Sink waste - through joists

[ldoodle]

Hey,

I'm designing my bathroom refit. The layout in the design at the moment puts the sink on the opposite wall to where the external stack is, so I thought about taking the sink waste straight down, and through 2 joists where it will boss in to the internal part of the toilet waste.

In the attached image, the red circle is where the toilet currently is, with the pan connector dropping straight down under the floor, so the stack actually enters the house under floor already. As you'll see, the design extends the stack to the opposite wall to where it enters the house.

View media item 70688
Unfortunately the bath needs to go where it is in the design, because at the moment it's where the toilet and sink are in the new design, but due to width constraints I can only get a <700mm bath in, and I want 750mm at least.

Alternatively I could get a pan connector that has a boss on it, but I'd need an open backed toilet for that. This is the one I currently had in mind, which wouldn't work with a bossed pan connector.

http://www.betterbathrooms.com/toilets/calder-toilet-and-seat/

Thanks

 

[MJGas]

What are the depth of your joists?

 

[ldoodle]

Not sure, but I do know there is a maximum hole size calculation based on the depth/height of the joists.

But even so, if they're big enough to allow for a 40+-mm hole, is underground sink waste 'allowable'?

 

[ldoodle]

Does where in the joist have a bearing on max. diameter hole?

It would be about 200m away from where the joist sits on a supporting wall.

 

[MJGas]

Off the top of my head a hole should be drill between 0.25 and 0.4 of the span of the joist. And the hole diameter size should be no more than a 1/4 of the joist and drilled in the centre.

 

[ldoodle]

Hang on, I said 40mm thinking that was the diameter of the waste, but for basins it's 32mm, right?

So I'll need 130mm joists or more;

130mm * 0.25 = 32.5mm

 

[Madrab]

If your joists span from left end support to right support and is approx 2.4m as in your drawing, then the closest to the end of the span you can place the hole is 1/4 of the spans length, that would make it 600mm (0.25x2.4m), not the 200mm you were looking at.

 

[newbuildinstaller]

32.5mm hole for a 32mm pipe??

You will need a 40mm hole at least for a 32mm pipe to provent pipes ticking when hot..

I recently did the same thing for a cust.

I ran the basin waste backinto the wall then chased thewaste out of the wall and ran it into the back of the WC into one of the bossed pan connectors you mentioned.

 

[ldoodle]

If your joists span from left end support to right support and is approx 2.4m as in your drawing, then the closest to the end of the span you can place the hole is 1/4 of the spans length, that would make it 600mm (0.25x2.4m), not the 200mm you were looking at.

That's fine to be honest. It can boss into the soil pipe wherever in the run as I can take it parallel to the joists for x length before elbowing

 

[ldoodle]

32.5mm hole for a 32mm pipe??

Wasn't saying that would be enough, just the *minimum*. What's the next size pipe down - could I run 32mm from the basin down to and under the floor, but use a reducing elbow (if they exist) to go through the joists. From the elbow to the soil pipe could be as short as 600mm, if I drop the vertical run right next to the first joist.

 

[Madrab]

You don't want to use anything smaller than 32mm waste for the basin, can run into draining issues if you did. The next down is 21.5mm overflow pipe but that's too small.
The other alternative would be to chase the wall and insert solvent weld waste pipe to run to the soil pipe or box section, not as tidy though I'll grant you.

 

[denso13]

 

[ldoodle]

With chasing, the wall the toilet will be backed on is breeze. I guess 40mm pipe would break the 1/3 chase depth, certainly the 1/6 depth for the horizontal run.

 

[dcawkwell]

I might be missing something but why don't you just go parallel to the soil stack and take it outside and then join to the soil stack. much easier.

 

[muggles]

...for basins it's 32mm, right?

Sort of right, maximum run is 1.7m from the trap to the stack, if you need to go any further than that Building Regulations require you to upgrade to 40mm waste