Own a Commercial Building? Low Slope Roofing Defined

Low slope roofs, otherwise known as flat roofs, are typically installed on larger commercial buildings using a similar process as asphalt shingled roofs, but utilizing different materials.  As a general rule, the low slope installation procedure involves three interconnected components, which include the roof membrane, roof insulation, and the roof deck. The low slope roof system’s two main components - the membrane (or type of surface) and insulation - are applied on top of the roof deck (think wood deck); these three united parts can be defined as the overall roof assembly. 

Roof assemblies with a pitch (slope) of less than a ratio of 3:12 are considered low-slope roofs. Generally speaking, roof assemblies are designed in two basic configurations: compact (“warm”) roofs, and ventilated (“cold”) roofs. Referencing the National Roofing Contractors Association’s Roofing & Waterproofing Manual (5th Edition), compact and ventilated roofs are defined as follows:

  • Compact or warm roof designs are configured with each component placed immediately on top of the preceding component. The insulation is placed directly on top of the deck (or vapor retarder), and the membrane is applied directly on top of rigid insulation. The namecompact is given to these systems because each component is in immediate contact with the adjacent component, and the assembly is thus compact – with no space provided for ventilating the roof assembly.
  • Ventilated or cold roof designs locate the insulation below the deck, allowing for a ventilation space. This space or cavity for ventilation typically occurs above the insulation and below the deck. In ventilated roof designs, the temperature of the membrane and the deck remains close to the outside air temperature, which, in many climates, is typically colder than the temperature inside the building for most months of the year.

There are several factors that need to be considered when deciding which roofing system most completely meets the needs of a particular facility. Some of these conditions are general; others are specific to the building in question. 

Holt’s Commercial Roofing experts provide building owners with a comprehensive explanation of repair and replacement options at no cost.  If you have questions or issues with your current commercial building’s roof, contact us today to set up a no-cost estimate.