Final answer:
The question is related to building codes specifically addressing the height restrictions and egress requirements for certain residential dwellings. The IBC or IRC set forth regulations that must be adhered to, including size, height, and setbacks from boundaries.
Step-by-step explanation:
The question pertains to the code requirements for detached one- and two-family dwellings as well as multiple single-family dwellings (townhouses), specifically focusing on their height restrictions in relation to the number of permissible stories above the grade plane. Codes like the International Building Code (IBC) or International Residential Code (IRC) establish criteria for the size and height of buildings, including accessory structures, to ensure safety and maintain uniformity in building practices. These codes often include provisions regarding building setbacks from streets and boundaries, which dictate the distance between a building and the property line, and can also influence the number of rooms and overall layout of a dwelling.
While the exact number of stories allowed above grade plane for these dwellings is not provided in the question, it is implied to be limited to ensure a "separate means of egress," which is crucial for occupants' safety, particularly in emergencies. Such restrictions are intended not only for the safety of the residents but also to manage the urban form and ensure compatibility with the surrounding community.