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Advice needed - Shower waste pipe question (Read 23789 times)
YeoYeo
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Advice needed - Shower waste pipe question
May 18th, 2013, 7:37pm
 
Hi all,

I'm currently renovating an old Victorian property part of which is installing a new bathroom suite and shower. The room underneath the bathroom had a floating ceiling which I've now removed. All the previous copper and waste pipes were routed through this cavity which I've now ripped out as it was a right mess.

My problem is my current plumber wants to route the new shower waste pipe under the existing joists in the same way, meaning I would have to lower my ceiling in the room below 6" so he can connect to the previous 40mm waste pipe ( a small part is still in place near the external wall) which goes through the external wall to the stack and he says he needs the fall for the pipe. I would prefer to keep my 9' ceiling height.

The length of the pipe from the trap would be about 3m and the joists under the bathroom are 7" X 3".

Questions

1. Is he being a lazy *"$#?
2. I researched some books and they seam to suggest a fall between 18mm and 90mm per meter would be sufficient is this correct?
3. If question 2 is correct is it safe to drill 40mm holes for the waste pipes in my 7" X 3" joists including the necessary fall difference between joists?

Any advice would be appreciated.

cheers.

YeoYeo.
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Re: Advice needed - Shower waste pipe question
Reply #1 - May 18th, 2013, 10:05pm
 
40mm holes in a 175mm joist is quite large, and the holes would not end up all in the center of the joist, which is where they should be.  Threading a length of waste in through joists would also be a struggle, without having a multitude of joints, unless you get the holes all perfectly in line and perfectly angled.

I would say dropping the ceiling would surely be the best way to go, not sure it would really require the full 6"?  A shame the joists run the wrong way, or that you cannot route with the joists to a wall, and then box in along the under side of the floor against the wall...

I seem to recall 18mm per meter being the absolute minimum, and the maximum length being 3m (although I think this is often stretched).

Scruff will be online at some point, and he is a wealth of knowledge.
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Re: Advice needed - Shower waste pipe question
Reply #2 - May 18th, 2013, 10:23pm
 
Hi, You don't give the total length or the number of bends etc.

I would not even consider cutting a waste into a 170mm joist.

Fall should be 1 in 30 roughly, and soil pipes 1 in 40.

More info please about what will be connecting to the pipe, you may want to consider 50mm or move fittings to better postions.
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« Last Edit: May 18th, 2013, 10:24pm by thescruff »  
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YeoYeo
Re: Advice needed - Shower waste pipe question
Reply #3 - May 19th, 2013, 12:26am
 
I believe its just the shower waste pipe everything else in the bathroom can connect to the toilet waste pipe. As for bends etc. its a straight run with the main stack almost directly outside the exterior wall maybe 200mm further on.

i.e. 3m from shower trap to wall + cavity wall width (~200mm) + 200mm gap from wall to main stack. (straight with no bends)
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Re: Advice needed - Shower waste pipe question
Reply #4 - May 19th, 2013, 8:16am
 
40 mm should be ok for that than with a minimum fall over the 3m off 34mm.

I would try and fix it to the wall below the ceiling every 7-800mm so as to avoid any sag at a later date, and make provisions for an access cap for cleaning.

Lastly try to include an auto air admitance valve at the shower end.

depending on the property you can buy covers that look like an old beam, maybe an idea if you don't want to lower the ceiling.

for example.
http://www.replicabeams.co.uk/
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« Last Edit: May 19th, 2013, 8:24am by thescruff »  
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Re: Advice needed - Shower waste pipe question
Reply #5 - Jul 10th, 2013, 9:48am
 
May I piggy back this post and ask a somewhat related question?  I have had a new shower fitted being fed by combi boiler with ok pressure but nothing close to power shower.  I have a slimline tray with fast flow waste - 90mm but the shower tray just fills and floods.  I have taken out the trap and the water escapes ok but clearly this is not a solution as hair and all sorts could go down.  The waste feeds into the soil pipe which is approx 1.5m away.  There must be a reason for this and I am concerned that the fall is not sufficient.  My plumbers solution - drill holes in the trap.  I have had a lot of other problems with this plumber.  Is he fobbing me off? Smiley
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Re: Advice needed - Shower waste pipe question
Reply #6 - Jul 11th, 2013, 8:12am
 
Not sure what he is saying, can you post a pic or sketch.

Is the soil pipe vented and what size is the waste pipe.
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Re: Advice needed - Shower waste pipe question
Reply #7 - Jul 11th, 2013, 1:50pm
 
The trap is there to form a water barrier to noxious smells, which could otherwise travel up the soil pipe and into the house, rather than collect hair as hair is unlikely to block the drains.

We have a Matki fast flow shower waste but find that if it gets even a few hairs in it, it somehow reduces the flow enough to flood the tray.  It just needs very regular cleaning.
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Re: Advice needed - Shower waste pipe question
Reply #8 - Jul 11th, 2013, 6:11pm
 
I assumed the trap he was talking of was one that is placed over the outlet to trap hairs etc.  I don't think he was talking about drilling holes in the actual waste  Grin
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Re: Advice needed - Shower waste pipe question
Reply #9 - Jul 12th, 2013, 7:44am
 
Quote:
I have a slimline tray with fast flow waste - 90mm but the shower tray just fills and floods.


So what make/model of trap do you have?

Quite a few traps are designed to fit a big hole in the tray but the actual hole the water goes through is no bigger than a size standard trap.

If you need a high flow trap it would be reasonable to use 50mm/2" pipe but amazingly many big traps are designed for say 1.5" pipe and come with adaptors to suit 2" - so there is an inherent constriction compared to one that is 2" right through (if you get what I mean). Totally stupid design IMHO. Better traps are available.

The insert in most top access traps forms the u-bend/water seal so removing it or drilling holes in it would also reduce the depth of the u-bend. That could make it easier for sewer gas to get in. I suppose you could try that, if it causes a problem you could buy another identical trap and use the insert to reverse the change.

Simpler solution might be to use a lower flow shower head. It might even feel more powerful.
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Alicat66
Re: Advice needed - Shower waste pipe question
Reply #10 - Jul 12th, 2013, 8:50am
 
Hi.  Thank you all for your replies.  The shower tray and waste are Merlyn and this is the link to the details http://www.merlynshowering.com/product/waste/  Apologies as I am having trouble uploading the picture but this will take you straight there.  

Currently the shower is brand new and never been used.  I was just testing it and the found it to flood.  Inside the main white plastic body of the waste is essentially a cup which fills and then once full overflows and disappears.  It is billed as a fast flowing waste and our water pressure is about 3 bar and delivered from a combi boiler, so power pump or extra power, pretty average water flow.  Thanks so much for your help everyone
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Re: Advice needed - Shower waste pipe question
Reply #11 - Jul 12th, 2013, 9:12am
 
That type are very good so it suggests another problem.

Is it air locking and need a vent, or is there a restriction.
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Re: Advice needed - Shower waste pipe question
Reply #12 - Jul 13th, 2013, 10:27am
 
I agree should work ok.

You originally suspected the fall on the 1.5m pipe might not be adequate. Can you still access that to check what the fall is?

Just to be sure it's not the shower can you measure the flow rate? Get a bucket of known capacity and time how long it takes to fill. Post the capacity of the bucket and the time and we can work it out.
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