I am moving the fall pipe for a roof of approximate 15metres long and need to create a soak away (not on mains drains). How big should I make the soak away? I am planning to dig a hole in the lawn 5 metres from the house and fill with rubble then cover over with dramp proof membrane then top soil.
Volume of void = 50mm x (area of roof drained.)
Void =gaps between rubble. Rubble isn't very efficient in this respect. Consider using the purpose made plastic crates.
mark
How many square metres of roof will it need to drain? How permeable is your sub soil?
Then dig about on the web to see what rainfall you get for your area. I think there are standard figures for use in this sort of calculation.
Is your area free-draining? I live in a low spot where because of the high water table I can't use a soakaway so had to use a sewage treatment plant instead of a septic. It would just fill with water. The test is to dig a cubic hole about 30 cm on each side in the area where you want your soakaway. Fill it with water and see if it drains dry within a reasonable time.
You are probably OK but it's worth checking.
Peter Scott
and within weeks it will simply be buried rubble as the soil will get in and fill all gaps.
If you are going to dig a hole, put a few bricks at the bottom, then get beer crates (or milk crates) and then wrap the whole lot in weed barrier and fill in around it with 18mm stone. Your pipe should go into the top of this. All you are doing is creating a holding tank - you can use an upturned dustbin if you like, provided you can get it down deep enough so that you can get a foot of something over the top, either soil or grass or paving etc.
HTH
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