Neighbors' Wi-Fi slowing yours: interference in apartment buildings

Open the Wi-Fi settings in an apartment and you'll see a long list of networks: the flat next door, upstairs, downstairs, across the hall. Each one is a router talking on the same limited set of channels as yours. That's why Wi-Fi in a building can be fine on a Sunday morning and poor every weeknight.

How neighbors affect your Wi-Fi

Wi-Fi is polite: before transmitting, a device listens, and if the channel is busy it waits. When a neighbor's router is on the same channel, your devices and theirs take turns. The more networks nearby, the more waiting.

• On 2.4 GHz there are only three channels that don't overlap. In a building, every one of them is shared by several networks.
• On 5 GHz there are many more channels, and walls weaken each network faster, so your neighbors' signals reach you less.
• Evenings are worst, because that's when everyone is streaming.

The symptoms look like weak coverage but aren't: response times that jump around, occasional lost requests, speed that varies by the hour even in the room next to the router. See full bars but slow Wi-Fi.

Why a louder router doesn't win

Turning up transmit power, or buying a router with bigger antennas, doesn't give you priority. It mostly makes your network another loud voice in the same crowded room, and your phone still has to answer at its own, much lower volume.

What actually helps

1. Use 5 GHz wherever you can. In an apartment the distances are short enough, and the band is far less crowded. See 2.4 GHz vs 5 GHz by room.
2. Keep the router in the middle of your apartment, not against the wall you share with a neighbor. Your coverage stays inside your walls and theirs has to cross more of them. See where to put the router in an apartment.
3. Leave channel selection on automatic, and restart the router occasionally so it re-evaluates. Modern routers do this reasonably well; hand-picking a channel helps only until the neighbors' routers move.
4. Keep 2.4 GHz narrow. If your router lets you set channel width, 20 MHz on 2.4 GHz overlaps less with everyone else.
5. Wire what doesn't move. A TV, console or desktop on a cable is one less device competing for airtime.

Measure at the busy hour

Interference changes through the day, so a single test at lunchtime can mislead you. WiFi Heatmap measures response time, its variation and lost requests; map your flat once in the morning and once at nine in the evening. If the same rooms get much worse at night with the router untouched, the problem is the building, and the fixes above are the ones that help.