Just after a bit of advice on how to attach a glass and steel balustrade (1200m high)to the top of a retaining wall.

The wall is built of a single row of 7N concrete blocks, layed on their broad side, so 215mm deep, 100mm thick, 440mm long, about 2.5m high, on top of this is a layer of 50mm thick, 900 long 215 wide concrete paving slabs.

Balustrade is an L shape, one end will be attached to a concrete wall.

Roughly how deep do I need to go for the fixing at the base of each post? Do I need to go deeper than the first layer of concrete blocks? As it’s attached to the wall and also an L shape that should reduce the possibility of it pulling off the top row of blocks? Or do I need to go deeper and put in threaded rod 2-3 blocks down then bolt each steel post into these?

Thanks!

I build stuff so not an engineer but I’d want to see a plate a minimum of 300mm further down the wall bolted with resin
I did applied mechanics to o level standards and can still remember moments
The 1200mm has so much leverage to accidentally pull up the one course of block no matter how well it’s built

I wonder if clockwise and anti clockwise moments are still taught at school along with the coefficient of friction Greek u

As a structural engineer, I’m more concerned that you may have a retaining wall 2.5m high, built from a single row of 7N concrete blocks laid on their broad side, so 215mm deep. I’d be worried about a wall of those dimensions even if it only had to stand up to wind load.

What is it supposed to be retaining?

What length is the wall and L return?

I would like to think a retaining wall that high will be much wider at the bottom and reducing in width as it gets higher and maybe the last 3 course only 215mm wide

Sorry yeah wall is a few courses deep at the bottom, and also buttressed on the front edge in a few places, and tied into the wall of the house. It’s retaining soil but has been there for ages with no sign of movement.

Drop is 2.5 m max but decreasing to about 1m at the L corner, then on the other side of the L it the drop decreases to 0 in about 1.5m

L shape is 4.4m from house to corner of L, then 6m on the other side of the L but after 1.5m it’s pretty much buried. So balustrade or whatever I erect is to protect a fall from the 4.4m house to corner length, the. About 2m along the other side, until the ground meets top of wall level.

The inside of balustrade is protected from wind by the house, so wind direction blows onto the outside corner of the L.

Is my patio / house going to fall down?!

How about using the correct brackets to fix the posts (lower down) to the front of the wall?
Did this on our balcony because I did t want anything drilled I to a flat roof – works really well.
I’d be wary of the free end that was unsupported.

IANASE obvs.

Stainless box steel with a plate to spread the load along the run
Or remove the paving slabs and fit some channel, weld feet to channel
Core out a deep well, chemfix ss tube and drop bulestrade onto that
Box ss steel posts with flat tops, bolt verticals to that, chemfix the ss posts into the retaining wall, yes there’s an offset but it migjt be able to be engineered out.

wall is a few courses deep at the bottom, and also buttressed on the front edge in a few places, and tied into the wall of the house. It’s retaining soil but has been there for ages with no sign of movement.

That’s good to read. So the short 2m leg of the L is supported by the long leg, but only at the end, and the long 4.4m leg is supported by the short leg and the house wall. How robust the fixings need to be, in practical terms, depends on how rigid the balustrade is (ie, how many fixings will is share a load onto, and what kind of activity will take place (ie, two people sitting in chairs, 20 people standing drinking, teenage kids running about, would you be concerned about liability to visitors).

In terms of legal requirement I don’t know if it counts are part of the house and may be subject to Building Regulations. If it is, it’s relevant whether you’re in England & Wales or Scotland. For E&W, it has to resist the loads in BS EN 1991-1-1 with National Annex, and PD 6688-1-1. That’s not helpful unless you have copies of those BSI documents and unfortunately I’m now retired and don’t.

To summarise, how laterally rigid will the balustrade be, do you need practical resistance to the likely loads or compliance with codes and regulations, in which case, are you in Scotland?

reading all the above, ive decided im just going to get a company that knows what theyre doing to inspect the site, build and fit it, much less worry!

I’m curious..is the wall 2.5m high but only 100mm thick as in wall width? this would be a strangely thin and high wall, maybe not something you would want to be leaning on.

I’m curious..is the wall 2.5m high but only 100mm thick as in wall width?

I think its 215 wide (from the original description)

If its individual posts with a seperate handrail then i would core drill down through the coping stone, the first 2 blocks then into the third block (so about 300mm total)
Resin fix the posts directly into the holes.
You can buy all the components to screw / glue together and save yourself a small fortune

I took it that the blocks are laid flat.

^^ yeah blocks are laid flat

If its individual posts with a seperate handrail then i would core drill down through the coping stone, the first 2 blocks then into the third block (so about 300mm total)
Resin fix the posts directly into the holes.
You can buy all the components to screw / glue together and save yourself a small fortune

Yeah that’s what I’m looking at, posts, glass and handrail. If each post has 3 bolt holes at the base, is my idea of threaded rod (resin fixed down to 3rd block) then the post screwed down onto the rod not strong enough? The places I looked only did the posts in standard lengths so I’d have to try and find longer post to resin those in, and core drilling would be harder? If your method is much stronger then I’ll look into that!

It is the “strongest” way, as the post will become an integral part of the wall and give it some strength.
What you suggest will work, but IMO it would just be satisfactory.
Cheapest way (assuming you have a way of cutting it square) is to buy full lengths of tube to cut to the length you want. Or use someone like Brundles and get them to cut to length.
You can also find a local drilling company to come in to core drill the holes. If you mark out where you want them, they will knock them out in no time (and probably get them straighter too )

Can you hang a bracket over the wall and down the face or would that look toss

From a practical aspect, there’s no benefit in fixing the balustrade more strongly than the strength of the wall. If you bolt the posts into the top block, all that’s stopping it tipping over is the mortar under that block (in tension) and at the sides (in shear). The weight of one block is negligible. If you embed it in the top two courses, the interlocking of the blocks probably means you have the mortar under two blocks and the weight of 3 or 4. Embedded in 3 blocks, you might have the mortar under 3 and the weight of 8 or 10. After that there’s no benefit as you overlap with the next post.

What you actually get depends how strong the mortar is, how well it’s laid, shrinkage cracks in the vertical joints, etc. Whether it’s strong enough depends (as my post above) on what you need, but you’re unlikely to make it much stronger as it will be limited by the wall strength.