- Watch out
- What it costs
- Experienced readers
- Remember
- In BIMpedia
On most projects the model and the drawings are meant to be one thing seen two ways. In practice, sheets are edited after export: a dimension is overridden to "look right", a fire rating is typed into a tag, a room is renamed on the plan, a wall is drawn with lines because it was quicker. Each edit is small. Together they create a set that says something the model doesn't, and site builds from the set.
| Edit | What it looks like | Why it's risky |
|---|---|---|
| Overridden dimension | A dimension whose text was typed over | The number no longer measures anything |
| Typed tag or area | Text that looks like a tag | It won't update when the model changes |
| 2D lines | A "wall" or "duct" drawn as lines | Missing from schedules, quantities and clashes |
| Renamed on the sheet | Room name changed in a text box | Room data, signage and FM follow the model |
| Old revision | Sheet printed from an earlier model | Everything on it may have moved since |
How to check
- Revision first. Compare the sheet's revision and status with the CDE. An old sheet makes every other check pointless.
- Typed text. Look for dimensions, tags, areas and notes that were typed rather than read from the model. Many authoring tools can highlight overridden dimensions and text-only tags.
- 2D content. Look for linework standing in for elements: walls, openings, equipment, fire stopping.
- Names and numbers. Compare room names and numbers, door numbers and fire ratings with the model's properties.
- Raise, don't fix. Record each difference as an issue to the author, with the sheet, the revision and the model value.
Try it: find what was edited by hand
A level 1 plan of a small clinic wing as it was issued, and what the model holds. Some things on the sheet were edited by hand after it was exported. Click every place where the drawing says something different from the model. (A teaching sheet drawn for BIMpedia.)
| On the sheet | In the model | Your check |
|---|---|---|
| Room 1.01 Waiting · 22.4 m² | IfcSpace 1.01 Waiting, area 24.0 m² | Not marked |
| Room 1.04 Consult 2 · 16.8 m² | IfcSpace 1.04 Consult 2, area 16.8 m² | Not marked |
| Room 1.05 Store | IfcSpace 1.05 Clean utility | Not marked |
| Grid B–C: 3600 | Grids B–C 3,600 mm apart | Not marked |
| Door D07: 900 wide | Door D07, overall width 1,000 mm | Not marked |
| Wall between 1.02 and 1.03 | No wall element there | Not marked |
| Door D03 tag: FD60 | Door D03, FireRating EI 30 | Not marked |
| Grid line B | Grid B at the same position | Not marked |
| Note: ceiling 2700 | Ceilings at 2,700 mm | Not marked |
| Title block: Rev P03 · S2 | CDE: revision P04 shared on 12 March | Not marked |
The general arrangement plan tags a door "FD60". The model's door carries EI 30, because the tag was typed during a late change and never pushed back into the model. The fire strategy review uses the drawings and passes; the door schedule for ordering comes from the model and orders EI 30 doors. The mismatch is found at the fire officer's inspection.
Before issue, the coordinator lists every tag on the fire plans that isn't reading the model. Door D03 shows up. The architect confirms FD60 is right, updates the model, and the tag is replaced with one that reads the property. The schedule and the drawing now come from the same value.
Your team issues 40 sheets next week. Write a five-line check the authors run before issue, and say who signs it off.
Key takeaways
- Sheets drift from the model through hand edits: overridden dimensions, typed tags and areas, 2D lines, renamed rooms, old revisions.
- Annotation that reads the model (tags, schedules, dimensions) stays right; typed text doesn't.
- The contract says which governs when they disagree; often the issued drawings, sometimes the model.
- Check typed annotation, 2D-only content and the revision on every issued sheet.