Sewer vents are a hit and miss problem among plumbers and drain cleaning services. For one, an occluded pipe cuts off the flow of air from the roof vent when water is inundating the sewer line. So, even if the pipe occlusion is in the drain arm, the ventilation will be a problem. However, the problem does not necessarily get solved through the roof vent.
Another reason sewer ventilation is difficult to finger as the culprit for a slow drain is a lot of preparation is needed to scale the roof to perform a visual inspection of the roof vent to confirm it is clear or blocked. Most people would rather try their hand at cabling the line first, than to go on a roof as part of the diagnostic protocol.
There are a few signs to follow in order to know if you are having a vent problem. If you are draining the tub, and you can hear gurgling in the sink in that bathroom or nearby fixtures, you have a ventilation problem.
If you drain a fixture higher in elevation than another, and the water slowly leaves, only to arrive in the lower elevated fixture, then quickly drains from the lower fixture, you have a vent problem.
If your roof vent is totally blocked, you won't even be able to flush the toilet. Unless you inspect the roof vent, you may be lead to believe you have a blockage in your main sewer line.
Animals, such as birds and squirrels will make their nest in a sewer vent, penetrating the roof. Sewer vents are appealing as shelter due to heat which will rise through the sewer vent and almost come forcefully as heat rises in a cold environment.
Covering roof vents only makes the roof vent more appealing to the animal, now, due to the fact it is now acting as a shelter with heat. So, what can we do? Do we roll the dice and accept the possibility of an animal finding its' way to the roof vent, choking off air flow to the sewer with a nest?
Fortunately, plumbing technology has evolved, taking the animals in consideration. Mechanical vents, such as "E-Cap" will cover the roof vent act as a cover animals can not penetrate.
Diagnosing and fixing the drainage problem for a sink, shower or bathtub may be a long and difficult process. Be safe. If fixing the issue is something that is risky or not being understood, contact a drain service company. The range of pricing for a company who cares to do the job correctly is within $145.00 - $225.00. This depends on material used in piping, age of the house which would help the plumber understand the plumbing code that was used in assembling the plumbing system, access to the plumbing and what is assumed to be creating the blockage.