Category Archives: Plumbing

Drainage and Venting Systems

Drainage systems are comprised of all the piping and fittings that carry the waste products of a plumbing system to a municipal drainage system. To a plumber, each piece of pipe and each fitting has a name and a purpose…for example – the pipe that continues from just outside your house to the street is called a “Building Drain”, a drain pipe that connects to another drain pipe is a “branch” and a pipe that acts as a drain for one fixture and as a vent for another – is called a “Wet Vent”. Fittings also have specific names and functions. There IS a difference between a “Tee” and a “Sanitary Tee or Tee-Wye”. Elbows can be had in long turn and short turn, each being used in a differing situations.

Piping and associated fittings are available in different materials, and may be prohibited by code for differing applications. Cast iron “No-Hub” is generally seen in commercial applications, but many homeowners decide to have their plumber install for vertical drains (stacks) to attenuate noise. Some may even have the entire house plumbed in cast iron! This can be very expensive in labour and materials, so it is a decision that will really affect the bank account. Housing today tends to be done in A.B.S. (Acrylonitrile Butadiene Styrene) or PVC (Polyvinyl Chloride) mainly for cost savings, but both are very reliable materials and available at plumbing wholesalers’ and hardware stores (limited selections).

Every fixture in your home must be vented properly, to prevent the escape of harmful sewer gases into your home. A vent allows air into the system to balance pressures caused by waste flowing away. The p-traps that you find under fixtures (pre-built into water closets), create a water barrier between your house and the drainage system, and their associated vents protect them from losing their seals. It is the protection from these materials and gases that has contributed to the overall national health not seen in the not so distant past. Vents will either terminate in open air (at roof usually), or connect to a vent which does, and in colder climates are usually increased in size before passing to outdoors. The increased area of opening guards against the moist discharged gases freezing and creating a situation where air will not circulate within the plumbing system. One disadvantage to the increased termination size is the opportunity for birds to nest! There are also “Automatic air vents”, which are frowned upon by inpectors, and are usually used when it is impossible or highly expensive to extend a proper vent to outside air or branch vent. In British Columbia where I operate my plumbing business, the latest plumbing code allows the use for these type of situations, but only one is allowed, and it must conform to C.S.A. standards (as do all pipe, fittings and fixtures). Auto air vents are made of plastic, and have a rubber diaphragm and spring that allow air into the system when draining and close to not allow sewer gases to escape when nothing is draining. These fittings usually have a male thread (1-1/2″ or 2″) to allow connection to the vent pipe. Vents should grade upwards (opposite of drainage pipes), but if not, they will still function (though not as well) unless they have created a point where condensation will accumulate and block air movement.

Most drainage systems work by gravity, and must grade or slope downwards in the direction of flow by a minimum amount to be effective and trouble-free. By plumbing codes, grade is usually 1/4 inch per foot for pipe sizes 3 inch and less, and no less than 1/8 inch per foot for 4 inch and over (maximum size normally found within a residential application). If greater slopes than the minimums are used, better flow will be achieved. Caveat: Too great a slope and solids may be left behind, as the effluent flows faster – possibly causing a blockage. For the piping between a trap and its associated vent pipe, the fall (or grade) should be no more than the diameter of the pipe, and no less than 1/4 inch per foot for the reason stated in the last sentence. Drainage piping that cannot maintain these minimums must be piped to a sump system which is pumped to a drain which does flow by gravity. All of these rules are meant to keep the system operating with little to no intervention.

There are codes in every city and municipality that regulate the installation of plumbing systems, and these can vary between cities, provinces/states, so it is always wise to refer to your local regulations for actual requirements. Building and plumbing inspectors are very helpful to homeowners doing their own plumbing, as they prefer to have it done right by whomever is installing. Don’t be afraid to ask, and DO get a permit!