Walls, coated glass, insulation, building layout and the frequency band can weaken a usable outdoor signal before it reaches your phone.
The building can be the main obstacle
Reinforced concrete, metal cladding, foil-backed insulation and modern energy-efficient glazing can attenuate radio signals. Basements and internal rooms add more material between the handset and the mast, while lifts and underground car parks can behave like partial metal enclosures.
Frequency affects penetration
Lower-frequency mobile bands generally travel further and penetrate buildings better than higher-frequency bands, although network design, mast position and available capacity still matter. A phone may therefore show fast 5G near a window but fall back to 4G or lose service deeper inside.
Why two people get different results
- They use different networks or MVNO arrangements.
- Their phones support different bands and antenna designs.
- One phone has more suitable operator firmware or carrier settings.
- One line has Wi‑Fi Calling available and the other does not.
- The tests were made at different times or in different parts of the building.
Practical ways to improve reliability
- Test by a window and on a higher floor to confirm whether the structure is the problem.
- Enable Wi‑Fi Calling on a compatible phone and plan.
- Compare another network with a temporary SIM or eSIM.
- Use only a lawful, Ofcom-compliant repeater where there is usable outdoor signal.
- Report a sudden change to the network if service used to work in the same place.
A signal problem caused by the structure is not repaired by repeatedly resetting the phone. Establish the location pattern before changing settings.
How to confirm that the building is responsible
Compare the same phone and SIM immediately outside, by an external window and in the weakest internal room. If performance falls progressively as more structure sits between the phone and outdoors, the pattern supports a building-penetration problem. If service is equally poor outside, investigate network coverage, an outage or device compatibility instead.
How to tell whether the change actually worked
Compare the same phone immediately outside and inside the building. A sharp change points towards building loss, while similar failure across a wider area may indicate coverage or an outage. Record the affected floor, room, window position and whether Wi‑Fi Calling remains dependable.
- Remove a thick or metallic case only as a controlled comparison.
- Check another network before buying hardware.
- Do not install an unapproved repeater.
Official sources
- Ofcom — Improving your indoor coverage
- Ofcom — Using a repeater to improve indoor mobile signal
- Ofcom — Map Your Mobile
Facts checked: 25 July 2026. Network features, device menus and coverage can change. Recheck your exact phone model, software version, network and plan before relying on a feature.
