Factors Affecting Range and Performance of All Wireless LAN Systems
Range estimates are typical and require line of sight. Basically that means you will need a clear unobstructed view of the antenna from the remote point in the link.

Keep in mind that walls and obstacles will limit your operating range and could even prevent you from establishing a link. 

Signals generally will not penetrate metal or concrete walls.

Trees and leaves are obstructions to 802.11 frequencies so they will partially or entirely block the signal.

Other factors that will reduce range and affect coverage area include metal studs in walls, concrete fiberboard walls, aluminum siding, foil-backed insulation in the walls or under the siding, pipes and electrical wiring, furniture and sources of interference.

The primary source of interference in the home will be the microwave oven.

Other sources include other wireless equipment, cordless phones, radio transmitters and other electrical equipment.

Due to the increased gain, installing range extender antennas in the presence of interference could actually yield equal or worse range.