Blocking/Unblocking Building Units 
Use
You can block building units by setting the blocking indicator for the building unit in the unit’s planning characteristics. If you set the blocking indicator for a building unit, you must also specify the reason for this block.
You can no longer use blocked building units in subsequent functions. Existing relationships between these building units and other objects are retained.
If you want to release a blocked building unit for further use, you can unblock the building unit.
Procedure
The Maintain Plan. Characteristics of Building Units screen appears with the list of building unit for which you defined planning characteristics.
To unblock the building unit, deselect the Blocking Indicator checkbox, and delete the blocking reason.

You can define blocking reasons of your choosing in Customizing for IS-H. For more information about this, see the section entitled Define Blocking Reasons in the IS-H Implementation Guide.
The system proposes the validity period of the building unit for the validity of the planning characteristics. You can change these dates. However, the validity period of the planning characteristics has to lie within the validity period of the building unit.
You return to the initial screen.
See also:
Maintaining Planning Characteristics