How to: Add a project output reference
To deploy non-SharePoint project assemblies (or .xap files in Silverlight projects) to SharePoint, add them as a project output reference.
This process creates a solution build dependency between the two projects. Projects associated with project output references are built before the SharePoint project is built and deployed.
To add a project output reference
Load a solution that contains at least one SharePoint project and one non-SharePoint project.
In Solution Explorer, choose an item in the SharePoint project node.
In the Properties window, choose the Project Output References property, and then choose the ellipsis () button next to it.
In the Project Output References dialog box, choose the Add button.
In the properties pane, choose the arrow next to the Deployment Type property, and then choose an appropriate value for the non-SharePoint item you are referencing, such as ElementFile.
Choose the arrow next to Project Name, choose the name of the non-SharePoint project item, and then choose the OK button.