It would all be in the truss engineering package.
Some trusses are designed to receive an attic floor and be used for storage, they just need to be designed for that.
Try this, though.
From the 2006 IRC. (underlining is mine)
- R802.10.4 Alterations to trusses.
Truss members shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional. Alterations resulting in the addition of load (e.g., HVAC equipment, water heater) that exceeds the design load for the truss shall not be permitted without verification that the truss is capable of supporting such additional loading.