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  1. #1
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    Default Shed build - waterproofing and slab?

    I just brought a 6m x 6m x 2.4m Stratco Shed. I'm pouring the slab first then bolting the shed to the slab. The wall sheets are 2.4m high which means the walls should sit on top of the slab (leaving room for water to come in I imagine). Should the slab be exactly 6m x 6m or would it be beneficial to little bigger? (like 100mm or something).

    I wanted the wall sheets to be a little longer so they can go down the sides of the slab but they turned out being 2.4m and thus should sit on the slab. I'm really wanting to get the best water seal possible. I need some wisdom and knowledge before I get the slab done. Once it's done it done. Cheers.

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  3. #2
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    I reckon it's better for the walls to just overhang the slab and then fill the resulting gap between the floor and the steel with expanding foam.

  4. #3
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  5. #4
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    On all of my doors, I have two roller doors and a single entry door, the concrete starts to fall towards the door opening from about 300mm inside very slightly, around 150mm it slopes a tad more and about 50mm from the edge of the concrete, more slope again. The whole drop from about 300mm in is close to 15mm, with about 7mm coming from the last 50mm, which coincides to where the roller door rubbers sit.

    My slab was put in after the shed was erected, easier to do slight slopes that way.

    One of my brothers had a slab done first, with six pieces of steel that the shed is bolted too, inserted in the slab. His slab is dead flat, he gets water coming in under his roller doors, he has two doors as well. Drives him nuts.

    His shed required a lot of mucking around to seal the gaps, my shed didn't have that gap problem and I won't be around when the walls start to rust, Bluescope mightn't be around by then either.

    Mick.

  6. #5
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    I agree with the last post, but I would also suggest that before pouring the slab in the erected shed. I would place poly water proof membrane around the inside edges of the shed , taped to the walls, so that it extends above the slab ht.

    This will stop the concrete contacting the steel,, .

    Alternately when you box the slab , allow a 25mm step for the walls to sit down into , this will also carry through to the doors, again when erecting the shed, again water membrane up walls and under the edge.

    these should stop any water ingress.

    Jeff

  7. #6
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    Quote Originally Posted by BobL View Post
    I reckon it's better for the walls to just overhang the slab and then fill the resulting gap between the floor and the steel with expanding foam.



    The surest way to ensure no water entry. Best to lose 50mm from height and have wall sheeting overhang than to pour slab inside shed ( thus losing some height anyway).

  8. #7
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    30mm loss in wall height is better than an indoor pool.

  9. #8
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    Quote Originally Posted by BobL View Post
    I reckon it's better for the walls to just overhang the slab and then fill the resulting gap between the floor and the steel with expanding foam.
    That's kinda what I was thinking. I was just a bit worried with my 2.4m sheets and 2.4m wall frame if I bring the sheets down 50mm there will be a gap at the top of 50mm.

    I've never put up a shed before so I'm not sure what to expect.

  10. #9
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    Normally the shed frame height is between 30 and 50mm less than the sheeting. standard design is for the sheets to go down below the top of the slab. Your wall sheets wont go to the top of the frame as the corrogations will hit the underside of the sloping roof sheets. This will give some overhang to the bottom of the wall sheets. If you are fitting a gutter then any gap between roof and wall sheets would be behind the gutter and gable end discrepancy would be covered by barge caps.

  11. #10
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    Quote Originally Posted by hayythere View Post
    That's kinda what I was thinking. I was just a bit worried with my 2.4m sheets and 2.4m wall frame if I bring the sheets down 50mm there will be a gap at the top of 50mm.

    I've never put up a shed before so I'm not sure what to expect.
    It's much better to put up the shed first, then line the inside bottom of the sheets with 10 mm polystyrene and then pour the floor. Of course then you lose the some wall height but the floor can sit mostly beloe the bottom of the shees so the loss in wall height can be as little as 10 mm. see picture below. The board is there just to act as form work for the floor pour and can be removed afterwards.
    An alternative to the PS foam is fibre cement which is more robust but messier to cut.


    It this case I would use expanding foam to fill the gaps resulting from ridges in the sheeting.

    A slightly more complicated arrangement is this one.


    If you absolutely want full 2.4 m high you will have to add some small offcuts to the sheets.

  12. #11
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    OK call me old fashioned, but I really don't like dyna bolts to hold down sheds! I am a firm believer in Threaded rod cast into the slab/pier in the appropriate place to bolt on your columns. I also like to use 13mm (minimum) diameter or larger,depending on the size and spacing of the columns. Doing it it this way means that the floor can go in after the shed goes up and seal against the walls so no water or vermin can enter. Also it means that at this time of the year it is a whole lot more pleasant to work in the shade than in the stinkin' heat. As mentioned falls to doorways can be accurately and effectively placed to work properly Whether you are doing the job your self or paying someone, to have congenial working conditions means for a better job in the long run
    Just do it!

    Kind regards Rod

  13. #12
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    Dec 2009
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    Quote Originally Posted by chambezio View Post
    OK call me old fashioned, but I really don't like dyna bolts to hold down sheds! I am a firm believer in Threaded rod cast into the slab/pier in the appropriate place to bolt on your columns. I also like to use 13mm (minimum) diameter or larger,depending on the size and spacing of the columns. Doing it it this way means that the floor can go in after the shed goes up and seal against the walls so no water or vermin can enter. Also it means that at this time of the year it is a whole lot more pleasant to work in the shade than in the stinkin' heat. As mentioned falls to doorways can be accurately and effectively placed to work properly Whether you are doing the job your self or paying someone, to have congenial working conditions means for a better job in the long run
    I would call you old fashioned I am afraid. (Not that that is a bad thing!)

    I have never seen a structural failure from properly installed dynabolts, and I have 10+ years in the shed sales and erecting business (I am talking in the thousands of sheds). People (and let's say females) who run into our sheds with cars invariably shear the column before the hold down brackets or dyanbolts fail.

    The other reason not to pour wet concrete up against your sheets is that you void your BHP warranty, and expose the whole shed to early and aggressive corrosion and rust. Also, you cannot just "uninstall" the shed easily, the damn thing is concreted in the ground.

    These days, any skilled concreter, can get rollerdoor set downs correct, as is done on a house slab. And there are many aftermarket shed products that provide vermin sealing, such as the excellent Vermaseal from Campbells Shed Products.


  14. #13
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    Quote Originally Posted by banjoping View Post
    I would call you old fashioned I am afraid. (Not that that is a bad thing!)

    I have never seen a structural failure from properly installed dynabolts, and I have 10+ years in the shed sales and erecting business (I am talking in the thousands of sheds). People (and let's say females) who run into our sheds with cars invariably shear the column before the hold down brackets or dyanbolts fail.

    Be that as it may; are you aware of any other steel framed structure that is fixed with dynabolts? For mine, it is easier and more secure to set the bolts in the concrete mass than to trust that a correct sized hole can be accurately drilled in the set concrete whether it be for dynabolt or chemset. To outlay a rather large amount of money on a structure that is to be expected to last a long time, not to utilise what can be considered best practice methods of construction is folly in my opinion.

  15. #14
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    When I did my shed, I didn't get the slab accurately enough boxed and some of the boxing moved a little (I was a lot younger with a lot less experience). But I sat the cladding on the edge of the slab with some flashing I had folded cheaply to cover the edge of the slab. I folded the membrane inder the slab in before sitting the flashin down and the wall cladding on it, so I could tape it to the inside of the flashing. It's quite sealed although much of the membrane on the inside has been replaced by dirt and dust after several flood events we have had here in the past 30 years - which seems to seal just as well..... The last few floods have not produced any leaks at all (there was so much dirt erosion in the water, it completely sealed my shed door and roller door as well - about 3" high!
    I had to dig my way back into the shed....).
    Joe

  16. #15
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    Quote Originally Posted by wun4us View Post
    Be that as it may; are you aware of any other steel framed structure that is fixed with dynabolts? For mine, it is easier and more secure to set the bolts in the concrete mass than to trust that a correct sized hole can be accurately drilled in the set concrete whether it be for dynabolt or chemset. To outlay a rather large amount of money on a structure that is to be expected to last a long time, not to utilise what can be considered best practice methods of construction is folly in my opinion.
    The majority of steel framed houses are fixed with dynabolts.

    95% of common sheds are lightweight steel structures. They are not fabricated steel structures, where things such as cage bolts and cast in hold downs become a necessity due to the engineering.

    I take your point though. You are right, that a secured hold down method is the better fixing method.

    Anyway, we've gotten a bit off track.

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