Hollow wall construction refers to walls built using hollow clay tile, concrete block or tile, hollow walls of solid masonry units, and hollow monolithic plain concrete. The 1935 Miami Dade Building Code p225 244 outlines specific regulations for these structures to ensure stability and fire resistance.
General Provisions and Support
Hollow walls must be supported at right angles to the face at intervals not exceeding sixteen (16) feet, unless the building-inspector grants discretion (p. 226). Lateral supports may include cross walls, piers, or buttresses. If piers or buttresses are used for lateral support, they must be of reinforced concrete or structural steel and poured with the ends of the spandrel wall sections acting as forms (p. 226). Walls dependent on floors for lateral support require provisions to transfer lateral forces to the ground (p. 227).
Thickness and Height
The minimum thickness of hollow walls is determined by height and story level, as specified in Table No. 4 (p. 227). Key requirements include:
- The uppermost twenty-five (25) feet of such walls shall not be less than twelve (12) inches thick (p. 227).
- Each successive twenty-five (25) feet measured downward from the top must increase thickness by at least four (4) inches (p. 227).
- One-story private garages and residences may have eight (8) inch thick hollow walls (p. 228).
- Grade A hollow clay tile or Grade A Special hollow concrete block may match solid masonry wall thicknesses if not exceeding two stories (p. 228).
Air Spaces and Materials
When air spaces are incorporated, the combined area of air spaces and cellular space in the tile must not exceed forty-five (45) percent of the gross cross-sectional area of the wall (p. 227). Masonry walls combining solid and hollow units must meet the minimum thickness requirements for hollow walls (p. 227). All materials must conform to Chapters 24 and 26 of the code (p. 227).
Bonding and Piers
- Bond: All contact surfaces of hollow masonry units must be solidly embedded in mortar with a full bond (p. 228). If multiple units make up wall thickness, inner and outer courses must bond at vertical intervals not exceeding three courses (p. 228).
- Piers: Hollow tile or concrete block cannot be used for isolated piers unless cells are filled with cement grout or concrete and reinforced with at least four 3/8” bars anchored into the foundation (p. 228). Grade A hollow clay tile is exempt from this reinforcement requirement (p. 228).
Chases, Recesses, and Fire Walls
Chases and recesses in hollow walls are permitted only to the extent allowed for solid masonry walls under similar conditions (p. 228). They must be built in, not cut out. No chases or recesses are permitted in fire walls if they reduce thickness below code minimums (p. 228).
Hollow masonry fire walls are prohibited in fire-zones No. 1 (p. 235). Otherwise, they must be at least sixteen (16) inches thick, or twelve (12) inches for Group H and I buildings (p. 235). Combustible members framing into hollow fire walls must not project more than four inches, and spaces around them must be filled with fire-resistive materials (p. 235).
Related Concepts
- masonry-wall-construction
- reinforced-concrete-wall-design
- fire-wall-construction
- 1935-Miami-Dade-Building-Code_p225_244