Building Signal Guide

Building Penetration and Signal Loss

Signal loss through common UK building materials. How to calculate indoor cellular requirements and when an external antenna is the only viable solution.

15-25 dB

Typical signal loss modern building

Concrete

Highest loss material

Low-E glass

Worse than concrete for cellular

Outdoor first

Always prefer external antenna

Building Material Signal Loss Table

Material	Loss at 800 MHz	Loss at 1800 MHz	Loss at 3500 MHz
Standard clear glass	2-4 dB	3-5 dB	5-8 dB
Low-E coated glass	15-25 dB	20-30 dB	25-35 dB
Lightweight wood/plasterboard	2-5 dB	3-6 dB	5-8 dB
Brick (single skin)	5-8 dB	7-12 dB	10-15 dB
Reinforced concrete	15-25 dB	20-30 dB	25-40 dB
Metal sheet (steel door, panel)	>30 dB	>30 dB	>40 dB
Wire mesh/rebar-heavy floor	15-20 dB	18-25 dB	25-35 dB

Cumulative Loss: The Real Problem

The table above shows loss through a single layer of material. In a real building, the signal passes through multiple layers. A router in a basement industrial unit might see: exterior reinforced concrete wall (20 dB) + interior concrete partition (15 dB) + steel DIN rail panel (30 dB) = 65 dB of attenuation. If the outdoor signal is -80 dBm RSRP, the antenna inside the panel sees -145 dBm — below the noise floor.

This is not a recoverable situation by changing the router or SIM. The only solution is to bring the antenna outside.

The Rule: Antenna Outside, Router Inside

The cellular antenna belongs on the outside of the building or vehicle. The router sits indoors. A cable connects them. This is not optional in problem locations — it is the only workable architecture.

For typical UK commercial buildings, an outdoor wall-mounted or mast-mounted MIMO antenna will recover 15-30 dB compared to an indoor antenna. That converts a marginal 2-bar signal to a solid 4-5 bar connection in most cases.

Cable loss matters: an outdoor antenna on a 10-metre LMR-240 run at 1800 MHz loses 1.3 dB. That is far less than the 15+ dB you gain by moving the antenna outside. See the cable loss calculator to confirm your specific run is worth it (it almost certainly is).

Frequently Asked Questions

Why does my router show 4 bars on my phone but the IoT device struggles indoors?

Your phone is a much more sensitive receiver with aggressive signal processing optimised for marginal conditions. An industrial IoT router may have similar or better sensitivity, but it depends on how deep inside the building it is installed and whether the antenna is effective in that position. A phone in your hand near a window is in a fundamentally different position to a router on a DIN rail inside a metal panel inside a concrete building. Bring the antenna outside.

Is Low-E glass worse than standard glass for cellular signal?

Yes, significantly. Low-E (low emissivity) glass has a metallic coating (typically silver or tin oxide) to reflect infrared heat. This same coating reflects and absorbs cellular RF. Modern energy-efficient buildings with Low-E double or triple glazing can lose 15-30 dB through the glazing alone — comparable to a reinforced concrete wall. In new commercial builds, assume the glazing is a major barrier to cellular signal.

My IoT device is inside a metal cabinet. Can it still connect?

Metal enclosures completely attenuate cellular signals. A closed metal cabinet is a Faraday cage. You must run an antenna cable through a feedthrough to an external or at minimum remote antenna. Some industrial enclosures have purpose-built antenna feedthroughs. If yours does not, IP65-rated cable glands with the correct cable are the right solution. Do not leave gaps or rely on signal leaking through ventilation slots.

Talk to Peter Green

Tell me your router model, location, and application. I will specify the right antenna.

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