Vertical Duct Is Accumulating Elevation Error Floor by Floor

Fast answer

Stop chaining each new section from the last joint. Re-establish the riser from the project benchmark, floor elevations, and intended connection points, then determine where the accumulated error began.

What to check

1. Measure the current joint elevation from a verified floor benchmark.
2. Compare installed section lengths and joint takeups with the shop drawings.
3. Check support elevations on prior floors.
4. Verify the final equipment or branch connection elevation.

Do not

Do not hide cumulative error by squeezing every joint or changing several fittings without a measured correction plan.

Ask the foreman

“The riser is now off at the fourth floor even though each joint looked close. I rechecked from the floor benchmark and found the error has accumulated. Where do you want the correction made?”

Why it matters

Small takeup and layout errors can compound over several floors and leave the final connection far out of position.