Building a lean to

Discussion in 'Carpenters' Talk' started by woodburner, Sep 24, 2007.

  1. woodburner

    woodburner New Member


    I would be ever so grateful for advice on this.

    I am building a lean to which will accommodate a 4 x 4 m polycarbonate roof. I always tend to over engineer things but what specs would you recommend timber wise?

    I was going to use a 150 x 50 wall plate chem bolted to the house

    6 Joists of 150 x 50

    2 posts of 150 x 150 connected by beams either side of 150 x 50.

  2. dirtydeeds

    dirtydeeds New Member

    over engneering isnt a problem but you should still use common sense to avoid waste

    even when over engineering always take account of the "headline" product, in this case the ploycarbonate sheets

    most plycarbonate sheets that are 4m long are produced in widths of 800, 900 or 1000mm wide

    set your rafters at centres that match the sheet widths

    six rafters on a 4m run gives 667mm centres, it doesnt match any of the standard sheet sizes
  3. woodburner

    woodburner New Member

    Sorry d,

    I was not being precise about the width of the roof. It comes in kit form comprising 5 sheets of polyc 700mm wide.

    Would it be ok to use mini joist hangers bolted to the wall/ridge board to hold the rafters? I am aware that the rafters would have to be cut to accomodate the hanger.

  4. J.T. Builders Ltd

    J.T. Builders Ltd New Member

    sounds fine to me, apart from you will want 1 or 2 rows of noggins in between the rafters.

    also you don't need to cut the rafters around the joist hangers, if you have a 150 x 50 wall plate.
  5. woodburner

    woodburner New Member

    Thanks JT,

    Yes, there will be noggins.

    Do the rafters have to be cut if they are to slope 15 degrees? This is the part of the project that is holding me up because I don't know how to achieve this 15 degree slope when the rafters are sitting in joist hangers.

  6. J.T. Builders Ltd

    J.T. Builders Ltd New Member

    If it was me.

    for a poly carb room, i would just sit them in joist hangers

    like these

    and cut the legs off to the correct length.

    and cut the end of the joist off at 15 degrees,

    put a BM in the oter end, so you can nail it to the other plate, then level the top of the rafter with the wall plate then nail the joist hanger on, in every hole, and spike the BM end.

    does that make sense?

    you could put the hangers on first and notch the rafters, but as there isn't alot of weight on there, i would have thought it would be fine the way i said.

  7. woodburner

    woodburner New Member

    Thanks for taking the time to respond.

    I have spare mini truss hangers and was going to use these having notched the rafters.

    What is a BM?
  8. J.T. Builders Ltd

    J.T. Builders Ltd New Member

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