![]() For the moment this is about the typical roof design that most people would be used to seeing – an uninsulated attic space outside the thermal envelope of a home. An unventilated roof is less common in mainstream construction and is more often seen with vaulted or cathedral ceilings. Having said all this, it is worth pointing out before we get too far that there are ‘unventilated roof’ designs as well we will get to that below. All these effects are why air barriers in homes are so important for durability and energy efficiency. In spring when this ice melts, it will seem like you have a roof leak when in fact there is none (spoiler alert – if your roof ‘leak’ happens on a sunny day, it’s not a ‘leak’). Why Roofs need to be ventilated and how to ventilate a roof properly Why roof vents are neededĭuring winter, warm and humid air escaping though any punctures in ceiling air barriers (which includes poorly installed pot-lights) will condense as it migrates though a wall assembly and meets a cold surface this causes frost and ice to form. Wind pressure as well as interior mechanical ventilation also affects the air pressure in a home and will force air out any breach in your air barrier. And air will find any hole no matter how small it is. Warm air rises, so there is always more air pressure at the higher points of any house or building, as in the top floor ceiling. ![]() Exterior siding and roofs should be viewed as a rainscreen just keeping precipitation away from the control layers of the wall – your thermal, air and vapor barriers. This is a simple product of physics and the realities and limitations of construction.Ī heated interior space should be airtight, have a proper vapor barrier or vapor retarder in cold climates and temperate climates, and the right amount of insulation for your climate zone. It is pretty much inevitable that at least some warm, moist air from living areas will find its way into the roof of a building and bring with it the very real risk of frost and ice forming in a cold climate, or mold and rot in a temperate climate. ![]()
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