In single-family houses, the sewerage works by gravity, which means that sewage under its own weight flows into the sewer, sewage treatment facilities for domestic wastewater or a drainless sump, popularly known as a septic tank. To make this possible, there must be an air supply to the sewer risers.
Without air access to the risers, during, for example, flushing toilet water, negative pressure would be created, which would lead to siphoning of water into the siphon (water seal) of the bath or washbasin. Through such an open sewer, gases called flow gases will enter the house, which not only have an unpleasant odor, but can also be dangerous, such as methane or hydrogen sulfide.
To prevent this from happening, (or at least one of them - preferably the one that is most heavily loaded) must extend beyond the roof and end in an exhaust hatch, also called a chimney or exhaust chimney. It allows not only to aerate the sewer, but also to remove channel gases into the atmosphere.
It is only important that the ventilator, which protects the house from sewage fumes, is located above the upper edge of the windows, both installed in the roof slope and in the walls of the house. In accordance with the technical conditions that buildings must satisfy, its distance from windows, measured horizontally, must also be at least 4 m. These conditions also apply to the air intake of mechanical supply and exhaust ventilation with heat. heat exchanger, usually located in the wall of the building.
Attention! It is forbidden to lay channels that ventilate sewers, not only in exhaust and smoke ducts, where damage to plastic pipes is possible, but also in ventilation ducts.
The exhaust hatch above the roof must be protected not only from rain and snow, but also from the possibility of birds nesting in it. Its cross section must be at least vertical.
The hood must protrude at least 0.5 m above the pavement on a steep roof (more with a slight slope) and 1 m on a flat roof so that it does not become clogged with falling snow.
Types of extractors
There are many types of vents on the market in various colors and shapes. They are mostly made of plastic, but metal and ceramic vents are also found.Many roof manufacturers offer ventilation chimneys that match their material and design.
Number of hoods in the house
The exhaust hatch is not only a small additional expense - it is also a potential roof leak point that requires careful sealing, both in the plane of the roofing and in the roofing membrane. That is why the number of vents is usually limited and they are not made on every riser. It is acceptable to make one hood for two risers, for example, a kitchen and a bathroom, if possible: we have a non-working attic, and both risers are not too far from each other. It is only necessary to make sure that the exhaust pipe has a correspondingly larger section - it must be at least 1/3 larger than the section of the exhaust pipes on individual risers.
The remaining risers, without ventilation chimneys above the roof, must be equipped with aeration valves.
Air intake valves
Ventilation valves are installed at the ends of risers that do not end with an exhaust air vent. They provide air flow to the sewer, but do not let channel gases into the room - therefore, they can be safely installed inside the house.
Ventilation valves are mounted vertically at the end of the riser - usually under the ceiling of the highest floor or in the attic under the ridge. They can even be placed on the ground floor - for example, in a technical room next to the sewer outlet into the sink. It is only important that the valve is at least 10 cm above its siphon.
Obviously, air must flow to the intake valves, so they should not be closed tightly.However, they can be covered with a removable plate, for example, so that air from the room enters the valve through the slots around it.
Article written in collaboration with a plumbing services website
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