Appraise my drainage design

[PSC88]

Hi we are currently at foundation stage and having to rework our drainage design, mainly as we demolished an existing bungalow and wanted to use the same connection.

 

In hindsight we should have dug a trial hole to existing connection and worked the falls backwards, however we relied on some old drainage plans which turned out to be a few 100 mill out leaving us with a very tight fall or having to raise the finished floor level by 300mm to gain the fall.

 

We had a review with our building inspector who decided shorter runs under the building to get the fall to work.

 

I have attached the image and the blue lines are our new proposed routes.

 

Ideally I wanted as much of the drainage outside of the building as possible but looks like this isn’t possible.

 

Any thoughts or advice positive or negative would be welcome 

[Nickfromwales]

4 IC’s too many here, if you can run these pipes under the slab however you want?

 

For my current client I simplified 5 IC’s down to…….. 1. Passed BC with flying colours, and had the BCO out today to do a stage inspection, all flying colours.

 

Architects go nuts on these, drainage ‘engineers’ not far behind, but sense / sensibility should prevail.

 

Zero sense appears to have been applied to the above, sorry. 

[saveasteading]

There is something to be said for getting drains outside by the shortest route, but you could combine some probably.

I can't work out what the bottom two are  for... one seems to be an existing drain but also relaid new.

Same for the top one.

 

Inlet chambers aren't expensive but so many might be ugly.

[Mr Punter]

I don't know why you redesigned this.  Are you short on fall?  You have about the same number of ICs as the original.  Not sure why the line at the front has moved 6 metres.  It may prove another obstruction.  Very large property!  Can you feed the drawing to an AI chat?

Edited yesterday at 09:19 by Mr Punter

[Spinny]

Are you certain you can't replace the old bungalow connection with something lower to get you the fall you need ?

Presumably that could be possible providing the main public sewer is low enough.

Also perhaps you could move the connection to the public sewer to connect lower down the slope/fall of the public sewer.

Have you discussed this with your sewer utility company ?

No doubt there would be cost involved but still probably small compared with your total budget and contingency.

 

PS Have you made sure you have a good mains water connection ?

Edited yesterday at 13:34 by Spinny

[PSC88]

Hi thanks all for the reply.

 

the number of Inspection chambers or manholes will most likely be reduced to 4 so ignore all the noise on the above drawing this was my rough sketch.

 

it was redesigned due to being short on fall. We are on a private estate so to connect on to the road isn’t an option due to the cost and also the time it will take to get the various permissions.

 

the fall worked fine with the bungalow but due to the property being larger we are pushing the connection to the boundary of the property which gives us about a 1:80 fall only just but the inspector has stated he would be much more comfortable with a 1:60 which is achievable by shortening the runs and going under the build 

[PSC88]

It’s not to scale the drainage and man holes positions just a rough sketch of location 

 

we have added the additional manholes at the front and back so if needs be it can be rodded externally 

[saveasteading]

1 hour ago, PSC88 said:

more comfortable with a 1:60

He isn't a designer and is used to seeing very poor workmanship where 1:80 flattens out in places to a still legitimate (presumably)  1:100. But do check the numbers.

You can hold your ground on this, just build it well.

[PSC88]

2 hours ago, Spinny said:

Are you certain you can't replace the old bungalow connection with something lower to get you the fall you need ?

Presumably that could be possible providing the main public sewer is low enough.

Also perhaps you could move the connection to the public sewer to connect lower down the slope/fall of the public sewer.

Have you discussed this with your sewer utility company ?

No doubt there would be cost involved but still probably small compared with your total budget and contingency.

 

PS Have you made sure you have a good mains water connection ?

we want to avoid any drainage works outside the boundary of the property due to it being a private estate and the costs/lenght of time taken to get permissions to dig the road 

[PSC88]

49 minutes ago, saveasteading said:

He isn't a designer and is used to seeing very poor workmanship where 1:80 flattens out in places to a still legitimate (presumably)  1:100. But do check the numbers.

You can hold your ground on this, just build it well.

The redesign going under the property actually shorted the runs considerably and allows much more flexible ratios for the falls but I’m not a drainage expert so was just more dubious with having the main fouls drains under the property rather then around it 

[Mr Punter]

If you are that tight on fall, could you raise the building by 200mm?  Hardly noticeable I would think.

[saveasteading]

1 hour ago, PSC88 said:

drains under the property rather then around it 

The arguments against drainage through a building are.

1. if there is ever a problem then it is more difficult to resolve.

2. houses move up and down seasonally and could  damage a pipe.

3. in a refurb there might be more work.

 

1. If  built properly thee shouldn't be any problem. If there are rodding points anything is sortable

2, with plastic pipes they bend , not like old clay or iron pipes.

 

 

 

[saveasteading]

1 hour ago, PSC88 said:

want to avoid any drainage works outside the boundary

Quite so, but you can expose the existing pipe on your side and join into it. The levels will probably be fine to use, working backwards to the house.

[PSC88]

Here’s a clearer more concise drawing

 

 

[PSC88]

2 hours ago, Mr Punter said:

If you are that tight on fall, could you raise the building by 200mm?  Hardly noticeable I would think.

It would need to be 350mm which is our fall back 

[saveasteading]

If the fall works now, why does it need to be increased?

05 seems to be redundant. 02 requires turdal U turns so needs improvement.

Rainwater can be simplified by combining the runs.

[Mr Punter]

Keep the higher bits as close to the surface as possible, especially of it is path only.  300mm min cover is fine and you could do less at a pinch.  Use the mini shallow ICs at the sides and back and for corners where you will add a 45 either end.  Avoid clashes with the surface water system.  Make sure the foundation is low enough where the pipes cross at the front.  This can just be short sections.