Sink basin waste fall advice

[Mshing80]

Hi I am trying to figure out my bathroom sink waste problem
Renovating the bathroom and the wife wants the sink the opposite side of the room. The stack is in the opposite corner the only way I can get to it is through 2 joists that have already been cut for the old shower waste.
If I do this my sink waste will be in an L shape, from the stack to the first bend I have a fall of over 100:1 it is around 1m long then an elbow joint. Along the joist From the elbow joint to where the pipe will need to come vertical through the floorboards (around another metre) there is hardly any fall.

Would this work ok or should I look to get a pump?
I really dont want to drill any more holes through the joists. Green i can get a fall. Red is where it is almost level

 

[ShaunCorbs]

15mm a meter min

the notches in the joists look deep max you can do is 1/8th of the depth

 

[Mshing80]

15mm a meter min

the notches in the joists look deep max you can do is 1/8th of the depth

The notches are 1/8 of depth yes.
I know the min fall, I need a way around this as I have no alternative route. Would a waste pump resolve my lack of fall?

 

[ShaunCorbs]

How much fall do you have ?

 

[gpbeck]

If the notch by the 2 standing screws is 1/8, you must have a 50cm tall joist there!

 

[Mshing80]

How much fall do you have ?

The pipe along the green line falls just short of 1.5cm between the elbow and second joist. I will need to put a bend in to make a steeper drop to get it to the stack. The pipe along the red line there is barely any fall.

If the notch by the 2 standing screws is 1/8, you must have a 50cm tall joist there!

Yea sorry, this one is more like 1/4. These cuts are from the old shower waste that I took out. These were done by the builder who made the extension! This is why I am not keen in making any further holes in the joists.
Whoever built the extension to our house needs shooting, found some shocking things

 

[Ric2013]

May I suggest any bend, especially under the floor, should be a swept bend rather than a knuckle bend (look up these two terms on any web browser for pictures)?

 

[Mshing80]

May I suggest any bend, especially under the floor, should be a swept bend rather than a knuckle bend (look up these two terms on any web browser for pictures)?

Thanks for the comment but doesn't really answer my OP.

No one got any advice if this pipework would be ok if a pump was installed on the waste?

 

[Ric2013]

Thanks for the comment but doesn't really answer my OP.

No one got any advice if this pipework would be ok if a pump was installed on the waste?

If you fit a waste pump, I think you can use 22mm pipework and can even run with a negative fall. You'll need to check manufacturer's installation instructions for the pump. I think the feeling may just be that a pump is a last resort.

Personally, if that is in your own house, I suppose my thinking is that, so long as that waste pipe is going to be accessible and you aren't about to tile over the floor, I would consider using your proposed run with minimal fall, supporting the pipe every 50cm, upgrading the waste to 40 or 50mm (1.5" or 2") instead of the presumably 32mm or 1.25" you currently have if you can, sweeping the bends, and deburring all cut tube meticulously. You may find that while it does not meet the recommendations of the building regulations Approved Documents, it may still work perfectly well.

This wouldn't be best practice and it's a risk, but, if it doesn't work, then you haven't wasted much money and can then go on to fit a pump. Personally, I would find a way of making the pipe have 15mm per m drop or relocate the basin as I'm a plumber, but, in fairness, a study of old sewers run at varying drops did not show increased incidence of blockage even at drops of less than 1:1000 and a washbasin is unlikely to overload a short length of 2" pipe to the point that it is running full bore, even if laid almost level. This is why I think you might get away with it.

 

[WC1]

If you fitted a pump you would redo that run entirely. I.e. not use what you've got. Look up saniflo 10 golden rules. Pumps pump up, not down. At least then you could brace the joists