Garden Wall Project - help required

r896neo · 6 Jul 2014

joining of the 2 skins adds strength but a single bound together wall with no ties would be stronger

Hence the need for a 9'' block wall and facing brick.

For example If your were rendering the wall instead of using brick you could have it 13'' block for the first 18'' of height then 9'' up to the top.

You could almost get away with just 9'' block work on its own but not quite in my opinion which i why the 9'' blockwork plus brick skin will give a wall that is strong enough and deal with the staining problems associated with retaining walls using brick.

the 13'' block work is just required to get you out of the ground as its quicker and cheaper to lay than starting your nice brick just to bury 4 courses of them.

You can alternatively bring your concrete up to nearer the surface by making it much thicker and start immediately with the brick and block but you'll need to work out whether that is cheaper than buying the extra blocks. Its obviously faster but if your DIY'ing the cost is perhaps more an issue.

By all means repost a simplified question regarding heights and wall thickness in the building forum and get some more opinions as some may think a 9'' wall is fine.

Personally i work by the rule of 600mm is the max retaining wall height for just 9'' blockwork

spiidey · 8 Jul 2014

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spiidey · 8 Jul 2014

Ok, so we're now looking at a second option.

http://www.ukpavingsupplies.co.uk/wp-content/uploads/2012/12/Croft-walling-design.png

http://www.marshalls.co.uk/homeowne...rmation-sheets/croft-stone-garden-walling.pdf

This mentions a maximum height of 600mm - is that 600mm above ground, or 600mm including the first block that it is suggested is below ground?

Also, has anyone else used this product/method and how did they rate it?

Finally, how far away from the existing boundary fencing do we need to build the wall (i.e. as we need to excavate earth, how much of a gap from the fence do we need to leave to prevent the fence/concrete supporting the fence from collapsing)?

r896neo · 8 Jul 2014

There are many similar products to the one in your link and i use the tobermore secura walling all the time.

they are much easier and faster to build and don't need a concrete footing but the material cost is much higher than blocks.

The tobermore one is suitable for up to 900mm. You may not be able to get it if your in the south of england though as they are based in Northern Ireland and only have stockists in the north of england as far as i know.

It would be much simpler for you if your not confident building brick/block.

Fence wise you'd need to leave at least 2 feet preferably 3 to an existing fence post and take into account that the post will put stress on your wall.

Bearing in mind that you need to also dig out an extra 6-8'' for backfilling with clean stone for drainage.

Your other option is to replace the fence posts with much longer ones into virgin ground behind the new wall. A lot of work though but i have had to do it in the past to get the wall near the boundary.

spiidey · 9 Jul 2014

r896neo said:
There are many similar products to the one in your link and i use the tobermore secura walling all the time.

they are much easier and faster to build and don't need a concrete footing but the material cost is much higher than blocks.

The tobermore one is suitable for up to 900mm. You may not be able to get it if your in the south of england though as they are based in Northern Ireland and only have stockists in the north of england as far as i know.

It would be much simpler for you if your not confident building brick/block.

Fence wise you'd need to leave at least 2 feet preferably 3 to an existing fence post and take into account that the post will put stress on your wall.

Bearing in mind that you need to also dig out an extra 6-8'' for backfilling with clean stone for drainage.

Your other option is to replace the fence posts with much longer ones into virgin ground behind the new wall. A lot of work though but i have had to do it in the past to get the wall near the boundary.

Thanks for this - have asked Tobermore for a quote. We're just outside Edinburgh so hopefully the Northern English stockists will be able to supply/deliver to us.

Do you have the product/company names for the other products that are similar to Tobermore Major / Marshalls Croft (i.e. mortar free retaining walls)? - I'd like to do a bit of research to understand what range of products will fit within our budget.

Also, would you be able to identify what types of stones would be required for backfilling - I'd be keen to keep costs down particularly for this item so if you have any knowledge of this that would be greatly appreciated.

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Incidentally, I got a reply from Marshalls and the wall height is 600mm from the existing ground (so c. 700mm including the bottom row of bricks that will sit below ground level).

spiidey · 10 Jul 2014

I asked Marshalls the following questions [bold] and got the replies [italics] noted.

1. What additional drainage (e.g. drain tile) is required, if any?

The backfill zone consists of 300mm of free draining material followed by the backfill material. This free draining material should equal the height of the wall and any additional drainage should not be necessary. The use of a perforated pipe at the base of the can be used if there is the possibility of water pressure build-up behind the retaining wall.

2. Do we need a reinforcement grid as part of the backfill?

In general, reinforcing grids are not necessary with small retaining walls and in this case with the Croft Walling not exceeding 600mm in height can be omitted.

Further queries:-

(a) Marshalls appear to be ambiguous on the use of a perforated pipe at the back of the bottom of the wall. What is the view on the inclusion of a perforated drainage pipe – is this required based on what I’m intending to do?

(b) My understanding of the backfill zone behind the wall is that there should be 300mm width/depth of free draining material, followed by a further 300mm width/depth of “backfill material”. What is this backfill material? Can I use the existing soil on site that I’m excavating?

(c) I agree with the minimum distance requirements from the existing fence (3 feet or 900mm). Should I also allow a further 600mm on top of the 3 feet for the backfill zone (so effectively the wall will be 1.5m from the fence)? Or can the backfill zone be within the 3 feet allowance, so that the wall would be 900mm from the fence?

(d) Should the free draining material / backfill material / backfill zone as a whole run at an angle from the vertical?

r896neo · 10 Jul 2014

I can't offer other suppliers as i'm in northern ireland so we don't have the same mftrs.

As for the drainage fill 300mm is way overkill for a small wall like yours. 150-200mm is plenty.

As for the material it needs to be some sort of free draining aggregate. any kind of 20mm gravel would be ideal. You can use larger broken brick type rubble but would need a geotextile membrane to seperate it from the soil behind.

The Backfill they are on about is just the dug out soil.

There is no need to use a land drain pipe if its not connected to anything. Water will weep through walling like this without weep holes etc as would be needed on a masonary wall.

The fence is more of a judgement call. I would be very nervous about trying to dig within 2 feet of a post. You should try and compact your backfill in as much as possible once the wall is built.

Just to be clear, because you are at the boundary you don't need to use back-fill apart from your drainage material. So you can just cut your vertical face, build the wall and then backfill with your clean stone.

spiidey · 11 Jul 2014

r896neo said:
I can't offer other suppliers as i'm in northern ireland so we don't have the same mftrs.

As for the drainage fill 300mm is way overkill for a small wall like yours. 150-200mm is plenty.

As for the material it needs to be some sort of free draining aggregate. any kind of 20mm gravel would be ideal. You can use larger broken brick type rubble but would need a geotextile membrane to seperate it from the soil behind.

The Backfill they are on about is just the dug out soil.

There is no need to use a land drain pipe if its not connected to anything. Water will weep through walling like this without weep holes etc as would be needed on a masonary wall.

The fence is more of a judgement call. I would be very nervous about trying to dig within 2 feet of a post. You should try and compact your backfill in as much as possible once the wall is built.

Just to be clear, because you are at the boundary you don't need to use back-fill apart from your drainage material. So you can just cut your vertical face, build the wall and then backfill with your clean stone.

r896neo, once again, many thanks for your very comprehensive and helpful reply.

Just so I'm clear on this then, I am only backfilling with the 20mm gravel, the depth of this backfill of gravel to be 150mm-200mm back from the wall?

i.e. I am not backfilling with any kind of soil as that soil is effectively already there?

So I'd be allowing 900mm from fence for existing soil and further 150mm-200mm for backfill, meaning wall would be 1050-1100mm from fence?

And the requirement for the backfill "soil" is simply to provide additional strength behind the wall so that it doesn't topple back on itself?

And in terms of the drainage, I don't need a land drain pipe as given the construction method of the wall (i.e. no mortar in gaps), the water simply weeps through the gaps between the stones? And this is ok even at the bottom of the wall where the land drain pipe would have been in a typical masonry/mortar wall?

Do we need a damp proof course on this type of wall?

Finally, do we need either impervious soil behind the top of the wall, and/or landscape fabric between the gravel and the backfill soil, as shown in Figure D of the link below?

http://www.familyhandyman.com/lands...ow-to-build-retaining-walls-stronger/view-all

spiidey · 13 Jul 2014

Anyone able to help with this?

Particularly, the reference in r896neo's post re "brick type rubble" that could be used for the drainage behind the wall - what type of product am I actually looking for and what type of geotextile membrane do I need?

If on the other hand we go with 20mm gravel for drainage (as opposed to "brick type rubble",) we've just priced up the 20mm gravel from B&Q as (remarkably) that seems to offer the best deal and its coming in at c. £300 for the amount of backfill gravel that we need, so keen to understand if the "brick type rubble" + geotextile membrane would offer us a saving.

http://www.diy.com/nav/build/buildi...ggregates/B-and-Q-Gravel-Natural-20mm-9273143

r896neo · 13 Jul 2014

your positioning of the wall sounds fine. You don't need a dpc. you don't need land drain pipe.

You certainly dont want any impervious soil as you want it to be free draining or your building a dam which will hold water behind and exert massive pressure on the wall.

You should ideally use a geotextile membrane like terram 100 or equivalent. On a wall your height its probably not going to be an issue if you use 20mm gravel in your drainage backfill.

Any kind of clean rubble is suitable. it would need to be broken up into small bits 2'' size or less. If you use rubble then you will need a membrane because the chunks are bigger and irregular shaped and therefore so are the voids between them and without a membrane the soil will filter into these voids and block them up which will compromise the free draining nature.

You can buy 20mm stone in bulk bags.

SittingBull · 13 Jul 2014

That seems rather expensive for gravel for drainage! Contact these folk in Edinburgh and see if they'll deliver to you. Bulk bag of washed gravel 20mm £35 or so. Can't offer you any advice on your retaining wall but I'm following your progress as I may wish to do something similar in the future!

http://www.thistlebuildingsupplies.co.uk/pdfs/price_guide/Price List A5 April 2014 Web.pdf

Alternatively if you have a local quarry you could contact them - my father in law normally drives a trailer over to one who load it up for much less than elsewhere.

spiidey · 14 Jul 2014

r896neo said:
your positioning of the wall sounds fine. You don't need a dpc. you don't need land drain pipe.

Thanks for this.

r896neo said:
You certainly dont want any impervious soil as you want it to be free draining or your building a dam which will hold water behind and exert massive pressure on the wall.

Again, thanks for this. How is the effect at the top of the attached link achieved (i.e. they’ve got plants in soil at the back of the top of the wall)?
http://www.marshalls.co.uk/homeowne...rmation-sheets/croft-stone-garden-walling.pdf

r896neo said:
You should ideally use a geotextile membrane like terram 100 or equivalent. On a wall your height its probably not going to be an issue if you use 20mm gravel in your drainage backfill.

If we’re using the 20mm gravel do we / should we be using a membrane? The total area to be covered by the membrane would be circa 18m2. Not sure how much that would cost!

Thistle Timber do "20-10mm gravel" for £5/bulk bag less than B&Q, and it comes washed. Is "20-10mm" gravel ok for what we're doing?

http://www.thistlebuildingsupplies.co.uk/pdfs/price_guide/Price List A5 April 2014 Web.pdf

(2nd page under "Aggregates and Sands Bulk Bags")

r896neo said:
Any kind of clean rubble is suitable. it would need to be broken up into small bits 2'' size or less. If you use rubble then you will need a membrane because the chunks are bigger and irregular shaped and therefore so are the voids between them and without a membrane the soil will filter into these voids and block them up which will compromise the free draining nature.

Thanks. What type of supplier would we get rubble from?

r896neo said:
You can buy 20mm stone in bulk bags.

Thanks. Having looked on the B&Q site again, the £40 bulk bags are indeed better value. Will also check out Thistle Timber.

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The wall is going to be running at a slope backward of about 10 degrees back from the vertical. When I’m cutting the existing soil out, should the slope for the other side of the backfill also run at 10 degrees back from the vertical, or should this simply be vertical?

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Finally, what type of sand do we need that ties in with the Marshalls guidance:-

http://www.marshalls.co.uk/homeowne...rmation-sheets/croft-stone-garden-walling.pdf

(Stage 2 on first page)

Washed Building Sand
Washed Concrete Sand
Granite Sand
White Coloured Sand
Something else?

http://www.thistlebuildingsupplies.co.uk/pdfs/price_guide/Price List A5 April 2014 Web.pdf

spiidey · 14 Jul 2014

SittingBull said:
That seems rather expensive for gravel for drainage! Contact these folk in Edinburgh and see if they'll deliver to you. Bulk bag of washed gravel 20mm £35 or so. Can't offer you any advice on your retaining wall but I'm following your progress as I may wish to do something similar in the future!

http://www.thistlebuildingsupplies.co.uk/pdfs/price_guide/Price List A5 April 2014 Web.pdf

Alternatively if you have a local quarry you could contact them - my father in law normally drives a trailer over to one who load it up for much less than elsewhere.

Thanks for this - will take a trip down to them today to see what they can do for us.

They have "Type 1" at Thistle Timber

http://www.thistlebuildingsupplies.co.uk/pdfs/price_guide/Price List A5 April 2014 Web.pdf

(page 2 under "Aggregates and Sands Bulk Bags")

for £28.87/bulk bag inc. delivery which is about half the price of what we've seen online.

http://www.ukpavingsupplies.co.uk/product-category/building_aggregates/

Is this MOT Type 1 that ties in with "Stage 2" of the Marshalls guidance in the link below:-

http://www.marshalls.co.uk/homeowne...rmation-sheets/croft-stone-garden-walling.pdf

SittingBull · 14 Jul 2014

Yes that's the same MOT Type 1 for compacting as a sub-base

Used often under driveways, roads and concrete in general!

spiidey · 15 Jul 2014

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Garden Wall Project - help required

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