R305.1 & 305.1.1

Sections R305.1 and R305.1.1 are titled 'Minimum height' and 'Basements' and covers the requirements for ceiling heights. Minimum ceiling height for specified areas of a dwelling is established. The purpose of this section is to provide for general health and well being, as well as to provide space for smoke to dissipate in the event of a fire, which allows occupants time to escape before being overcome by smoke. Section R305.1 has 3 exceptions and R305.1.1 has 1 exception which allows for a limited reduction in ceiling height in specified areas. The purpose of all the exceptions is to allow for a practical application of construction.

The model shows a section of a one-story dwelling with a basement and an attic with the minimum allowed ceiling height labeled for each area. The main level has habitable rooms, a hallway, and a bathroom. The bathroom has areas with a reduced ceiling height per exception #2. The attic contains a 70 sq. ft., square habitable room with a sloped ceiling height reduction allowed per exception #1. (The floor is highlighted to denote the room split in half, showing that at least 50% of the room has a ceiling height of 7 feet.) The basement contains a habitable room, a hallway, a laundry room, and other non-habitable space, as well as ducts projecting into the habitable room, hallway, and non-habitable rooms as allowed per exception #3 to R305.1 and the exception to R305.1.1. It is prudent during the plan review to check how ducts are going to be run in a basement, especially where they cross beams, to assure ceiling height will be compliant.