A wall does not affect every Wi-Fi signal in the same way. The material, its thickness and the route the signal takes through a building all influence how much of it gets through.
What Happens When a Wi-Fi Signal Meets a Wall?
A Wi-Fi signal is radio-frequency energy carried by radio waves, which routers use to send and receive information. When the waves meet a wall, the signal reaching a device can be reduced.
Some of that reduction is transmission loss: the signal becomes weaker as it passes through the wall. Radio waves can also be reflected, refracted or diffracted by building materials, changing the signal that continues towards the receiver. Transmission loss is measured in decibels (dB), a unit used to express how much signal is lost. The receiver then converts the arriving signal back into the information sent by the transmitter.
Why Do Some Walls Weaken Wi-Fi More Than Others?
Wall material and construction affect how much radio energy passes through, so a light partition and a heavy concrete wall can produce very different losses. At 2.4 GHz, light drywall has a transmission loss of 2.5 dB, compared with 22 dB for heavy concrete.
Laboratory tests by the National Institute of Standards and Technology (NIST) included brick, concrete, glass, plywood, lumber, drywall and reinforced concrete. The tests used different material thicknesses to measure how attenuation—the weakening of a signal—changed with the distance the radio waves travelled through each material.
Why Does 5 GHz Wi-Fi Often Lose More Signal Than 2.4 GHz?
Wi-Fi at higher frequencies generally travels less far and penetrates solid objects less effectively than lower-frequency Wi-Fi. The difference between losses at 2.4 GHz and 5 GHz depends on the material:
| Wall material | Loss at 2.4 GHz | Loss at 5 GHz |
|---|---|---|
| Heavy concrete | 22 dB | 44 dB |
| Light drywall | 2.5 dB | 3.5 dB |
These figures show a larger difference for heavy concrete than for light drywall. Wi-Fi at 6 GHz also penetrates objects less effectively than lower-frequency Wi-Fi.
Why Can Wi-Fi Loss Vary Between Similar Rooms?
Wi-Fi loss can vary between rooms because signals encounter different materials, travel different distances through them and meet obstructions at different angles. The angle at which a signal hits an obstruction, and the distance it travels inside it, affect penetration.
NIST measured material losses at 2 MHz intervals across two frequency ranges: from 0.5 to 2 GHz and from 3 to 8 GHz. A separate NIST report published in 2008 summarised radio-signal experiments in 12 large building structures, including tests at wireless LAN frequencies. Those measurements found that signals varied considerably across the buildings as well as being weakened by construction materials. A wall’s material matters, but it is not the only factor shaping the signal that reaches a device.
