How to achieve the proper rate of air exchange?
It is one of the most overlooked procedures in building systems. The principal is simple. If you have an air space there needs to be a means of exchanging the air. The most common way to achieve the proper rate of air exchange is by convection the law that hot air rises and cold air falls. Vents at the highest point of the attic space as well as equal amounts of vents at the lowest point of the attic space can easily achieve the convection required. Another aspect of the roof/attic building system that is closely related to the attic ventilation is the vapour barrier and insulation of the attic. All homes create heat and moisture and it is important to minimize the transfer of the warm moist air from the living space into the attic space. That is where a continuous vapour barrier and a sufficient amount of insulation, are important for a proper functioning building.
In our area where we are fortunate to have beautiful old homes, homeowners often convert the attic space into a living space. This is a great use of space. However, it is essential to ensure that the contractor converting the space takes proper ventilation into account. Too many times roofing contractors are called out to ‘roof leaks’ that are not ‘leaks’ at all, but condensation due to a lack of air exchange.