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Posted: Tue Apr 20, 2010 10:21 am
by joanna
Hi
First posting so bear with me. I am a gardener, not a builder.
I want to build a raised bed 50cm high against a 2m high retaining wall (holding next door neighbors garden). At the base of the wall are several large drainage holes, 5cm or so diameter. I want to build the bed from concrete blocks and clad these with paving slabs. I don't want to cut large holes in these slabs at all but the side edge is less prominent if I do need large holes. Would i need some kind of drain inside the bed to take the water to the side? The surrounding soil is clay.
Posted: Tue Apr 20, 2010 11:03 am
by seanandruby
yes jo you will need to continue the drainage on. Get a length of filter pipe to go all round the inside against the base of wall and surround in stone. You can, as you say: ''make larger holes to the sides.'' put weep holes at the front between the slabs.
Posted: Tue Apr 20, 2010 6:23 pm
by lutonlagerlout
when you say "build the bed with blocks and clad with slabs " isnt this overcomplicating it?
marshalls and stonemarket (and others i am sure) do some very very nice blocks for planters, much less likely to fail than slabs stuck on to blocks
cheers LLL
ditto what sean said 
Posted: Tue Apr 20, 2010 7:29 pm
by rab1
know this is a strange question but should the neighbour with the retaining wall be draining into someone else's garden?.
???
Posted: Tue Apr 20, 2010 8:51 pm
by seanandruby
it's got to drain rab. It's better than the other option.
Posted: Wed Apr 21, 2010 9:19 am
by joanna
Hi
Thanks for the help. Just to make things a bit more complicated, I want to be able to use the top of the new wall as a seat using a 289mm width slab as capping. I have been looking at building the wall from hollow blocks with reinforcing rods in the corners to get the thickness without building two parallel block walls. Is this a good idea? also whichever method I use how do I get the drainage through both sides of the block and the slabs on the outside? do i run a pipe or is putting a hole all the way through right at ground level enough?
Posted: Wed Apr 21, 2010 11:01 am
by seanandruby
i'm not sure of the block dimensions but it's ok to make it a seat to. cut your holes just a bit large so you can place some pipe in it and grout it in for weep holes.
Posted: Thu Apr 22, 2010 8:39 pm
by joanna
Thanks sean you have been really helpful
Posted: Thu Apr 22, 2010 9:31 pm
by seanandruby
your welcome, glad we can help.