Slope of bath waste into soil stack too steep?

[SJRSJR]

Hello

I'm adding a 50mm waste from a bath/basin into a soil stack, which already has two separate shower wastes connected. The only available position for a boss strap would mean a 19cm drop over a 107cm run. I can see the regs say this is too steep, but adding a vertical drop to get a shallower slope would mean the pipe would lie below the top of a window. Is this a big deal? I plan to add a rodding eye in case of blockages but I wondered if there are any other suggestions/solutions that would keep me on the right side of Building Regs. Thanks

 

[opps]

I do not know the answer but will be intrigued to find out why that would be considered too steep.

 

[avonmouth]

That's not to steep.
You just need a minimum of 18mm per metre or in old money we always laid drainage at 40-48 inches to one.

 

[SJRSJR]

I do not know the answer but will be intrigued to find out why that would be considered too steep.

I think it's about the water flowing quicker than the solids which get left behind (presumably hair) and possibly sucking out the water in the traps.

That's not to steep.
You just need a minimum of 18mm per metre or in old money we always laid drainage at 40-48 inches to one.

Ah okay. I'd thought the maximum you could get away with was 90mm per metre. (The first couple of metres in the bathroom has the correct fall, it's when it gets to the outside that it's steeper.)

 

[catlad]

I think it's about the water flowing quicker than the solids which get behind

Yes, you don't want it so steep that the solids get left behind.

 

[SJRSJR]

Yes, you don't want it so steep that the solids get left behind.

What would be considered too steep?

 

[catlad]

What would be considered too steep?

How long is this run?

 

[denso13]

Hello

I'm adding a 50mm waste from a bath/basin into a soil stack, which already has two separate shower wastes connected. The only available position for a boss strap would mean a 19cm drop over a 107cm run. I can see the regs say this is too steep, but adding a vertical drop to get a shallower slope would mean the pipe would lie below the top of a window. Is this a big deal? I plan to add a rodding eye in case of blockages but I wondered if there are any other suggestions/solutions that would keep me on the right side of Building Regs. Thanks

As above it's fine. It's just water from a bath/basin.

 

[Madrab]

BRegs state that the fall on a waste pipe should be between 18-90mm/m, this is to stop the water going 2 slow and solids dropping out of the flow or 2 fast and then the flow can get too turbulent and create the same outcome of solids dropping out.

Not as much of an issue when it comes to bath/basins as there is very little in the way of solids in the waste water, as say a toilet but if too steep it can still reduce its self cleaning abilities. What you might need to watch out for is water velocity, one for water noise/turbulence and two for self syphoning, so the run may also need to be vented.

 

[SJRSJR]

How long is this run?

1.07m

Not as much of an issue when it comes to bath/basins as there is very little in the way of solids in the waste water

What about long hair?

Thanks for everyone's input. If there is a blockage problem I've got the rodding eye. If there's siphoning issue I could change basin trap to an anti siphon trap. (I don't think I could do it with the bath, it comes with its own trap.)

One last question hopefully. As the pipe is coming into the soil stack at a steeper angle, is a straight boss adapter the right fitting or is there a better one? Thanks

 

[denso13]

If there's siphoning issue I could change basin trap to an anti siphon trap.

That would mean it all comlpies with the regs.

Deposition of solids is only for large pipes/sewers, even then it hasn't been proven, just conjecture.

 

[denso13]

One last question hopefully. As the pipe is coming into the soil stack at a steeper angle, is a straight boss adapter the right fitting or is there a better one? Thanks

Straight boss with 2 45 degree bends into it which you can adjust, level into the branch and at an angle to the waste outlet.

It'll also reduce the gradient a bit.

 

[SJRSJR]

That’s great, I’ll give that a go. As you say, it’ll also reduce the gradient. Thank you!

 

[Madrab]

And just ensure there isn't another stack entry on the opposite side.

If there's siphoning issue I could change basin trap to an anti siphon trap.

if the basin is @ the head of the run then ideal, fit one anyway to avoid any gurgling in the basin, if the bath is @ the head then a full bath letting go can sometimes pull on it's own trap but that would probably be a test it and see. Check the bath trap has a large enough seal too - 50mm min.

 

[SJRSJR]

And just ensure there isn't another stack entry on the opposite side.

Thanks, there isn’t.

if the basin is @ the head of the run then ideal, fit one anyway to avoid any gurgling in the basin

By that you mean the highest point? If so, yes, I’ll put an ant-siphon trap on that

Check the bath trap has a large enough seal too - 50mm min

Sorry, what does that mean? The bath has a 40mm trap (which came with it) and 40mm pipe. Is that inadequate?