Building Planning and Construction Types (Chapters 5 and 6)
Heights, areas, and what "Type" means
Chapter 6 defines the five construction types - I and II (noncombustible), III (exterior noncombustible), IV (heavy timber, now including mass timber provisions), and V (combustible) - each split into A (protected, higher-rated) and B (unprotected or lower-rated) categories for I, II, III, and V. Chapter 5 then combines occupancy group with construction type to produce allowable height in feet, allowable stories, and allowable area per story.
Layer the increases in a fixed order:
- Start with the tabular height, stories, and area for the occupancy/type pair.
- Apply the sprinkler increase to height and number of stories and to allowable area.
- Apply the frontage increase where the building fronts on public ways or open space of adequate width.
- Check special allowances: unlimited-area buildings, mezzanines (which usually do not count as stories), basements, and parking beneath.
Traps
- Sprinklers are not a free pass - the increase is limited and depends on full NFPA 13 coverage, not partial protection.
- Frontage increase is calculated, not assumed. Perimeter open space must be measured properly and the increase caps out.
- Mezzanines are not stories, but they count toward area and must comply with the mezzanine provisions.
- Area is per story, and multi-story buildings use a ratio calculation rather than simply comparing one floor to the table.
Worked example / rule of thumb
A fully sprinklered, Type V-B, Group B building sits on a site where half the perimeter fronts a public way. The tabular area is modest, but the building gains the sprinkler area increase (a doubling, not a tripling) plus a calculated frontage increase before comparing to the actual floor area. Rule of thumb: calculate the base number first and write it down; every increase is applied to that written base so you do not compound multipliers incorrectly.