A case bay, also seen as case-bay, is a space between two girders. Girders are structural supports used in construction to distribute the weight of a structure and create some rigidity to maintain structural integrity. Another term, tail bay, is used to specifically indicate the space between a girder and a wall. Within a given structure, there can be large numbers of case bays and tail bays, although they are not usually visible once flooring and ceiling materials are installed.
Also called beams, girders are an important part of a structure. They are visible as people start building up and out, providing structural integrity to the frame of the building and offering a surface to walk on as people work on the structure. They may be made from metal, wood, concrete, and engineered materials and are usually very large, coming in I and square shapes, depending on the kind of construction. Placement of girders is determined by architects during the design phase of the structure.
If a case bay is too large, the structure may not be strong and rigid enough as a result of the large blank space in the framing. Putting girders closer together to create smaller case bay spaces will make the structure stronger, but can also result in an excessive number of girders, creating waste during the construction phase. Having girders too closely packed can also be a problem for the structure, as they are extremely heavy and will add to the overall load of the structure and may make it too rigid.
Case bays can create a space for running utilities like plumbing, electrical wiring, and phone in structures where people want to conceal the utility lines. The girders support beams, structural members used to carry the weight of flooring and roofing. The arrangement of girders and beams and the size of each case bay opening can vary, depending on the type of structure and how it will be used, with the goal being an even and safe distribution of weight, without any hot spots created by individual beams or girders taking weight alone or bearing too much weight.
As a structure is worked on, the case bays may also be filled with insulating material to deaden noise, as well as cutting down on energy costs by limiting the flow of heat or cold across barriers like floors and roofs. If utilities are concealed in a case bay, notes will be made in the building plan so utility workers know where to go for maintenance and repairs. Access hatches may also be created to make it easier to get to the case bays.