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Can I scan some rooms and draw the rest of the same home?

Yes. Scanned and drawn rooms live side by side in the same home, and the areas are added together across both. Here's how to split the home up, and where the seam needs to sit.

Why mix the two methods at all?

Because each fails in a different place. A LiDAR scan is strong when you're standing in the room and can get all the way around the walls — it catches irregularities, alcoves and door and window placements you'd never have measured yourself. A drawing is strong when you're not in the room, or when the room is impossible to walk around in.

Most homes have both kinds of room. A typical detached house has five or six rooms that are easy to scan, and two or three that are awkward: the garage full of bikes, the 1.4 m² pantry, and the attic you reach through a hatch. Forcing the whole home through the same method costs either time or accuracy.

Split the home up by asking one question

The question isn't "how important is the room", but: can I walk along all four walls with the phone in hand?

If yes, scan it. If not — because the room is too narrow, too full, too dark, or not accessible — draw it, and measure it with a tape measure instead.

Typically scan: living room, kitchen, bedrooms, entrance hall, bathroom, home office. Anywhere there's enough floor space to walk beside the furniture.

Typically draw: garage and carport, garden shed, unconverted attic, basement rooms with shelving up to the ceiling, walk-in wardrobe, pantry, utility room, and any room in a home you've only seen in a listing.

How to do it in practice

1. Scan first. Do the easy rooms while you're in the home with your phone out. These give you the geometry the rest needs to match.
2. Measure the difficult rooms with a tape measure while you're still there. Note width, length and ceiling height in centimetres, and write down which wall the door sits in and how wide it is. Take a photo of the room — it helps your memory more than you'd think.
3. Draw them in afterwards. On the drawing board, drag out the rectangle, type in the measurements in whole centimetres, and add the door and windows. The paper works in internal measurements — that is, wall face to wall face — exactly what your tape measure shows.
4. Join the rooms together. Drag the drawn room over to the scanned one it borders. Walls snap to each other and become a single shared wall, so two rooms never count the same square metres twice.
5. Check the total. Compare the home's combined area to what you know from the official building register or the listing — and remember that your figure is internal, so it should come out smaller.

The seam: where the drawn meets the scanned

The only place a mixed home can go wrong is where the two kinds of room meet. Three things keep the seam tight:

The shared wall must only exist once. When you drag a drawn room up against a scanned one, the walls need to snap together. Leave a thin gap and the home counts square metres that don't exist — overlap the rooms and some go missing. In HouseSense, two rooms can't sit on top of each other, precisely to prevent the latter.

Measure the wall thickness in one spot. If the door sits in the wall you need to hit, you can measure the thickness in the door opening with a tape measure. A typical plasterboard interior wall runs around 10-12 cm and a masonry interior wall around 11-15 cm, but measure it rather than trust a range from an article.

Let the scanned room decide. If there's disagreement about where the wall sits, move the drawn room, not the scanned one. The scan is a measurement; the drawing is a rendering.

The arithmetic: what a gap costs you

Say you've drawn a garage at 6.00 × 3.00 m and pushed it up against the house's scanned gable end — but with an 8 cm gap between them, because the walls didn't snap. The gap is 6.00 m long and 0.08 m wide: 6.00 × 0.08 = 0.48 m². That's under half a square metre and sounds irrelevant.

It is, for the area. But in the 3D model there's now an 8 cm crack running the whole way up, in the takeoff you get an extra 6.00 × 2.40 = 14.4 m² of wall surface that doesn't exist, and the garage floor sits 8 cm off from the house's. The mistake is cheap in square metres and expensive in everything else. So: always check that the walls actually meet once you've dragged a drawn room into place.

The other way round: fixing a scan on the drawing board

The mix works backwards too. If you've scanned a room where the sensor got confused — an alcove that vanished behind a bookcase, a door that landed 40 cm out of place, a wall that bows where you know it's straight — you don't have to rescan the whole floor. In HouseSense you can correct the geometry on the paper: move a wall, set an opening to the size you measured yourself, or draw in the bit the scanner never saw.

That's the fastest route in practice: the scan gives you most of the home while you're walking around, and the drawing board gives you the last few pieces where you've measured it yourself.

What to write down while you're in the home

What ruins a mixed takeoff is almost always that you're missing one number and have already driven home. Note, for every room you don't scan:

• width and length in centimetres, measured at roughly 1 metre height and not against the skirting;
• an extra measurement at the opposite end, if the room seems off-square — write down both figures;
• ceiling height;
• which wall the door sits in, its width, and which way it opens;
• the windows' width and height, and how high above the floor they start;
• anything protruding into the room: a chimney breast, a pillar, a duct box, a dropped ceiling.

With that note in hand you can draw the room in at home — and the result is just as accurately measured as the scanned room next to it.

Is a mixed home worse than a fully scanned one?

No, but it's only as good as your own measurements in the drawn rooms. A scan tells you what's there, even when you hadn't thought to look. A drawn room tells you what you yourself saw and measured — no more, no less.

As long as you've measured the drawn rooms with a tape measure rather than guessed them, there's no weak end to the home. If you did guess them, you at least know exactly which rooms to be sceptical of. That's still better than a drawing where the guess and the measurement can't be told apart.