Retaining walls..... again!!

I've been reading about retaining walls over the past couple of weeks and there's so much conflicting information out there. I know every job is different but every time I read a how-to it says something different.
anyway, here goes...I have an extension on the back of my house put up by the old owners in the 80s. That's fine but it looks like that when they dug out the footing, the earth they dug out they left in the back garden and stuck a few flags on it to form a patio area (if you can call it that!). The garden in general slopes up about a ft in height over a 25ft distance so not a huge amount.
The first two ft against the back wall of the extension however slopes down very slightly ( as it should two brick below damp course) then the slope starts rising all the way to the back.
Wanting a flat area, I've dug out a 10ft square patio area at the back of the extension (through various layer of shite concrete that the lazy builders didn't bother removing) that slopes away from the house. I've measured from two brick below DPC the 30mm (flags) + 25mm(sand) + 75mm(hardcore) and created a 25mm drop over the 9ft for drainage. That i'm not too worried about it but at the end of the 9ft is the rest of the garden where the grass was before I took the turf off.
From the height of the patio there will be about a 1ft to 1.5 from the top of the flags to the grass level. To compensate for this i'm going to build a small retaining wall and a step. I've dug the footings at the end of the patio 9in deep and 17in wide filled them with a 1:2.5 cement,sand mix.
I now plan on building a retaining wall of two brick thick with a top soldier layer as edging for the grass.
Some questions...
Have I gone about this the right way?? I also plan to leave vertical weep holes 1m spaced at 1 course about flag level of drainage??
Do I need a DPC for this, or as it's in direct contact with the earth there will be no point? or can you but a dpc along the back of the wall - but then how will it drain??
What happens if i render the wall ? how will it drain?
Would it be better to do a single skin of normal bricks and a skin of concrete blocks for greater strength??
Should i leave a gap between the two skins and fill it with mortar for stability ?
Should i join the two skins of brick together using butterfly wall ties for greater strength, stability??
Considering the height of the wall and the fact that it is only really holding back a ft and half height of ground am I going a bit overboard with all this.
Just want to make sure I'm doing the right thing.
Cheers if anyway can help!!
Jt
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I took a simple option and built a retaining "dry" stone bank sloping back at 45%. Frogs came to live in it and ate all my slugs but I doubt if it would last forever if kids were climbing on it.

I wouldn't do that. You are storing up maintenance problems for the future Anna
~~ Anna Kettle, Suffolk, England |""""| ~ Plaster conservation and lime plaster repair / ^^ \ // Freehand modelling in lime: overmantels, pargeting etc |____| www.kettlenet.co.uk 01359 230642
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snipped-for-privacy@hotmail.com (John) wrote in message
If you draw a diagram I might get a clue what youre talking about.
Regards, NT
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<<<snipped>>>
If you follow this system on your build, then you won't go far wrong:
http://www.pavingexpert.com/featur03.htm
This site also has a lot more info' on it about all type of hard landscaping and patio feature and builds, so it might be worth a read through for you.
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Yeah i've spent hours reading through pavingexpert.com but sometimes the information can be a little hard to understand. Not from a technical point of view more from a "i am doing this way" or "am i doing it that way". It's like for example i've done the footing for the wall as per the recommendations in my DIY book. A builder friend came round last night and said that the footing were 'impressive' and that they were probably more substantial that than the ones they build for the extension. The problem is more everyone tries to cover themselves from a legal standpoint so give information on worst case. I'm only putting up 3 courses of bricks but i've done footing for this and above.
J
PS i'll try and throw a diagram together
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landscaping and

Don't forget that pavingexpert has a forum section. They're normally good for clarification of information that's contained within the site itself.
Your point about tying the two skins together with butterfly wall ties... you could side-step this problem by using a bond other than stretcher bond - for instance english wall bond (there are references for the common bond types on paving expert). In this case the skins would be completely tied together by the bricks themselves.
I'm not a bricklaying expert by any stretch of the imagination, but I would have thought that with only a 30 to 45cm high retaining wall you're going to have a fair bit of forgiveness if anything in the design is wrong - you don't have the massive weight of earth against it that you would with a 1m+ retaining wall.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
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Thanks Richard,
I've looked at the different type of bond and was thinking along the same lines. As you say i can't imagine that a few brick courses are really going to make much of an impact on the foundations i've put down - so i should be pretty much ok. I'll check the forum out anyway.
Thanks J
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They recommend a polymer DPC 6" above ground, with no other means of tying the brickork above it to the brickwork below. Surely it would simply sit on it loose. Not sure I like that idea, not for a straight run anyway.
Regards, NT
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On 14 Jun 2004 01:45:46 -0700, snipped-for-privacy@hotmail.com (John) wrote:

Sir
Im my garden I have a 2 foot high retaining wall, out of single skin decorative brick, with very little foundation, no weep holes. It works fine, so I guess that yours will be more than adequate.
Yesterday I poured the footings for a 1.8m high retainer, the footings contain 800 quids worth of steel, and a 1000 quids worth of concrete. The design work cost me 600 quid. This is the other end of the scale, but overall its only two cources of blocks thick, however the middle will contain 100mm of steel reinfoced concrete. There are no weep holes, I have not worked out the cost of the waterproofing and drainage products.
Aparently the rule of thumb is height / 4 = thickness.
In reality your design sounds the bees knees. Whats the worst that can happen if it falls down - from what you descibe - dented pride.
Enjoy building Rick
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Is this 4x figure really realistic? For what kind of walls, just retaining? I'm guessing a 10 foot high 4" wall wouldnt quite meet your approval. :)
BTW your expensive figures, why were they so high? I've not done wall design and construction before, but may need to some time for a retaining wall. A bit of advance clue would be handy!
Regards, NT
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On 18 Jun 2004 16:11:38 -0700, a particular chimpanzee named snipped-for-privacy@meeow.co.uk (N. Thornton) randomly hit the keyboard and produced:

That's for a mass concrete (unreinforced) wall with direct load coming from above, such as an external house wall. For unrestrained walls, I gather it's height/3. A 10' (3.05m) high garden wall would need to be at least 3'4" (1.02m) thick
--
Hugo Nebula
"The fact that no-one wants a piece of this
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(N. Thornton) randomly hit the keyboard and

Then I would have to wonder what you mean by 'need.' Mine's nowhere near 3'4", its concrete block, and its still there.
Regards, NT
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There is a retaining wall about 10ft high next door, connecting to the upstairs of the house via a concrete bridge. It was a self-build house and, when it came to be sold, the building society insisted that the original wall should be demolished and rebuilt to proper civil engineering standards.
The new wall is just 2 bricks thick, but on the inside are a series of massive reinforced concrete slabs. Each slab is about 1ft thick. The bottom slab extends about 6ft backwards, and each succeeding slab is then slightly shorter. So there is a pyramid of reinforced concrete behind the wall.
There is extensive drainage which (afair) pipes through the bottom slab.
The whole exercise apparently cost something over 15000 about 10 years ago.
--
Tony Williams.

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