Drainage design for extension

[MattPope]

Just spoke with the architect concerning the drainage design as recommended by various members here.

I'll have to check this but the existing inspection chamber along the right side of the house has an invert level of 495mm I am told. If so then the idea of the run from the kitchen gulley to this chamber might be ok (except it'll need to be relocated to avoid the new foundation trench):

14m run at 1/60 leaves an IL of 260mm
14m run at 1/80 leaves an IL of 320mm

So is it feasible to have a radial bend and rodding eye across the back of the extension? The advantage of this would be the new floor slab would not cover the drainage run making it a simpler build but is it too shallow?

Thanks once again.

Matt

 

[^woody^]

Normally, you would need a chamber at any connection or change of direction. The BCO would only deviate from this if the stuff going down the drain is minimal, unlikely to bock or there are other access means, for rodding

The problem with the rear sink and a shallow fall is one of build up of grease, but as there is just a sink on this run then you could argue that there will be no problems

It does seem feasible to take the sink run around the back, but I'd put a chamber at the top rear corner so that both runs are rodable. If it gets desperate , then you could move the gulley sideways to shorten the run and then use some wastepipe along the wall from the sink to the gulley

All this would have to be confirmed with the BCO first, as its a bit non-standard

 

[theoldun]

Until you get half dozen levels thrown round, you are wasting your time grasping at straws. It would take 30 mins to throw the levels round and work them out.
You quote. Existing IC has an invert level of 450. As previous levels have been below FFL assume this is the same. With me so far. You then state.14m run at 1/60 leaves an IL of 260mm. 14m run at 1/80 leaves an IL of 320mm Besides being incorrect, is completely irrelevant to what you are trying to achieve.
Firstly the line in question technically should be at a fall of 1/ 40 due to the fact that there is no WC on the line You can not drop down to 1/80 unless there is a WC on the line, but lets be generous and say your BCO will let you get away with 1/60.
Top of bottle gulley is path level 150 below finished floor level. Outlet of bottle gulley is 207 below gulley grating, fall at 1/60 over 14m is 233. Add 150+207+233 = 590. Now you state that existing manhole invert is 450, so you can not get in. Do you understand what we are saying? There is a way that it possibly could be done, but until you have some levels and measurements, then we are all wasting our time.
One other thing, 9 times out 0f 10, you put your drainage in after your footings but you do not do your founds or footings until you know that your drainage will work.
Regards oldun

 

[MattPope]

You're right oldun, I do need the levels before being sure what will or will not work. I'm working away from home right now so I'll have to do this when I get back. To hire a level or get someone round.....

I should have mentioned that the invert level of the IC (495mm) is against the old path/patio level - this was the architect's value. The values used previously were from one builder who called over and he really did not give me the confidence that he had much experience designing drainage runs. The advice on here has been very helpful and I have learned a lot. It was helpful to know that a 1:40 invert is required for the run along the back. I guess that given the 495mm is against the path a 14m run at 1:60 gives an invert level of 320mm then this would accommodate a 207mm bottle gulley but a 1:40 drop would give an invert level of just 145mm which obviously doesn't accommodate the bottle gulley. The best that can be achieved is 1:48 unless the 14m run is reduced in length as per Woody's suggestion.

Thanks for the ideas. I'll be back with some levels but I'm feeling more confident than at the time of the original post that this will work.

Cheers.

Matt