In my line of work, I frequently get asked “what causes WiFi interference?”. In a word: everything. WiFi signals in both the 2.4 GHz and 5 GHz ranges are susceptible to all obstructions. It’s just that some cause more interference that others. For example, a dry walled partition isn’t going to slow down your wireless signal much, but a plaster or cement block wall certainly will. Below is a short list of indoor and outdoor obstructions I’ve had to deal with over the past few years when designing, deploying and performing wireless site surveys for various businesses:
WiFi is easy — as long as you have the wireless spectrum all to yourself. For most, people’s experience with WiFi is simply a matter of going to their local Best Buy, buying a consumer grade wireless router and plugging it in at home. If they live in a suburban area where the houses are fairly separated, these people really don’t have much to worry about in terms of interference.