of their carbon calculation tools or technical standards. These are the accepted reference values when project-specific data is not yet available.

• Open reference databases. The ICE Database (Circular Ecology) and Eurocode 1 Annex A, for example, both provide density values for common construction materials and are freely available. Use these as a cross-check or fallback when neither of the above is available.

Density Reference Table for Infrastructure Materials

Indicative values for early-stage carbon estimates. For detailed design and formal carbon reporting, always verify against project specifications, geotechnical reports, or national authority guidance.