Stucco, Adobe and Metal Walls: Why Wi-Fi Dies Between Rooms

Many Northern Nevada homes are built of stucco over block, adobe, brick or steel framing, and many shops are metal. Wi-Fi that is fine in a wood-framed rental can fade in the next room. This guide uses a National Institute of Standards and Technology study to explain why, then gives placement rules that work with heavy walls.

What did NIST test?

NIST Interagency Report 6055, “Electromagnetic Signal Attenuation in Construction Materials,” is a laboratory study from NIST's Construction Automation Program. Researchers placed samples of building materials between two antennas and measured power loss at 2 MHz intervals from 0.5 to 2 GHz and from 3 to 8 GHz. The materials were brick, masonry block, eight concrete mixes, glass, plywood, lumber, drywall, reinforced concrete, steel reinforcing bar grids, and combinations such as brick-faced block.

The study did not test stucco or adobe by name, so this guide does not quote numbers for them. It does show how materials of similar kinds behave, which is enough for placement decisions.

What were the results?

NIST reports that plywood, lumber studs, glass and drywall let signals through easily: a 13 mm plywood panel dissipated only 10% of the transmitted power, two layers of solid fir planks 76 mm thick dissipated 30%, and a 19 mm glass panel dissipated 30%. Concrete is a harder case: the study notes that a signal passing through a 305 mm concrete wall would lose about 90 dB at 8 GHz, a large loss that NIST says can be recovered from background noise in a laboratory but cannot be counted on in a busy real-world setting.

The report also says that, in general, attenuation per millimeter increases with increasing frequency. That is why the 5 GHz and 6 GHz Wi-Fi bands reach less far through walls than 2.4 GHz, as in our band guide.

Why do stucco, adobe and metal matter?

Thick masonry, such as block, brick and adobe, behaves like the dense materials in the study: a lot of material for the signal to cross. Stucco is often applied over a wire mesh, and a metal grid blocks or scatters radio in a way wood does not; NIST tested steel reinforcing bar grids for this reason. A metal roof, metal siding or a steel-framed building adds a shield around the whole space.

The same logic applies to objects inside the house. A router behind a large appliance or a mirror, or in a cabinet with a closed metal door, is in a poor spot.

What should you do about it?

Put the router in the open, near the middle of the house, and up off the floor. Count the heavy walls between it and the rooms you use most, and move it to reduce that count. Use 2.4 GHz for devices far from the router, and 5 GHz for devices close by. Where one router cannot reach, run a cable to a second access point, which beats any wireless repeater; see Ethernet for the things that matter. Our placement guide and mesh guide go further.

A shop or metal building

A metal building needs an access point inside it. A signal from the house will not pass through the walls in a usable way, so run a cable or a wireless bridge, as in the shop and barn guide. For a wireless link into a house from outside, the roof antenna sits outdoors for this reason, and its position is chosen by a path survey rather than by what is convenient inside.

To see what a High Desert connection would involve at your address, send the address through the check form. A person looks at the path from the nearest tower and calls you back, and you can describe your walls on that call.