Timber sizes for lean-to with lightweight roof

Discussion in 'Carpenters' Talk' started by Redvee, Jun 25, 2021.

  1. Redvee

    Redvee New Member

    Hi, I'm looking for some guidance sizing timbers for a lean-to pergola with a solid polycarbonate roof.
    I've done a bit of looking around at different projects and come up with a rough design based on a bit of research and a lot of guesswork.
    It's a bit of an unusual design as it has to nest under the eaves of an existing building and is bounded on three sides of an existing courtyard.
    My timber sizes my be a little OTT, but I'm also planning to hang a swing seat from the main beams, so I wanted to allow a little extra capacity for that.
    I've attached a rough draft of the design and I'd be grateful for any advice as I'm a little out of my depth when it comes to sizing up timber.

    Overall size is approx. 4.5 long x 2.6m at widest point (slightly tapered) ; height 2.3m to underside.
    Pergola is fixed to existing blockwall along one long side and one gable and supported by two 4x4 posts along the other long side.
    Rafter sizes 6x2 spacing is 550mm, max. span of rafter is 2.3m, with a 300mm cantilever at the apex.
    The rafters are supported off horizontal beams, with a max. span 2.6m - I have used doubled up 6x2s for these as I was unsure about the whole load of the roof being supported off these.
    I've allowed for a few extra braces for rigidity - the attached .pdf will explain it a little better (I hope).

    Any advice or recommendations would be gratefully received as I'm struggling here.
    Many thanks.
     

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