Wi-Fi and walls: what really blocks the signal

Not all walls are equal: one plasterboard wall costs you almost nothing, one reinforced concrete wall can end your Wi-Fi. How to tell which is which.

Updated · 3 min read

In this guide
  1. What each material costs you, roughly
  2. The hidden factor: the angle
  3. 2.4 GHz vs 5 GHz through walls
  4. What to do, in order
  5. Find out which wall is the problem

Wi-Fi travels through air easily and through matter badly. Every wall, floor and piece of furniture takes a bite out of the signal, and the bites are very different in size. That's why the same router covers a whole timber-framed house but dies two rooms away in an older apartment.

What each material costs you, roughly

From least to most damaging:

  • Plasterboard, wood, glass: a small loss. You can cross several without trouble.
  • Hollow brick, breeze block: a noticeable loss, and it adds up quickly over two or three walls.
  • Solid brick, stone, thick plaster: a heavy loss.
  • Reinforced concrete: a very heavy loss. The steel mesh inside acts like a screen.
  • Tiles on a masonry wall, common in kitchens and bathrooms: heavy.
  • Metal: fridges, metal doors, filing cabinets, boilers, lift shafts. Metal doesn't attenuate the signal, it reflects it.
  • Foil-backed insulation and heated floors: often the worst surprise in renovated homes, because a whole floor or ceiling becomes a metal screen.
  • Mirrors and large aquariums: mirrors are metal-coated, and water absorbs the 2.4 GHz band particularly well.

The hidden factor: the angle

A signal crossing a wall straight on passes through the shortest possible thickness. A signal arriving at a sharp angle travels through much more material, sometimes two or three times more. This is why a room diagonally across the house is far worse than a room the same distance away in a straight line, and why moving the router a meter along the wall can change a room's connection completely.

Floors have the same rule: the best path between floors is usually the stairwell, not the concrete slab.

2.4 GHz vs 5 GHz through walls

  • 2.4 GHz passes through walls better and reaches further, but it's slower and crowded with neighbors' networks and other devices.
  • 5 GHz is faster and cleaner but loses much more in walls.
  • 6 GHz (Wi-Fi 6E/7) is faster still and even shorter-ranged.

For a far room behind two masonry walls, a solid 2.4 GHz connection often beats a broken 5 GHz one. Most routers and mesh systems choose automatically, but if your far room struggles, letting devices use 2.4 GHz there is a legitimate fix, not a defeat.

What to do, in order

  1. Move the router, even slightly. Get it out of the cabinet, up off the floor, away from the fridge and away from the corner. See where to put your router.
  2. Open the path. Put it near the door of the room, so the signal goes through a doorway and a corridor instead of through the wall behind the sofa.
  3. Pick the right band for the far room if your system lets you.
  4. Don't fight concrete with radio. If a reinforced wall or a heated floor sits in the way, no router or extender will punch through it. Carry the connection with a cable, MoCA over TV coax, or powerline adapters, and put an access point on the other side.

Find out which wall is the problem

Attenuation numbers in articles are averages. Your wall is your wall: the only way to know is to measure on both sides of it. Map the home room by room, and the map shows where the signal falls off a cliff. The cliff is the wall you need to go around, or around which to place a mesh node.

WiFi Heatmap does exactly that on your iPhone: a floor plan of your home, colored by how the connection actually behaves in each room, so you can see the wall that's costing you the bedroom.