I successfully use Wifi through one concrete wall for streams up to 15 Mbit/s. You will need a Wifi monitor to find the best channel (1, 6 or 11)
Client: Dual Antenna 2.4 GHz WLAN-N USB Adapter for RPi2/Libreelec (tried 5GHz as well, works also, but less signal strength, less software stability)
Access Points that work rock solid: Dedicated AP like WD My Net N900 or Apple Mac Mini server late 2012
Access Points that did not work reliably: Any Linux/hostapd solution, main internet router providing lots of service at the same time.