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PVC Pipe | Stormwater | Plumbing Supplies

PVC Pipe Stormwater - 90mm or 100mm? Plumbing Supplies

Welcome to, where we provide not only quality plumbing supplies but also knowledge and expertise to help you make informed decisions.

We recently had a conversation with one of our regulars, a plumber, about PVC Stormwater fittings and pipes, and we wanted to share some insights with our readers.

One of the questions that came up during the discussion was whether it makes sense to "upgrade" from a 90mm stormwater pipe to a 100mm stormwater pipe. The customer had a large property and was concerned about the rigidity and water flow capacity. While there is a steep increase in price from a 90mm to a 100mm stormwater pipe, here are a few key points to consider before making a decision:

Firstly, it's important to note that the slope of the pipe affects the flow rate, so it's not simply a case of a 100mm stormwater pipe always having a greater flow rate than a 90mm stormwater pipe.

Secondly, if you're looking for extra rigidity, it makes sense to consider a HDPE pipe as opposed to a PVC pipe. While it will cost more, it's extremely hard to break a HDPE pipe, and it will simply deform. Additionally, you can consider using a DWV pipe (Drain Waste & Vent pipe) made of sewer grade PVC, which is much stronger than stormwater PVC.

The main question to consider is how much water the pipe is catching, where you live regarding rain intensity, and the risk of flooding in your dwelling due to overflowing. A 100 mm stormwater pipe has 20% greater capacity than a 90mm stormwater pipe, but it all depends on the Annual exceedance probability. This refers to the probability that a given total rainfall over a given duration will be exceeded in any one year.

To determine the correct size pipe for your needs, AS3500.3 states that you need to design for a AEP 1% for box gutters and 5% for eaves gutters. If this is your stormwater drainage for a house, there's a very high chance it's going to be eaves gutter. Google BOM IFD and input the coordinates of your building. Multiply the AEP (mm/hr) by the roof area and divide by 3600 to get your total flow rate for the roof. Once you have calculated that, you can select the correct size pipe. Keep in mind that you will also need 600mm of cover over your pipe if it's a trafficable area.

At, we pride ourselves on offering a wide range of quality plumbing supplies such as hower heads, shower head washers, teflon tape, duct tape to make your life easier. We supply Australian standard products Australia-wide and dispatch on the same day in most cases.

We hope that the information we've shared has helped you make an informed decision about whether upgrading to a 100mm stormwater pipe is worth the extra cost. As always, if you have any questions or concerns, don't hesitate to contact us. We're here to help you with all of your plumbing needs. Thank you for choosing Stay safe, and we look forward to serving you soon.

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