What do I do if a window is missing from the scan?
LiDAR doesn't see through curtains, blinds or closed shutters — it measures whatever surface it hits first. If a window is covered when you scan, it can simply be absent from the drawing, and the fix is to add it back in by hand afterwards.
Short answer: No, LiDAR does not see through curtains, blinds or closed shutters. The sensor measures the distance to the first surface it meets — if that surface is a curtain hanging in front of a window, the scan believes the curtain is the wall. The window behind it is therefore never registered at all. You usually only spot this once you review the drawing afterwards and notice that a window you know is there simply isn't. The fix is to add it manually with the correct measurements, not to re-scan the room.
Why can't LiDAR see through fabric?
LiDAR works by sending out light — typically in the near-infrared spectrum — and measuring how long it takes for that light to be reflected back to the sensor. That time is translated into a distance. A tightly woven curtain or a closed blind reflects the light just as a wall does, because the light cannot penetrate the fabric or the slats. The sensor therefore has no way of knowing there is anything further back — it simply registers the nearest surface, whether that is a wall or a piece of fabric.
The typical situations where a window goes missing
- Blinds pulled all the way down during the scan, especially in bedrooms or offices, where they are often closed during the day.
- Heavy blackout curtains — more so than ordinary curtains, because they are specifically designed to block light, including LiDAR light.
- Closed exterior shutters or roller blinds that are visible from outside but completely cover the window from the inside.
- Large furniture in front of a low-set window, such as a sofa pushed right up against a bay window — the same principle as fabric, just with a piece of furniture instead.
How do you spot that a window is missing?
The most reliable method is to review the drawing room by room while you are still in the property, comparing it with what you can actually see around you. A missing window is often easier to overlook than an incorrect surface, because the drawing simply shows a perfectly ordinary, unbroken wall where the window should have been — there is nothing eye-catching to react to, only an absence. So check systematically: is a window marked for every exterior wall you remember having one?
Does it matter beyond how the drawing looks?
Yes, in several ways. A missing window means one fewer entry in the window and door schedule, which can give a contractor the wrong basis if you ask for a quote on new windows — the contractor works from the list, not from a site visit alone, at least not in the initial stage. It also affects a daylight study: a window that doesn't exist on the drawing contributes no daylight to the calculation, even though it does in reality. And it affects the wall area in a takeoff report for painting — if the window isn't subtracted, the calculation assumes more wall surface than actually needs painting.
How do you correctly add a missing window?
You need three things: which wall it sits on, the width and height of the opening itself, and how far up from the floor it starts — what is called the sill height. You take those measurements with a tape measure or a laser distance meter directly on site, the same approach as if you were measuring it up from scratch with no scan involved at all. As long as you have physical access to the window — even if it was covered during the scan itself — the follow-up measurement is every bit as accurate as a scan would have been.
Can you avoid the problem next time you scan?
Partly. Draw back curtains and open blinds before scanning a room, if that's practical. If a window is permanently covered — for example a basement window with a fixed exterior roller shutter for security reasons — there is not much to be done about the scan itself, and you should plan for it to be measured and added manually afterwards regardless.
Does the same apply to a missing door?
Yes, the principle is identical. A door hidden behind a large piece of furniture, or a door that stood wide open flat against a wall during the scan, may in some cases not be registered correctly as its own opening. The fix is the same: measure it manually and add it to the drawing with the correct dimensions and placement.
A concrete example: the basement room with a fixed roller shutter
Picture a basement room with two windows — one ordinary and visible during the scan, the other fitted with a fixed, exterior roller shutter installed for burglary protection, which is almost never rolled up. After the scan, the drawing shows only the one window, while the other exterior wall appears completely solid. If you later need a quote on new basement windows, a contractor who only sees the drawing without having visited the property will assume there is only one window to replace — a mistake that only surfaces once the contractor is on site, unless you correct the drawing first.
Why is it important to get the sill height exactly right?
The sill height — the distance from the floor to the bottom of the window — is used for more than just how the drawing looks. It factors into daylight studies, because a low-set window lets more daylight straight into the lower part of a room than a high-set window of the same width. It also matters for furniture placement: a coffee table or a bookcase meant to stand against the wall under the window needs to fit there without blocking the light or reaching up into the glass itself. An inaccurate sill height — guessed rather than measured — can therefore produce a daylight study or a furniture plan that looks right on screen but doesn't match reality.
What HouseSense does
In HouseSense, you can mount a door or window the scan missed directly onto a wall in editing mode — tap the wall, choose "Mount door/window" and enter the width, height and position. The added opening is then treated exactly like the scanned ones: it counts in the window and door schedule, in the takeoff, and in the 3D model, as if it had been part of the original scan.
How to go about it
- Draw back curtains and open blinds before scanning, wherever practical — that prevents most cases.
- Review the drawing room by room while you're in the property, and check each exterior wall against what you actually see.
- Measure the missing window or door with a tape measure, the same approach as if there were no scan involved at all.
- Add it manually in the app, so it's included in the schedule, the takeoff and the 3D model on equal footing with the rest.