how to communicate two xbee in closed room?



we are using a xbee s1. but our main problem is closed room not communicate a two xbees?table top is inside a room and display is outside.

we are tested two xbee modules within a room. Then they communicated without a problem. But when we tested those modules by keeping it in different rooms, there was no communication.

It almost sounds like there is enough attenuation in the building structure to block the signal. What is the wall made from and how far do you want to go?