The importance of ventilation
During this time of year it is vital that the ventilation of your home is adequate enough to avoid these issues.
a lack of vents. It is not uncommon to see a complete lack of ventilation. In these cases, the high temperatures within the roof covering will induce a rapid breakdown of the materials. This not only affects asphalt shingle
roofs, but also flat and tile roofs that use roll roofing as the primary water barrier. It is also common to find high levels of moisture in these attics, which promotes moisture-related issues, such as rotting sheathing and mold growth.
inadequate venting. Poorly vented roofs will show some of the same issues as roof systems having no venting, but to a lesser extent. Particularly in northern climates, there will be evidence of ice damming and moisture on the roof sheathing. In some cases, inadequate venting will eventually manifest as rusting shingle nails, and even frost on the underside of the roof sheathing in cold weather.
too much ventilation. In some cases, this can be a problem, particularly with large but poorly screened vents that allow rain water to enter the attic space. The key with ventilation is to strike the correct balance between insulation, moisture barriers and ventilation. A bad installation is, in many respects, worse than none.
Very often, inspectors will see instances of poorly installed insulation blocking the soffit and other vents. These should be reported as in need of repair.
false vents. It is all too common to see what appear to be vents installed that are, in fact, not connected through the structure. Inspectors will sometimes see instances of ridge vents apparently installed, but the roofers did not trim back the roof sheathing along the roof's peak to allow the vents to actually work.
damaged vents. It is recommended that all vents be visually inspected for proper operation wherever possible. Be sure to check to ensure that the flashing system is in good shape and is not leaking. Inspectors will often see vents that have been mechanically damaged, or galvanized vents that are rusting away. These deficiencies should always be reported as in need of repair or replacement.
ice damming. This is typical of poorly insulated vented roofs in colder climates and is caused by snow melting on the roof above the home's heated envelope, and then running down the roof and being trapped by frozen snow and ice above the eaves. The ice will act as a dam and force water to back up under the roof covering, rotting out the sheathing or migrating through into the interior of the structure. The cure for this is an adequate design incorporating proper insulation, ventilation, and an ice and water shield installed under the roof covering in potentially affected areas.
Content from InterNACHI.org