Just installing a roof is not enough- proper roof ventilation makes a huge difference in your summer cooling bills. The flow of air is very important to create good ventilation. Talk to the experts at Triad Installations about our solutions to proper ventilation for your roof. You can read the testimonials of our satisfied customers who have saved on their utility bills after installation of a new roof.
Theory behind venting
The intent of roof venting varies depending on climate, but it is the same if you’re venting the entire attic or if you’re venting only the roof deck. In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent any moisture that moves from the conditioned living space to the attic. (See “Energy Smart Details” in FHB #218 for more on ice dams.)
In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. In mixed climates, ventilation serves either role, depending on the season.
how much ventilation should you have? Without exception, you should talk to a professional to determine what your home requires. Generally speaking, you need a ratio of 1:300, where for every 300 square feet of ceiling space, you need 1 square foot of attic ventilation. That said, air resistance and interference (such as vent grates) reduces the area of true ventilation. In other words, the entire vent opening doesn’t count as vented space.
Understanding Roof Ventilation!
In cold climates, the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow, and to vent moisture that moves from the conditioned space to the attic (ventilation acts to bypass the vapour barrier created by most roof membranes). Melted snow, in this case, is caused by heat loss from the conditioned space. The heat loss is typically a combination of air leakage and conductive losses. The air leakage is due to exfiltration from the conditioned space (often because a ceiling air barrier is not present) and from leaky supply ductwork (often because ductwork located in attics is not well sealed) and from penetrations like non-airtight recessed lights. The conductive losses are usually from supply ductwork and equipment located in attic spaces above ceiling insulation (ductwork is typically insulated only to R-6—whereas ceiling insulation levels are above R-30). Conductive losses also occur directly through insulation, or where insulation is missing or thin.
In hot climates, the primary purpose of attic or roof ventilation is to expel solar heated hot air from the attic to lessen the building cooling load. The amount of cooling provided by a well ventilated roof exposed to the sun is very small. Field monitoring of numerous attics has confirmed that the temperature of the roof sheathing of a unvented roof will rise by a few to no more than 10 F more than a well ventilated atticShare this!