Does a Load-Bearing Wall Block WiFi? dB Loss Chart

Q: Does glass block WiFi?

Plain glass barely matters — 2 to 4 dB. But coated glass, Low-E double glazing and fire glass with embedded metal mesh are heavy blockers at 15 to 30 dB. That is usually why indoor WiFi fails to reach a balcony or garden.

Q: Will foil or a reflector behind the router boost signal?

It gives directional gain at the cost of every other direction. A metal reflector behind an AP can push energy down one axis, which occasionally helps long narrow layouts. The gain is normally much smaller than simply moving the AP to a better spot, so try that first.

Q: Why can I see my neighbour WiFi but still have dead spots at home?

Listing an SSID needs almost nothing — around −90 dBm is enough for the name to appear. Usable throughput needs better than −70 dBm. There is a 20 dB gap between seeing a network and being able to use it.

Yes, and walls are the single biggest signal killer in a home. A reinforced concrete load-bearing wall costs about 17 dB at 2.4 GHz and 25 dB at 5 GHz — one wall removes more than 98% of the power. Here is the full chart.

WiFi wall attenuation dB chart for glass, wood, brick, concrete and metal doors — Chart: Measured penetration loss (dB) across residential building materials at 2.4 vs 5 GHz

Wall loss reference chart

dB is logarithmic: every 3 dB halves the power, every 10 dB cuts it to one tenth. Keep that conversion in mind while reading.

Typical loss for a single perpendicular pass
Material	2.4 GHz	5 GHz	Power remaining (2.4G)
Wooden door / stud partition	3 dB	4.5 dB	≈ 50%
Plasterboard partition	3–5 dB	4–7 dB	≈ 35–50%
Plain brick wall	7 dB	10 dB	≈ 20%
Load-bearing brick wall	10 dB	15 dB	≈ 10%
Concrete wall	12 dB	18 dB	≈ 6%
Reinforced concrete load-bearing wall	17 dB	25 dB	≈ 2%
Concrete slab (floor/ceiling)	18 dB	25 dB	≈ 1.6%
Plain glass / glass partition	2–4 dB	3–6 dB	≈ 40–63%
Coated glass / metal door	15–30 dB	20–40 dB	< 3%

Note the last row: metal shields far more aggressively than concrete. Fridges, metal doors, Low-E coated windows and metal wiring cabinets all cast pronounced signal shadows.

Why hitting a wall at an angle is worse

Every number above assumes a perpendicular pass. In reality signal rarely meets a wall head-on — at an angle the ray travels a longer path inside the material, and the effective thickness scales as 1/cos θ.

At a 60 degree incidence the effective thickness doubles, so a 7 dB brick wall actually costs 14 dB; near grazing incidence it gets worse still. This explains a common observation: a room reached diagonally often measures worse than a more distant room reached straight through a doorway. Where you can, line the main path up with a door opening rather than cutting across corners.

How many walls before you hit a dead zone?

At 20 dBm, 8 m distance, with −95 dBm treated as dead:

Cumulative wall loss at 2.4 GHz, 8 m
Walls crossed	Cumulative loss	Received strength	Usability
0	0 dB	−45.3 dBm	Excellent
1 brick	7 dB	−52.3 dBm	Excellent
2 brick	14 dB	−59.3 dBm	Excellent (borderline)
3 brick	21 dB	−66.3 dBm	Usable
1 concrete load-bearing	17 dB	−62.3 dBm	Usable
2 concrete load-bearing	34 dB	−79.3 dBm	Weak
3 concrete load-bearing	51 dB	−96.3 dBm	Dead

Rule of thumb: 2.4 GHz survives about two load-bearing walls, 5 GHz only one. Beyond that, add an access point or run cable rather than buying a more powerful single router — transmit power is capped by regulation (commonly 20 dBm / 100 mW), so there is very little headroom.

Why wood ignores the load-bearing flag

Ticking load-bearing on a wooden wall has no effect in the simulator; it is deliberately ignored. The reason is practical: timber partitions are essentially never structural, so marking one load-bearing is a data-entry mistake — and even genuine timber structural walls are nowhere near concrete in thickness or loss. Ignoring the flag prevents a mis-tick from distorting the result.

Map your own walls

The chart gives per-wall magnitudes, but real signal is the sum of every loss along the path plus distance loss and corner diffraction. Assign a material to each wall in the WiFi Signal Simulator and mark the load-bearing ones — you will see immediately which room is weak from distance and which is blocked by one specific wall.

FAQ

Does glass block WiFi?

Plain glass barely matters — 2 to 4 dB. But coated glass, Low-E double glazing and fire glass with embedded metal mesh are heavy blockers at 15 to 30 dB. That is usually why indoor WiFi fails to reach a balcony or garden.

Will foil or a reflector behind the router boost signal?

It gives directional gain at the cost of every other direction. A metal reflector behind an AP can push energy down one axis, which occasionally helps long narrow layouts. The gain is normally much smaller than simply moving the AP to a better spot, so try that first.

Why can I see my neighbour WiFi but still have dead spots at home?

Listing an SSID needs almost nothing — around −90 dBm is enough for the name to appear. Usable throughput needs better than −70 dBm. There is a 20 dB gap between seeing a network and being able to use it.

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