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building a pergola

Discussion in 'Renovation & Home Improvement' started by Allgood, 26th May, 2016.

  1. Allgood

    Allgood Well-Known Member

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    Ok builder people,

    I want to build a free standing pergola for our PPOR. 4x6 metres with a pitched roof. Looking at using 4 corner posts with another post in the middle of the 6 m side to reduce the span to 3 m, so 6 posts in total.

    The plan is to do something rustic and solid in keeping with other outbuildings on the farm. I'd like to fill in up to one metre high with old corrugated iron and have a corrugated iron roof. Ideally the timber would not be painted or stained to keep the weathered look.

    It's in a very high wind area (west facing to get the view) and I don't mind it being a little chunky so I'd rather go oversized than under-do it.

    I'd love any suggestions on timber sizes. I want to go all hardwood, but cannot believe the price of recycled timber! Please excuse my terminology, im new to this building game...

    What do you think about the following in hardwood:

    Posts: 150 x 150
    Beams: 240 x 45??? - Or should it be something like be 190 x 45 or even 190 x 75?
    Trusses: 90 x 45 - 900 apart or bring back to 700? - These will be across a 4m span.
    Battens: 18 x 75

    Or I could do the 2 outside beams with a ridgebeam. In this case would I use the same sizes as above (ie 90x45 rafters & trusses, 240x45 ridgebeam and sidebeams and 18x75 battens) The ridgebeam would be a 6 m span without a centrepost.

    I'd love any feedback on the timber sizes, or any other advice.

    Thanks in advance.

    Allgood
     
  2. Brian84

    Brian84 Well-Known Member

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    Hi all good,

    Hardwood is the right timber to use.

    Sizes for materials
    Posts 150x150 is more than enough. You could even get away with 90x90 as a minimum.

    Pitching beams- the sizes you have stated will be fine as it's just a tin roof so the 240x45 or the 190x75 will work.

    The roof trusses will be good for anything over 70x35 with only a 4m span.

    If you are doing a conventional roof you could use 90x45 as long as you put in some under purlins. Conventional is cut and make everything onsite.

    I would use thicker batterns like a min thickness of 35mm. Also on top of the rafters or trusses you will need to put some hoop iron strapping or speed brace on the roof of its a high wind area.
     
  3. bob shovel

    bob shovel Well-Known Member

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    Have you had a search around the bush for some wood to use for posts? A chain saw might be cheaper!
     
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  4. Allgood

    Allgood Well-Known Member

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    Thanks mate, @Brian84 when you talk about a conventional roof, do you mean trusses at either end with a ridgebeam across the top and then rafters 90x 45 with under-purlins as below. (with purlins being the horizontal bar)

    upload_2016-5-26_15-20-27.png
     
  5. robboat

    robboat Well-Known Member

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    What is the "very high wind area"......top of a hill or in a windy area near the coast?

    Your foundations are the most important thing as the uplift from the structure will be considerable if it is a gusty area.
    What about termites or water?
    Are you putting down a concrete slab for the flooring?
    Your sizes for hardwood are good - just make sure they are correctly fastened.

    Have you thought about doing the roof frames in steel? I understand you want to match it to the other buildings but that makes it very easy to build a strong frame.
     
  6. Brian84

    Brian84 Well-Known Member

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    The under purlins for a conventional roof as in this pic would run down the left and right side of the roof on the underside of the rafters and will need to be strutted to a hanging beam assuming there are internal support walls because it's a pergola.

    In this pic the horizontal member that you see going left to right is called a collar tie and iOS purpose is to stop the roof from moving left to right and also stop the rafters caving in on themselves.

    A conventional roof does not have trusses, it is all ridge beams, under purlins, struts, rafters etc. the purlins in a roof serve the same purpose as a web would in a pre fabricated roof truss. The webs in a roof trusses are designed to transfer a load from the rafter down to the bottom chord or ceiling of the truss.
     
  7. Scott No Mates

    Scott No Mates Well-Known Member

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    Poke your nose through Bunnies or Jack of all trades Masters of none. They have diy project cattle dogs.
     
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  8. Allgood

    Allgood Well-Known Member

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    Ok thanks, so given there are no internal walls maybe I should do a series of trusses 800 apart. Do you think thats the best option or would it be too messy, or not strong enough?
     
  9. Aaron Sice

    Aaron Sice Well-Known Member

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    The Law Resource have AS 1684 for a free download.

    Have a look at the timber framing code charts too. They will tell you everything you need to know.

    Remember as well that timber suppliers and sizes differ across states. Difficult to get a 170s here in WA and pretty difficult to get 240s in Tas.
     
  10. Scott No Mates

    Scott No Mates Well-Known Member

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  11. Brian84

    Brian84 Well-Known Member

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    You can do either type of roof. Because you are doing metal roof you can have a max spacing between rafters up to 900mm centres and roof tiles max of 600mm spacing. If you are doing it yourself then you would be best off doing trusses as you don't have to work out any measurements for rafter lengths.
     
  12. bob shovel

    bob shovel Well-Known Member

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    I'm not sure what the look is but here's a few ideas anyway
    images.jpg images (1).jpg images (2).jpg
     
  13. Allgood

    Allgood Well-Known Member

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    Thanks everyone. So I've found a guy who can supply most of the timber. It's recycled from an old house so it will be very dry. Just how much harder do you think it will be to work with than new hardwood. Ie drilling, nailing etc. Would it be much easier to just bite the bullet and go new. I haven't worked out comparative prices but I reckon second hand would only be around 30% cheaper... at a guess.
     
  14. Scott No Mates

    Scott No Mates Well-Known Member

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    Seasoned hardwood - you'll need to drill and bolt most connections as you may not be able to drive nails into the timber without splitting it.
     
  15. bob shovel

    bob shovel Well-Known Member

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    Could add to the look though, big coach bolts in the hard wood
     
  16. Allgood

    Allgood Well-Known Member

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    Thanks, what about using a nail gun? Would that split it too?
     
  17. Allgood

    Allgood Well-Known Member

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    Yeah, I was thinking I'd bolt the bigger stuff, like where beams join the posts.
     
  18. bob shovel

    bob shovel Well-Known Member

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    Do you have a rough idea what look you're after?
     
  19. Allgood

    Allgood Well-Known Member

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    Going for the 'still standing after 12 months' look :D.
    We've got a few corrugated iron sheds and our 3 car shed is pretty close to it. It's corregated iron and has similar size posts and wood to what I'll use. Im thinking of something that looks a little like a cabin, (ie pitched roof). Probably with a railing around a metre high with corrugated iron below it and open on the top. We've got heaps of corro iron lying around that's nicely weathered.

    That's the plan. We'll see what happens in the end! :rolleyes:
     
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  20. bob shovel

    bob shovel Well-Known Member

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    Nice. Go the hard hard wood. Harder work but sounds like the hard work will be worth it.