Help needed draining a new patio

[Zebrano]

Firstly Hello.

Secondly a bit of backgound. I'm currently in the process of laying a 40m2 sandstone patio in my back garden. The patio will sit against the house and project into the garden about 5m where it reaches a retaining wall (about 400mm high) holding back my sloped (towards the house) garden. The house has been extended and the door in the new extension is about 50mm lower than the patio doors on the original house, I therefore plan to have the patio fall away from the house and down towards the extension side leaving me 150mm below both doors. So thats the background, now to my questions.

By running the fall in this direction I'm running away from the only access I can find to the surface water drainage, however by running this way I do end up very close to an existing foul manhole which is about 1.7m deep. My questions are:

1. Can I break into this foul manhole to drain the surface water from the patio even though I have a dual system? (BTW the rest of the drain is encased in concrete so I can't break into it at any other point other than the manhole)

2. If I can do the above, can I have the surface water enter the manhole significantly above the benching, say 1m down to just discharge into the sewer from above?

3. If I can't do 1 above do you have any other suggestions? There is a chance that the surface water drain is below the foul drain, but this would mean digging an exploratory trench about 2 m deep!

Thanks

Zebrano

[Tony McC]

1 - yes, as a last resort, but any conmnection MUST be trapped. Is there no way a soakaway could be used?

2 - yes - this is known as a dropshaft connection when done on site, but what you'd probably do would better suit an internal dropshaft: much less work. All this assumes there is room inside the chamber to accommodate and internal dropshaft.

3 - It's very, very rare for SW to be deeper than FW, but, if there is a SW pipe available, it should be used in preference to the FW, regardless of its depth.

[Zebrano]

Hi Tony

Thanks for your response.

Unfortunatley I live on very heavy clay and so a soakaway is not really possible.

I'll try and find the SW as the first option, the problem is I'm not 100% sure were it is as the nearest manhole is about 25m away, I have a hunch but will mean an awfull lot of digging if I'm wrong. If I can't find it I'll use the internal drop shaft as I've plenty of room inside the chamber.

Thanks again for your help