Key takeaways
- That is why energy-efficient, green-rated buildings often have worse indoor mobile coverage than older ones.
- Mobile signals between 700 and 2700 MHz are radio waves, so a coating designed to reflect infrared also reflects a large share of mobile signal.
- A drop of 15–20 dB or more between the two points to the façade.
- IT parks, corporate offices and co-working spaces with curtain-wall glazing.
Glass offices look as if they should be full of signal. They aren't. Many workers in shiny new business parks and IT towers find that calls drop at their desks while the old brick building next door does fine. The reason is the glass. Modern energy-saving glass is coated with ultra-thin metal layers that reflect heat, and they reflect mobile signal along with it.
Quick answer
- Low-emissivity (low-E) and solar-control glass carry microscopic metal or metal-oxide coatings that reflect heat, and radio signals too.
- Coated double glazing can cut mobile signal far more than clear glass, often on the order of tens of decibels.
- That is why energy-efficient, green-rated buildings often have worse indoor mobile coverage than older ones.
- The fix is to collect signal outside the glass envelope (roof or façade) and distribute it inside with a signal booster.
What is low-E glass, and why is it everywhere?
Low-emissivity glass has an invisible coating, often containing silver or other metal oxides, a few nanometres thick. It lets visible light through but reflects much of the infrared heat. In India's climate, that means cooler interiors and lower air-conditioning bills, which is why low-E and solar-control glass have become standard in new offices, hotels, hospitals and premium apartments, and why they help buildings earn green ratings.
Why does it block mobile signal?
Thin metal layers conduct electricity, and conductive surfaces reflect radio waves. Mobile signals between 700 and 2700 MHz are radio waves, so a coating designed to reflect infrared also reflects a large share of mobile signal. Double or triple glazing with coatings on more than one pane makes it worse.
| Building material | Typical effect on mobile signal |
|---|---|
| Clear single glass | Small loss |
| Brick wall | Moderate loss |
| Reinforced concrete wall or slab | High loss |
| Low-E or reflective coated glass | High loss, sometimes similar to concrete |
| Coated double-glazed units | Very high loss |
| Metal cladding panels | Very high loss |
The exact loss depends on the coating, the frequency and the angle, but the pattern is consistent: the more energy-efficient the façade, the harder it is for mobile signal to get in.
Signs your building has a "glass problem"
- Strong signal on the pavement outside the building, weak signal as soon as you walk in.
- Better signal near open doors, terraces or a broken or open window than near closed glass.
- Older buildings nearby with ordinary windows have better indoor coverage.
- Desks at the window aren't much better than desks in the middle of the floor.
Measure it: take a dBm reading outside the entrance and another at a window desk. Our signal strength checker shows how. A drop of 15–20 dB or more between the two points to the façade.
Which buildings are affected?
- IT parks, corporate offices and co-working spaces with curtain-wall glazing.
- Showrooms, car dealerships and malls with large glass fronts.
- New hotels and hospitals designed for energy efficiency.
- Premium apartments with full-height glazed windows and balconies.
How do you fix weak signal in a glass building?
You can't fix it by removing the glass, and you shouldn't: it saves energy. The answer is to go around the glass:
- Put the outdoor antenna outside the envelope, on the roof or a façade bracket, where signal is strong.
- Run low-loss cable through an existing service shaft into the floor that needs coverage.
- Amplify with a booster matched to your operators and floor area.
- Distribute inside with ceiling dome antennas above false ceilings, or panel antennas on walls.
A bonus: the same glass that keeps signal out also helps keep the boosted signal in, so indoor antennas cover the floor efficiently.
For a typical office floor, a high-gain multi-operator kit like the SIGLIFT SL-850-27DB covers up to 10,000 sq.ft. For a single showroom or apartment, a compact kit is usually enough. See our page on network boosters for offices, and the installation guide for antenna placement.
Tips for builders and architects
- Plan in-building coverage at design stage: reserve shaft space and rooftop mounting points for antennas.
- Specify a cable route to each floor so coverage can be added without breaking finished ceilings.
- Test signal in the first finished floor before the whole façade goes up, while changes are still cheap.
Frequently asked questions
Does tinted window film block mobile signal?
Some do. Metallised solar films contain metal layers and can reduce signal noticeably, while non-metallic ceramic or dyed films have less effect. If signal fell after a film was installed, the film is a likely cause.
Why is my phone signal worse in a new office than in my old one?
New buildings often use low-E glass, metal cladding and heavier construction for energy efficiency and safety. All of these block mobile signal more than older brick and clear-glass buildings.
Will sitting near the window help in a glass building?
Less than you'd expect. With coated glass, the window itself is a barrier. Open doors, terraces and balconies help more than closed glass.
Can a booster cover several office floors?
Each floor needs its own indoor antennas, because concrete slabs block signal between floors. One kit with splitters can serve a few floors in a small building; larger buildings use a kit per floor or zone.
Working behind glass with no signal? Send SIGLIFT your building's location, floor area and a couple of signal readings on WhatsApp at +91-9650237601 for a free coverage plan. Trusted by customers like the High Court of Delhi, DLF and PVR Cinemas.
Written by the SIGLIFT technical team — mobile signal booster specialists for Indian networks. Last updated . Questions? Talk to us.
