You know that roofers install vents on residential roofs, but what about your commercial flat roof? How much ventilation does a flat roof need? The answer depends on the type of roof you have: a cold roof or hot roof.
Any type of roof, from TPO to EPDM, can be either hot or cold. It depends on where the insulation is installed. Hot roofs have the roof deck, then insulation, then the roofing material. Cold roofs have insulation beneath the roof deck, which is beneath the roofing material.
Hot roofs need to be ventilated and cold roofs don’t—but why?
Why Do Some Flat Roofs Need to be Vented?
Especially during the winter, you might wonder why your roof needs vents. After all, aren’t those vents letting your warm, conditioned air escape outside? A little bit, but ventilation is still key to prevent some serious problems that might develop in your building otherwise.
Warm air rises and will naturally collect in your home beneath the roof. If you have a hot roof, this warm air changes the temperature of your roof decking, as it isn’t protected by insulation. The difference in temperature between the roof deck and the outside air causes condensation.
You’ve probably experienced this affect when you get into your car on a cold morning. You turn on the heat, and the window develops some frost.
In a roof, that thin layer of condensation is a big problem. It can slowly rot out decking and your roofing materials, even dripping down onto whatever is beneath it. So, that moisture and heat needs a way to vent outside. Vents ensure that a roof will be the same temperature as the air outside of it.
That’s not to say that roof ventilation is only valuable in the winter. In the summer, differences between your roof temperature and the outside air can still cause condensation, especially interstitial condensation—or water trapped in the layers of your roof.