Though there are many types of roofing systems, they are all similar in terms of bidding and requirements for coordinating with other subcontractors.
1. Tapered roof insulation is used on most flat roof construction projects (despite the terminology, flat roofs do have a slight slope, commonly 1/4″– 1/2″ per foot). Roof insulation serves a dual purpose by creating the drainage slope for the roof and by providing thermal roof insulation. Thermal insulating properties of insulation are commonly expressed in terms of an R-value. Roofs are required by code to be constructed with a value of R-30. The R-value may be given as an average of 30 or a minimum of 30 (Figure 20.1). This distinction must be recognized and understood, as it carries a substantial cost impact.