Soil Pipe Stack

March 2, 2013 | 4 Comments

What is a soil pipe Stack?

A soil pipe stack is the collection pipe and vent for the above ground drains. The soil pipe connects the above ground drainage to the mains drainage below ground. These pipes usually in older homes are external and run down the wall. Normally in newer properties the stack is internal, which is normally boxed in or included within the internal walls.

Soil Pipe Stack

What does a Soil Pipe Stack look like?

What does a soil pipe do?

The soil pipe stack carries the waste from one or more floors. The internal drains pass waste to the soil pipe/vent stack. Each of your household facilities, i.e the toilet, sinks, shower etc, has its own drain piping that connects to the soil pipe.

How does a soil pipe work?

When a Plumber/builder first fits the internal drains, he will install the drains with a fall. The word fall means that the drain is out of level, i.e one end is higher than the other. Fall should be between 18-45 mm per metre.  The waste due to the surge of water flows down and out through the drains due to gravity and this inbuilt fall the soil then flows to the vertical outlet pipe. As the soil pipe is vertical this allows gravity to send the waste into the main drains below ground. The top of the soil pipe is open to allow the fumes to vent into the atmosphere. If the top of the vent/soil stack pipe was capped off then a vacuum would be created and nothing would flow.

Soil Stack Diagram

Conection from toilet of the Soil Stack Diagram

What do I need to install a soil pipe?

Apart from the soil pipe plumbing materials, you will need basic hand tools, hacksaw,file, level, tape measure, hammer drill, masonry bits,screwdriver,a ladder suitable for the job and a helpful aid is a roll of masking tape. This will assist you in cutting the pipe square.

It is always advisable to wear the correct Personal Protective Equipment (PPE), or in other words, minimum goggles and gloves.

Soil Stack Tools

This is one of many Soil Stack Tool

How do I install a soil pipe?

This is based on an external soil pipe but it will relate to an internal as well.

From the inlet provided by the builder to the mains drains, then build up the soil stack. Building up from the ground level then to install a small section of pipe 150-200mm long. To which you will install a roddable access joint. This allows the removal of the access cover and rod the the drains in order to clear any blockages. The out fall drains from the facilities need to connect to the stack. Extending the pipe work vertically, then to accommodate the pipe work required to branch off to take the internal drains. When building up the stack, the soil stack needs to be checked it is level and securely fixed to the wall with the pipe brackets. To connect the other services it will require a 92.5 degree branch coupling. If needed to couple up two straight lengths of pipe this will require a single socket. Smaller branch connections can be fitted to a Boss Pipe connector. Once up to the eaves of the building you need to extend out and up. To do this you will fit two offset bends with a straight piece of pipe cut to the required length to extend out past the eaves and guttering. Then finally a vertical piece of pipe extending up 900mm above any opening to the property, with a balloon grating to the top.

The clips to the stack should be installed no more than 2m apart, working at any heights can be very dangerous. Make sure that have the ladder secured and where possible tied at the top. Your safety is paramount. Always follow health and safety.

Am I required to do anything else to the new soil pipe?

Newly installed soil stacks should be tested in accordance with Part II of the Building Regulations. You should contact your  Council’s Building Control Officer for advice and to book an appointment.

Your inspector who attends will need to see an air test been done. This requires what is called a U-Gauge.  You can hire the U-Gauge Equipment from most good tool hire shops. Please make sure you test the installation before you book the building inspector. This will save you time and effort in getting your work approved. The Hire company will explain how to use the gauge if you ask. To carry out the test you seal off all the open ends of the drains servicing your facilities, on one of the ends you fit a tee to which one end you fit the U-Gauge, and a small hand pump to the other.

Once the gauge is in place and you have sealed off all the inlets, now you must pump up the pressure to 38mm on the gauge. The pressure must remain at this for a minimum of 3 minutes, if it does not hold pressure, have a helper apply soapy water to each of the joints whilst you keep pumping up the system. The joint at fault will start to bubble. Strip down the joint and make good, then re-test the system. Once you are satisfied that the system is holding pressure book the Building Inspector, Job Well Done.

Tips about the soil pipe stack to remember.

  • The masking tape around the pipe to help you cut a straight joint.
  • Remember to measure twice and cut once.
  • Always clean off the swarf, and champher the pipe.
  • Never use soap, oil or grease to ease the installation of the pipe as this effects the seal. Use the correct Silicone lubricant supplied where you purchased the materials.
  • Secure the pipe correctly.
  • Safety always comes first, this is not a job for you on your own.



4 Comments so far

  1. mary ison on March 2, 2013 6:33 pm

    There is a lot more to building a house than meets the eye, I am currently watching the progress of a building being built and have a reasonably good view of the walls being built, if I don’t see soil stacks on the outside of the building then I know they’ll be on the inside. It is actually very interesting seeing the building from it’s very footings.

  2. mary ison on March 2, 2013 6:39 pm

    Even just a soil pipe has to be carefully planned with rodding access and boxing in although I don’t know the reason why people would actually have soil stacks on the inside of a building unless it’s safer for the access side of the situation with maybe no ladders or scaffolding needed.

  3. steve on March 6, 2013 10:01 am

    Hey Guy,
    Can you give me any tips on removing an old soil pipe from the wall. Its been there for ages and the bolts are painted over and cant remove them.

  4. admin on March 22, 2013 4:33 pm

    Reply back to Steve, firstly is health and safety as it can be very dangerous. Once you are safe then the best way to take down the old cast iron soil stack is to get a sledge hammer and then to break away but this is no job for anyone that has no body strength.

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