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Why don't my scanned rooms line up on the floor plan?

Because each room is measured on its own and has to be pieced together afterwards. When the piecing-together fails, the drawing must not guess at the placement — so the rooms sit in a row until you set them in place yourself.

What actually happens during a scan

A LiDAR scan does not measure the house as one large object. It measures room by room, and each room is processed afterwards in its own local coordinate system — as if each room lay on its own sheet of paper with its own zero point.

Afterwards, all those sheets of paper have to be laid on the same table, in the correct position and rotation relative to each other. This is called merging the geometry, and it is this step that decides whether the floor plan looks like a home or a stack of loose rooms.

The merge uses the movement the phone tracked along the way: that you walked from the living room through a door into the kitchen, and how far, and which way. If it loses that thread, it also loses how the rooms sit relative to one another.

The five reasons the thread breaks

• The screen turned off, or the app was put away between two rooms. The next room then starts from scratch with no knowledge of where the previous one was.
• You walked through the doorway too quickly. The transition between two rooms is the hardest point in the whole scan — it's where the sensor has the least to work with.
• The rooms were scanned on different days. Two scans from separate sessions have no shared movement to tie them together.
• You carried the phone down a staircase with the screen facing away. Floors are already difficult, because the change in height has to be accounted for too.
• There are no overlapping surfaces. Two rooms that only share a closed door don't have much in common to compare.

Why the app doesn't just guess

It would be easy to place the rooms where they "probably" belong and let the drawing look finished. HouseSense doesn't do that, and it's a deliberate choice.

The reason is that a guess doesn't look like a guess. A floor plan where the kitchen sits next to the living room because that's usually where it is gives exactly the same visual impression as a floor plan where it was actually measured — and you cannot tell the difference afterwards. So instead the rooms are set out level, in a row, never on top of one another, and that emergency placement is never saved as though it were measured. The row is a visible signal that the placement is missing.

The principle behind it is the house's own: the drawing may be tidied up, but the numbers may not. Each room's own measurements are measured and correct, even when they sit in a row. What's missing is only their position relative to each other.

How to put them in place

1. Start with the largest room. Put it where you want the home to sit, and let it be the anchor.
2. Bring the neighbouring rooms up against it, one at a time, in the order you actually walk through the home.
3. Let the walls snap together. Two rooms that border each other should share a wall. In HouseSense, wall edges snap to their neighbour, and two rooms can never sit on top of one another.
4. Use the doors as your answer key. A door should face the door it is. If the doors line up, the rooms usually do too.
5. Check the total at the end against the public building register or the sale listing — and remember that your figure is internal, and therefore should be smaller.

The sums: what an air gap costs you

You join two rooms, but end up with a 6 cm gap between them along a 4.50 m wall. The gap covers 4.50 × 0.06 = 0.27 m². In the home's total floor area, that's nothing.

But in the 3D model there is now a 6 cm crack running all the way up to the ceiling; in the takeoff you get an extra wall surface of 4.50 × 2.40 = 10.8 m² that doesn't exist; and if a painter is pricing the wall surfaces, you'll be paying to paint a wall that isn't there. The error is cheap in square metres and expensive in everything else. So always check that the walls actually meet once you've moved a room.

How to avoid the problem next time

• Scan the home in one go, if you can. One continuous walk gives the best fit.
• Walk slowly through doorways. Pause for a moment in the doorway and let the phone see both the room you're leaving and the room you're entering.
• Keep the screen on and the phone facing forward the whole way, including while walking from room to room.
• Take stairs slowly, with the phone pointing ahead, not down in your pocket.
• Open the doors, so there is something shared to see between two rooms.

When the order still can't be recovered

Sometimes there simply isn't enough information, and it isn't worth rescanning the whole home for it. That's when the drawing board is quicker: you move the rooms into place on the grid and let the wall edges snap. Each room's own measurements are still scanned and measured — only the placement is something you've set yourself.

If you're unsure where a room should sit, measure two figures on the spot: the distance from the door frame to the nearest corner, in both rooms. Those two figures usually settle the connection unambiguously.

Is a hand-drawn home free of this problem?

Yes — and it's the drawing's one clear advantage. When you draw the rooms yourself, there is never anything to merge: you place the rooms as you draw them, and walls snap together immediately.

In return, a hand-drawn home only knows what you yourself measured. That's the trade-off: a scan can find slants and alcoves you would never have spotted, but it has to be pieced together afterwards. The drawing is assembled from the start, but it finds nothing on its own.

In practice, the best workflow is usually both: scan the rooms, and piece them together on paper afterwards if the merge couldn't work it out on its own.