Backfill and Drainage Data Page
(A) DRAINCOIL (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 draincoil should be below floor level.
The draincoil should be free draining or to stormwater sump or other suitable outlet.
If draincoil is to go to soakhole, see below.
(B) Fine 7mm (1/4") granular material around the draincoil. Place about 100mm (4") below the draincoil 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.
SOAKHOLE A soakhole 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 soakhole will not overflow and cause further problems.
The finished top surface of the soakhole should be at a level - below - that will not allow the water to back up the draincoil.
This also means that the surface of the soakhole 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 soakhole.
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 soakhole and 300mm (12") max depth (under ground).
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