Retaining wall drainage

[mo-uk]

Hi

Patio goes to a brick wall that is 3 walls high. Behind the brick wall is turf.

There are no proper drainage channels near to the wall.

If we wanted water that rolls down the patio to the brick wall to go behind the brick wall and into the mud (underneath the turf) what is the ebst way to achieve this?

Drill some floors at the bottom of the brick wall so the water can gothrough it. Then have some shingle or something underneath the grass to hold the water until it goes into the mud?

[Suggers]

eh?

[seanandruby]

The idea is for the water to fall into shingle behind the walls, through the turf on top of the mud and through weep holes to your patio.
You can't drain a patio to go behind the wall and expect water to wait it's turn to drain away. You will have to drill some weep holes into the walls, so that it drains through the turf on top of the mud.......etc. The patio will need it's own drainage on the other side of the wall, also to take the water from behind the wall. For it to work the opposite way, you would have to ensure that the drainage is a lot deeper than the patio, on the garden side, and runs to a soakaway, or other low point.

[mo-uk]

Maybe a picture will help demonstrate.

http://img219.imageshack.us/img219/8572/73904864.jpg

It is worth nothing that the wall does not support the weight of the mud (not really anyway) and the mud comes up about 1.5 bricks high. The wall is 3 bricks high in total.

So the blue line is water at the bottom of the patio slope meeting the bottom of the brick wall .I am suggesting some holes for the water to travel through and into lots of shingle UNDERNEATH the turf and some mud.

Yes, when it rains there will be water on the turf and coming through the wall so that area will have a lot of water.

In terms of drainage is shingle good for holding water before it can slowly soak into the mud? how much and how deep of shingle would you need?

[seanandruby]

Is it april 1st?

[seanandruby]

You really do need to try and put your drainage on the patio side of the wall.

[mo-uk]

The grass side of it doesnt need to drain OUT of the wall - its been like that for 20 years and the water drains fine within the turf

the issue is where the water from the patio side goes

unfortunatley having a drain on the patio side of the wall is not really possible.

[mickg]

you either need to cut the patio paving to form a channel approx 150mm to 200mm wide and 600mm deep and fill with gravel for the water to drain into

cut the patio flags and install drainage channels which will still need to drain somewhere but you would not see gravel at the edge of your patio or do something similar as the diagram below



for detailed construction click here

depending on the ground conditions you might be able to dig only 400mm - 500mm and fill with clean gravel but you would only know the answer to this

just drilling holes in the mortar joints will soon get clogged up with detritus you need to open all the joint in the brickwork with at least a 25mm drill bit and make sure its kept clear

[mo-uk]

mick - thats exacty what i was thinking - i'll have to look up this perforated land drain thing though!

will pea shingle be ok as the gravel or is there a suitable cheap alternative?

[mickg]

the cheapest clean stone whats available in the area where you live, either 20mm or 10mm in size does not matter what ever is the cheapest

[mo-uk]

can i just clarify something

if i use the perforated pipe - all it does is act as an extra place to hold the water right? it doesnt have to connect to someother drainage system

if i use a plastic pipe is there not a danger of it collapsing under the weight of gravel if it is say 50cm deep?

would you place it on top of the soil or even more gravel?

having read this

http://www.pavingexpert.com/drain03.htm

it just looks liek it can be used as an extra thing to hold the water for a while before it drains

i only ask because i wasnt going to obther with it but it looks like i might be able to get some for free..

[lutonlagerlout]

normally mo the perforated pipe would have the slots facing up to collect the water,the pipe would then lead to an outfall or ditch of some kind
I installed one a few years ago next to some school playing fields and when it rained the water came out of the out fall like a fire hose,but better that than putting pressure on the wall
cheers LLL
PS if you have the normal pipe you can perforate it yourself but cutting 100mm slots every 50 mm,slow work though

[mo-uk]

ill not bother with the pipe

bought 5 bags of gravel from b and q today and will need a fair few more.

I will go approx 15cm wide and 30cm down

if i am having holes in the wall say 60cm apart do you think i need to gravel all the way along the back of the wall or could i get away with just doing say 15cm each side of the hole and 30cm down

i.e if the holes are 60cm apart would the water ever get to the 30cm bit in between them? i would guess not.

[seanandruby]

never skimp on materials.

[cookiewales]

never skimp on materials.

ditto its not wise recipe for disaster buy a bulk bag from wickes they also deliver ps pipe helps bigtime ??? :;):