A drawing revision is a formal, recorded change made to a drawing after it has already been issued. Once a sheet leaves your office and lands in a contractor's hands, you can no longer just edit it quietly, every subsequent change has to be tracked, numbered, and communicated so that everyone on site is building from the same version. The whole point of drawing revision standards is to answer one question at a glance: is the sheet in my hands the latest one, and what changed since the last time I looked?
In our studio in Vilnius, we treat a revision as a small contract with the contractor. The moment a drawing is "issued for construction," its content becomes a reference that people pour concrete and order steel against. A revision is how we say: this part is now different, here is what moved, and here is the date it became official.
Why drawing revision standards exist
On a real project, dozens of sheets get reissued many times, a door gets relocated, a beam is resized, a setback changes after a planning comment. Without a disciplined revision system, you end up with three "final" versions of the same plan floating around in email threads. Drawing revision standards prevent that by enforcing three things:
- A unique revision identifier on every reissue (a letter or number).
- A dated, described log of what changed and why.
- A visual marker on the drawing showing exactly where the change is.
Different standards govern the exact format. In the UK, BS EN ISO 19650 and the older BS 1192 shape revision and status coding; in the US, practices align loosely with the National CAD Standard and AIA conventions. They differ in detail, but the underlying logic, identifier, log, marker, is universal.
The revision block
The revision block (sometimes "revision table" or "revision schedule") is a small table, usually tucked into the title block in the corner of the sheet. Each reissue adds one row. A typical row contains:
- Revision number or letter, many offices use letters (A, B, C…) for pre-construction issues and numbers (1, 2, 3…) once the drawing is issued for construction.
- Date of the revision.
- Description, a short, plain-language note: "Door D-04 relocated 300mm east per RFI-112."
- Initials of who drew and who checked it.
The revision block is the audit trail. Months later, when someone asks why a wall moved, the block tells you it happened at Rev 3 on a specific date, and the description points to the instruction that drove it. A clean revision block is one of the clearest signs of a well-run drawing set.
The revision cloud
A revision cloud is the freehand-looking, bumpy outline drawn around the area of the sheet that actually changed. Where the revision block tells you that something changed, the cloud tells you where. It is almost always paired with a small revision tag, a triangle or delta symbol carrying the matching revision number, placed next to the cloud.
The convention most teams follow:
- Make the change to the drawing.
- Add a row to the revision block with the new number and a description.
- Cloud the changed region and tag it with that same number.
- On the next revision, remove the previous clouds and cloud only the new changes.
That last step matters. Clouds are meant to highlight what changed at this issue, not accumulate forever. If you never clear old clouds, the contractor can no longer tell what is new, which defeats the purpose.
Version control across the drawing set
Revisions live at two levels: the individual sheet and the whole set. A single architectural plan might be at Rev 4 while a structural detail two tabs over is still at Rev 1. To manage this, teams maintain a drawing register (or transmittal log), a master list of every sheet and its current revision. When a package is issued, the transmittal records exactly which revision of each sheet went out, on what date, to whom, and for what status (for example, "For Construction" or "For Information").
The status code is the partner to the revision number. ISO 19650 uses suffixes like S0–S7 to express whether a drawing is a work-in-progress, shared for coordination, or fully authorized for construction. A sheet can be at the same revision but a different status, and the difference decides whether the contractor is allowed to build from it.
Common mistakes we see
- Editing an issued drawing without bumping the revision. Now two different PDFs share the same revision number, the worst possible failure, because nobody can tell them apart.
- Vague descriptions. "General updates" tells the contractor nothing. Name the element and the reason.
- Stale clouds. Old revision clouds left on the sheet make the current change invisible.
- Set and sheet revisions drifting apart without a register to reconcile them.
FAQ
What is the difference between a revision and a version?
In practice they are often used interchangeably, but "revision" specifically means a tracked, numbered reissue of a drawing that has already been formally issued. A "version" is a looser term that can include internal work-in-progress drafts that were never issued and never given a revision number.
Should the revision number reset between project stages?
Many offices switch notation rather than reset, letters (A, B, C) during design and tender, then numbers (1, 2, 3) once a drawing is issued for construction. This makes it obvious at a glance whether a sheet is pre- or post-construction issue. Check your project's BIM execution plan or CAD standard, since this varies by region and client.
Who is responsible for adding revision clouds?
Whoever makes the change is responsible for clouding it and updating the revision block, but the checker is responsible for confirming the cloud, tag, and block row all match before the sheet is reissued.
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