Ceiling joists must have bearing support similar to that of rafters. The bearing must be Ш" on wood or metal, and not less than 3" on masonry or concrete.
The most important thing to remember about ceiling joists is that if they are used to tie the rafterbearing walls at opposite ends of the building, then those joists must be securely attached to the walls, to the rafters, and to each other at the laps. If the ceiling joists do not run parallel with the rafters, an equivalent rafter tie must be installed to provide a continuous tie across the building.
The IRC calls for a minimum ceiling clearance of 7′. The IBC requires 7′-6" with the exception of bathrooms, kitchens, laundry, and storage rooms, where it can be 7′.
There are three exceptions to this rule. First, beams or girders can project 6" below the required ceiling height if they are spaced more than 4′ apart. The second exception is for basements without habitable spaces. These may have a minimum height of 6′-8" and may have beams, girders, ducts, and other obstructions at 6′-4" in height. The third exception is for a sloped ceiling. Fifty percent of the sloped ceiling room area can be less than the minimum ceiling height. However, any portion of the room less than 5′ in height cannot be included in figuring the room area. (See "Ceiling Heights" illustration later in this chapter.)
Trusses are an engineered product. This means that an engineer or design professional must design them for each job to form a roof/ceiling system. Components and members of the trusses should not be notched, cut, drilled, spliced, or altered in any way without the approval of a registered design professional.
