Approved for new build

[Ivor Windybottom]

It isn't going to work is it. If the manhole is only 14" deep and it really is 33metres, you need ~40cm fall for 1:80 - it'll be out the ground by the end.

It may be possible (just) if for example the floor is higher than the ground. Definitely needs careful working out, with accurate measurements and drawings.

Also 1 in 80 is the limit. You shouldn't go beyond this to stretch it out, or it's likely you'll get blockages.

 

[mrrusty]

It may be possible (just) if for example the floor is higher than the ground. Definitely needs careful working out, with accurate measurements and drawings.

Also 1 in 80 is the limit. You shouldn't go beyond this to stretch it out, or it's likely you'll get blockages.

Agreed - I was assuming the 14" deep extended the whole 33m - the ground may not be flat. Over that distance, this is a job for an old fashioned water gauge - couple of bits of clear tube and a hose pipe, then you can see exactly what you have to play with...

"the ground may not be flat" - of course, Murphy's law says it slopes the wrong way.....

Also 1 in 80 is the limit

You can push it a little - 1:100 is acceptable e.g. https://www.drainageconsultantsltd.co.uk/about-drains/drainage-gradients-falls/ , but the challenge at such a shallow gradient is keeping it consistent over that distance - very small deviation and you'll get a low section that won't drain.

 

[Ali2487]

It isn't going to work is it. If the manhole is only 14" deep and it really is 33metres, you need ~40cm fall for 1:80 - it'll be out the ground by the end.

I have calculated and Ian terrible at maths, that the house floor base level needs to be approx 40cm higher than existing ground level in order to accommodate the fall. Does anybody know whether that sounds roughly about right? Is there a specific equation I can use to figure this out?

If the run exposes the pipes then I'd obviously backfill, compact the soil and setup the retaining walls.

 

[mrrusty]

I have calculated

You really do need to survey this - the ground may look flat but may not be and it'll make all the difference to your calcs.

 

[freddiemercurystwin]

I have calculated and Ian terrible at maths, that the house floor base level needs to be approx 40cm higher than existing ground level in order to accommodate the fall. Does anybody know whether that sounds roughly about right? Is there a specific equation I can use to figure this out?

If the run exposes the pipes then I'd obviously backfill, compact the soil and setup the retaining walls.

No the floor level is not normally 40cm higher than the ground level, all of this should have been considered during planning by your designer. What does that last sentence even mean?

 

[Ali2487]

No the floor level is not normally 40cm higher than the ground level, all of this should have been considered during planning by your designer. What does that last sentence even mean?

Engineer didn't know this at the point when he drew so will be reverting back to him to ensure its all correct.

The last sentence means that if the ground level needs to be high, then I plan to use the soil we dig out (if possible) to backfill and raise the existing ground level