Plumbing Best Practices

[Dan F]

As mentioned in another thread, am finding some issue with work our plumber is doing, but I'm not 100% clear on what is expected, so have various random questions.

 

Is there a list of best practices I can find somewhere on the forum or the internet I wonder?   Otherwise,  I'll jot them down here as they come up, as might be useful for others too:

 

1) Is there a miniumum height, at which an SVP should be reduced down to a 50mm vent-pipe next to a first-floor WC?

2) Is there a maximum number of bends between WC and main vertical SVP pipe?

3) When using MLP,  am I right in assuiming 90 degree bends should really be avoided at all costs?

4) I've read about Uponor, Hep20 & copper options for supply pipe, but when it comes to santiary/drainage pipework, what are the recommended products?

6) Should all drainage everywhere have swept bends, or is this only important in some key areas? e.g. 50mm+

7) Are these sizes right

- Shower 50mm

- Bath 40mm

- Basins 32mm

- Kitchen/Utility Sink 50mm

 

[Dan F]

8 ) Is the use of 50mm vent-pipes (to AAV in loft) OK, or should 75mm be used?

9) To what extend is supply piping supposed to be fixed (including when going through webbed-joists)?

Edited February 14, 2021 by Dan F

[Dan F]

I'm going to try and answer some of my own questions, based on reading...  Anyone want to mark my answers? ?

 

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1) Is there a miniumum height, at which an SVP should be reduced down to a 50mm vent-pipe next to a first-floor WC?

No, but it would be advisable to only reduce to a vent-pipe above the "spill level"

 

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2) Is there a maximum number of bends between WC and main vertical SVP pipe?

No, but bends need to be kept to a minumum, falls respected and swept bends used.

 

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3) When using MLP,  am I right in assuiming 90 degree bends should really be avoided at all costs?

Avoid wherever possible. You shouldn't need to avoid them "at all costs", unless you've undersized your pipe to start with.

 

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6) Should all drainage everywhere have swept bends, or is this only important in some key areas? e.g. 50mm+

Swept bends is best practice. Building regs only requires in specific situations:   i) 75mm branch -> stack ii) Junctions on branch pipes of about same diameter.  Swept bends are also strongly advisable for food waste disposal units.

 

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7) Are these sizes right

- Shower 50mm

- Bath 40mm

- Basins 32mm

- Kitchen/Utility Sink 50mm

Yes.  Although building regs only requires 40mm for showers, 50mm is advisable.

 

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8 ) Is the use of 50mm vent-pipes (to AAV in loft) OK, or should 75mm be used?

According to building regs: one size down from discharge stack is permitted in 1-2 storey houses, but never less than 75mm.

Edited February 16, 2021 by Dan F