Some do. Autodesk’s own guidance lists fixing warnings as a way to keep a model fast, and the Performance Adviser built into Revit says duplicate instances slow down selection and model updates. The warning list itself isn’t what slows you down. What it points at is: two copies of the same desk, two walls on one line, a room boundary Revit has to work around.
In our test in Revit 2026, 2,000 duplicate desks made moving every desk take about two and a half times as long. Most of that was the extra elements, not the warnings. Saving and file size barely changed. If you only want the fix, jump to There are identical instances in the same place.
What Autodesk says about warnings and performance
- The Revit Help page on modelling efficiently lists reviewing and fixing warnings regularly, next to purging unused content and limiting joins.
- The Help page on preventing data corruption says to keep warnings to a minimum, because many warnings make it more likely that Revit struggles to update the elements involved.
- Every edition of Autodesk’s Model Performance Technical Note since Revit 2010 gives the same advice, and adds that warnings about overlapping room boundaries should be fixed promptly.
- The Performance Adviser, a set of model checks built into the Revit API, has a rule for duplicate instances: they take up memory, slow down selection and model updates, and make schedules wrong. A second rule says overlapping walls slow down joins and geometry updates.
None of these sources gives a number. Autodesk doesn’t say how many warnings are too many, so we tested one kind ourselves.
What we measured
We placed 2,000 desks in an empty Revit 2026 project, then added extra desks in two ways: as exact duplicates on top of existing desks, which raises one “identical instances” warning each, or spread out on their own, which raises none. Same number of elements, with and without warnings. After a warm-up run, we ran each test three times and took the median.
In each cell, the first figure is with duplicates and the second with the same number of desks spread out.
| Extra desks | 250 | 1,000 | 2,000 |
|---|---|---|---|
| Placing them | 0.34 s / 0.16 s | 1.25 s / 0.68 s | 2.72 s / 1.53 s |
| Moving every desk | 1.73 s / 1.67 s | 2.50 s / 2.46 s | 4.03 s / 3.26 s |
| Changing the desk type | 1.01 s / 0.98 s | 1.31 s / 1.47 s | 2.02 s / 1.83 s |
| Saving | 0.63 s / 0.53 s | 0.68 s / 0.67 s | 0.79 s / 0.78 s |
| File size | 3.79 / 3.77 MB | 3.88 / 3.84 MB | 3.98 / 3.91 MB |
For comparison, the clean model with 2,000 desks took 1.47 s to move every desk, 0.87 s to change the desk type and 0.59 s to save, at 3.75 MB.
- Placing duplicates took about twice as long as placing the same number of desks elsewhere, in every run. That’s Revit checking every new copy against what’s already there and recording a warning.
- Once they’re in the model, the warnings themselves cost little. With 2,000 duplicates, moving every desk took 5% to 26% longer than with the same number of desks spread out. With 500 or fewer, the difference was lost in the noise between runs. Changing the desk type, saving, reopening and file size showed no clear difference.
- The extra elements cost far more. Compared with the clean 2,000-desk model, the model with 2,000 duplicates took about 2.5 times as long to move every desk and 2.2 times as long to change the desk type. Deleting duplicates pays off mostly because it removes elements, not because it clears warnings.
This is one simple family in an empty project on one laptop (Revit 2026.4, Intel Core i7-13700H, 32 GB RAM, NVMe SSD), so treat the numbers as a direction, not a rule. Duplicates of heavier families, like furniture with nested parts or fittings with connectors, may cost more.
There are identical instances in the same place
Revit shows this when two instances of the same family type sit in exactly the same spot. You see one desk. Schedules count two, and Revit carries both through every update.
It usually comes from:
- pasting the same selection twice with Paste Aligned
- copying elements to a level that already has them
- running a placement script or Dynamo graph a second time
To remove the extra copies:
- Open Manage › Inquiry › Warnings.
- Expand There are identical instances in the same place. Each warning lists the two copies.
- Tick one copy in each warning, not both, then click Delete Checked. Revit deletes exactly what you tick.
- Open the Warnings dialog again to check the group has gone.
On a model with hundreds of these, ticking one per pair takes a while. Fixing the cause first, such as a group that was pasted twice, can clear dozens at once.
Which warnings to fix first for speed
Start with the warnings Autodesk ties to performance:
- There are identical instances in the same place
- Highlighted walls overlap
- A wall and a room separation line overlap, and other room boundary overlaps
Then work through the rest by type. Our guide on how to fix warnings in Revit covers the other common ones.
How many warnings is too many?
There’s no official number. Autodesk asks you to keep warnings to a minimum but doesn’t set a limit, and the figures you’ll see on forums, like 200 or 500, are rules of thumb. The trend tells you more: export the list from the Warnings dialog every week or two and check the count is going down, not up.