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PVC Pipe | Stormwater | Plumbing Supplies

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

One of the perks over the course of our day at our plumbing supplies store, is the chin wags with our regulars. It is great to hear their stories and never gets old.
The other day one of our regulars, a plumber talked about PVC Stormwater fittings and pipes.
Unexpectedly this led to a robust discussion with a few good points raised. We thought it might benefit our readers to share. Please have a read and let us know what you think!
As we know, 90mm PVC stormwater pipe  is the standard size fitting in Australia.
The customer asked whether it makes sense to "upgrade" to a 100mm stormwater pipe? The customer had a large property and he would be using a ride on mower. So the extra rigidity would give him a extra piece of mind and possibly more water flow capacity.
There is a steep increase in price from a 90mm to a 100mm stormwater pipe.
Is the extra cost of a 100mm PVC stormwater pipe worth it?
Here are a couple of points we talked about
  • The slope of the pipe effects the flow rate. So it is not simply the case a 100mm stormwater pipe will always have a greater flow rate than a 90mm stormwater pipe
  • For extra rigidity it makes sense to go fro a HDPE pipe as opposed to a PVC pipe. It will cost more but it is extremely hard to break a HDPE pipe and it will simply deform. You can also think of using a DWV pipe (Drain Waste & Vent pipe). The DWV pipe is made of sewer grade PVC and is much stronger than stormwater PVC
  • The question really is about catering to 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.
  • A 100 mm stormwater pipe has 20% greater capacity than a 90mm stormwater pipe. Therefore it all depends on how much water the pipe is catching, where you live regarding rain intensity and the risk of flooding in your dwelling due to overflowing.
  • The best solution we reached was - 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 calculated that, you can then select the correct size pipe. You will also need 600mm of cover over your pipe if it's a trafficable area. stock a large range of plumbing supplies such as shower heads, shower head washers, teflon tape, duct tape to make your life easier ! We supply Australian standard products Australia wide. and in most cases dispatch on the same day.

Hope you enjoyed the above the information. Talk to you soon. Stay safe.
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