Roofing does more than just cover a structure to keep things under it dry. Roofs must also breathe, in the sense that they must have adequate air flow to dry moisture, to melt snow and to aerate structural materials. Without proper ventilation, roofs develop problems that can cause leaks into the interior of the house. Though porches are generally more open, their roof areas still require adequate venting to prevent moisture buildup and other problems.
About Roof Ventilation
Roofs are exposed to the elements in both intense heat and frigid cold. In addition, rainfall soaks the surfaces and creates a moist environment under the roofing material that can degrade the roofing material and deteriorate building structures. Ventilation helps to reduce these problems by allowing air to flow across roof surfaces to dry them out. The air flow also helps to melt snow and ice, allowing it to slide off the roof surface. Roofs generally have a number of venting devices including ridge vents, soffit vents, fans and mechanical types of airflow assistance.
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Roof Problems Caused by Poor Ventilation
Roofs that do not have sufficient ventilation can have a problem with condensation, in which heat warms the moist surfaces under the roof causing them to leak and stain interior ceilings. Because the roof remains moist a good deal of the time, mold and mildew growth can also be a problem, causing unsightly black or greenish stains on ceilings and walls. In cold climates, poor roof ventilation can also cause the buildup of ice on roofs. Melting snow then backs up behind these "dams" causing leaks into the roofing material and into the interior of the home. Ice dams can cause thousands of dollars of damage to roofs and interior building materials.
Porch Roof Problems
Though porches are more open to the air, they may still have ventilation problems under the roof. Porches are often attached to the house. Problems with porch roofs can cause intrusion of water into the interior of the house. Porch roofs can also develop ice dam problems like the rest of the house's roof. A wet roof can cause mold to grow on the underside of the porch ceiling. Condensation can cause leaks and unattractive stains on porch ceilings.
Adding Ventilation to Porch Roofs
If your porch has developed ceiling stains or problems shedding snow and ice in the winter, try providing additional venting for the roof system. Louvered vents provide good air flow for roof areas. Knee vents that fit along the area where the roof joins the house can also provide good ventilation for porches, according to the Roofing Contractor Review website. Installing additional soffit vents can also help to increase the airflow to dry out roofing materials.