In a conventional attic, with fiber based insulation, the roof, the insulation and ventilation all work together as a system.  If one component fails, it can lead to damage in other areas. 

It is understood that the roof system, provides a dry environment in the building below. The insulation helps to maintain a comfortable temperature in the occupied area, by keeping warm air inside during the heating season, and hot air outside during the summer months.  Ventilation helps to keep the attic cooler in the summer, and vent excessive moisture from the attic area in the winter.

If an attic does not have adequate insulation, heat loss may occur from the occupied space.  The heat rises through the insulation, causing a warm attic.  The warm temperatures can cause condensation on the underside of the sheathing and melt snow on the roof. This may lead to the formation of Ice damming along the lower roof edges.  The ice damming in turn, leads to water backing up and possibly entering the attic underneath the shingles. This water ingress then further damages the insulation and the drywall below.  Continual water damage can lead to more severe mold problems.   It should also be noted that ice damming may be caused by external factors such as extreme temperature changes and even the direction of the roof line.  For example, a warm sunny winter day may cause the snow to melt near the top of the roof, cooler evening temperatures can cause the melt water to refreeze and subsequent ice damming.  Chimneys, vent stacks and bathroom exhaust fans may also contribute to snow melting and ice damming

By ensuring adequate attic ventilation, heat escaping through poor insulation and a poorly sealed ceiling, can be vented to the outdoors minimizing building damage.  However, the problem of heat loss still remains.  When addressing poor insulation concerns, it is imperative that the attic ventilation be addressed also.

Proper ventilation allows air movement through the attic.  It is not enough to simply install roof vents, air must be allowed to enter the attic at the eaves and then escape near the peak of the roof.  Styrofoam or cardboard vents should be placed at the eaves to keep the insulation away from the roof and to allow air into the attic.  Eave vents or Moore vents, should be installed at least every four feet along the eave.  Local building inspectors may require a vent in between every rafter. 

Roof vents can be a ridge vent, fixed vent a “whirly Bird” or a powered fan, or a combination.  Roof vents should be installed by a qualified roofing contractor that understands the ventilation requirements for your building.