Problems With Plumbing Ducts in Roofs

Plumbing Venting

• All plumbing fixtures in your house connect to drainpipes, which in turn also connect to the plumbing ducts or vent pipes. Without venting, the sewer gases that build inside the plumbing’s drainpipes would be forced into the house. The vent pipes provide a means for the sewer gases to escape safely into the open air. Exposure to sewer gases can cause people to feel sick, or in some extreme cases to die of asphyxiation. The plumbing ducts or vents serve a second purpose, allowing fresh air to flow into the house’s drainpipes. As some air is lost each time waste water flows down the drainpipes and to the sewer or septic tank, fresh air flows into the pipes. Without fresh air flowing in, the plumbing does not maintain the same amount of pressure, which in turn affects how the water flows through the pipes.

Obstructions

• Sometimes tree leaves, twigs and bark fall into the plumbing vent openings above the roof and create an obstruction. Animals may build a nest in the vent opening, or begin dropping food down the pipe for storage. Once an obstruction blocks either part or all of the air flow in the pipe, you must climb onto the roof to locate and remove the obstruction. Choose a day without high winds, precipitation or ice to go onto the roof. Shining a flashlight down the vent pipes’ openings can help you see where a deep clog is located. You may pull out the debris using a drain auger’s hooked end or a flexible retriever tool. If you cannot reach the obstruction, you may knock it free by blasting it with water from a garden hose.

Ice Formation

• Once the outside temperature dips below freezing, ice may begin forming inside the plumbing vent pipes. As the warm and moist air from your house’s plumbing rises in the vent pipes, that air contacts the cold sides of the vent pipes inside your house’s attic. As condensation forms on the inside of the pipe, it may freeze. You may immediately remove the ice obstruction by climbing onto the roof and pouring hot water down the vent pipe, although the roof may be very slippery and dangerous. Wrapping insulation around the vent pipes inside your attic provides a long-term solution, keeping the pipe walls warm enough that the vapor in the sewer gases does not condense.

Leaks

• Because the plumbing vent pipes penetrate the house’s roof surface, they may become the source of water leaks. The vent pipes have a metal flashing piece that fits around their base, covering the roof penetration. The flashing should be positioned under the shingles that sit above the vent pipe and above the shingles that sit below the vent pipe to create a tight seal. Sometimes the nails that hold the flashing down may loosen, allowing water under the flashing. Replacing the nails with rubber-washered screws prevents this problem. A rubber boot piece fits around the vent pipes themselves, connecting to the flashing to create a watertight seal. The rubber boot may crack and become brittle as it ages, requiring replacement.