With this modified RF24 module It could go through four walls with a distance of about 100 feet.
This module should also nearly double the distance over a standard nRF24 module when used with line of sight applications; like RF planes, quad-coppers, cars and boats (100s of meters). I have not made any clear line of sight tests. In my tests there were kitchen appliances and cabinets and closets full of stuff between the transceivers.
Checkout this instructable : Enhanced NRF24L01 radio with a DIY Dipole Antenna modification..