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Extending concrete slab balcony (just a bit!)

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  1. #1
    mxh
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    Default Extending concrete slab balcony (just a bit!)

    I currently have a suspended concrete slab balcony that is tiled. It's approx 7m * 3m and one long side and one short side have railings (the other 2 sides are the house walls). The balcony is one floor up.


    The feet of the existing metal railings are set about 10cm in from the edge of the balcony - I assume they're screwed to, or either set into the concrete, and have been subsequentlty tiled around.


    These railings are too low so I'd like to replace them - I would like to put in wooden posts (probably with stainless steel wire, but that's not overly relevant). I'm also going to retile the whole area.


    I'll cut the existing railings off flush with the tiles, and install new fenceposts on the edge of the concrete slab (see this image - https://s-media-cache-ak0.pinimg.com...d7a22a71a9.jpg - for an idea of what I mean, just pretend it's the concrete slab that the uprights are attached to, not wood).


    However, I'd much prefer the posts to appear to be 'within' the balcony, not right on it's edge (see see http://www.johnbridge.com/wp-content...itra-deck6.jpg as an example), and I'd also like for the balcony to have a 'clean' edge (ie the bottom of the uprights not visible) so that I can tile the edge.


    Is there any reason that I couldn't bolt a length of wood on the outside of the uprights, put some ply across the gap, then tile across this gap and down the new edge. Overall I would have 'extended' the balcony by approx 150mm, but none of this area would be expected to take any weight as it's all under, or outside of, the new railing.


    Obviously extending a balcony in this way and expecting it to be weight bearing would be asking for trouble. But what I'm wanting to do is cosmetic only, but would I be breaking any rules in doing this? Or are there better ways to achieve this?

  2. #2
    1K Club Member Pulse's Avatar
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    Default Extending concrete slab balcony (just a bit!)

    asking for trouble I think, wood and concrete don't mix well, lots of waterproofing and rot issues. I'd go powdercoated aluminium bolted to top of slab. It is hard to fix strongly to the edge of a slab with lots of reo in the way and you need to use chemical anchors to avoid fracturing the slab.


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  3. #3
    4K Club Member Marc's Avatar
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    I wouldn't even try to drill into a balcony slab let alone on it's edge.
    Science is never settled,
    it advances one funeral at the time.
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  4. #4
    Je pense, donc METRIX's Avatar
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    Quote Originally Posted by Marc View Post
    I wouldn't even try to drill into a balcony slab let alone on it's edge.
    Really, I drill them all the time, fix whatever you need with either ANKA'S or chemset, Dyna's are not suited.

    Regarding the OP, sounds like a bad idea what you propose, I would coredrill and set new Stainless posts in from the edge and tile around these.
    Mieux vaut prévenir que guérir

  5. #5
    4K Club Member Marc's Avatar
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    Eeuu, gives me the shivers just thinking about drilling a balcony slab ... ha ha I think of pieces of concrete falling off exposing rusted steel 10 floors up ...
    Science is never settled,
    it advances one funeral at the time.
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  6. #6
    mxh
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    Thanks for the replies - always looking to learn, so would like a bit more info on some of the comments


    Quote Originally Posted by Pulse View Post
    asking for trouble I think, wood and concrete don't mix well, lots of waterproofing and rot issues. I'd go powdercoated aluminium bolted to top of slab. It is hard to fix strongly to the edge of a slab with lots of reo in the way and you need to use chemical anchors to avoid fracturing the slab.


    What's the waterproofing issue if I used treated timber? And everything would be covered by tiles, and possibly waterproofed first. I don't see why the wood would rot any more than wood in any other outdoor locatuon. Or is it something to do with being up against concrete?


    Quote Originally Posted by Marc View Post
    I wouldn't even try to drill into a balcony slab let alone on it's edge.

    Why not? I've not drilled into a balcony slab before, so genuinely interested in any concerns you'd have with drilling.


    Quote Originally Posted by METRIX View Post
    Regarding the OP, sounds like a bad idea what you propose, I would coredrill and set new Stainless posts in from the edge and tile around these.

    Can you expand on why you think it's a bad idea. Not disagreeing that maybe it is, but just interested to know why.

    Thanks again

  7. #7
    1K Club Member Pulse's Avatar
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    Default Extending concrete slab balcony (just a bit!)

    hidden wood in wet areas is a bad idea, exterior timber is ventilated so subject to wet and dry cycles, detailing involves allowing free drainage of water and protection of end grain.

    hidden wood rots without your knowledge, the only warning might be when someone falls from your balcony in 15 years, after the waterproofing has failed.


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  8. #8
    mxh
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    Quote Originally Posted by Pulse View Post
    hidden wood in wet areas is a bad idea, exterior timber is ventilated so subject to wet and dry cycles, detailing involves allowing free drainage of water and protection of end grain.

    hidden wood rots without your knowledge, the only warning might be when someone falls from your balcony in 15 years, after the waterproofing has failed.


    Sent from my iPhone using Tapatalk
    So it's just the fact that I'd be boxing in the woodwork that's the issue? For example, if I left it exposed (as per the first link in my original post) then this wouldn't cause the same concerns?

  9. #9
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    I suggest you get an engineer's opinion, given the that it is an elevated balcony.

  10. #10
    Je pense, donc METRIX's Avatar
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    Quote Originally Posted by mxh View Post
    Thanks for the replies - always looking to learn, so would like a bit more info on some of the comments


    Can you expand on why you think it's a bad idea. Not disagreeing that maybe it is, but just interested to know why.

    Thanks again
    It would be hard to attach something to the edge of a slab such as a timber box, then tile over this, your just asking for trouble with different expansion rates, not to mentions it's simply not done that way.

    To extend a slab successfully, you need to drill into the side of the slab, form up the new section, chemset bars in, then pour new slab, for your situation this would not be feasible as you will have a cold joint between the two, which would be a weak point and it's to small to be of any use.

    Stick with what's there, work with the existing slab, your just creating a whole lot of work for an inferior result with no real gain.
    Cut off what's there already, fit new stainless posts, chemset these in, then tile, this will give a more professional finish and be far superior for safety.
    Mieux vaut prévenir que guérir

  11. #11
    mxh
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    Thanks - that's fair enough.


    I have to admit that I have an ulterior motive for wanting to extend the slab. Currently it overhangs the wall / windows / doors underneath by about 100mm, which doesn't give much protection from the elements. With even the smallest breeze in the right (wrong!) direction, rain, plus water running off the balcony, are blown onto the windows and doors.


    My thinking was that by extending the slab by approx 150mm it would give much better protection. Plus it would also give a clean finish - ie a tiled edge. Having to put a gutter along the edge won't be so asthetically pleasing, and it would only help with protection from the runoff rather than the rain. If my idea (of extending the balcony) is not really feasible, what other options are ther for protecting the windows & doors from the elements?

  12. #12
    Je pense, donc METRIX's Avatar
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    Extra 100 - 150mm won't do bugger all to keep the rain off, what about putting an awning over the windows.
    Mieux vaut prévenir que guérir

  13. #13
    mxh
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    Quote Originally Posted by METRIX View Post
    Extra 100 - 150mm won't do bugger all to keep the rain off, what about putting an awning over the windows.
    The windows and doors go right up to the base of the concrete slab, so there's no wall above them to attach the awnings to. Which would mean that I'd have to attach the awnings to the edge of the slab - and as we've seen from previous comments, drilling into the edge of the slab doesn't get a lot of support. Although the bolts for an awning wouldn't need to be as large as for the railing, so maybe this would be a more acceptable idea?

  14. #14
    Golden Member havabeer's Avatar
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    how thick is the slab?

    there's a bit of a difference between anchoring an m6 bolt for some awnings and some 10 - 12mm bolts for a hand rail, your basically just turning the hand rail into a giant lever trying to snap the concrete. I'd just re tile and close the windows when it rains....
    another solution might be to just cut off the old posts that you don't like (not sure if these are round or square) and just find a slightly smaller post that will fit in the inside of the old posts, can cut these at any height you want (assuming its above 1m or what ever the codes says about hand rails at that height) and just glue it in place.

  15. #15
    4K Club Member Marc's Avatar
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    Post a picture. May be you can build a small protection for the window, something like this

    Science is never settled,
    it advances one funeral at the time.
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  16. #16
    mxh
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    Quote Originally Posted by Marc View Post
    Post a picture. May be you can build a small protection for the window, something like this
    I'll take a photo at the weekend, but I don't see the house in daylight during the week at this time of year. But the issue with something like the above is that a) there's no wall above the doors & windows - just the overhanging slab, and b) the balcony is about 11m long (sorry, not sure where I got 7m from in my first post) and about 7m of that is window and doors - so some big spans are required.

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