Why does the scan think my window is a door?
A 3D scan recognises openings from shape and position, not from function. A low-set window, a French door or a floor-to-ceiling window can easily end up in the wrong category — and it is simple to fix once you notice it.
Short answer: because the scan guesses from geometry — an opening's height, width and how close to the floor it starts — not from what you yourself know it to be. A window that runs all the way to the floor, or a door with a tall glass panel, look far more alike in pure geometry than they do in reality. The fix is usually to correct the category by hand afterwards, which is a small edit — not a reason to scan the room again.
How does a scan decide whether an opening is a door or a window in the first place?
Most automatic room scanners work from rules of thumb based on measurements: an opening that starts close to floor level and runs a long way up is read as a door. An opening that starts some way up from the floor — typically around sill height — and does not reach all the way down is read as a window. That works well in most ordinary rooms. The problem arises when an opening breaks the pattern: a floor-to-ceiling window has no sill for the algorithm to recognise, and a door with a large glass panel can in some cases look, geometrically, like a tall window.
The situations where it typically goes wrong
- French doors and floor-to-ceiling windows. The two types can be nearly identical in size — only their use tells them apart, and use is not something a scan can see.
- Very low, wide windows. Basement windows or windows in a conservatory that sit close to the floor can lack the sill the algorithm is looking for.
- Glass sliding doors. The frame is often slim and the glass panel fills most of the opening — visually closer to a large window than to a traditional door.
- Openings with no frame, or a very slim one. The less visible the frame, the harder the shape is to categorise unambiguously from geometry alone.
Does that mean the scan itself is wrong?
Not necessarily. The measurements themselves — the width, the height, the position in the wall — can easily be correct even though the category is wrong. That is an important distinction: a door filed as a window is still an opening with the right dimensions, it is simply labelled wrong. It is therefore a fast fix, and one that never requires rescanning anything — you correct the category, not the geometry.
Why does it matter to fix, rather than leave it be?
Because the category feeds into other calculations further down the line. A window-and-door schedule listing every opening for a quote typically sorts by type — a carpenter fitting a new door will look at the door list, not the windows. A takeoff for a daylight study often only counts sunlight through what is categorised as windows. If a French door is wrongly counted as a window, it can be missing from the door list and turn up incorrectly in the daylight calculation — even though the opening's actual size is entirely correct.
Can you prevent the mix-up while scanning?
Not entirely — it is a limitation in how geometric recognition works, not something you can avoid by scanning "better". A couple of things do help, though: scan slowly past unusual openings such as floor-to-ceiling windows and glass doors, so the sensor has good time to capture the whole shape precisely, and avoid standing with strong backlight shining straight through a large glass surface, which can itself give unreliable readings around the opening.
What if an opening is missing entirely, rather than wrongly categorised?
That is a related but different problem. An opening that was not captured at all — for instance behind a curtain or a blind that was drawn during the scan — does not simply turn up with the wrong category, it is missing altogether. The fix there is not to recategorise anything, but to add the opening by hand afterwards, with the right size and the right position on the wall.
A concrete example from an extension with a lot of glass
Picture a conservatory or a garden room with three large glass panels: two fixed windows and a sliding door out to the terrace, all at nearly the same height and with slim frames. Judged on geometry alone, the three openings can look more alike than they really are — only one of them can actually be walked through. This is exactly the kind of room where it is worth spending a couple of extra minutes going through every opening by hand afterwards, because the consequence of a mistake here — a sliding door missing from the door list while a window that is really a door turns up incorrectly in the daylight calculation — is bigger than in an ordinary room with clearly different openings.
What does it mean for a quote from a contractor?
A contractor pricing new windows and doors often works from a list sorted by type, because prices, fitting time and materials differ between the two categories. If the contractor is handed a list where a French door is wrongly shown as a window, the estimate risks resting on a wrong assumption about what actually needs replacing — a door typically costs more to fit than a fixed window of the same size, partly because it has moving parts and a threshold involved. This kind of error is therefore not just cosmetic; it can affect how close a quote lands to the final price.
What HouseSense does
In HouseSense you can convert an opening from door to window or back with a single tap, right inside editing mode — tap the opening and choose "Change to …". The correction takes effect everywhere the category is used: the window-and-door schedule, the takeoff and the 3D model all become consistent immediately. The opening's actual measurements — width, height, position — are untouched by the correction; only the category changes.
How to check it systematically
- Go through every opening in a room with unusual windows or doors first. Floor-to-ceiling panels and glass doors are where the mistake most often sits.
- Correct the category, not the measurements, when an opening is wrongly classified but correctly measured.
- Check the window-and-door schedule afterwards. A miscategorised opening can otherwise slip into the wrong list once you pass the takeoff on to a contractor.
- Add it by hand if an opening is missing entirely — that is a different fix from recategorising an opening that was already captured.