# Forum Home Renovation Fences & Screens  Balcony balustrades - bolting posts to concrete

## gindy

Hi everyone! 
I'm planning to built wire rope balustrades on my balcony (actually garage roof). I'm planning on using 90x90 posts and 40x90 top rails, in stained treated pine, but if anyone has any other suggestions I'm listening!  :Smilie:  
The main question I have is how to attach the posts to the concrete roof. It is tiled on the top and sides. Plan A is to cut a notch out of the bottom of the posts so that the posts can be bolted to the side of the slab, but also sit on the slab, as pictured here: www.gindyphotography.com.au/shared/1.gif
Would there be any problems with this approach? Should I cut the notch half way through, ie 45mm? The roof is only 143mm thick at the thinnest end, including tiles, Should I use dynabolts for this, and if so how would I space them? Alternatively, I remember seeing another approach involving gluing threaded rods into the holes with some sort of 2-part adhesive from a chalking gun. 
If that isn't going to work. plan B is to use bolt-on post supports or stirrups like this www.gindyphotography.com.au/shared/2.gif and Online Hardware Store - HardwareFast - Australia 
Again, what fixing should I use, and what would the minimum distance from the edge be? 
Thanks guys!  :Smilie:

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## METRIX

Hi 
Don't bolt the posts to the side of the slab for various reasons to do with the slab edge, but mostly because the balustrade will be to close to the edge of the slab, you need to set the posts back around 100-150mm from the edge. 
The stirrup are usually used in conjunction with another support, such as an end bearer on a deck, or a pergola, they are not the best choice for working in isolation as they can allow movement of the post. 
If you are doing Stainless wire, there is a LOT of tension placed on the posts because you are pulling the wire from one post to another post, and there will be at least 11 wires for each run, this adds up to a high lateral force being put on the posts, If the posts are not 100% stable you will get problems, and a stirrup is probably not the best choice for this, a plate such as the ones shown in the picture could be your answer, you could put the timber post in the plate and bolt through it, then bolt it to the concrete, the standard and corner ones would be what you might be looking at. 
Have you considered to use stainless or steel posts [galvanised] designed for this purpose, these are easier to fix down to concrete with either Dyna Bolt or Chemset because the have a welded plate on the bottom, and you will get good strength from a steel pole, bolted down , vs a timber on in a stirrup. 
You can then use timber for the Railings, remember to build the balustrade to BCA requirements, and with wire balustrade they must be tensioned correctly so the wires cannot spread apart [BCA requirements state the amount]. 
I have attached some info from the BCA to help you out.

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## gindy

Thanks Metrix Building! 
When you say the posts should be 150mm back from the edge... is that regulations and/or a structural requirement or...? It seems a long way in to me. 
I've thought of the stainless posts, but the ones I've seen were so expensive, and I'm trying to keep costs down. I'll see what I can find in steel. If I can find a way to do it with timber posts that ends up looking good and is structurally sound, I'd prefer to go that way rather than using metal posts. 
What do you call those plate things you attached (so I can search for them)? Wouldn't they fill up with water? 
Cheers!

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## METRIX

Hi Gindy, 
Sorry I should have explained, set the posts back so the cables are around 100 - 150mm in from the edge, so if you are using 90mm posts then the post would need to be 55-105mm in from the edge.
You mentioned it was on top of a garage, so I assume the height is considerable, therefore I would be setting the post back from the edge a bit more for safety, plus you don't want to be drilling and dyna bolting too close to the edge of the slab, might be better to look at chemset method instead of Dyna bolts as these can explode the concrete if put to close to the edge and if tightened too much. 
We usually have our posts in on a deck around the width of a decking board back from the edge, this is due to the double bearers setting the position of the post at a pre determined distance, then we will run a decking board around the perimeter of the deck to frame it, and depending if there is to be an overlap to allow boards to also run down the posts or if the framing board is the last board with no boards running down the posts the distance of the cable will be around 82mm to 97mm in from the edge. 
At higher distances it would be better to have the cables set back a little further for safety as the cables will flex and open up a gap which a fixed balustrade won't do, so for your one which is on top of a garage I would set them back a bit more. 
Your right the post plates will get water in them, but they usually have a drainage hole in the bottom to allow any moisture out, and you would set your post to not be resting on the bottom, these are really for Steel posts. 
Looking around I may have found an answer for you, the T blade bracket is designed for fixing timber posts to concrete, Dyna bolt it down and cut a 8-10mm slot in the post and bolt the post over the bracket, the one below is made by Tuff Hardware from Advansa, also see the doc attached from HIA. 
Also note a Pine Post of 90mm will have no where the strength of a Hardwood post when pulled from both directions in a corner. 
Good Luck, let us know how you go.   http://www.advansa.com.au/

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## gindy

Thank you! 
Those T-blades look like they'll do the job. I suppose I'd install them with the blades perpendicular to the wires, to better resist sideways loads eg someone leaning on the fence, as the top rail would keep the posts from bending over due to the tension of the wires... right? 
I might be able to get started on this today!  :Smilie:

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## METRIX

Yes make sure the side blades run in the direction of the cables
ensure you use galvanized or stainless steel dynas probably M12 size depends on the sized holes in the plate 
Yes the top rails will assist to support the posts.

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## blocka

I was looking at attaching posts to a concrete balcony as well, but planned on horizontal wooden slats instead of wire.
But anyway was thinking how concealed are the t-blades. Do they stick out the sides of the post? Does the post sit of the ground leaving a noticable gap?
How about something like Titan Post Anchors
I cant see anything similar in Australia but they look like a neat solution.

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## METRIX

Horizontal slats would be no no on a balcony, as these can be used as a ladder by small children to climb over and fall off. 
I hear you say, so can Stainless wires, but it is harder for a child to get balance on a 3mm wire as opposed to a piece of fixed timber.

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## blocka

The balustrade at the moment has lattice infill so is a good climbing device, but i know what you mean. Do you think i can get the horizontal slats close enough together to be OK?

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## METRIX

> The balustrade at the moment has lattice infill so is a good climbing device, but i know what you mean. Do you think i can get the horizontal slats close enough together to be OK?

  You could but it depends on how much light / view you want out of that area, Lattice is a different product that the openings are little squares and can be hard to get a foot hold onto it, where a piece of horizontal timber is perfect to put your foot onto it, and kids fingers are small, so they can get into situations where you might think it's ok because your fingers don't fit. 
At the end of the day anything can be used as a ladder and needs to be considered, Lattice, wires etc can all be used as climbing aids, you just don't want to promote is by putting up something that makes it easier.

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## perestroika

Thanks guys, the above posts do answer some of my questions. But I have more!
In my case the slab is 80-90 mm thick. It's a front balcony that is also the main entry to the house. A large brick hob (actually an old brick flower bed) is on the slab around the perimeter and the existing balustrade (cement "vase" balusters) is fixed to that hob. I'm planning to remove the hob and fix new (wrought iron or aluminium) balustrade directly to the slab (after tiling, of course). Problem is, the supporting wall is single brick, so the slab edge sits on half a brick width. The front edge of the slab is covered with half brick so that it looks good. This area makes me a little nervous thinking how to reliably fix the balustrade to the slab. 
Questions:
1. Do I have to go in by more than standard 100-150mm? 
2. Is the 80-90mm slab thickness enough to hold posts?
3. How about waterproofing? The post fixing will pierce the waterproofing, can it be re-sealed reliably?  
Any input is appreciated!

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