The Forgotten Cool Roof
Above Sheathing Ventilation
ASV is the concept of ventilating the air space between the roof cladding material, the roof deck, and subassembly. This allows the roof cladding temperature to be closer to the outdoor ambient temperature and reduces heat gain passing through the insulation during summertime scenarios.
• Roofs experience much higher temperature fluctuations than any other surface
• Higher than ambient during sunny days, by 50°F or more
• Lower than ambient during dry, cloudless nights by 10-20°F
• Ventilation mitigates this effect
• Decouples thermal connection between panel and insulation
• Always works to push roof temperature toward ambient outdoor temperature
• Ventilation may be natural, forced, or throttled • Solar gain drives ASV; the higher the solar gain, the more air flows through the cavity
