Attic, Insulation, Ventilation & Interior
Roof system ventilation and insulation are important for a number of reasons, including:
temperature (or heat) control;
energy efficiency; and
the prevention of chronic ice dam formation.
Ventilation of attic areas is intended to prevent the accumulation of moisture vapor in the attic-roof space and to dry low levels of condensation that may form on the underside of a roof deck. Ventilation is also intended to reduce the temperature of the roof deck during hot periods to improve shingle durability. Reducing attic temperature through ventilation and insulation also improves energy efficiency during hot periods. And in the case of ice dams, elevated attic and roof temperatures during the winter can cause snow on the roof to melt. Insulation and roof ventilation help to keep the roof’s exterior surface cold and minimizes the development of melted water and, consequently, ice dams.
Ventilating roofs in hot and humid conditions may add -- rather than remove -- moisture from attics and enclosed roof spaces. However, not ventilating a roof may void the manufacturer’s warranty and slightly decrease the life expectancy of the asphalt shingles due to the increased temperature of the roof surface.
In colder climates, roof ventilation serves to remove humidity and condensation from the roof-attic space and helps to prevent the chronic formation of ice dams at eaves.
Tile, concrete and metal roofing materials are not similarly affected. It is possible to have an unvented attic space, but such a choice may require designing the attic-roof space as a conditioned space, similar to that required when creating a habitable space in the attic. There are several sources that provide detailed information for designing an unvented attic. Traditional attic ventilation remains a cost-effective though imperfect solution for moisture control.