Light well /retaining wall with tiered planters

shimmy · Post: # 42669Post **shimmy** Fri Oct 30, 2009 5:11 pm

Hi all. New to this great site! I will try to be to the point, it's a little complicated...My friends are having an existing basement level living area extended into their garden to create a new bedroom. Outside the bedroom they want to create a small open light well and paved area by building a retaining wall from the already layed basement slab to 203cm high, ground level. The ground level is flat. From the new paved area to ground level they want to create 4 levels to be tiered planters.

Along the way, they sacked their architect and indeed the first structural engineer for various reasons. They now have their original builder, and a second structural engineer on board.
As I am a Designer, my friends asked me if I would kindly design the planters for them and also do an artists impression of what their light well would look like...which I did. I also did some research on building retaining walls. To the crux...

The builder was intending to build the R. wall using poured concrete re-inforced with steel grid, as per structural engineers drawing, to a thickness of 250mm. On the 2 side walls this would be vertical, but on the bedroom facing wall it would be tiered. The builder then intended building the planters on the R. wall tiers using blockwork. Then the whole lot, walls and blockwork, would be finished in render and painted to give a clean architectural look.

I don't want to create problems where none exist, especially as a little knowledge can be a dangerous thing, but I have suggested to my friends that there are some issues that neither the builder and maybe the engineer have not taken into account. I would like your opinions please on the following:

There was no intention to have a drainage infill buffer zone on the earth side of the retaining walls with any kind of water outlet or weep pipes.
There was no intention of having any waterproof membrane behind the wall. The earth would be up tight behind it.

The planters would be block built onto the tiered step levels on the retaining walls, rendered and paint finished, with no drainage at all.

The builder HAS confirmed that all the render finish would be with waterproofing additive...mmm, not sure about that.

There is the provision for a linear drain to go in just outside the bedroom wall to take water from the small paved area, which at the moment would slope towards the house.

One thing I'm sure of...unless they want to grow bog plants or water lillies in the planters, without drainage they are as good as useless...but more importantly, what would be your thoughts on the points above. I have suggested to my friends that the render finish may be damaged, stained or blown before too long due to the R. wall becoming soaked. The same could also happen to the blockwork render. I am assuming that the engineer has factored in any Hydrostatic pressure complications to the retaining wall, but I will check. But why no mention of drainage to relieve this, nor waterproofing the ground side?

Sorry, I did end up waffling a bit! Look forward to your replies!
Shimmy.

Suggers · Post: # 42691Post **Suggers** Fri Oct 30, 2009 9:59 pm

I'm a great fan of the Kriblock system - anything above 2m - looks harsh to begin with - have to excavate, then refill with the spoil - then add topsoil - after 2yrs you don't know it's there - plus, great fun planting into the sections - will post photie when I get a min.
Retaining walls are always a nightmare - releasing the pressure of the water build-up is always the prob - the "Titanic" approach always fails inthe end - you have to roll with it, whether it's a small paved terrace or a mammoth retaining wall - mother nature will have you over.
Regards.

Sat Oct 31, 2009 12:48 am

never saw any retaining wall designed without weepholes, and normally some kind of drainage at the rear of the wall .
my engineer tells me the build up of water is the biggest cause of walls failing so it must be addressed, i take it the rebar is tied into the foundation concrete?
how does any water get away from that low level you are talking about? pumped or gravity?
LLL

4000th post BTW :;):

Edited By lutonlagerlout on 1256950149

Post: # 42694Post **seanandruby** Sat Oct 31, 2009 1:30 am

Hi shimmy. a photo and/or your sketch would be helpful. What provision, if any has been made for draining behind the main wall and wing walls. Has the existing slab had any thickening, extra steel, starter bars added, where the walls are going?

Suggers · Post: # 42697Post **Suggers** Sat Oct 31, 2009 2:00 am

4000 ? - bloody nora !! - congrats old bean - learnt loads from your posts - we should have a pint one day ? - as you know, not too far away.

Suggers · Post: # 42699Post **Suggers** Sat Oct 31, 2009 2:39 am

LUTON 4000

Sat Oct 31, 2009 9:23 am

n1 suggs
I am in stain albans tonight (apparently) will update later
LLL

shimmy · Post: # 42704Post **shimmy** Sat Oct 31, 2009 9:59 am

Wow. Thanks for the quick replies. I was watching my email for reply notifications...of which I have none. So good job I checked directly!
Am trying to link my drawing...it will help explain. Also will come back with answers to your other questions shortly. Thanks all.

shimmy · Post: # 42720Post **shimmy** Sat Oct 31, 2009 3:41 pm

Ok, tried to get picture across, but got techie problems with my pc at the moment.
To answer your questions:The foundation slab I believe is either 200mm or 250mm thick and I do believe it has a DPM layed beneath it. All the retaining walls will be rebarred to it.
Any water accumulating in the well area will have go to the main sewer towards the front of the property. I have heard the builder muttering about a pump...I don't think he's sure yet if gravity will do the job yet.

Any thoughts on the integrity of the render finish?

Also, if the planters are constructed using blockwork, should the inside of the planter be sealed with a waterproofing product. If so, any suggestions. I think it has been accepted that the planters must now have drainage.

From a quick update this morning, I believe the rear of the retaining walls will now have a DPM, but have heard nothing about weep holes or drainage.

One other thought in my mind, if the blockwork is to be render finished, do the top edge corners need to have edging bead, or whatever it's called?...A/ for extra strength and B/ to ensure a good clean line.
Sorry about the sketch, I realise you're all trying to imagine the situation. B****y computer!
S

Sat Oct 31, 2009 5:14 pm

this really is qualified structural engineer territory,we can only tell you what we have done under their guidance on other jobs ,but the bottom line is the engineer designs it and the builder does as the engineer says
good luck
LLL

Post: # 42732Post **seanandruby** Sun Nov 01, 2009 8:00 am

Any wall that height poses a danger, especially as it is retaining a public footpath. Maybe you should speak to building control.