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How do I draw a multi-storey house without a scanner?

One floor at a time, then stack them using two fixed anchor points: the staircase and one outer corner. Here is the method that keeps the floors lined up.

The problem with multiple storeys

One floor is easy: you measure the rooms and draw them. The problem starts when the first floor has to sit exactly above the ground floor. Each floor can be measured correctly on its own and still end up half a metre out of line with the other, simply because nothing ties them together.

A LiDAR scan solves this by measuring the whole house in one continuous coordinate system. Without a scanner, you have to give the drawing that continuity yourself — and it only takes two measurements per floor.

The two anchor points

1. A corner of the house — your zero point

Pick the same outside corner on every floor, say the north-west one. On each floor, measure from that corner to the first internal point. That way you always know where the inside of the floor begins relative to the outside of the house.

If the house has the same footprint all the way up, this is simple: the outer walls are the same, and you can draw the floor's outline with the same figures. If the upper floor steps in — as with sloped walls or an extension — just measure the extra step from the same corner.

2. The stairwell — what ties the floors together

The staircase exists in two places at once, which makes it the best lock. On each floor, measure:

• The stairwell's width and length.
• The distance from the house's chosen corner to the stairwell's two nearest edges.

Those figures should place the stairwell in the same spot on both floors. If they don't, you've measured something wrong somewhere — and you've found the mistake before it ever made it onto the drawing.

The other things that run through the house

Besides the stairs, there are usually two or three vertical elements that are identical on every floor, and which can serve as an extra check:

• The chimney. If it stands 1.20 m from the outer wall in the living room, it stands 1.20 m from the outer wall upstairs too.
• The soil pipe and wet rooms. Bathrooms are often stacked directly above one another, precisely because of the drain.
• The outer walls themselves. Their thickness can differ between floors in older houses — measure it in a window reveal on each floor, don't guess.

If just two of the three line up, the floors are correctly positioned.

The maths you use to check

The house is 9.60 m wide on the outside. The outer wall measures 35 cm. Inside, the house is therefore 9.60 − 2 × 0.35 = 8.90 m on both floors.

On the ground floor, two rooms sit side by side across the width: 4.12 m + 0.11 m partition wall + 4.67 m = 8.90 m. That checks out.

On the first floor, three rooms sit side by side: 2.80 + 0.11 + 3.05 + 0.11 + 2.83 = 8.90 m. That checks out too — and because both floors land on the same internal figure, you know they can be stacked without drifting apart.

If one floor comes to 8.90 m and the other to 9.25 m, something is wrong. You've probably missed a wall, or used the wrong wall thickness.

Floors with sloped ceilings

On a first floor tucked under the roof, the floor area is larger than the area you can actually stand up in. So measure two things in every attic room:

1. The full floor dimension from wall to wall, including under the sloped section.
2. The knee-wall height and the distance from the outer wall to the point where the ceiling reaches 1.50 m — or whatever height you count as usable.

Draw the full floor in the plan, and mark the sloped wall's boundary as a dashed line or a note. That way you can later see how much of the room can actually be furnished, without the floor plan lying about where the floor ends. Bear in mind that a room with a sloped ceiling rarely counts in full towards the area the property is officially registered with. That is a different figure from your own measurement, so the two numbers won't match.

How this looks in an app

In HouseSense, a home can be drawn instead of scanned, and floors are kept as separate plans that stack on top of each other. The approach is the same as on paper: draw the ground floor first, place the stairwell, then draw the next floor with the same outer frame.

Two things help keep the floors honest: every measurement is worked out internally, wall to wall — the same figures you take with a tape measure yourself — and shared walls between two rooms snap together into one common wall, so the same centimetres are never counted in both rooms. Once the floors are in place, the 3D model is built from the plans, and areas are calculated per floor and for the whole home.

The order, in short

1. Pick one corner of the house as the zero point for every floor.
2. Measure the house's outer dimensions and outer-wall thickness on each floor.
3. Measure each floor's rooms: two sides, the diagonal, partition-wall thickness, opening widths and distance from the corner.
4. Measure the stairwell from the zero point on both floors — and the chimney, if there is one.
5. Check that rooms plus walls add up to the house's internal dimension on each floor.
6. Draw the floors and stack them using the stairwell.

And the limit that holds no matter how many floors there are: a floor plan cannot tell you whether a wall is load-bearing — not even if the wall sits in the same spot on both floors, which is often a hint that it is. If a wall is coming down, get a building surveyor or an engineer to assess it on site.