Unless you’re a qualified plumber or drainage engineer, soil pipes and waste pipes can be a minefield to navigate. There are lots of pipes inside a property and lots of pipes that exit the property too so usually unless you have prior experience, understanding which pipe is which can be an issue. One of the most common problems is confusion between a soil pipe and a waste pipe. So how does a soil pipe differ from a waste pipe?

In the most simple terms, both pipes carry waste from our homes to the sewer but there is a crucial difference between the two types. A soil pipe is designed to carry soiled water from the toilet, urinal or bidet to the sewer. A waste pipe carries water from your sinks, shower, washing machine or bath.


What is a soil pipe?

As already mentioned, a soil pipe is for soiled water. This type of pipe will carry water and solids into the sewer. While any pipe could physically perform the task, the soil pipe, also known as a soil vent pipe, as installed in most homes has a specific quality. First, it is of a dimension to allow solid waste to pass. Second, it is vented in a very specific way to maintain a safe environment and reduce odours. Soil pipes are vented high at the top or near to the top of a building, thanks to soil pipe stacks, to allow gases produced by waste to vent safely into the atmosphere. Such gases can be harmful to health so venting them high keeps them out of the way. This is a vital feature of soil pipes and it forms part of building regulations too.

What is a waste pipe?

A waste pipe is often a smaller diameter pipe that carries waste water from your sinks, washing machine, shower, bath and any other appliance you may have that uses water. It can be narrower than a soil pipe as the waste pipe is only designed to carry water. It also doesn’t need the same venting system as a soil pipe. Wastewater does not typically generate harmful gas so does not need to be vented high above ground level.

Soil pipes and waste pipes in older and new properties

How your property handles waste depends on its age. Older properties may use separate soil and waste pipes to exit into the sewer. Newer houses may use a single system. Older properties tend to use both a waste and a soil pipe that exit separately until they reach the drain. They would then combine and exit your property underground to the sewer. Newer properties use a simpler single pipe system that utilises an internal soil stack. This is a thick vertical pipe that reaches above your gutter to provide safe venting. Both soil and waste pipes will run from your toilet, sinks, shower, washing machine, urinal, bidet and any appliance that voids water and join the soil stack. The stack will run directly into your underground drain.

Older homes that have been converted may have a mixture of the two systems. They often use an external soil stack connected to the main drain with all pipes joining the stack. Using the right pipe is critical, especially for soiled water. If in doubt, always contact a professional.

Call us on 01752 692 221 for more information on the differences between soil pipes and waste pipes.

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