Soil pipe fall

[NEWBUILD]

I am installing a bio-disc waste system in a new build on a sloping site. Does anyone know if there is a max fall from house soil pipe to inlet on septic tank?

 

[Softus]

1 in 200 is normal - is there any particular reason you want to make it more than this?

In other words, what is the problem you're trying to solve?

 

[NEWBUILD]

Thanks for quick reply! The tank is to be positioned down slope from the house . There is a drop of about 2 m in 50m. The top of the tank would have to be above the natural ground level to get anywhere near 1:200 just wondered if a steep drop would cause solids to be left behind!

 

[Softus]

At 1 in 25 I think you'll have problems.

The first problem will be getting the LABC to pass it - have you produced plans for this?

 

[NEWBUILD]

Building control have passed the plans but we will see what we can do about reducing the slope

 

[freddiemercurystwin]

If in doubt just contact the officer who dealt with your application, he's likely to be happy to advise.

 

[Softus]

In that case I'm confused.

Did LABC approve some detailed plans, or is the builder having staged inspections?

If the former, then what has alerted you to the possibility of problems?

If the latter, then do you have an architect on the job?

Edit: good advice from FMT.

 

[softlad1971]

Have a look at this site

http://www.pavingexpert.com/drainage.htm

 

[neilsumner]

You're right foul sewerage has a fairly narrow band of acceptable flow rate. Too fast and the fluids run away too quickly, too slow and it just blocks up.
I know that the self cleansing velocity for storm water drainage is 0.75 meters per second which is where the 1:200 fall comes from.
EDIT: that doesn't mean 1in200 equals 0.75m/s but that the longfall should be no shallower than 1:200. Like I said you get a bit more leaway with storm water drainage.

You can modify this a little by choosing a different pipe material but I don't think it'll make up for such a steep fall.

Can you raise the level of the tank a bit and bury it under an earth mound?

-Neil

 

[freddiemercurystwin]

Its called a backdrop manhole - refer to the drawing that refers to a backdrop manhole:

http://www.brettmartin.com/building/underground/technical_guide/openchannelmanholes.aspx

 

[freddiemercurystwin]

Or alternatively without the expense of a manhole:

page 15

http://pdf.hunterplastics.co.uk/pdf/underground/ugt7.pdf

 

[tanto]

why not lay a cascade system to reduce the chance of solids being left in the pipe? I had to use this to run a sewer pipe from house to Bio-disc at the bottom of slope approx 10 metres lower than the house and about 25 metres away. Building control suggested this method and were very helpful.

 

[NEWBUILD]

Thank you for all responses. very helpful