A bill of quantities straight from the IFC model

Manual takeoff is slow, and the revision redoes everything

Manual quantity takeoff from a model or drawing is slow and error-prone, and it is usually done under the same time pressure as the rest of the bid. A forgotten item or a misread area does not show in the estimate until it becomes a deviation in production. And when the model is revised, everything has to be recounted, and what is not recounted becomes wrong. Why the recount is the expensive part is something we have written about before.

The model in, traceable quantities out

Yesper reads the IFC model and DWG drawings, identifies the objects by type and class, and sums the quantities:

• Aggregates by building element and material: concrete volume in cubic metres and formwork area in square metres per wall and slab, reinforcement in kilograms, excavation and fill volumes split by soil and rock, pavement layers in square and cubic metres, water and sewer pipes in running metres per dimension and material, manholes and covers by count.
• Links every quantity to its source object in the model, so you can see where a figure comes from instead of trusting a lump sum.
• Cross-reads against an existing bill of quantities and flags differences per the Swedish measurement rules (MER): an item in the bill without a matching object, or a modelled object without an item.
• Handles revisions by re-running against a new model release and showing the difference against the previous one, down to the individual item.
• Estimates resource use from your historical projects and links the quantities to time and resources, as a first draft of the estimate.

The result exports to Excel in your own template: a bill of quantities where every row can be traced to an object. The same material carries on to the estimate and the quantity settlement, and serves as a starting point for machine control and setting-out.

When it earns its place

• At estimating stage, when quantities are to be taken off a BIM model or CAD.
• When you have received a bill of quantities from the client and want to check-measure it against the model.
• At model revisions, where quantities must be recounted and the difference against the previous release is what matters.
• Ahead of quantity settlement and unit pricing, where the quantity basis must be traceable all the way to the object.

A street reconstruction, two deviations and a revised model

Take an IFC model for a street reconstruction. Yesper sums the pavement by layer, the water and sewer pipes by dimension, and the manholes by count. The cross-read against the client's bill of quantities shows a kerbstone item in running metres with no object in the model, and a DN 400 stormwater pipe in the model with no item. When a revised model arrives a few weeks later you re-run the quantities and get a list of what changed: the excavation volume has grown 12 percent after a slope was redrawn. You resolve the deviations and export the quantities to Excel.

Traceable beats fast

The difference is not counting faster. It is that every quantity can be traced to an object in the model, and that the difference between two model releases becomes visible instead of hiding inside a recount.