Foul drainage across root protection zone

[WWilts]

New dwelling in rear garden of host dwelling. Land slopes down towards rear.

Foul drain to go from pumping chamber of new dwelling to existing drain of host dwelling. Problem: root protection zone of a tree enroute.

Any suggestions for how to cross the root protection zone above ground? Height difference about 1.5m. Probably less if invert of existing drain is the reference point.

 

Edited March 16, 2021 by WWilts

[PeterW]

Which pipe are you talking about ..? The pump out to the main drain of the other property ..??

[WWilts]

13 minutes ago, PeterW said:

Which pipe are you talking about ..? The pump out to the main drain of the other property ..??

Challenge is posed by the drain from the pumping chamber of new dwelling to the existing drain of the host dwelling. Part of the root protection zone intervenes. 

Routing the foul drainage from the new dwelling either under or over the root protection zone might work. But how exactly?

[Russell griffiths]

Can you not go around it, if it’s a pumped system it’s not relying on gravity so making the run longer shouldn’t be a problem. 

[PeterW]

So as @Russell griffiths says, it doesn’t need to go direct as long as you try not to have dips in the pipework. It will be in 50 or 63mm MDPE and can go whatever route you want. 

[WWilts]

Schematic diagram attached.

How to get the foul drainage of new dwelling N to the existing drainage without disturbing the tree? Under or over the roots? Trying to picture over the roots, along the Eastern boundary. MDPE on stilts? Something else?

Edited March 16, 2021 by WWilts

[Gus Potter]

Just a thought but if you got a drainage contractor in with a mole (makes a hole say for a cable / duct) under a road then you could maybe make an argument this way? Avoids trenching the ground and cutting all the roots.

 

In principle this may work. To start with aim to keep the mole deep in maybe low nutriant soil so you reduce the risk of damaging the primary roots. In practice.. I'll leave that up to your imagination.

 

If you don't want to imagine then get in a pro Arboriculturist who may be able to look at the soil, refine the general guidance on the extent of a root protection zone and keep you on the right side of the regs.

 

If you hit an obstruction using the mole then you can hand dig to clear it and.. while hand digging you make sure you don't cut the roots.

[Russell griffiths]

As gus said, do you have an arborists doing a method statement for you on how this should be done, or are the council not aware you are going down this route. 

[PeterW]

9 hours ago, WWilts said:

along the Eastern boundary. MDPE on stilts?

Has to be buried min 600mm. 
 

Depending on the tree type you may want to look at moling but in honesty I would be going down the west boundary and then going into the sewer directly or using the lateral drain. 
 

Have the sewage company been informed ..??
 

 

[WWilts]

1 hour ago, PeterW said:

I would be going down the west boundary and then going into the sewer directly or using the lateral drain. 

Yes, this has been the front-running option. Longer distance and needs to cut across front garden of host dwelling, hence exploring whether east side is feasible.
Presumably inverts for west side need not be 600mm below ground. 
Would you pump to near NW corner of host dwelling and then rely on gravity for the rest of the way to the manhole nr the public highway?

[WWilts]

1 hour ago, Russell griffiths said:

you are going down this route

To be decided

[PeterW]

So have you discussed / advised the sewage provider ..??

 

what is the sewer depth ..??

[WWilts]

4 minutes ago, PeterW said:

discussed / advised the sewage provider

Right from planning stage onwards.
Trying to sort out preferred options at our end before next stage in the conversation with them.

How about
Pumping chamber 
to
Relatively elevated insp chamber at NW corner of host dwelling
to
Slightly lower insp chamber at SW corner of host dwelling

to

Private manhole (appears to be relatively deep detachment chamber with vent pipe out of ground) nr public highway

[Mr Punter]

If you have a pump station, do the run in 90mm black MDPE.  Run it in the same trench as your other services.  Convert to 110mm brown pipe to a new chamber and gravity pipe to the sewer / final chamber.

 

If you have a high or variable water table, the pump station chamber needs encasing in concrete.

[WWilts]

10 minutes ago, Mr Punter said:

high or variable water table

3 to 5 m depth through the year

[ToughButterCup]

Half a day on BuildHub to solve a foul problem.  How much would you have paid an 'expert' to do the same eh?  This place is addictive.

[PeterW]

Sorry @WWilts you still haven’t answered my question !!

 

Has your sewage service provider agreed this approach...?

 

If you connect into that existing lateral connection then the law states the sewage provider takes responsibility for it from the point it supports two or more houses. That means it has to be adoptable, and of a standard they require. If not, you need to make it to their standards. In certain instances they may also insist on a primary connection to the sewer network, but they will advise. 
 

None of this is planning or building regulations approval related, you need to get the sewage provider approval first. 
 

 

[WWilts]

5 minutes ago, PeterW said:

None of this is planning or building regulations approval related, you need to get the sewage provider approval first. 

Noted.
What they need they will get. No question.
The decisions/options are about how to get it from the new dwelling to the existing manhole near the public highway. Once our preferred option is clear, the conversation with them can continue.
They want our foul drainage to go south (up an incline) instead of north.

Edited March 17, 2021 by WWilts

[WWilts]

On 17/03/2021 at 10:19, Mr Punter said:

If you have a pump station, do the run in 90mm black MDPE.  Run it in the same trench as your other services.

Does the black MDPE need to be protected at shallow depth in pedestrian areas? If so, what might be cost-effective options? 
And what would be a good way to protect it as it crosses under a driveway? (mainly cars/vans)

[PeterW]

1 hour ago, WWilts said:

Does the black MDPE need to be protected at shallow depth in pedestrian areas? If so, what might be cost-effective options? 
And what would be a good way to protect it as it crosses under a driveway? (mainly cars/vans)

Concrete. You basically put everything in a duct and concrete over the lot. 

[WWilts]

41 minutes ago, PeterW said:

concrete over the lot

Paving slabs? 

Reinforced/not?
Shutter and pour?

[PeterW]

Just back fill until the last bit you want concrete over is left then fill the gap - try and get at least 200mm over the ducts. No rebar or anything else needed. 

[Conor]

Cover it all in lean mix concrete. Nothing fancy required. Only really for driveways and roads, not needed for other areas unless very shallow.