Much protective construction is not built on an empty site. It goes into a building that already exists, often one that has to stay open while the work happens: a courthouse that cannot close, a clinic that sees patients every day, an administration building whose staff have nowhere else to sit. Retrofit work answers to the same threat as new construction, but the decisions that govern it are different, and most of them are about the building rather than the protective material.
This note is written for facility owners, engineers, specifiers and contracting officers planning ballistic protection inside an occupied building. It covers the order in which the questions should be settled and the points where retrofit projects most often lose protection between the drawings and the finished room.
Start with the protected line, not the product
The first decision is where protection has to be. In a retrofit that is rarely the whole building. It is usually a line around a defined space: a reception and screening point, a secure work area, a safe room, a records room, a control room or a set of offices. The threat assessment should say what that space is protecting against, written as a threat: the round, the number of shots and their spacing, and the standard and edition that defines it. UL 752 and NIJ-STD-0108.01 are the usual references for ballistic threat definitions. Whether forced entry or blast is also in scope should be stated at the same time, because each changes the assembly.
Once the line is drawn, walk it on the existing drawings and then in the building. Every wall, door, window, transaction opening, duct and cable that crosses it is part of the protected assembly. A retrofit that hardens three walls of a room and leaves the fourth, or the ceiling above it, has not protected the room.
Know what the existing building is
An existing building brings conditions that a new design would never choose, and the retrofit has to start from them rather than from the drawings alone.
- Construction type. Steel stud and gypsum partitions, unreinforced or reinforced masonry, cast-in-place concrete and precast panels each accept added protection differently. Record drawings are a starting point. Selective investigation confirms what is actually behind the finish.
- Structural capacity. Protective materials add mass. A floor slab, beam or foundation that was sized for an office partition may not carry a new protective wall without reinforcement. A structural engineer should confirm the load path before the material is selected, not after.
- Fire and life safety. Adding a protective layer to a fire-rated wall, or creating a new enclosed room, can change the basis of the existing rating, egress routes and sprinkler coverage. Someone should be named in the specification to evaluate that against the applicable code.
- Hazardous materials. Older buildings may contain asbestos or lead in the finishes and assemblies the work will disturb. A survey before design, which federal and state asbestos rules require before many renovations, reduces the risk of a stop-work order in the middle of construction.