Dade County Building Code (1935)

roof-construction-standards

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descriptionStandards for roof framing, coverings, drainage, and metal roofing specifications in the Miami Building Code.

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Roof Construction Standards

Roof construction standards in the 1935 miami dade building code (1935) mandate that roofs be framed and tied into the building framework to form an integral part of the structure (p. 242). The code specifies requirements for materials, structural design, coverings, drainage, and access, ensuring safety and durability. Section 4305 further details specific requirements for fire-retardant and ordinary roof coverings based on physical properties and installation methods (p. 295). Amendments in the 1940s and 1950s added detailed specifications for metal roofing and siding, as well as updated span tables for wood rafters (p. 335-340).

General Construction

The general requirements for floor construction apply to roofs, with specific exceptions. In Type II buildings, roof sheathing must be at least inches nominal in thickness (p. 242). Precast concrete or gypsum roof slabs must be at least 2 inches thick (p. 242). Reinforced concrete slab roofs must adhere to Chapter 26 specifications and need not be covered with any additional roof covering (p. 242, 297).

Structural Design

  • Trusses: Roof trusses must have well-fitted joints and tightened tension members before loading. Diagonal and sway bracing is required for all trusses (p. 242). Allowable working stresses are defined in Chapters 25 and 27 (p. 242).
  • Rafters: Roof rafters must be anchored as specified in Sections 2208, 2506(f), or 2508(c) and braced per Section 2208 (p. 242). Amendments to Section 2208 introduced specific span tables for roof joists based on fiber stress (1200 psi) and load types (flat vs. tile roofs). For example, 2x6 joists at 12-inch spacing have a maximum allowable span of 11’-0” for flat roofs (40# LL) and 10’-0” for tile roofs (50# LL) (p. 336). The use of 2x4 roof rafters is generally prohibited without specific written permission from the Building Inspector, with a maximum span of 8’-0” and a requirement for #1 grade lumber (p. 336).
  • Ventilation: “Flat-deck” type roof construction requires an air space of at least 18 inches from the top of ceiling joists to the bottom of roof rafters for ventilation (p. 242).

Roof Coverings

Roof coverings are required over all combustible roof construction. The class of covering is determined by Occupancy (Part III), Location (Part IV), and Type of Construction (Part V), as specified in Section 4305 (p. 242). Coverings are classified as “Fire Retardant” (Class A or B) or “Ordinary” (Class C) (p. 295).

Fire Retardant Roofings

“Fire Retardant” roofings must meet Class A or B specifications of the underwriters laboratories or specific physical requirements (p. 295). Acceptable materials and methods include:

  • Composition Roofing: Built from roll roofing, felt, or shingles. Layers must be thoroughly mopped with bituminous compound (air-refined asphalt or coal tar pitch) so no layer touches unmopped (p. 296). Top layers must be mineral-surfaced or covered with gravel/crushed rock (p. 296).
  • Hydraulic Compressed Shingles: Cement and asbestos fibers, at least 1/8 inch thick, laid over saturated felt (p. 296).
  • Metal Roofing: Corrugated, standing seam, or flat type, not less than No. 26 U.S. Gauge (p. 297). See also metal-roofing-and-siding-specifications for detailed amendments.
  • Slate: Securely fastened with non-corrosive nails penetrating at least 3/4 inch into sheathing, laid over saturated felt (p. 297).
  • Tile: Roof tile must absorb no more than 15% water weight and be cemented in place. First three courses must be nailed. Laid over mineral-surfaced roofing felt (p. 297).

Ordinary Roofings

“Ordinary” roofings meet Class C specifications or lighter layer requirements (p. 298). These include:

  • Single layers of No. 41 or No. 82 roll roofing (p. 298).
  • Asphalt shingles (p. 298).
  • Combinations of roofing felt and roll roofing (p. 298).
  • Wood Shingles: Must be 100% heartwood (e.g., red cedar, cypress) and 100% vertical grain. Specific thicknesses are required based on length (e.g., 16” shingles must measure 2” across 5 butts). Exposure to weather is limited to one-third of the shingle length (p. 298-299).

Metal Roofing and Siding Specifications

Amendments to the code (Ordinance No. 3703) provide detailed standards for metal roofing, which may be used as fire-retardant coverings.

  • Steel: Steel roofing may be corrugated, deck, standing seam, V Crimp, or flat type. It must have a protective coating (paint if not exposed to weather; zinc or other non-corrosive metal if exposed). Corrugated steel coated with asphalt and felt is permitted. Stainless steel without coating is approved. The minimum gauge is No. 26 when used on solid wood sheathing. Sheets must be lapped and sealed with mastic cement, fastened with galvanized roofing nails and lead or neoprene washers. If spanning between supports (e.g., purlins) without sheathing, the minimum gauge is No. 24, with corrugations at least 1/2” high. Load capacity must be established by manufacturer’s tables or calculations using a fiber stress of 18,000 psi (p. 339).
  • Aluminum: Aluminum roofing may be used similarly to steel. The minimum gauge is .024 (24 gauge) when used on solid wood sheathing. Without sheathing, the minimum gauge is .027, with corrugations at least 1/2” high. Load capacity must be established using a factor of safety of 2 and a fiber stress not exceeding 12,000 psi. Fasteners must be aluminum, hot-dipped galvanized, or cadmium plated. Aluminum sheets must not be in direct contact with steel members; bitumastic paint or similar coatings are required at contact points (p. 339-340).

Access and Drainage

  • Access: All buildings must provide access to attic spaces and through the roof via stairway, permanent ladder, or scuttle. Openings must be at least 2’x3’ and located in hallways or corridors (except for Group I and J buildings) (p. 242-243). Scuttles in roofs with Class “A” or “B” roofing must have tops and edges covered with approved incombustible material (p. 243).
  • Drainage: Buildings must have metal water downspouts connected to storm sewers or street gutters. If no storm sewer is available, downspouts must connect to a sump at least 3’x3’ and 4 feet deep, located at least 3 feet from footings (p. 243). Downspout diameter must be at least 1 inch per 150 square feet of roof surface, with a minimum of 4 square inches cross-section (p. 243). Weep holes are required where roof decks are enclosed by parapet walls to allow overflow (p. 243).

Protection of Adjoining Properties

When walls are carried up above adjoining roofs, the erecting party must protect the skylights and roofs of adjacent buildings. If the owner refuses permission, they must make their own roofs safe at their own expense (p. 242).

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