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Thread: Purlins ?

  1. #1
    Hesston4860s
    Guest

    Purlins ?

    Thinking of building a shed 80 x 60 16 foot to the eaves. Now I would like to go 20 foot bays I would prefer timber Purlins as I find them easier to work with but will timber start to sag at this span ?. Would I be better of going with Z purlins ? even tho these to me seam a lot more work.

  2. #2
    hilly bill
    Guest

    Re: Purlins ?

    Quote Originally Posted by Hesston4860s View Post
    Thinking of building a shed 80 x 60 16 foot to the eaves. Now I would like to go 20 foot bays I would prefer timber Purlins as I find them easier to work with but will timber start to sag at this span ?. Would I be better of going with Z purlins ? even tho these to me seam a lot more work.
    Timber will be fine as long as you go for the right size and fit them the right way up also you can put little braces on with angle iorn helps alot with snow load apparently.

  3. #3
    Hesston4860s
    Guest

    Re: Purlins ?

    Quote Originally Posted by hilly bill View Post
    Timber will be fine as long as you go for the right size and fit them the right way up also you can put little braces on with angle iorn helps alot with snow load apparently.
    I think the size timber I was looking at was 9x3 I did think about putting anti sag bars in the center of each span.

  4. #4
    hilly bill
    Guest

    Re: Purlins ?

    Quote Originally Posted by Hesston4860s View Post
    I think the size timber I was looking at was 9x3 I did think about putting anti sag bars in the center of each span.
    I recently built a shed and they looked at the grain on the end of each purlin and turned them all a certain way.They only have braces on about 3 on each side

  5. #5
    him
    Guest

    Re: Purlins ?

    Quote Originally Posted by hilly bill View Post
    I recently built a shed and they looked at the grain on the end of each purlin and turned them all a certain way.They only have braces on about 3 on each side
    buck up if u understand me, so the load puts it level, 9x3 should be fine but just check then for knots and there position/amount as some can slip though the quality checks, last time i checked here purlions wherent much dearer so the man opted for them, it was an extension to a weighbridge of a meal mill, and washed regularly, so there was a fear of timber rotting.

    for a cattle house, it would need to be well ventilated for them not to rust so we would perfer timber in that situation.

  6. #6
    btd-6
    Guest

    Re: Purlins ?

    Why are z purlins more work? I would think having wood purlins and messing around fitting anti sag bars would be even more work!

  7. #7
    DX 3.90
    Guest

    Re: Purlins ?

    Sorry but your wrong about Z'ds being more work, i would say z'd are lighter stronger, straighter and much quicker to put up. No messing trying to lift up heavy timbers drill and knock in bolts. Our straw shed is 20ft bays and has 9x3 timber purlins and they have all sagged a bit, just doesn't look as straight and tidy as Z'ds.
    And it's a bit of a myth about z purlins rusting, they will last aslong as most roofs. Just my opinion of course!!

  8. #8
    Fergieman
    Guest

    Re: Purlins ?

    You get different grades of 9x3's. Make sure you get top grade for 20' and you will be fine.

  9. #9
    multi power
    Guest

    Re: Purlins ?

    2 buildings where i work are 15ft bays but end bay is 20ft, all timber purlins, the 20ft bays are bigger wood n they are the only ones that have not sagged
    we have z perlins at home put up 1981 n they are rather rusty now

  10. #10
    crazy frog
    Guest

    Re: Purlins ?

    correct sized wood will hold up snow weight better than metal z purlins

    metal bends then kinks very easily where wood will bow and hold on longer

    just my take on it


    crazy

  11. #11
    Mo
    Guest

    Re: Purlins ?

    Get zeds properly specced, using 40's you'll crack on much faster than heavy variable timber, and the structure will be more rigid as you are spanning 2 bays by staggering the 40's.

  12. #12
    Oldmacdonald
    Guest

    Re: Purlins ?

    Quote Originally Posted by DX 3.90 View Post
    And it's a bit of a myth about z purlins rusting, they will last aslong as most roofs. Just my opinion of course!!
    If I remember tomorrow I'll take a photo of some very rusty Z's.

  13. #13
    Forage Trader
    Guest

    Re: Purlins ?

    I would never use z on a cattle building we have big sheds here that have rusted out steel sheets on z, they will by the screw fix holes, anything other than fibre on wood is a waste of your money I don't care if it's half the cost, I can send you pictures if you need further proof,

  14. #14
    Forage Trader
    Guest

    Re: Purlins ?

    Quote Originally Posted by Oldmacdonald View Post
    If I remember tomorrow I'll take a photo of some very rusty Z's.
    I don't think you need to I have seen loads of them to back you up

  15. #15
    Hesston4860s
    Guest

    Re: Purlins ?

    Thanks for the input so far. I'm gonna be using fibre cement for the roof and its for a mechinery shed in the end, might have straw in it for a couple of years first till I get more funds to clad the sides.

  16. #16
    PDR-Draughting
    Guest

    Re: Purlins ?

    Quote Originally Posted by hilly bill View Post
    I recently built a shed and they looked at the grain on the end of each purlin and turned them all a certain way.They only have braces on about 3 on each side
    The small angle braces you refer to are not to support the purlins they are added as a bottom flange restraint to aid the rafter. They are very commonly used in larger industrial buildings. Take a look up at the roof next time your in B&Q. They allow you to use lighter weight steels.

    Phil

  17. #17
    hilly bill
    Guest

    Re: Purlins ?

    Quote Originally Posted by PDR-Draughting View Post
    The small angle braces you refer to are not to support the purlins they are added as a bottom flange restraint to aid the rafter. They are very commonly used in larger industrial buildings. Take a look up at the roof next time your in B&Q. They allow you to use lighter weight steels.

    Phil
    Yes i remember the builder telling me now they are to stop the girder twisting under weight .

  18. #18
    Ian01
    Guest

    Re: Purlins ?

    For a machinery and straw shed, with fibre cement i would go z's every time. Make sure you get them speced right for baywidth and distance apart

  19. #19
    DX 3.90
    Guest

    Re: Purlins ?

    Quote Originally Posted by Oldmacdonald View Post
    If I remember tomorrow I'll take a photo of some very rusty Z's.
    What about some pics of sagging timber and cracking sheets and ridge cappers from timber moving!! It doesn't matter which is used if it for machinery but z's are the best!!
    I would imagine that if the z's have rusted out then the building has poor ventilation or or tin on z's which isn't ideal for stock, if using fibre cement on z's you shouldn't get condensation running down sheets and onto z's.

  20. #20
    Forage Trader
    Guest

    Re: Purlins ?

    if you are keeping livestock dont do it even for straw as you may want to put stock in one day that will rust z purlins in time

  21. #21
    fermerboy
    Guest

    Re: Purlins ?

    Well in this part of the world, there will be a hell of a lot of cattle buildings falling down in 20yrs time if all this stuff about Z purlins rust is to be believed.

    I would guess that nearly all new builds round here are Z purlin with fibre cement for cattle. Everybody is on 6m bays too.

    Think spec is more important.
    Since the big snow 3yrs ago the purlin size used locally has increased a fair bit.

    Make sure the end ones are longer to get 4 bolts on, also use sleeves at the rafters(effectively takes out 2ft of span).

    Don't believe anybody that says 40ft/12m ones don't need it. :cry:
    And most important make sure they are fitted with anti-sag rods and tied together at the top.

    We have wooden purlins on 15ft bays that are sagged to hell now, looks bad if nothing else, and cracks the fibre cement too.

    If the worst happens its not the end of the world to change purlins if you have to.

  22. #22
    MickMoor
    Guest

    Re: Purlins ?

    The supplier of Z purlins will have a purlin size calculator, usually downloadable. It gives the different options such as sleeved, butted, heavy end bay, staggered double bay etc. It calculates the size of purlin and thickness of steel, acording to sag bar and eaves beam arrangement you choose. Usually you have to enter a wind loading and snow loading for the area as well. Snow loadings will be different in the SW of Scotland to the Highlands for instance. Once again it comes down to getting a building designed properly. With timber purlins there is a limited range of sizes and a margin allowed for defects, so generally they are over-spec. I think diagonal roof braces are essential and rafter restraint even with timber purlins is a good idea.

  23. #23
    Forage Trader
    Guest

    Re: Purlins ?

    Quote Originally Posted by fermerboy View Post
    Well in this part of the world, there will be a hell of a lot of cattle buildings falling down in 20yrs time if all this stuff about Z purlins rust is to be believed.

    o.
    I have a shed here 150 x90 dad and i built our pride and joy you could fly a plane through the holes, would have been built in the mid 80ts, anothor 2cd hand bulding that must be 100 year old with fibre roof thats as good as the day it was built,

    Z purlins have no place on a farm

  24. #24
    culphim78
    Guest

    Re: Purlins ?

    Quote Originally Posted by Forage Trader View Post
    I have a shed here 150 x90 dad and i built our pride and joy you could fly a plane through the holes, would have been built in the mid 80ts, anothor 2cd hand bulding that must be 100 year old with fibre roof thats as good as the day it was built,

    Z purlins have no place on a farm
    Bollocks no shed round these have timber purlins all z purlins

  25. #25
    Forage Trader
    Guest

    Re: Purlins ?

    Drilled in the bottom, so when you drill box profile in the bottom where do the drill filings go, they stay between the sheets and form a rust bubble why anyone with even a pea of a brain can't see this is behond me

  26. #26
    hilly bill
    Guest

    Re: Purlins ?

    Quote Originally Posted by Forage Trader View Post
    Drilled in the bottom, so when you drill box profile in the bottom where do the drill filings go, they stay between the sheets and form a rust bubble why anyone with even a pea of a brain can't see this is behond me
    Arnt they drilled in the top with a tek screw ? ive both and cant fault either to be fair, wood can sagg a bit though especialy with fibre on i wouldnt be that keen on 6m bays with fiber and wood think i would want smaller bays 15` for wood and fibre, 6m with z and tin has been fine here.

  27. #27
    Forage Trader
    Guest

    Re: Purlins ?

    I have never seen tin drilled in the top, apart from mine that was done to stop it rusting

  28. #28
    hilly bill
    Guest

    Re: Purlins ?

    Quote Originally Posted by Forage Trader View Post
    I have never seen tin drilled in the top, apart from mine that was done to stop it rusting
    Ah i see what you mean now i thought you were talking about the purlins been drilled in the bottom and couldnt understand what you were talking about.

  29. #29
    Yale
    Guest

    Re: Purlins ?

    Perhaps zeds should have a coating of oil/grease with an air fed oil spray gun,a bit like you would on a Land Rover chassis,works on them.

  30. #30
    wr
    Guest

    Re: Purlins ?

    Cattle shed - Z purlins - 18 years - no rust - no sags


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