Refer to figure.
If a helicopter is hovering near the ground, some of the air passing through the rotor disc is recirculated. The recirculated air increases speed, if it passes through the rotor disc twice or more. This local increase of the Induced Airflow near the blade tips causes a loss of total rotor thrust.

Recirculation is always taking place to some degree, but over a flat even surface the loss of thrust due to recirculation is more than compensated for by the ground effect.

Buildings and hangars will increase recirculation on one side of the rotor disc and can effectively “suck” the helicopter towards the obstruction. If the helicopter is closer than a third of the disc diameter, the advancing blade is also affected, pulling towards the building, because the lift is disturbed on that side and becomes less effective.

Where the downflow is prevented from escaping properly, as when hovering near an obstruction, the effect will be to tilt you 90° from where recirculation was introduced, or even pull you down if all sides are affected (like in a courtyard), so a lot more power will be required.

Thus, when hovering in front of a building, the recirculation occurs at the front, but the disc will tilt to the left and make the left skid hover lower than usual.