It has been my experience that the structural members such as joists and roof trusses used in row houses almost always run from front to rear. This means that the real strength of the building is in the front and rear outside walls, not the shared side walls. There have been several examples of Lancaster City row houses that have had side walls that were struck by a large vehicle, leaving a large hole but not seriously structurally weakening the building. For example, several years ago an out-of-control dump truck punched a hole through the side of a row house at Chestnut and Franklin, which remained unrepaired for far too long while litigation over the damage dragged on. After the unfortunate family lost their home to the bank, the hole was fixed, and the building is now occupied.
Obviously a large commercial building cannot be built using the same criteria. The nearly half-block long Empire building had all of its joists and structural members running between the side walls, which then bear most of the weight of the building. This is why relatively minor damage to the building’s foundation caused so much of the structure to fail; when the century-old rock foundation was weakened by removing the soil which held it straight, it could no longer support the weight of the wall AND the floors AND the roof. With its structural integrity undermined, it fell down like a house of cards.
