Quantity take-off from IFC: weights by section, material and mark

Every element in a detailing model carries a section, a material and a length, so material summaries ought to fall straight out of it. In practice a great deal of time still goes into counting drawings and filling spreadsheets, usually because the model and the take-off live in two packages owned by two people, connected by an exported table that has to be redone after every design change.

Building the summary on the model itself removes that loop: a new version of the model means re-running the summary, with nobody re-checking anything by hand.

The summaries worth having

• By section: count, total length and total weight per section. This is what procurement and pricing use.
• By material: usage split by grade. Different grades cannot be cut from the same stock, so this decides how many purchase orders are needed.
• By mark: how many pieces carry each mark. Shop scheduling and dispatch checking use this.
• Totals: total piece count and total weight, for quotations and transport planning.

What throws the numbers off

Take-off accuracy depends entirely on how complete the model properties are, and missing properties are invisible in 3D — the element looks perfectly normal. The common cases:

• No material: weight cannot be derived and the element silently drops out. Such elements should be listed separately rather than quietly counted as zero.
• No section: same problem, and it cannot be grouped into any summary.
• Placeholder marks: some detailing packages issue a mark with a question-mark suffix before numbering has been run. These must be treated as having no mark at all, or a summary by mark will lump unrelated elements together.
• Weight properties that disagree with the geometry: some models carry weights computed by the exporter and some do not. Mixing the two sources produces unexplainable discrepancies in the total, so a summary should commit to one basis.