Some resources with full-time availability to the organization may have less than 100% availability for project work. For example, a technical resource may normally spend 70% of their time on support and maintenance issue and only have the remaining 30% of their time available for performing scheduled project work.
There are a couple of ways to do this:
1. You can adjust the percentage of a person's work day in their user profile. Go to 'administration,' 'users,' 'resource info' and simply insert the percentage of the person's workday that s/he will be allocated to projects.
2. Establish maintenance projects on a regular basis (i.e. yearly or quarterly projects) with these resources allocated so they show up on resource allocation reports. This allows them to be overallocated, but shows them as overallocated in reports.
An example for managing vacation time similar to using the maintenance project method, read Managing Resource Time Off