LIBRARY // ACCURATE MODELLING AND RESEARCH

Documenting Model Sources and Assumptions

Every model contains assumptions. Writing them down saves the next person from guessing.

A model can look precise even when parts of it are based on assumptions. Without documentation, users can't tell which elements are verified and which are estimates. Recording sources and assumptions helps others use models with appropriate confidence.

Why it matters

• Design decisions may depend on uncertain information
• Contractors may rely on models for quantities or setting-out
• Future users may not know the model's history
• Assumptions can be forgotten as projects progress

Sources of information

Model elements may be based on:

• Measured surveys or laser scans
• Old drawings
• Site observations
• Manufacturer information
• Design intent
• Assumptions

Each source has a different reliability.

Recording sources

Options include:

• Parameters on elements, such as an information source field
• Colour-coded views showing source or confidence
• Notes on drawings
• A model report

Assumption logs

An assumption log lists assumptions, such as wall build-ups or hidden structure, with:

• Description
• Location
• Reason
• Who made it
• How and when it'll be verified
• Status

Review the log regularly and update it when assumptions are confirmed or changed.

Accuracy statements

A short statement explaining the model's accuracy, such as survey accuracy and modelling tolerances, helps users understand limits.

Model purpose

State the model's intended purpose. A model built for space planning may not be suitable for fabrication.

Communicating with the team

Verifying assumptions

Plan verification, such as intrusive surveys, before assumptions affect critical decisions.

Handover

At handover, provide model documentation alongside the model. It helps owners and future teams.

Keep it practical

Documentation should be concise. Focus on information that affects how the model is used.

What to log

• Areas modelled from records rather than survey
• Assumed wall thicknesses or floor build-ups
• Elements simplified or omitted
• Agreed modelling conventions
• Open questions for the client or consultants

Keep it with the model

Store the log alongside the model, and update it with each issue. A log that's out of date is almost as unhelpful as no log at all.

1. 01Why it matters
2. 02Sources of information
3. 03Recording sources
4. 04Assumption logs
5. 05Accuracy statements
6. 06Model purpose

Hand it on

When models pass to another team or to the owner, the log explains what can be relied on.

Documenting sources and assumptions makes models more honest, more useful and less likely to mislead.

If your team needs extra production capacity for work like this, take a look at our Architectural production services, or tell us about your project.