Dade County Building Code (1935)

floor-construction-standards

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descriptionStandards for floor construction materials, spans, and fire-resistive requirements in the Miami Building Code.

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Floor Construction Standards

Floor construction standards in the 1935-miami-dade-building-code specify material requirements, structural integrity, and fire-resistive measures to ensure safety and durability. These standards apply to various floor types, including concrete, steel joisted, mill constructed, and wood joisted floors. Amendments in the late 1940s and 1950 introduced specific span tables for wood joists and detailed specifications for cellular steel floors.

General Requirements

All floors must be framed and tied into the framework and supporting walls to form an integral part of the building (p. 240). The type of floor construction is determined by occupancy and construction type, with specific fire-resistive standards outlined in Section 4303 (p. 240). To prevent separation of beams and girders, ties or bridging must be installed (p. 240).

Concrete Floors

Concrete rib slab floors must be at least 2.5 inches thick, while solid concrete floors must be no less than 4 inches thick (p. 240). Topping poured monolithically with the slab can be included as a structural part. Sleepers for wood flooring must not decrease the required structural depth unless placed in the direction of span and limited to 0.5 inch penetration (p. 240). Concrete joists exceeding 20 feet in length require one row of concrete bridging for lateral support (p. 240).

Steel Joisted Floors

In Type I or Type II buildings, steel joisted floors must have a reinforced concrete or gypsum slab at least 2.5 inches thick on top and a fire-resistive ceiling on the underside (p. 240). The slab must be sufficiently reinforced to support all loads between joists. Joists with solid webs are exempt from cross-bridging requirements, but other joists must be cross-bridged at intervals not exceeding 8 feet (p. 240). The lateral unsupported length at the top chord must not exceed 40 times the width of any compression flange (p. 240).

Cellular Steel Floors

Ordinance No. 3334 (1947) introduced specific standards for cellular steel floors, which consist of sheet or strip steel formed into an integrated system of parallel steel beams acting as both load-bearing members and continuous deck (p. 331).

  • Fire Resistance: In fire-resistive construction, these floors must have a minimum of two inches of concrete fill on top and a fire-resistive ceiling suspended from the underside, meeting national-board-of-fire-underwriters ratings (p. 331).
  • Material Specifications: Steel must meet american-society-for-testing-materials “Tentative Specifications for Light Gauge Structural Quality Flat Hot-Rolled Carbon Steel” (A24542T), Grades A, B, or C (p. 331). The thickness must be no less than U.S. Standard Gauge No. 18 (p. 331).
  • Structural Analysis: Floors must admit of rational analysis and be tested/certified by a recognized agency. Flexural stress values cannot exceed 60% of the yield point. If plastered ceilings are suspended, maximum deflection under full live load shall not exceed 1/360 of the span (p. 331-332).

Mill Constructed Floors

Mill constructed floors require at least 3 inches nominal spliced or tongued and grooved plank covered with 1 inch nominal flooring laid crosswise or diagonally (p. 241). A 0.5 inch space must be left between the flooring and walls to allow for swelling, covered by a molding (p. 241). Laminated floors using planks at least 6 inches wide set on edge must have broken joints to avoid continuous lines across the floor and must not be spiked to supporting girders (p. 241). Floor timbers must be at least 6 inches nominal in any cross-sectional dimension (p. 241).

Wood Joisted Floors

Wood joisted floors must be framed and anchored to supporting walls as specified in Chapter 25 (p. 241). Fire protection on the underside is not required unless specified by occupancy, location, or construction type (p. 241).

Span Tables

Ordinance No. 3703 (1949) added detailed tables for maximum allowable spans for wood joists in Type V buildings, based on a fiber stress of 1200 psi (p. 335-337).

  • Floor Joists: Spans vary by joist size (2x6 to 2x12) and spacing (12” or 16”), with different limits for 50# live load (second floor), 40# live load (first floor), and 30# live load (ceiling) (p. 335, 337). For example, a 2x10 joist at 12” spacing allows a span of 18’-0” for 50# LL and 22’-0” for 30# LL (p. 337).
  • Roof Joists: Similar tables apply to roof construction, with limits for flat roofs (40# LL) and tile roofs (50# LL) (p. 336).
  • Additional Sizes: An additional table covers 3x6, 4x6, 3x8, 4x8, and 3x10 joists, including spans for 10# live load (ceiling without usable attic) (p. 337).
  • Restrictions: 2x4 roof rafters are generally prohibited unless specifically permitted in writing by the building-inspector, with a maximum span of 8’-0” and #1 grade requirement (p. 336).

Specialized Floors

Public toilet floors must be made of impervious or non-absorbent materials such as asphalt, glass, marble, vitrified tile, or terrazo (p. 241). Public garages and service stations must have approved grease drains or traps in areas used for washing, polishing, or greasing automobiles (p. 241).

See also: 1935-Miami-Dade-Building-Code_p285_304

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