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Which joist hanger type and exactly where does it go?

Discussion in 'Floors, Stairs and Lofts' started by antonyc, 16 Jan 2018.

  1. antonyc

    antonyc

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    Hi everyone,

    I'm going to be doing a loft conversion soon. I'm in very early stages, chatted with a Structural Engineer briefly. He's had a quick look at my plans and made a suggestion about the structure and costs. I'm now beginning to finalise my drawings which I'm going to send to him again.

    The joist hangers and new joists would effectively replace the existing ceiling joist area in first floor. I've done something in the design which I don't know is acceptable. I've used both a joist hanger and also rested the joist on the wall plate - to me that makes sense... but who knows?

    Anyway, what I want to know is, where exactly can/should the joist hangers get attached to? The wall plate? Or underneath the wallplate? Or in between the top two courses of brick? Which type of joist hanger would I use? How do you know which one to use?

    Not being a structural engineer, I see a very simple approach; Simply wrap a timber joist hanger over the wall plate. Is this the way it would be done? Is this ok to do or would I have to use masonry joist hangers for this?
     

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  3. Ian H

    Ian H

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    A masonary hanger needs 600mm (ish) of masonary above it.

    Not sure about the hangers on the wall plate. I put a steel across mine with timber bolted into the web and hung the hangers/joists off that.
     
  4. If you're resting the joists on the wall plate, then you wouldn't use a joist hanger as well, but if the joists were to drop below the wall plate, then you'd use the joist hanner nailed in to the top of the wall plate.
     
  5. Notch7

    Notch7

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    Dont you need to couple the joist ends to tge rafters for lateral restraint?

    I think usually the joists sit on the wall plate then the bit that sticks out beyond the rafter is cut on parallel to it. Then they are connected to provide restraint.
     
  6. antonyc

    antonyc

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    OK, there isn't 600mm above where it can go. Does this mean that masonry joist hangers are a no go?
     
  7. antonyc

    antonyc

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    This! The joists do drop below the wall plate, so I'd use a timber joist hanger then and nail it to the wall plate.

    Do you know where I can read more about this?
     
  8. antonyc

    antonyc

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    I don't fully understand your reply... But the new joists are likely to be 7", whereas the current ones are 3". I cannot rest the new joists above the wall plate because of clearance. I'd prefer not to drop them 5" below the wall plate either because that is a large ceiling drop!
     
  9. Ian H

    Ian H

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  11. antonyc

    antonyc

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  12. Sorry antony, was there supposesd to be a picture attached to "This!". Yes, you need timber joist hangers, as these are more bendable that the masonary ones. If I've worked things out, then you're current 3" ones sit on the wall plate, so the new 7" ones would need to sit 4" below that level. Do I assume that the lack of clearance above the wall plate is due to the slope of the roof getting in the way. If you can post a picture, then we can judge the situation better. You could measure the joists to the edge of the wall plate, notch the end out to drop them down a bit, chamfer the top of the joists to make sure they clear any slope of the roof, and then slip the joist hangers under joists, and bend them over the wall plate, and secure evererything down.
     
  13. antonyc

    antonyc

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    There is supposed to be a picture, yes!

    Ok, I know the hangers which you're talking about. You're talking about these ones: http://www.bpcfixings.com/images/main-images/joist-hangers-timber-timber-connectors.jpg

    Your workings out are correct. The current ones do sit on the wall plate and the new ones would sit 4" below the bottom of the old ceiling joists. The lack of clearance is indeed due to the slope of the roof.

    Here is a different pic showing the problem and the solution (same solution as you).

    Antony...
     

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  14. Ian H

    Ian H

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    Last edited: 17 Jan 2018
  15. Ouch, that's tight. Are these joists going right across, or to a central wall etc. Getting them in position if the have to go full width, may not be feasible, and you may get one side notched out, but not the other. As you can see from the picture of the joist hangeer that you linked to, you need to consider the shoulder of the support when you fit them, so they may have to be set in a little lower than you anticipated.
     
  16. antonyc

    antonyc

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    They're going to a central load bearing wall. The span is around 3.4m. I don't know what you mean about the shoulder. I can't find any info about this. I imagine the straps have to wrap around the wall plate. I've just put it into CAD and it says the straps will wrap right around the wall plate onto the back of the brick!!! Is this allowed or what? Where can I find out about this?
     

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  17. Ian H

    Ian H

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    Anything round the back will be spare, you wouldn't be able to nail it anyway.
     
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