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  1. #1
    Join Date
    May 2008

    Default Replacing an existing deck

    I am an amateur looking for some advice about replacing a treated pine deck around my pool - the boards are splitting and lifting. The pool is a concrete pool sitting entirely out of the ground on piers below a rock cliff - so the deck is level with our yard but up to 3m from the ground level below - the area is about 50m2. The joists sit on the concrete lip around the pool edge (and posts/bearers away from the pool). I plan on using the existing posts, bearers and joists. Is this ok or should I replace them? They are treated pine about 10 years old.

    I would like to drop the joists so the deck is level with the pool (I plan to lay a row of sandstone pavers around the edge). This means rather than sitting on the pool edge the joists will butt agaist the lip (the lip is about the same thickness as a joist). What is the best way to secure the joists to the pool (the pool perimeter is about 25m)? Should I use joist hangers dyna-bolted into the concrete or can I dynabolt angle-iron to the concrete and have the joists sit on it? If the latter what size and thickness of agle-iron and size and spacing of bolts should I use?

    The existing pool posts are H5 treated pine and are buried in the ground (premably concreted). Are they OK like this? Someone suggested to me they should be in stirrups but I though that was only if they were sitting on a hard surface.

    I plan to use a composite decking board (eg ModWood). I want a hardwood look but don't want to be a slave to annual staining - and want something more environmentally friendly. Has anyone used composite decking and can recommend one?


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  3. #2
    Join Date
    Mar 2007


    Bit hard without a site visit, but a few comments:

    At that height it is likely that you would be required to get approval for what you propose as you are substantially altering the sub-structure - but would not if you simply replaced the decking.

    In any case re-use of the TP sub-structure is fine - should have 20-30 years or more in if is it is still stable and has no signs of failure. The H5 posts in-ground are fine too - what they are designed for and will be there for another 30 years easily.

    Is the pool concrete or is it fibreglass sitting inside a concrete retaining wall? If concrete you propose attaching to is the pool wall then I would be wary of drilling to attach dynabolts or anything else to it because of the risk of cracking in 10-year old concrete of unknown thickness or strength. If the concrete is just a retaining wall then the dynabolt solution to put in a new ledger for the joist ends to sit on is fine.

    The ledger could be steel angle as you say and it would need to be at least 50x50x8. Or you could bolt on a timber TP ledger say 90x45 and that would making fixing easier and no drilling into steel. Or you could just afix some posts from the ground to hold a new bearer in position below the pool lip - using dynabolts or masonary screws with the post sitting on a concrete pad at the base.

    Lowering the joists is quite a bit of work as they will all have to be lifted and the bearers lowered and the joists replaced. If the bearers or joists are over sized for the span you might be able to notch out either or both to gain the 19-22mm lowering you are after. But that is labor intensive and you need to confirm from span table etc that this would not weaken the structure.

    Easiest is to take off the joists then lower the bearers by re-housing and bolting them into the posts, adding the new bearer adjacent to the pool edge and below the pool lip (down the thickness of the joist + decking), refixing the joists and laying the decking.

    The composite decking works fine for poolside decks.

    At 3m heights on and edge this is non-trivial and potentially dangerous work. If it were simply pulling up decking and replacing it you could do so in stages just working off the existing deck, but what you propose is major structural work.

    You should seek some direct professional advice and assistance before going ahead (which is not to say it can't be done by a competent layperson under good guidance).

  4. #3
    Join Date
    May 2008


    Thanks Bloss for some great advice.

    The pool is full concrete 150mm thick but around the top rim there is a lip 300mm thick and 190mm high (below this it recesses back 150mm to the outer pool wall). I was planning to bolt into this lip. Is that likely to be OK? The joists are 140mm x 45mm so the lip isn't high enough to bolt a 90mm timber ledger with the joist on top which is why I was thinking of angle iron.

    Maybe a silly question but does it mater which way up the angle iron is? If I have it "upside down" the joist ends can sit flush against the pool lip.

    Given I can re-use the posts, as you suggest I was thinking of just cutting 140mm (+/- for deck and paver thickness) of the top and rehousing the bearers (240mm x 45mm) that much lower (not a small job as there are 14 posts about 2700-3000mm apart).


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