Star Bolts
Have you ever noticed eye-catching stars positioned on the fronts of masonry row homes in urban areas, such as Philadelphia, New York, Baltimore, and various other cities? The stars are not just ornamental; they are also functional.
From colonial times through post World War I, many buildings were made of load-bearing brick masonry and timber. Residential buildings of the eras, commonly known as row homes, were made of brick masonry walls and wood-framed floors and roofs. The wood framing, known as joists, often spanned side-to-side of the structures. The ends of the joists were seated in pockets in the masonry walls. Good quality construction also included iron anchors between the joist ends and masonry walls.
The joists braced the multi-story masonry “party” walls, but the framing configuration left the front and back masonry walls in need of alternative bracing techniques. The bracing techniques were required to overcome the tendency of the multi-story masonry walls to buckle. A common alternative technique included iron anchors similar the those mentioned above, except the alternative anchors were much longer to engage numerous parallel joists. Alas, nothing lasts forever. This holds true for building materials — especially iron encased in masonry that experiences countless cycles of wetting and drying by being an exterior mass wall (that’s a topic for another day). Over time, the iron anchors would decay and lose their effectiveness to brace the front and back masonry walls.
In the absence of sufficient bracing, the walls will begin to bow or buckle. If the problem is noticed before the buckling wall falls, a new anchor can be installed through the wall. The anchor includes a metal rod/tie, which passes through the masonry wall and engages a series of joists. Given certain constraints and details, wood blocking may be added between the joists to resist the horizontal force from the anchor. A “washer” is installed over the end of the rod that protrudes through the masonry wall. The intent of the washer is to distribute pressure on the brick masonry. A nut is then placed over the washer to tighten the assembly and brace the wall.
Inside the building, the anchor is often concealed in a floor cavity. However, outside the wall, the anchor would be clearly visible. To improve the distribution of pressure on the brick masonry and better brace the wall, a star shape is used. The star shape also serves to increase the visual appeal of the anchor.
While the star is actually a washer in this arrangement, the entire assembly is often referred to as a star bolt. The next time you are walking down a city street, watch for a star bolt or two...now you know that they are not just aesthetic; they are also functional.
