Decks

While reflective single-ply roof membranes and high-thermal roof insulations seem to have captured current interest in low slope roofing, they are just two of many items to be considered by facility managers in a roofing system.

Not only that, but roughly two-thirds of all low-slope roofing activity involves replacement or renovation. In these cases, there may be no designer of record, and critical information about the structure and roof may have been lost over time.

Since the foundation of any roof system is the roof deck, this column will focus on several of the roof deck systems that a building manager might encounter when contemplating roof work.

In addition to resisting gravity loads and lateral loading from wind and seismic forces, a building’s structural deck must satisfy these other design requirements:

  • Deflection resistance
  • Component anchorage technique
  • Dimensional stability
  • Fire resistance
  • Surface characteristic

While all these attributes may have been addressed by the building designer on the drawing board, the building manager needs to know what is overhead and what its current condition is. Things may have changed over time. Examples would be the conditions of occupancy, high interior humidity, corrosion of fasteners or the deck itself, installation of new equipment on the roof, types of roof membranes in place (especially if the roof has been re-covered since the original occupancy), and much more.

The basic roof decks commonly used with commercial membrane roofing systems are:

  • Steel – light-gauge, cold-rolled sections, welded or screwed to bar joists 
  • Wood sheathing – sawed lumber, plywood or OSB (oriented strand board)
  • Concrete – poured-in-place or precast
  • Gypsum – precast or poured-in-place
  • Cementitious wood fiber 
  • Composite decks of lightweight insulating concrete on corrugated steel or form boards
  • Thermoset, compacted asphalt fills