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Glossary of Roofing Terms - J

Jack: See Roof Jack.

Jack Beam: A beam which supports a truss, beam, or other member, dispensing with the need for a supporting column.

Jack Rafter: A rafter which is shorter than the other rafters in the same assembly, typically found in hip or valley locations.

Jack Truss: A truss which supports a beam, truss, or other member, dispensing with the need for a supporting column.

Joint: A location where adjacent surfaces or components meet or are joined together, whether with fasteners, mortar, or in some other way.

Joint Movement: The difference between the minimum and maximum widths of a joint as dictated by building or component movement. This movement is frequently due to thermal expansion and contraction.  

Joint Residue: Accumulated detritus, such as deteriorated masonry or old sealant, that should be removed from a joint prior to the application of sealant.

Joint Sealant: A weatherproof sealant typically used to fill the joints between masonry building components such as tilt-wall sections or expansion joints.  

Joint Tape: Tape used to seal joints between insulation boards.

Joist: Any of the parallel horizontal beams set from wall to wall to support the boards of a floor, ceiling, or roof of a building.

Joist Hanger: A metal bracket or strap used to secure the end of a joist.