# Forum Home Renovation Plumbing  Stormwater - continuous fall?

## davey1

I have a question about installing stormwater.  We recently had the roof & guttering replaced on our old place.  I am installing the downpipes this week, 100 * 75 into 90 mm PVC.  I was wondering how hard is it to re-lay the stormwater down one side of the house as the existing 90mm PVC pipes are broken & clogged with tree roots.  I have almost completed digging the trench alongside the existing old stormwater pipes.  It looks pretty straightforward to trace the existing route which is a straight line out to the existing outlet concreted into the kerb on the street.  I know it is preferable to keep the pipes as straight as possible for later clean-out purposes.  The house is on a flat block & the bottoms of the downpipes on the house walls are all higher than the kerb outlet on the street.  I noticed that the existing stormwater does not appear to have a continuous fall.
<o></o> Obviously without continuous fall parts of the pipes will have water in them all the time but I intend to connect & seal the joints properly using blue glue & keep plants (& their roots) well away from the pipes.  I also read a good tip is to run a length of copper wire alongside the length of the buried pipes as plant roots hate copper.
<o></o> The main thing I was wondering was whether it is essential to have one continuous fall out to the street?  Would water still drain away without this continuous fall?  Any other tips?
<o></o> Great site, appreciate any advice.

----------


## Bloss

If by constant fall you mean 'even' then that is not necessary - so long as there is fall it can be steeper in some sections than others - just shouldn't have a rise that goes against the flow. 
Without a fall all the way you run the risk of smells from water sitting in the pipework between rainfalls, backing up from the street if is that badly aligned as well as possible build up of silt and other stuff in the low sections that might encourage blockages.

----------


## davey1

Thanks for the advice.  I'm not confident of getting the ditch perfectly downhill all the way so the pipe has fall the whole way from the start of the house to the street.  There may be some level & maybe some very slight uphill bits.  This is due to the block being flat and the distance from start to finish being so long.  The difference in height between the start of the stormwater run in the ground to the street might only be 500mm over a run of approximately 50 metres. 
I guess having water sitting in the pipe in the past is part of the reason why it blocked up.  That and the fact there was a massive vine growing up the side of the house with roots that were feeding directly off a leaky joint in the old stormwater  :Cry:  
If I can be sure the water will run to the street I can deal with maintaining the pipe to ensure it is kept clear of silt.  The height of the guttering relative to the street is approximately 2600mm.  Would this be enough to get the water draining down the downpipes & out to the street, despite the relatively flat fall in the pipe lying in the ground?

----------


## wonderplumb

Mate your 500mm in 50m will give you the minimum fall required for storm water which is 1:100. Do yourself a favour and use 100mm pipe and make sure you prime the fittings before glueing.

----------


## davey1

Thanks heaps.  100mm & primer is going on the list!

----------


## Theremin

If you have water sitting in pipes then you also have the risk of mosquitos breeding.  In Queensland I think you must have <1mm mesh on all inlets/outlets where water will sit in the pipe.

----------


## Joister

as for what was recommended above - if you do a good job with your joins (as wonderplumb said be sure to prime) and there are no cracks vegetation shouldn't be a problem as there'll be no water to tease them into the pipe (at least that's what i've noticed with good pipe work)

----------


## Joister

ps - as per wonderplumb suggestion, going for the 100mm (i think it is AS/NZS1260 - used for waste, vents) also means you'll have a tougher pipe than the 90mm used for stormwater

----------


## davey1

Thanks guys, really appreciate all the advice. Want to do it once & properly so will be doing exactly as each of you have suggested. 
While finishing the trench I discovered what caused all the root problems. None of the joints in the existing pipes were glued plus the genius who installed the Telstra line to the house punched holes with what looks like a screwdriver to allow the conduit containing the phone line to pass through the stormwater pipe at a couple of places between the house & the street. The guy must have been having a bad day - he only had to move the flexible conduit up or down a few centimetres to make it go under or over the stormwater  :Doh:  It must have been a while ago as some roots in the pipe were about 40mm diameter each.

----------


## wonderplumb

Davey, you might find they were glued but there is too many people out there that dont prime stormwater fittings!!!

----------


## gumboot

Can you explain what is meant by priming storm water fittings please?

----------


## president_ltd

> Can you explain what is meant by priming storm water fittings please?

  use the pink/red stuff before the blue stuff. 
the priming fluid (typically pink/red) is essentially something that 'cleans' and causes small pits/eats into the pipe slightly - so makes for a surface for the glue (typically blue) to bond to a lot better. 
if in doubt, read the instructions on the glue.

----------


## wonderplumb

When UPVC pipe and fittings are made by extrusion and injection molding the molds and associated tooling leave a fine 'waxy' film on the pipe and fittings so they dont stick. If this isnt cleaned off with primer or 'primed' the glue which is a solvent cement will only eat into and weld the two 'waxy' surfaces together and not work to its full potential on the UPVC itself. 
Sure you might get a nice water tight seal that _may_ last a few years but more than likely only weeks or months. I have removed plenty of stormwater and some sewer that hasnt been primed and you can actually squeeze the pipe near the fitting to break the seal and pull the fitting off.
I think the thing that annoys me most, and a lot of plumbers do it _aswell_ as builders who do their own stormwater (depending on local council requirements) is the "nah bugger it its only stormwater" attitude. :Mad:

----------


## barney118

When my pool was installed I noticed they used the red stuff (primer) and then the blue stuff (glue) how easy it to do the right way. Its the same reason you use flux when silver soldering (copper) the flux cleans/ prepares the join.

----------


## wonderplumb

> When my pool was installed I noticed they used the red stuff (primer) and then the blue stuff (glue) how easy it to do the right way. Its the same reason you use flux when silver soldering (copper) the flux cleans/ prepares the join.

   They should have used the green glue on your pool as the blue stuff isnt pressure rated, also flux isnt required on copper to copper joints, its primarily used for copper to brass.

----------

