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The coordination meeting asks "does it fit?". A constructability review asks "can we build it, in this order, with this access, these lifts and these tolerances, safely and at a sensible cost?". The model is the same; the questions, and the people asking them, are different.
The model is clash-free and the plant room looks perfect. On delivery day, the two air-handling units arrive at 1.6 m wide. The only door is 1.2 m. The façade is cut open, a mobile crane is booked for a weekend, and the programme loses two weeks.
At the end of technical design, the contractor runs a two-hour review of plant spaces with the mechanical subcontractor's installation manager. In ten minutes he asks how the units get in. The team chooses units delivered in sections, specified before the order. Total cost of the finding: one meeting.
What to look at
A clash is a geometric conflict: two things in the same space, or too close. A constructability problem is anything that makes the work hard, unsafe or expensive to build even though nothing overlaps: no access to install, a lift too heavy, a sequence that traps a trade, tolerances that don't add up.
| Area | Ask | In the model |
|---|---|---|
| Sequence | What must be in place before this, and what does this block? | 4D sequence or section views by stage |
| Access and space | Can it be installed, tested and maintained? | Clearance zones around valves, panels, plant |
| Lifting | How heavy, how far from the crane, in how many pieces? | Weights on elements, crane radius drawn in |
| Tolerances | Do adjoining trades' tolerances add up? | Gaps at interfaces: façade to slab, pods to risers |
| Temporary works | What holds it up or keeps people safe while it's built? | Props, scaffold, edge protection modelled or marked |
Prepare the session
- Pick the scope: one package or one area per session (plant rooms, risers, the façade, the transfer structure).
- Prepare views for each concern before the meeting. Don't navigate the model live looking for things.
- Invite the installers: trade managers and, if possible, a foreman who has built the same thing.
- Bring the programme, at least the sequence for that area.
Record and follow up
Each finding becomes an issue: a viewpoint, a short description, an owner (designer, trade, planner or logistics) and a due date. Track them in the same log as coordination issues, so they're reviewed every week until closed. Some findings change the design; others change the programme, the logistics plan or a method statement. All of them are decisions that cost little now and a lot later.
A residential riser runs through 12 floors. The model shows, inside a 1.8 × 1.2 m shaft: a 300 mm soil stack, two 150 mm water risers, a 600 × 400 mm extract duct, and two cable trays. Fire-rated walls close the shaft on every floor. Isolation valves for each flat are inside the riser at each level. The programme shows the shaft walls built floor by floor ahead of the services, as the frame goes up.
Using the five review areas, list at least four questions you'd raise with the MEP contractor and the drylining contractor.
Key takeaways
- Clash-free is not buildable: sequence, access, lifting, tolerances and temporary works are the real questions.
- Invite the people who install the work, including foremen, not only design managers.
- Prepare views for each concern (risers, crane radius, plant routes, critical sequences) before the session.
- Record findings as issues with a viewpoint, owner and date, and track them like coordination issues.
Your notes
Related tool
Open a .bcfzip to review topics and snapshots, import them as issues, or export your issue log as BCF.
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