Aug 03, 2010 2:12 pm
I need some advice on a drainage issue down the side of my house.
Water is collecting there quite a bit against my foundations and I’m not sure of the best way to disperse it.
My Down pipes are connected to my rainwater tank via a wet system so connecting drains is out of the question. I have been looking at drywells but I’m still not 100% sure.
The soil is clay and the water just sits on top. The space down the side of my house is about 2.5m wide by 8 m long.
If anyone has any ideas that would be great as this is my first house and I’m stumped.
Re: Drainage issues3
Aug 03, 2010 3:00 pm
I had this same problem.
There should always be AG around the boundry of your house if your builder knows anything.
Check the plans of your house and you should find AG around there. AG pipe will be covered in volcanic rock which is red large stones, or scorier, which is blue or black or grey.
The clay maybe over the rock and the water cant get through. You will need to clear way the clay to get it draining.
I had the same problem, i dug away 5cms of clay covering the entire perirmiter of the house where the ag was, and now it drains well. No more pools around my house.
I then dug some trenches in the high and low spots towards the ag and covered the lot with river pebbles. Its all dry now and we had a really wet winter in my area.
If there is no ag around, you will need to dig some trenches, lay some ag and cover with rock, look up how to do this. You will basically need to direct the water away from your house to a point where it can be drained off.
Get to it though, u dont want soggy footings.
Re: Drainage issues4
Aug 03, 2010 3:37 pm
on the boundary is a small retaining wall (200mm high concrete slab for fence). We have out carport which goes to the boundary so no luck at having stormwater to the front of the house and at the back yard it is slighty sloped about 400-500mm high (we are putting in a retaining wall mostly for looks).
There are no AG pipes. So if i lay some trenches with pipes, will i need to dig a hole for the water to go to.
Re: Drainage issues8
Aug 03, 2010 4:04 pm
Righto so you have a house footing one side and a fence footing the other side, 2.5m apart with puddling in between. No way of draining water to another area so have to deal with it inside the area.
You need to construct a lateral leeching structure (french drain) as far away from the footings as possible, so say a 0.75m wide trench, 1m from your wall, 0.75m from the fence. Grade the dirt from the wall and the fence at 2% to the trench edges. Dig the trench say 1.0m deep. Line the trench with geofabric. Drop in a slotted ag pipe in a geomembrane sock. Backfill with a mix of crushed rock and free draining sand to 0.35m below finished level. Cover with geofabric. Fill with sand to finished level.
Could concrete the area between drain and house afterwards, or put in pebbles etc, but maintain the fall from house to drain edge.
Re: Drainage issues10
Aug 04, 2010 10:44 am
Yeah should be no worries. The grass will stabilise the top of drain area. One problem may be amount of sunshine it gets, especially in winter. May just mean that the grass goes dormant and a bit ugly for a few months of the year.
Re: Drainage issues11
Aug 04, 2010 11:32 am
Thanks heaps keen...I have been searching up and down and just wasnt sure on my options.
so just to make sure i understand what you saying....
I dig a trench, Line it with the fabric, ag pipe, stone, then sand and then i can place grass over the top.??
What actually happens to the water? Where does it go?
About 4 months ago i had a landscaping guy come out and said that they would need to dig some hole approx 1-2m deep, drop in a piece of PVC pipe with stone down the bottom with grates on top. Is this another option?
Re: Drainage issues13
Aug 04, 2010 12:02 pm
Ernie- it sounds like the landscaper was talking about a retention pit (or soakwell as those in WA call them...)
Re: Drainage issues15
Aug 04, 2010 3:00 pm
The water is contained in the retention pit and then slowly disperses into the surrounding soil, where any plants etc can use it...
Re: Drainage issues17
Aug 05, 2010 11:35 am
If the water cannot be drained away then the only option is for it to soak away. Wether you use a pit (soakwell) or lateral leeching structure (leech drain, french drain) the principle is the same - a void needs to be provided for the water to sit in while it soaks into the surrounding soil. Leech drains work better as they have more surface area. The void in this case is provided by the ag pipe and the spaces between the rock and sand mix. Yes I know ag pipes are usually used to absorb water from the soil and pipe it somewhere but another application is as part of a leech drain.
The geo fabric around the ag pipe is to prevent it silting up and reducing capacity, in the trench it is important as it stops what is called "pumping" - the tendancy of the surrounding clay to want to mix with the sand through the action of the water flowing into the drain. In your case get as tight a fabric as you can find or even double it up.
Obviously the leech drain will work better in sandy soil but you have to go with what you have got. By making the drain long and deep you maximise the spaces for the water to drain into. By grading the ground to the drain you ensure that in the case of temporary overflow the water should be sitting away from your house. Due to space restrictions there is a compromise between the width of the drain and the proximity to you house - you want the water as far away from your footings as possible.
Having a lawn over the drain means the roots will help to bind the surface sand together and use the moisture as well. Include plenty organic matter in the top 300mm.
Re: Drainage issues18
Aug 05, 2010 11:50 am
ernie9 - re your previous post, pcv pipe with grate on top - ie makeshift soakwell.
Very little surface area for water to penetrate (footprint of pvc pipe only).
Would take awful long time for water to drain away. Size of void - only as big as what the pipe length can hold, would fill up real quick. Grate on top - for pipe to silt up. How would water get into grate - would only work if surrounding ground is say paved and graded to the grate.
BTW if you were going to pave / conc the entire area then the leech drain setup would not be the go as it is not a rigid structure. In that case you would need a rigid soakwell ie conc with plumbing from a drainage trap or grate.
Should be fine though if you just want a path around the house, wait a while for settlement (6months) of the earthworks though and make sure there is a good strong flush kerb or sunstantial haunching on the edge of the paving. Backfill any subsidence with clean sand as it occurs.
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