A soil vent pipe is a perforated metal tube lying in an open trench at the bottom of your excavation and leading to the surface.

When you build above ground, such as at another level or on top of the basement floor, you need to install a cap over this pipe (and any others like it that lead from other areas of the excavation), and either attach a pipe to its centre or fashion a flat top over it. This cap also needs to be covered with a thick layer of gravel (3/4 minus is recommended) and then the usual 12 inches of soil; this coverage protects the pipe from erosion or breakage but still allows any gases in the soil pipe to be expelled.

How does a soil vent pipe work?

A soil vent pipe works by allowing foul gases from the lower depths of your excavation to escape. Gases such as methane, a natural by-product of decomposing organic matter and can be potentially explosive, need to escape from your excavation for safety reasons.

The soil vent pipe also keeps any groundwater present at a minimal level by evaporating and escaping through the drain waste vent into the air above. If groundwater accumulates, it can get into your basement and cause damage to the walls and foundation.

Soil pipes differ from waste pipes. Soil pipe stacks direct sewerage and waste water into the underground drainage system. A soil vent pipe disposes of waste from toilets. A waste pipe exhausts the waste water from bathrooms, sinks, washing machines, etc. By so doing, a waste pipe and a soil pipe both ensure buildings are a safe environment.

The venting system, which is a core part of the stink pipe, eliminates the foul smell.

The same venting system ensures that the atmospheric pressure in the drainage system remains balanced. The open vent will regulate pressure by allowing air to enter the space created by the exiting waste. If air pressure is unbalanced, positive pressure can push back waste water into the system, causing a sudden flow back into the house. Negative pressure can drain out the water leaving an empty trap in the toilet bowl. An empty trap will allow foul gases back into the plumbing system and the structure.

A foul water drainage system must be appropriately maintained. Ensure the venting top has a wire cage or a perforated cover to prevent debris or birds from entering the property's drainage system. A blocked soil vent pipe will hinder the smooth and fast flow of solid waste.

Blockage of the soil vent pipes can be caused by snag materials like toilet paper and wipes. This can cause clogging. In other cases, rough joints or rusty internal pipe walls, especially in cast iron pipes, can hold debris, allowing solid waste to build up.

Consult drainage specialists or reach out to an emergency plumber or a drainage engineer to help unblock a clogged main drain. Also, note that if you occupy older houses fitted with cast iron pipes, some of the cast iron pipes contained asbestos.

Why do I need a soil vent pipe?

When you build an excavation that is deeper than two feet (60.96 cm) - particularly one that goes below the frost line - you need to install a cap over your soil vent pipe and any others like it that lead from other areas of the excavation, and either attach a pipe to its centre or fashion a flat top over it. Otherwise, natural gases such as methane will eventually accumulate in such quantities as to make the enclosed space explosive, which would obviously be very dangerous. A cover also keeps out rainwater but still allows any gases or vapours present in small amounts to escape the excavation. As well, a cap keeps out any solid or liquid contaminants that might come from the sidewalls of your excavation, as loose soils and rocks tend to do when you dig down too far. This is why it's recommended that at least three feet (91.44 cm) or more of soil cover your foundation walls after construction if they are below ground level. In addition, anything buried underground changes over time due to decomposition and other natural phenomena. Thus buried fuel tanks, which were initially safe enough for use in an excavation before proper testing methods were available, may now leak harmful chemicals into the surrounding soil and groundwater long after they've been removed from service - unless the tank has been properly abandoned beforehand.

What should I use a soil vent pipe for?

A soil vent pipe is ideal if you're building a home, garage, shed, or any other structure that requires excavation. It is standard practice with large excavations to install one of these waste pipes as it removes any harmful gases and lets out groundwater.

Building regulations in most areas also require the fitting of soil vent pipes. Normally the local municipality will request the installation of a ventilated discharge pipe prior to starting any major excavation work on residential land. For more information on sanitary plumbing and drainage systems, take a look at the National Construction Code.

In storey buildings, the soil pipes from each housing unit must connect to the underground drainage system to dispose of solid waste. Each house unit's lateral waste pipe joins the main soil vent pipes. In such highrise buildings, the soil stack pipe is the vertical pipe to which all the waste water lateral pipes connect.

How do I build a soil vent?

To build a soil vent, you'll need a gas-safe metal pipe typically measuring between 1.5 and 3 inches (3.81 - 7.62 cm) in diameter for this purpose, as well as a 2 to 2 ½ foot long piece of plastic pipe leading from its centre hole to the surface. Depending on where you live and how quickly you'd like to have everything delivered, you can purchase these components from your local home improvement store or order them online. You should also take a trip to your hardware store and pick up a roll of black polythene tape, some short screws if necessary, one or two large metal washers or nuts, at least 18 inches (45.72 cm) of ¾ inch irrigation tubing, and a metal cap with both an inside hole and outside screw thread. The soil vent's components should include: A gas-safe metal pipe measuring between 1.5 and 3 inches in diameter A 2 to 2 ½ foot long piece of plastic pipe leading from its centre hole A roll of black polythene tape Short screws at least 18 inches of ¾ inch irrigation tubing Two large, matching metal washers or nuts. Optionally you can also purchase a flat, galvanized iron top if available in your area. This is simply a bigger version of the normal bolt used to secure caps or lids onto items that have been previously assembled but has two rings on one side, which allows it to be attached securely over the pipe's upper end and another flat metal surface below.

How do I install a soil vent?

Before you make your waste pipes, research or consult a drainage engineer and adhere to the building regulations in your area. After purchasing the building materials and being ready with the right equipment, you can now make the soil pipe.

Start by digging

Dig down at least two feet (60.96 cm) below the frost line and placing your plastic pipe in such a way that it leads out from the centre of your excavation to just above ground level.

Create a mould

Then create a mound of dirt on one side of the hole that's high enough for you to stand on when working inside the excavation. This is where you will attach your "vent cap," which is simply a large pipe and screw bolt.

Thread the cap

Next, place your threaded cap over the top end of your plastic tube and secure it tightly using either ¾ inch irrigation tubing or an appropriate length section cut from a standard garden hose. The tubing's diameter should be slightly smaller than the screw bolt-on your vent cap so that it can fit snuggly over the top of the pipe. Secure this with some short screws if necessary, then cut some ventilation holes into one side of your polythene tube that are big enough for you to stick a garden trowel through later on when cleaning out your vent. You can also optionally purchase some elbow fittings from your local hardware store if you're more comfortable working with these materials compared to plain lengths of rubber hose and metal piping. However, PVC /plastic irrigation tubing is perhaps best as it won't rust or corrode over time like many other types do - although they all work just fine in the end.

Attach soil pipe to elbow

After you've cut out some holes in the plastic tubing, push the polythene tube down into one of your elbow fittings and tighten it with a hose clamp. Make sure not to block the open end of the tube when doing this! Next, attach one length of metal piping to your elbow fitting on one side of the soil vent by screwing it into place firmly with some short screws or bolts before adding another shorter length that attaches to your cap bolt. This is where you will attach your "vent pipe," which leads up above ground level and gets capped off using either steel lids or more screw caps like you used for your excavation.

Add a flat iron top

At this stage, if you live in an especially cold climate, you'll need to add on your flat iron top, which is simply a large bolt with two rings on one side that will allow you to attach it securely over the vent pipe's upper end. If available in your area, this flat metal surface will give the sun more opportunity to warm air inside your soil vent, thereby preventing frost-related damage to plants growing nearby during winter. An optional but effective way of protecting your soil vent further against cold weather is by adding insulation around its lid using leftover foam padding or even straw bales.

Install the vent pipe

Once you've built your soil vent and added any necessary insulation, it should be ready for installation. Simply bury most of the structure underground with only the ventilation pipe sticking out so you can water surrounding gardens later on when they need it most. You can also optionally place some soil or mulch around the ventilation pipe's upper end to discourage animals, such as cats and dogs, from hanging around above your soil vent. This will prevent them from blocking your ventilation tube with dirt later on when looking for cool places to hide out in, so be sure to remember this if you have pets living nearby. Otherwise, they might spend all day digging near its base, which could lead to all sorts of other problems later down the line.

Do all soil pipes need venting?

No, but it's highly recommended given that too much moisture can cause plant roots to suffocate eventually. For this same reason, make sure not to install your soil ventilating pipes next to any plants growing nearby. This could ultimately lead to their death over time by depriving them of needed oxygen through the ventilation pipe's open end instead.