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  1. #1
    Join Date
    Mar 2014
    Posts
    2

    Default wood/concrete connection, replacing shed roof

    Hello all!

    I've been resorting to TOH ever since I bought my house. Most of the time the solutions suit the work directly, but this time I really don't know what to do, and since the task is quite specific, I decided to ask here.

    I couldn't attach the picture to this post (not a valid image file?!), so here's a link: https://lh3.googleusercontent.com/-n...ketch_roof.png


    To put that picture into words:

    - my shed was built using concrete posts (6x) between which concrete slabs where inserted. Then a 2cm diametre bolt was placed at the top of those posts, probably using a bore in the post itself. Overall, the shed is a rectangle with posts at each corner, plus two in the middle of the long sides.

    - a thick wood beam was placed along the top of each long side; it had to be bored as well to let the bolts through. The bolts where then bent onto the wood... It was on top of these beams that simple corrugated boards where fastened to make the roof. The angle was achieved by having the concrete posts on one long side be taller than the others.

    Now, both the corrugated plates and the wood beams need to be replaced (they rotted where the bolts securing the plate penetrate). I could try to bend the large bolts back into place and replicate the current arrangement. On the other hand, I'm wary that the wood is also rotten and going to rot further at the concrete/wood interface, because the concrete seems to get wet all the time. I also want to raise the roof by about 30cm, and that requires a good frame on top of that concrete..

    How would you go about connecting a wood frame to that concrete? Also, what would be a sensible scheme to prepare a wood frame on the concrete that would make building the higher roof on top of it easier (ie, since the concrete sides are not level, placing joists is harder..)?

    Jose

  2. #2
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,520

    Default Re: wood/concrete connection, replacing shed roof

    A picture of actual shed would help. Is this an open shed for storing firewood or such?
    Too bad the bolts were bent. They will probably break.
    New beams could probably be placed on a post support like are used on wood deck supports to get the wood off the concrete. You'd have to figure out a way to attach to post. Possibly expansion bolts or even tapcon screws.
    Another way to raise roof would be to cut pressure treated plates to set on to of the concrete posts. A number of 2x plates could be used to get the required height. Trim boards around the plates would hide the multiple plates and keep water off the concrete/wood interface.
    Try to give some overhang at the roof if possible to keep the rain off better.
    I would cut the joists like rafters with notches at either end. Once you figure out the first one, use it as a template for the rest.

  3. #3
    Join Date
    Mar 2014
    Posts
    2

    Default Re: wood/concrete connection, replacing shed roof

    Hi Ed,

    thanks for the reply. I couldn't upload any pictures of the shed, I'm afraid, same issue as the sketch, but I do have a rudimentary plan which I'm attaching. I'm guessing I have a layer setting off, because the roof does not actually show in the figures; in any case, the framing on top of the concrete is visible, especially the two wood beams that require replacing.

    By post support you mean that sort of metal anchor that is dug into the ground, and which then accomodates a wood beam? I'm not sure I can attach that sort of thing - the original bolts may have been cemented into the concrete posts, and if that's the case, I won't have space for another bore. But I do like the idea of having metal fittings between concrete and wood - if only I figure out how to attach them!

    A side question - assuming I manage to re-attach two wood beams to the concrete, I can start working on the roof. To raise it, I would actually prefer using some struts, and then work on the plane formed by their tops. My question is, is the roof stable if i do not use a joist or tie between the two wood beams, that is, if the only connection along the width of the shed is already at the top of the struts?

    Regards,
    RJ

    barraca_v1 (1).pdf

  4. #4
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,520

    Default Re: wood/concrete connection, replacing shed roof

    If you replace the beams and set them directly on the concrete posts use pressure treated wood.
    If the bent over anchor bolts break when you bend them straight, I would probably cut them flush and anchor a PT 2x plate on top of the post and attach the new beam to the new plate. Simpson and others make appropriate tie downs. AKA hurricane ties.

    If you strut up a walls 30cm( 12" ) the strutted up walls should be tied together at the top of the wall. Every 4' should do it. I assume the conc posts have enough lateral resistance if they have vertical reinforcing in them. If not, tying the beams at the posts would help. Although this is a small shed and may be overkill.

    Is the roof to be made of corrugated panel again? They would provide bracing at the top of the wall, but I would still brace it as previously mentioned.

    No reason to be tied to the existing bolts if the don't work out. Concrete can be drilled into to set expansion bolts and screwed into with tapcon screws. The anchors don't have to be in the center of the post where the old bolt is located. A new square plate with a bolt welded to it could be fabricated and attached to the top of the posts to anchor the beams. There are probably a half dozen other ways to do it. It usually comes down to what is cheapest and or easiest to do. It is a shed, so no real life safety issues are involved, but local building codes may have a say.
    Last edited by ed21; 03-24-2014 at 10:20 AM.

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