Foundations for a small wall

DrPhilG

I have a bit of grass, raised about a foot, connecting my front and rear gardens.

The rear garden is raised, with a low wall around it and I want to continue that wall down the side section.

The yard is concrete, and the section of grass I'm talking about has kerbing along it at present.

So the plan would be to build a wall, about 50cm high, along that strip on the outside of the existing kerb.

Would I need to dig founds for that? Or given the small size of the wall and the fact that there's nothing really leaning on it other than filling the soil/grass up a bit, and it being built on concrete, would it be needed?

Apologies if its a stupid question, I will be getting a pro in to check it out but I'm just checking to get an idea of how big a job it'll be.

Lumen

There's concrete under the grass?

DrPhilG

https://www.boards.ie/discussion/comment/120613957#Comment_120613957

Under the kerbing yes, not beyond it.

hesker

As an alternative would you consider planting shrubs and flowers on that bank instead. Would look way better imo

DrPhilG

https://www.boards.ie/discussion/comment/120616301#Comment_120616301

There are 2 reasons for building the wall in the first place, (sorry I should have mentioned them in the first place).

1 - we're putting limestone cladding on the rear wall and want to continue that right around the corner.

2 - I'm getting a robot mower and it will use that strip to drive between the front and back lawn.

So a wall and keeping the grass strip are both essential I'm afraid.

Lumen

https://www.boards.ie/discussion/comment/120613970#Comment_120613970

So not under the grass then? 😀

TBH you're not going to get a definitive answer because it depends on a factors which are unknowable from pics, like ground conditions. Standard wall foundations are double the width of the wall and about a foot deep, but as this is fairly low 6 inches depth might do; it I'd be inclined to ask the people quoting what they'd recommend and using that to filter out the "it'll be grand" cowboys.

I wouldn't personally build a block wall in this situation, I'd do a properly battered dry (field)stone wall without foundations (just topsoil removed). If there's no mortar and no render then there's nothing to crack and no maintenance to do, you can't get any hydrostatic pressure building up in the case of heavy rain and it's more environmentally friendly and more fun to build.

There are some clever ways to reinforce ground behind a retaining wall using horizontal mesh. Unretained soil shears vertically, so if you put in a layer or two of reinforcing mesh you can lower the surcharge on the wall without cement-based engineering.

policarp

Unless you are in a flood zone I wouldn't think foundations are necessary

for a garden wall.

CreadanLady

https://www.boards.ie/discussion/comment/120625721#Comment_120625721

You'll have a nice looking wall in 6 months time.........Disregard this nonsense OP.

This is what you need..... CC-SCD-02401 (tiipublications.ie)

From that you'll need a foundation 700mm wide and 225mm deep. Put an expansion joint through the foundation and wall at 6m centres.

DrPhilG

https://www.boards.ie/discussion/comment/120658309#Comment_120658309

Thanks for the link @CreadanLady

Whats confusing me is that the existing wall (been there nearly 20 years) doesn't seem to have this.

It's single block, on its edge (so the thickness of the wall is only 100mm), there are no expansion joints as far as I can see and I've lifted the copings off a fair way along it.

It looks (and I will scrape away a bit around the base) as though the existing wall was just built as is, on top of the concrete yard.

CreadanLady

Well yes, you can have that. And it may well be fine. But it would not be a good practice to build it that way. Possibly could do it this way by having a thickened yard slab edge with reinforcement.

Block on edge walls are dodge as they can easily topple if damaged or struck by a vehicle, or could be pushed over by extreme winds.

Block on flat is far more sturdy.

Expansion joints give you greater assurance against ugly looking cracks. the movement is absorbed by the joint instead. If you build a long length wall, it will definitely crack somewhere at some stage.

The detail i've given is the way to go if you want a sturdy wall that will be free of problems if built right.

DrPhilG

Thanks again @CreadanLady for the detailed response.

I'll be honest, I'll probably fire ahead with a less advisable route. I had a fella come in and give me a price to build the wall including digging up the existing concrete etc and he priced me at €10k. For a 25m wall that's less than 2ft high that seems mad. And even if it's a fair price, it would make the whole job prohibitively expensive.

The wall won't be exposed to the weather at all, won't be in any danger of being hit by a car, and won't have any pressure against it as most of the soil behind it is already held by the existing kerbing.

So whilst I'm probably going to plough on against your advice, I do appreciate you giving it and I'll speak with the guy doing the work to see if there are any additional measures we can take to be on the safe side.

And if in doubt, I'll just pull the plug.

monseiur

If I understand you correctly - you plan to take down the post & rail fence and replace it with a 500mm block wall. Firstly remove top soil then dig a trench approx 9'' wide and 6'' to 8'' deep. Make allowance for pillars which will be wider. Fill this trench to top with concrete and add two runs of 1/2'' or 3/4'' rebar. Try to get the finish as level as possible, it will make the block layer's life a lot easier when he's laying the first row of blocks. Judging by the photo this wall will be higher than wall at back of house so you may have to step your foundations down gradually to meet this wall. The birch tree will have to go too😉

DrPhilG

https://www.boards.ie/discussion/comment/120661021#Comment_120661021

Hi @monseiur, you don't understand me correctly I'm afraid! I'm probably doing a poor job of explaining myself.

The proposed wall is to be built onto the base of the existing concrete yard, on the yard side of the kerb. So no plans to disturb the current grass shown here other than to add some soil and level the grass a bit.

The fence etc stays, so it'll be fence, then strip of grass, then wall, then yard.

These pictures might make more sense. The red lines in pic 1 are where the blocks of the wall would be placed.

And for height, it would be only maybe 500mm high, to tie in with the existing wall at the back (the right in this pic)

Excuse the crappy photo editing.

CreadanLady

Look, you could do it and, sure, it might be fine and last if the footpath slab is strong and if the build-up under it was done right day one. But nobody can tell you that it will last and won't crack, or that it won't crack the footpath over time.

What you'd be doing is just chancing something cheap and cheerful and and hoping for the best that'll it'll last. That is all anyone can tell you for what you are proposing.

The fact of the matter is, what you are proposing would not be a good practice and no assurance of its longevity could be given. What's more, if you plan on banking up soil at the back of the wall, built as you propose, it will almost certainly fail in a relatively short time.

I have given you a detail drawing for what would be a good practice in building a wall. This is something that will last many many years.

So you have 2 choices here - a) build the cheap and cheerful option and hope for the best, and accepting the uncertainty that comes with it and accepting that it may well fail in a relatively short time, or b) invest time and money in a good quality build that can be assured to last for a long time.

The choice is yours here, and it depends on what your priorities are and whether you place more personal value on speed and cheapness vs quality and higher cost.

You've been given all the information one could give here. There really is no more to be said about it. You just have to choose which one suits you best.

The other thing you need to mind here is that AJ cover. Don't let the wall interfere with the opening of that. It might seem obvious, but you'd be surprised at the things you'd see done.

CreadanLady

The other thing i am curious about is why you want to build that wall? A 500mm high wall won't benefit for privacy, or any other benefit that I can think of, but it will make maintaining the grass behind significantly more difficult.

Imagine yourself trying to muscle a lawnmower down that narrow strip of grass, and it constantly slipping downhill getting wedged in at the butt of the wall. Imagine all the crap and detritus that'll naturally tend to accumulate down at the back of that wall. Think of the weeds that'll take hold and be hard to get rid of because the mower can't get them growing up the back side of the wall. Think of yourself in there with a strimmer after the mower trying to cut them, and slipping and falling back on your arse all the time on the steep slope.

If I saw a wall like that built 1m in from a boundary fence, on a footpath, I'd be thinking what on earth is the f-ing point of that thing.

will a robot mower even handle that slope? It might sure. But it would also equally well travel along the footpath. you could just include the footpath as part of its "field" when setting it up.

Also building that wall with the cladding on it too will narrow your footpath. There will be a right pinch point at the chimney. Ideally you should still be allowing enough room to get a wheelchair past.

monseiur

https://www.boards.ie/discussion/comment/120661930#Comment_120661930

A picture speaks a thousand words !. You can build a 500mm wall there no problem, just scrape off and power wash moss, lichens etc. and perhaps brush on a coat of unibond / polybond (mix 2 : 1 - half a litre of polybond mixed with one litre of water) to ensure that the mortar adheres well to concrete.

Regarding height of wall, the standard 100mm block is 225mm (9'') so two rows will give you 450mm - 50mm lower than required and if you add a third row your wall will be 675mm For a 500mm wall lay a row of bricks on top of two rows of blocks.

The 25m. wall should take roughly 120 blocks and 120 bricks - say 2 to 3 days work for a handyman working on his own.....and you were quoted €10k. for the job.

DrPhilG

Well in fairness the fella with the €10k quote was going to dig the place to bits and go the founds route.

Thanks for the info.

I'll measure the wall properly, I'm estimating that 500mm height at the minute.

bfclancy2

https://www.boards.ie/discussion/comment/120665178#Comment_120665178

120 blocks and 120 brick, should be done by lunchtime in fairness

monseiur

https://www.boards.ie/discussion/comment/120665427#Comment_120665427

I know your tongue is firmly in your cheek...but for others to understand there's a little more to it than laying the blocks. Blocks, sand, cement etc. has to be brought to site + concrete mixer. The existing concrete slab has to be scraped & power washed. Site has to be cleared of all waste / leftovers when work is completed..... + tea breaks, chats with client, trips to builders suppliers etc. 🤣

monseiur

https://www.boards.ie/discussion/comment/120665225#Comment_120665225

I know of a big 4 bed dormer bungalow & separate garage built last summer all by direct labour. Two lads did all the block work - cost €8,500, client supplied all materials & scaffolding.

DrPhilG

@monseiur I checked today, the wall will be 550mm in height.