When are decks required to have guard rails?

The requirement for guard rails on decks is established primarily for safety reasons, aimed at preventing falls from elevated structures. In Virginia, the building codes mandate that guard rails must be installed when a deck is higher than 30 inches above the ground. This height is considered the threshold where the risk of injury from falling increases significantly, particularly for children and individuals who may be less stable.

Option B aligns with the standard safety regulations that are intended to protect both the homeowners and any guests. Building codes take into account various factors including the average height of a fall and the likelihood of an individual inadvertently leaning or falling over the edge of a deck.

The other heights listed in the other answer choices do not meet the mandated requirement as established in the building codes. Heights lower than 30 inches may not justify the same level of hazard due to the generally reduced risk of serious injury from such falls, which is why these options are not correct in this context.