Advice on connecting fast flow shower waste

[Milleniumaire]

As I'm sure you experts will agree, joists always seem to be in the wrong place and while mine could be worse, it could also be better.

I have placed the shower tray in position to get a view on how the McAlpine fast flow waste will fit and the good news is that it will fit, however, it is too close to the joist to run the 40mm waste pipe straight through the joists and external wall as I had intended.

Here are some photos to show the issue:

20200419_104140

• Milleniumaire
• 20 Apr 2020

20200419_104207

• Milleniumaire
• 20 Apr 2020

20200419_104407

• Milleniumaire
• 20 Apr 2020

The last photo is the view from the side of the tray showing how close the trap is to the joist. This joist is the one that the waste pipe needs to run through and then through the external wall.

I suspect I will need to position the trap, so the connection is pointing away from the joist (like I have positioned it on top of the tray) and then use bends to run round to the joist. Using "sharp" bends so close to the trap concerns me as I want to ensure the flow is not restricted too much due to the shower tray being low profile. I did wonder about using a flexible piece of pipe, which would allow a more gradual bend around to the joist, but I'm not sure if this is a good idea.

I would appreciate any guidance on the best way to connect this trap to the waste pipe that needs to go through the joist. I confess, this is my first attempt at doing something like this.

 

[terryplumb]

Use a Mcalpine Flexi , form a wide radius ,and straight out the wall.

 

[denso13]

Make sure the hole is not too big and in the correct place https://www.eden.gov.uk/planning-an...ing-control-guidance-notes/notches-and-holes/

 

[Milleniumaire]

Make sure the hole is not too big and in the correct place https://www.eden.gov.uk/planning-an...ing-control-guidance-notes/notches-and-holes/

Thanks for the link. I am aware of the constraints of notching/drilling through joists, so much so that I paid a structural engineer to do some calculations for me, for both the installation of a heavy stone bath and the shower.

Because the joists at the edge of the room are doubled up, he said there is no issue in drilling through them in the shower area. Having said that, as my plan to go straight through the joist from the trap has now been thwarted, due to the proximity of the trap to the joist, I have the option of running the waste pipe internally to a position between 0.25 and 0.4 times the span of the joist. The only issue may be the fall, as obviously the 40mm'ish hole, needs to go through the centre of the joist.

I found the following flexible pipe, which may make it easier to get the angle I need to go through the joist either directly from the trap or from a length of waste pipe connected to the trap.

However, I have read that the use of flexible pipe should be avoided, but I don't see much of an alternative, due to the angles I need to deal with.

 

[Madrab]

Nothing wrong with flexi pipes as long as they are used correctly. Fall is important for any waste pipe setup to ensure it is self cleaning, especially with a flexi pipe in the run, either that or raise the tray a little, just use solid packers on top of the joists. If you are able to run the waste pipe, left then can you not turn the tray through 180Deg so the outlet is better placed?

 

[Milleniumaire]

Nothing wrong with flexi pipes as long as they are used correctly. Fall is important for any waste pipe setup to ensure it is self cleaning, especially with a flexi pipe in the run, either that or raise the tray a little, just use solid packers on top of the joists. If you are able to run the waste pipe, left then can you not turn the tray through 180Deg so the outlet is better placed?

Hi Rob, turning the tray 180 degrees is something I have considered, unfortunately the waste outlet would be directly over a joist.

Although the tray is currently sitting on the joists, it will actually be sitting on a piece of board to raise it higher, I just don't know how high it needs to be yet. I will be installing UFH, probably the type that slots into 18mm routed boards, so all the existing boards will be replaced and then there will be a structural layer on top of that, plus tiles. I want to be able to get the top of the shower tray as level with the top of the tiles as possible, so there's a good chance it will be raised by another 25mm, which certainly helps with the fall and the ability to drill through the middle of the joist.

Regarding the use of flexible pipes, I have read that they tend to reduce the diameter of the usual 40mm pipe, but maybe that depends on how compressed they are. Also, I believe the longer pipes (like the McAlpine flexcon2) can sag, so they need to be supported, which shouldn't be an issue in my install. That's partly why I was looking at this shorter flexible pipe, although a longer one would give a much more gradual bend, so may still be the one to use.

I want to ensure I get the best flow rate possible through the trap and the waste pipe.

 

[Madrab]

If you use a McAlpine then you should be fine, they're very well made as against other manufacturers that can narrow significantly.

I would keep your mind open and be flexible as to the finished tray height. It would be better to change a design if a given height is needed to ensure the shower is trouble free, rather than compromise the tray install to try and slot it into a given look to fit a utopian design.

 

[foxhole]

I found they are not UV stable so if used to pass thru wall any part in daylight detoriates and becomes brittle.

 

[Milleniumaire]

I found they are not UV stable so if used to pass thru wall any part in daylight detoriates and becomes brittle.

I would only be using it under the bathroom floorboard so UV shouldn't be an issue. However, that does remind me that the other thing I read is that flexible pipes shouldn't be installed in inaccessible places, just in case they need to be replaced. I confess, I'm not sure why they would need to be accessible, any more than some waste pipe joints that "might" start to leak!

Once the bathroom floor is down, it is down for good (until the next refurb) and the only access would be via the ceiling of the room below.

 

[lostinthelight]

Would it be possible to turn the trap away from the joist and turn the outlet down if needed into a solvent 135 the with enough pipe between to drop to the required level,then make a solid loop out of 135's instead of a flexie?

 

[Milleniumaire]

Would it be possible to turn the trap away from the joist and turn the outlet down into a solvent 135 the with enough pipe between to drop to the required level,then make a solid loop out of 135's instead of a flexie?

Thanks, that's a great idea. I hadn't considered using 135 degree elbows, but I like the idea that the bend would be more gradual than when using a 90 degree elbow.

Having never done this before, I'll have to buy some pipe and bends from screwfix and experiment, although I do have the 135 bend that came with the trap.

I suppose the other advantage of using even a short piece of flexible pipe is that it gives a little more room for error!

 

[Nige F]

Those 90 degree fittings should never be used on wastes - the 92 degree ones are swept. As to the 135's - you can get M+F ones so more variations can be done than just F+F. Set it all out dry, then put a pencil mark across the socket/pipe joint. It'll all glue together accurately.

 

[lostinthelight]

Those 90 degree fittings should never be used on wastes - the 92 degree ones are swept. As to the 135's - you can get M+F ones so more variations can be done than just F+F. Set it all out dry, then put a pencil mark across the socket/pipe joint. It'll all glue together accurately.

I put 2 to make sure one sometimes blurs when twisting

 

[Milleniumaire]

Today I found a pack of Floplast 40mm solvent 135 degree elbows in my plumbing box, so thought I would try to see how the run from the McAlpine shower trap would look. Unfortunately, I realised straight away that the existing 40mm waste, which is stamped with "Marley Extrusions" wouldn't fit into the Floplast elbows. The diameter of the elbows is much too big for the pipe! Initially, I didn't think the pipe would fit into the McApline shower trap as this trap has an insert that fits into the pipe. After cleaning the end of the pipe I managed to push it in, but it is a very tight fit. Unfortunately, I have to use this pipe as I have an existing pipe run outside that I will be making use of and just need to fit a new length of the pipe through the wall to connect up to it. Due to the way my old shower was fitted, I was able to recover a reasonable length of the pipe to re-use it.

Any idea why the Floplast solvent fittings are too big? Is this likely to be the case with all solvent fittings? The fittings used for the old shower are Marley push fit. I suppose I could buy some of these seeing as they haven't leaked in 22 years!

I had a look on the Marley website and they listed three types of 40mm waste pipe and fittings that I would be interested in; pushfit, solvent and ABS. Not sure what the difference between solvent and ABS is, but they both appear to use solvent glue! There doesn't seem to be many places online that sell Marley.

Despite the incompatibility of the Floplast and Marley fittings, a rough mock-up did show I could use 3 x 135 degree elbows to produce a gradual bend from the trap.

 

[Hugh Jaleak]

The fittings used for the old shower are Marley push fit.

That may well be your issue, Push Fit and Solvent weld are not compatible. IIRC push fit is a slightly bigger OD and doesn't fit the McAlpine traps with the insert in the outlet very easily, whereas solvent weld is a snug fit.

All solvent weld systems should be compatible, across the manufacturers, but push fit systems vary. Push Fit is also made from Polypropylene, which cannot be solvent welded. Only way of joining the two types is a compression waste fitting, but if in an awkward spot under a floor, these are better avoided.

MUPVC and ABS are different types of plastic, both will solvent weld, hence the 2 different types listed.