How to check a drawing revision properly

A new revision lands. The transmittal lists twelve sheets, the revision schedules show one line each, and there are clouds on most of them. It is tempting to read the clouds, nod, and file the old set. That is how changes slip through: a cloud marks what the author meant to change, not everything that did change.

Here is a routine that catches the rest without spending a day on it.

1. Start from the transmittal, not the drawings

Before opening anything, compare the transmittal with your current register:

• Sheets added — new numbers you have never seen. These are often where the real scope change is.
• Sheets removed or superseded — a sheet missing from the new issue may have been merged into another one, or may simply have been forgotten.
• Sheets reissued at the same revision letter — usually a mistake, sometimes a silent change.
• Sheets renamed — the same content under a new number breaks every reference to the old one.

Write these down. They decide which comparisons matter most.

2. Compare the linework, not just the clouds

Lay the old and the new sheet over each other and look at the difference, not at either sheet on its own. A good comparison shows three things at once: what was removed, what was added, and what stayed. Red for removed and blue for added is a common convention, with unchanged linework in grey.

What to look for in the result:

• Changes outside any cloud. These are the ones nobody told you about. Treat each one as a question for the designer until it is explained.
• Dimension text that changed while the geometry did not (or the reverse). Either the drawing was corrected, or one of them is now wrong.
• Moved grid lines and levels. A shifted grid moves everything set out from it, on every discipline.
• Changed notes and specifications. A one-word change in a note (“galvanised” → “stainless”) can be a large cost change.

If almost the whole sheet lights up, the two revisions are probably not on the paper in the same place — the sheet was re-plotted at a different size or the title block moved. Align them first (by two matching points, such as two grid intersections), then compare again.

3. Work through the set by risk, not by sheet number

Twelve sheets do not need the same attention. A useful order:

1. Sheets with changes outside the clouds.
2. Setting-out sheets: grids, levels, general arrangement plans.
3. Sheets that other trades build from — structure for MEP, architecture for finishes.
4. Schedules (doors, finishes, equipment), because one changed row can affect many plans.
5. Everything else.

4. Check the knock-on effects

A change rarely stays on one sheet. For each real change, ask:

• Which other sheets show the same element? Plans, sections, elevations, details and schedules should all agree.
• Do the references still point to the right places? Detail callouts and “see sheet …” notes break when sheets are renumbered.
• Does it touch another discipline? A moved wall can clash with a duct, a beam or a light fitting. Overlaying the disciplines in different colours makes these visible quickly.

5. Record what you found where people will act on it

A list of changes in an email gets lost. Put each finding on the drawing itself:

• Cloud and comment the change on the new sheet, so whoever opens it sees it.
• Raise an RFI for any change you cannot explain or that conflicts with something else.
• Flag cost and time effects to the commercial team the same day — late change notices are much harder to recover.

Then update your register so the old revision is clearly superseded. Keeping markups attached to the right sheets across revisions saves re-doing the review next time.

A five-minute version for small revisions

When a revision really is small:

1. Check the transmittal against the register.
2. Run a comparison of each reissued sheet.
3. Look only for changes outside the clouds.
4. Note anything unexplained as an RFI.

That alone catches most of the problems that cause rework.

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Want to try it on two of your own sheets? The free drawing compare tool shows removed and added linework in your browser without uploading anything.