Duplex and Villa WiFi: Planning Multi-Storey Coverage

How much does a slab actually block?

The third row is the important one: routing through a void costs only 1.5 dB, saving 16.5 dB versus the concrete slab. That margin alone decides whether an upstairs room lands in "excellent" or in a dead zone.

Why two floors is not simply double

Intuitively two slabs should cost 36 dB, but measurements disagree. Signal does not dutifully penetrate each floor vertically — it leaks around stairwells, along exterior windows and through service risers. ITU-R P.1238 measurements give roughly 19/31/43 dB for 1/2/3 floors, a clearly saturating curve.

The simulator fits this with L·(1 + 0.6·(n−1)), giving 18/28.8/39.6 dB. The meaning: the first slab is the expensive one, and each additional floor adds less. So "no signal on the third floor" is usually not runaway accumulation — it is simply having dropped below receiver sensitivity.

A void beats being directly overhead

This is the most counter-intuitive part of multi-floor planning: a diagonal path through a void often beats a short path straight up through the slab.

Here is a calculable example: a ground-floor AP, 3 m storey height, 20 dBm transmit power. Target A sits directly overhead (3 m in 3D) — the shortest path, but it pays the full 18 dB slab and lands at −51.4 dBm. Target B is 5 m away horizontally (5.83 m in 3D), almost twice as far, but its ray passes through the stairwell void for just 1.5 dB and lands at −42.9 dBm — B is 8.5 dB stronger than A.

The practical lesson: put the ground-floor AP near the stairs, not in the middle of the house. Give the signal a chance to travel up through the opening and the upper floor often needs no AP of its own.

Recommended setups by size

Small duplex with a double-height living room

One AP on the lower floor near the stairwell usually covers both levels. Add a second only if the far end upstairs is still weak. This is where voids pay off most.

Two-storey house, no void, concrete slabs

One AP per floor with wired backhaul. Wireless backhaul through a slab leaves only about 2.7 m of usable spacing at 5 GHz, which is not practical.

Three storeys and up

Start with one AP per floor, all wired back to a switch on the ground floor. Do not expect signal to reach the third floor from the first — the saturating model already charges 39.6 dB, and distance loss pushes it into the dead zone.

With a basement

Basements are usually concrete on all sides, effectively an extra layer of heavy shielding. Give it a dedicated AP on a wired link.

Building a multi-floor model

The WiFi Signal Simulator models floor by floor. Use "+ Add floor" to stack levels, each with its own walls, storey height and slab material, and "Copy walls from floor below" to avoid redrawing. Use Void Opening to mark stairwells and double-height rooms with a rectangle. When you switch floors, APs on other floors still contribute to the one you are viewing — exactly what you need to decide whether the upper floor requires its own AP. The built-in duplex villa template already includes a void and cross-floor APs.

Step by step

1. Build the ground floor：Draw the walls, then set storey height (3 m by default) and slab material (concrete, 18 dB by default).
2. Mark the voids：Switch to Void Opening and drag a rectangle over the stairwell, atrium or double-height room. An opening drawn on floor N represents a hole in the slab between floor N and N+1.
3. Add the upper floor：Click "+ Add floor", use "Copy walls from floor below" to get the outline instantly, then adjust it.
4. Place APs and verify across floors：Put an AP on the ground floor, then switch to the upper floor and simulate — the lower AP still contributes, so you can see exactly what the void delivers.

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