Building Systems Design Notes

Excavation and Fills

  • Excavation and fills for structures must not endanger life or property.
  • Excavation requires ensuring adjoining property's soil stability.
  • Excavations on public property must be restored within 48 hours, unless the Building Official permits otherwise.
  • Contact all public utilities before excavation to locate underground facilities.
  • Permanent excavation and fill slopes should not exceed a 2:1 (horizontal to vertical) ratio.

Footings, Foundations, and Retaining Walls

  • Footings and foundations must be appropriate and adequate to sustain superimposed loads under seismic or external forces.
  • Retaining walls are required where abrupt ground level changes may cause soil instability.
  • Retaining walls restrain soil to a slope it would not naturally keep.

Floor Construction

  • Floors must be integrated into the framework and supporting walls.
  • Floor construction should prevent beam and girder lateral buckling.

Roof Construction and Covering

  • Roof coverings must be fire-retardant or ordinary, based on fire-resistive requirements.
  • Roof trusses should have well-fitted joints and tension members, with diagonal and sway bracing.
  • Roof drains, adequate for water discharge, should be at low points, preventing water flow onto public property (except Group A and J Occupancies).
  • Flashing and counterflashing are required at roof and vertical surface junctions.

Stairs, Exits, and Occupant Loads

  • Stair and exit construction must meet occupant load requirements.
  • Occupant Load: Maximum people allowed in a space; calculation uses Floor Area / Unit Area per Occupant.
  • Refer to Table XII.1 for Unit Area per Occupant values.
  • Exit needs are determined by the largest occupant load.
  • Exits should remain unobstructed, excluding code-permitted projections.
  • Every building should have at least one exit.
  • Upper floors (over 10 occupants) must have at least two exits.
  • Floors with 500-999 occupants need at least 3 exits.
  • Floors with 1000+ occupants need at least 4 exits.
  • Total Exit Width = \frac{Occupant Load}{165}
  • If two exits are required, separate them by at least 1/5 of the area's perimeter; arrange three or more at reasonable distances.
  • Maximum travel distance to an exit: 45m (without sprinkler system), 60m (with sprinkler system).
  • Exit doors must open from the inside without keys or special effort.
  • Exit Door Dimensions:
    • Minimum Width: 0.90m
    • Minimum Height: 2.00m
    • Opening: at least 90 degrees
    • Maximum Leaf Width: 1.20m
  • Prohibited Exit Doors: Revolving, sliding, and overhead doors.
  • A floor or landing should be on each side of an exit door, no more than 50mm lower than the threshold.
  • Corridors/exit balconies should be at least 1.10m wide.
  • Stairway Width Requirements:
    • More than 50 occupants: 1.10 meters
    • 50 or fewer occupants: 0.90 meter
    • Less than 10 occupants: 0.75 meter
  • Handrails should not reduce stairway width by more than 100mm.
  • Maximum Stair Riser: 200mm
  • Minimum Stair Tread: 250mm
  • Minimum Stairway Headroom: 2m (from the nosing).
  • Landing length equals stairway width; no more than 1.20 meters for straight runs.
  • Maximum vertical distance between landings: 3.60 meters.
  • Handrails are needed on both sides; intermediate handrails required for stairways over 3 meters wide.
  • Handrail height: 800-900 millimeters above the nosing.
  • Handrail Exemptions: certain Group A/B occupancies, and stairways with fewer than four risers.
  • Winding Stairways: Allowed if the required tread (250mm) is provided 300mm from the narrow end; no tread should be below 150mm.
  • Circular Stairways: Can be exits if minimum tread width is 250mm.
  • Mezzanine floors over 185m^2 or 18m in dimension need at least two stairways.
  • Aisles must be available in buildings with seating, tables, etc., leading to an exit.
  • Aisle width: at least 0.80 meter (one side), 1.00 meter (both sides).
  • Maximum aisle travel distance to an exit: 45 meters.
  • Maximum of 7 seats between wall and aisle, or 14 seats between two aisles.
  • Seat Spacing: Minimum 840mm back-to-back, with seat width not less than 450mm.

Penthouses and Roof Structures

  • Penthouses on non-Type V structures cannot exceed 8.40 meters above the roof (for tanks or elevators).
  • Penthouses should only shelter mechanical equipment or vertical shaft openings.