ATTIC VENTILATION

ATTIC VENTILATION

Poorly ventilated attics are a source of concern due the potential for moisture collection from condensation on the wintertime cold surfaces of the sheathing and wooden roof members. This condition can lead to long term dry rot and in excessive cases can cause moisture penetration into the interior of the home resulting in stains and surface deterioration of the finish materials.

Such limited ventilation conditions can also lead to roof ice damming. This condition occurs when snow melt occurs on the heated roof and the resulting water runs down to the cold roof overhang at the eaves where the water re freezes to create the unwanted ice dam. Once the water runoff is blocked by the ice dam, it rises above the shingles and penetrates under the shingles to gain admittance to the interior of the house. Staining seen at the ceiling/wall juncture is usually indicative of roof ice dams.

All recently installed roofs now have a water membrane, commonly called ice shield, installed underneath the shingles along the roof eaves and extending a minimum of XX inches over the interior of the house to provide protection against this happening. However, with both adequate insulation and sufficient attic ventilation ice damming tends not to be a problem.

In those older home I’ve inspected containing copious amounts of attic insulation (exceeding 12 inches) it usually means a past history of roof ice damming. While standard amounts of attic insulation (6-12 inches) are important, even more important is the provision of cold circulating air within the attic keeping the roof sheathing cold and avoiding snow melt on the roof. To achieve this circulation requires both the low side venting, such as the soffit vents at the eaves as well as the high side exhaust venting which is provided by ridge vents and/or gable end vents. The omission of either one or the other prevents adequate ventilation. More recent construction almost always includes ridge venting on the roof which has proved to be superior to gable end venting. Ridge venting is commonly added during shingle replacement on older roofs as well.