- Watch out
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- Experienced readers
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- In BIMpedia
A model makes it easy to try options: two staircases, three façade rhythms, four plant room layouts. That is one of its strengths. The trouble starts when options leave the designer's desk. Other teams can't tell an option from the design; they coordinate against it, route around it and price it. And when nothing is ever declared settled, nobody can build on anyone else's work.
In a CDE, work in progress belongs to the team that is developing it. Shared information is for others to use. Options are work in progress; a shared model should hold the design as it currently stands.
The architect keeps two staircase options in the main model, one over the other, and shares it for coordination. The MEP engineer routes a duct around both; the structural engineer sizes trimmers for both openings. Two weeks later the architect picks option B, and half of everyone's work on option A is thrown away.
The architect explores both options in their own work in progress, compares them with the structural engineer at a short meeting, and shares only option B. At the end of the stage, the design team publishes a one-page fixity list: grid, levels, cores and risers fixed; partitions and ceilings may still move.
Saying what is fixed
| Stage (typical) | Usually fixed | Still moving |
|---|---|---|
| Concept | Site, massing, number of storeys | Almost everything else |
| Spatial coordination | Grid, levels, cores, risers, plant room sizes | Partitions, ceiling layouts, services routes in detail |
| Technical design | Structure, main services routes, façade | Fixtures, final sizes within tolerance |
At the end of spatial coordination, sort these items.
Fixed or still moving?
End of spatial coordination. Sort each item.
- Structural grid
- Floor levels
- Main cores and risers
- Plant room size
- Partition positions inside the floor plate
- Ceiling grid layout
Key takeaways
- Explore options in your own work-in-progress; share only the chosen option, or each option clearly named.
- At each stage, say what is fixed (grid, levels, cores) and what may still move.
- Others can build on fixed information; they should only follow moving information.
- A change to something declared fixed is a formal change, logged and communicated.