Stairwells are some of the toughest spaces to scan well. They’re narrow, closed in, often dark, and each flight looks just like the last. Most scans go wrong for one of five reasons. This guide shows you what those problems look like, why they happen, and how to avoid them.
Symptoms and Causes
Mistake 1: Restarting the Capture Mid-Flight
What it looks like. The flight bends partway up. Floors do not stack cleanly above one another. Two halves of the same stair sit at slightly different angles.
Why it happens. Stairwells don’t give the scanner much to work with. The walls are plain, the steps all look the same, and there’s no furniture to help keep track. If you stop in the middle, the scanner has to figure out where it is using features that look just like the ones before. Small mistakes then add up for the rest of the flight.
How to avoid it. Scan each flight in one smooth go, from the bottom landing to the top. If you need to pause, do it on a landing, not on the stairs. Only break at floor levels, never in the middle of a flight.
Mistake 2: Skipping the Landings
What it looks like. The stair exists but does not connect to anything. Total rise is missing or obviously wrong. The flight floats between two floors without meeting either.
Why it happens. Landings can seem like empty space, so people often walk through them without scanning. But landings connect the stairs to the floors above and below. The total rise is measured from floor to floor, not just from step to step.
How to avoid it. Begin on the lower landing and end on the upper landing, making sure to scan each for a few seconds. For return stairs, scan the half-landing carefully too, since it connects the two flights.
Mistake 3: Pointing the Device Along the Flight
What it looks like. Wall surfaces are clean, but the steps themselves are soft, rounded, or partly missing. Individual treads are hard to distinguish. Nosings disappear.
Why it happens. When you walk up stairs holding your phone, you usually point it forward and a bit upward, just like where you’re looking. This records the wall and ceiling ahead, but misses most of the steps you’re on.
How to avoid it. As you go up, tilt your device down at the steps and a bit toward the center of the stairs. Try to get both the tops and fronts of the steps in view. Going down, your device angle is usually better, so a second pass down often helps.
Mistake 4: Losing the Ceiling Line
What it looks like. The stair is complete, but you can't measure headroom. There is no surface above the flight to measure to, or the soffit appears only in patches.
Why it happens. Headroom is measured straight up from the edge of the steps to whatever is above. If you scan the steps but not the ceiling, there’s nothing to measure up to.
How to avoid it. Scan the whole height of the stairwell, not just at eye level. Focus on the underside of the stairs above you. On return stairs, this is usually the lowest spot and the one that matters for headroom. Be sure to scan any joist or bulkhead near the top of a flight.
Mistake 5: Letting the Geometry Repeat
What it looks like. On a return stair or a multi-story shaft, two flights overlap in the model, or one appears twice, or the upper flight sits where the lower one should be.
Why it happens. Every flight in a stairwell looks almost the same. The steps, walls, and handrails all repeat. When the scanner relies on what it sees, it can’t easily tell one floor from another.
How to avoid it. Scan one flight at a time and make sure to overlap at the landings. Add something unique to each scan if possible, like a door, window, floor number, or fire extinguisher. If the stairwell has no features, scan a bit of the hallway at each level so each scan has a clear reference.
Two More Things That Cost You a Rescan
Poor light. Stairwells are usually the darkest spots in a building. Even with LiDAR, the scanner uses the camera, so a dark stairwell drifts more than a bright room. Turn on the lights, and if that’s not enough, bring a work light instead of settling for a bad scan.
Moving too fast. Go about half as fast as you normally walk. When you turn at a landing, turn your whole body instead of just twisting the phone. Spinning the device quickly in a repetitive space is the fastest way to lose tracking.
Checking Before You Leave
You can spot all five of these problems while you’re still on site, but you can’t fix them later from your desk.
- In the preview, move around the flight and check it from the side. A bent flight is easy to see from the side but hard to spot from above.
- Make sure both landings are closed. Check that the stairs connect to a floor at each end, not just floating in space.
- Check the treads. Each step should be clear and separate, not blended together like a ramp.
- Look up and make sure there’s a ceiling or soffit above the stairs.
- For multi-storey stairs, check that the flights stack right on top of each other, not beside or through each other.
A flight that fails any of these takes a few minutes to rescan while you are standing in it. For the measurement side of the job, including the tolerances a stair has to meet, see How to Capture Stair Dimensions Safely and Accurately. For the wider capture process, see How to Scan a Building.
Standing in the building now?
FAQ
Why does my stairwell scan come out bent?
Tracking drifted during the capture, usually because the session was stopped and restarted mid-flight. Stairwells give a scanner few distinctive features to hold position against, so errors compound. Capture each flight in one continuous run from landing to landing.
Why can I not measure the total rise of my stair?
The landings were probably not captured. Total rise is measured floor to floor, so a flight with no landing at either end has nothing to measure between. Capture several seconds of each landing at the start and end of the run.
Why are the steps soft or missing in my model?
The device was pointed along the flight rather than down at it. Walking upstairs naturally points a phone forward, capturing the wall ahead rather than the treads. Angle it downward at the steps as you climb.
How do I capture headroom in a stairwell?
Sweep the full height of the space so the capture holds both the tread nosings and whatever crosses above them. Headroom is measured between those two, so a scan with no ceiling data cannot produce it.
Why do the flights in my multi-story stair overlap?
Every flight looks the same, so a capture has little to distinguish one level from another. Scan one flight per session, overlap at the landings, and include something distinctive in each session such as a door, a window, or a floor number.
Do stairwells need better lighting than other rooms?
They benefit from it. Tracking uses the camera even on a LiDAR device, so a dark shaft drifts more than a lit room. Turn the stair lights on, and bring a work light if they are inadequate.
How many passes does a stairwell need?
One good pass up is usually enough, though a second pass downward often improves tread and riser detail, because the natural device angle on the way down points at the steps rather than past them.
