Oikodomisis

Calculating Wi-Fi Range and Interference: How Wall Thickness, Concrete Reinforcement, and Mirrors Kill the Signal

You have chosen the best equipment, bought the most expensive Access Points and placed them correctly in the ceilings. And yet, you go into the next bedroom, close the door, and the Wi-Fi "lines" on your phone drop by half. What went wrong?

The biggest mistake that homeowners (and many technicians) make is to plan the network by looking at the floor plan of the house on a blank piece of paper, as if there were no walls. But Wi-Fi isn't magic. They are radio waves (Electromagnetic Radiation). As these waves try to travel through the physical world, they collide with the building materials of your home, are absorbed, reflected and "die".

As engineers, we call this loss Attenuation. Let's see how it's measured, which materials in your home are the "absolute killers" of the signal, and why mirrors and underfloor heating require special attention.

1. How we measure Signal "Death" (dBm)

Wi-Fi power is measured in Decibel-milliwatts (dBm), and the scale is always negative. The ideal is to be as close to zero as possible.

Every time the signal passes through an obstacle, it loses some dB (Decibels). Let's see what each material costs him.

Illustration for 1. How we measure Signal "Death" (dBm)

-30dBm

You are literally next to the Router (Perfect).

-50 to -60 dBm

Excellent signal for comfortable 4K streaming and gaming.

-70dBm

The signal is getting tired. Speed ​​drops noticeably.

-80dBm

You are in a "dead zone". Constant disconnections.

2. The "Enemies" of Wi-Fi: The List of Building Materials

Illustration for 2. The "Enemies" of Wi-Fi: The List of Building Materials

A. Drywall and Wood (The Friendly Neighbor)

If you have drywall partitions, you're in luck. Light, porous materials are almost "transparent" to radio waves. Loss: About -2 to -3 dB. An Access Point can comfortably cover 2 or even 3 rooms separated only by plasterboard or wooden doors.

B. Classic Brick Wall (The Common Obstacle)

The classic Greek double road wall (brick - insulation - brick and plaster) has enough thickness and density. Loss: About -6 to -10 dB (depending on wall moisture). Depending on the distance, the signal can go through ONE such wall and still be satisfactory, but if two walls are in between, Wi-Fi (especially 5GHz) will "kneel".

C. Reinforced Concrete (The "Terminator")

The columns, beams, walls of the elevators and floors (slabs) are made of concrete that has a dense mesh of thick irons (rebar) in it. Loss: Can exceed -15 to -25 dB. The Faraday Cage Effect: The iron mesh inside the concrete acts as a shield that traps and cancels electromagnetic radiation. If you have the Router on the ground floor, don't expect the signal to go through the ceiling plate to get good reception on the 1st floor.

D. Mirrors and Metal Furniture (The Reflector)

A mirror is not just glass. On its backside there is a metal coating (silver or aluminum). Metal wardrobes, large refrigerators and bathroom mirrors do not absorb the signal, they reflect it. When Wi-Fi hits the mirror, it bounces back, collides with the new incoming signal, and creates "noise" (Multipath Interference). Placing a Router behind a large wardrobe mirror is like putting a bulletproof vest on it.

E. Water (The Invisible Wall)

The 2.4GHz frequency of Wi-Fi is exactly the same frequency that your Microwave Oven uses to heat the water molecules in the food! Water absorbs radio waves. What does this mean in practice? Large aquariums are absolute walls for Wi-Fi. Underfloor Heating (which is pipes filled with water, under the floor) creates an inaccessible, "water shield" between floors.

3. Frequency Determines the Winner (2.4GHz vs 5GHz vs 6GHz)

Not all Wi-Fi speeds are affected in the same way by obstacles. The laws of physics are inexorable: The higher the frequency, the shorter the range.

  1. 2.4 GHz (The "Delivery"): It has a low speed and huge movement, but its waves are big and "heavy". They penetrate walls and doors with great ease, reaching far.
  2. 5 GHz (The "Sports Car"): It's more than twice as fast, but its waves are "close". If they meet a thick brick wall, they are almost completely absorbed. It often covers only the room it's in (and a bit of the next door).
  3. 6 GHz (Wi-Fi 6E/7 - The "Hypercar"): Offers astronomical speeds, but practically only works with line of sight. If you put a wall or heavy door between you and the 6GHz Access Point, the signal will simply disappear and your device will "drop" to 5GHz.
Illustration for 3. Frequency Determines the Winner (2.4GHz vs 5GHz vs 6GHz)

4. How to calculate (and solve) the problem

Illustration for 4. How to calculate (and solve) the problem

In professional design, we don't roll the dice on where the antennas go.

The 1 Wall Rule

In designing for 5GHz speeds, we estimate that the user should never be more than one (1) wall away from the Access Point. If it wants to pass a second wall, we add a second Access Point.

We don't go up and down floors

Because of the metal reinforcements in the concrete slabs, each floor (even in small maisonettes) must have its own, dedicated Access Point, connected by Ethernet cable to the central panel (as we learned in PoE).

Summarizing

To enjoy seamless internet, you need to see your home through the eyes of... physics. Avoid hiding Access Points behind TVs, aquariums or mirrors. Recognize that concrete, pillars and thick bricks are impenetrable barriers to the high speeds of 5GHz and 6GHz. Placing more (and strategically placed) Access Points is the only solution to defeat the weakening of building materials.

Next Step: We solved the problem of coverage inside the house. But, in the summer we all want internet in the garden, on the grill or next to the pool. Using "indoor" antennas outside is a recipe for disaster.

Moving on to the ultimate outdoor guide: Outdoor Wi-Fi Access Points: Installation, IP proofing and grounding for gardens, pools and outdoors.

Related Articles

Correct Placement of Access Points: Why ceiling mounting in the center of the room is always the best solution Network Heatmaps (Wi-Fi Planning): How professionals plan the perfect coverage without "dead" zones before the building is even built Mesh Network vs. Ceiling Access Points (APs): What is the best, most permanent solution for a large house or hotel Outdoor Wi-Fi Access Points (Outdoor Wi-Fi): Installation, IP tightness and grounding for gardens, swimming pools and outdoor areas

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