Backfill and Drainage Data Page
Note: Use the data below as a guide only. Different areas may have different rules and/or regulations. It is always advisable to check with your local authority regarding drainage issues.
(A) DRAIN COIL (perforated flexible corrugated plastic pipe) Usually comes in sizes from 65mm (2 1/2") diameter upwards. The size would depend on the amount of water to be discharged.
The drain coil should be below floor level.
The drain coil should be free draining or to storm water sump or other suitable outlet.
If drain coil is to go to soak hole, see below.
(B) Fine 7mm (1/4") granular material around the drain coil. Place about 100mm (4") below the drain coil and 100mm (4") above.
(C) Backfill with free draining 20mm (3/4") granular material.
WATERPROOF MEMBRANE Apply a waterproof membrane to wall such as 'Mulseal' or 'Flintkote' or similar tar like substance. Usually require 3 coats and is readily available from most building merchants. Detailed instructions come on the products container.
(D) 12mm (1/2") or thicker polystyrene protective sheeting. This is to stop the draining granular material from scratching through the waterproof membrane.
(E) Masonry wall. If wall is not in good repair, ie bricks with cracks etc. Then plaster over before applying the waterproof membrane.
SOAK HOLE A soak hole should be positioned approx 3 meters (10ft) from a building and also at least 3 metres (10ft) from a boundary. It should be clear of other buildings so that water from the soak hole will not overflow and cause further problems.
The finished top surface of the soak hole should be at a level - below - that will not allow the water to back up the drain coil.
This also means that the surface of the soak hole should be light granular soil for excess water to seep out and allow evaporation to occur. Water will not soak through clay walls of a soak hole.
A trench 450mm x 450mm x 5 metres (18"x 18"x 17ft) long is suitable. If room does not permit, a cubic metre (36 cubic ft) hole is generally used. The pipe enters in the top of the soak hole and 300mm (12") max depth (under ground).
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