Flexi poo pipe

[Dee]

Maybe this sketch can explain my problem better.

Middle drawing is top down view and bottom drawing is side on.

The bottom/ ceiling joists are 4x2s

The void is about 140mm

The length of horizontal pipe will be about 3.8m.

So; Can I achieve enough fall along 3.8m with such a narrow void?

 

How much fall would this be?

 

How much can I notch out of the lower joists to achieve the fall?

 

Does a smaller bore soil pipe exist, say 75mm?

 

Will I need a vented pipe? (Don't even know what it is!)

 

Am I trying to achieve impossible?

 

Any help appreciated!

 

 

 

[Mike]

7 hours ago, Dee said:

The void is about 140mm

The length of horizontal pipe will be about 3.8m.

How much fall would this be?

The minimum fall is 18mm/m, so 3.8m x 18mm = 69mm

 

7 hours ago, Dee said:

Can I achieve enough fall along 3.8m with such a narrow void?

69mm fall + 110mm pipe = 179mm. That's not going to fit through a 140mm void.

 

7 hours ago, Dee said:

How much can I notch out of the lower joists to achieve the fall?

In the correct part of the span, by can notch 0.15x the height of the joist, so 0.15 x 100mm = 15mm. Which is not enough. If the ceiling joists are oversized that would give you some leeway, but if they're only 4" x 2", then from the picture that seems unlikely - it would need to be a very short span to get away with less.

 

7 hours ago, Dee said:

Does a smaller bore soil pipe exist, say 75mm?

It wouldn't comply with the regs to use something smaller. Not unless you use a pumped 'macerating' WC - which come with some issues (typically visual appearance, noise & maintenance).

 

7 hours ago, Dee said:

Am I trying to achieve impossible?

No, it just makes it harder. Possible options include:

• The macerating WC
• Running the pipe below the ceiling in a boxing. The void therefore becomes irrelevant.
• Replacing the ceiling with a lower one to provide a bigger void
• Replacing the ceiling (or part of the ceiling) at the same height, but suspended on a metal framework instead of timber joists. That would easily give you the void you need.
• Reinforcing the relevant existing ceiling joists - for example with metal plates - to enable you to make deeper notches. Technically you'd need a structural engineer for that.

7 hours ago, Dee said:

Will I need a vented pipe? (Don't even know what it is!)

The soil pipe would need to turn vertically up the wall next to the WC and be fitted with an 'air admittance valve'. Otherwise flushing the WC would risk breaking the water seal in the WC and letting the sewer gasses into the room.

 

[Dee]

Thanks everyone. I think I have to abandon the idea of a small cloakroom, or my late husbands idea 😪 .

Lots of vety helpfully advice

Thankyou !