IBR roofing requirements





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  1. #1
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    Default IBR roofing requirements

    Hi all
    I need to do a 6x6 garage roof in IBR. I know about the 5 degree slope but i want to use single trusses ( Beam), not a rafter. What are the truss and cross purloin dimentions for this span please.
    I was guessing a 50 x150 truss at 750 spacing with 4 or 5 purloins of 76x50 but I am just a 5volt engineer so help me out please.

    Also the sheeting will be within parapett walls, is there any new magic sealing method or is the old metal flashing still the way to go??

    regards
    G

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    Default Re: IBR roofing requirements

    just use a 150x50x20 purlin across, spaced 1500 from top to bottom. A 150 lip channel can span 6 m easily. So 6 of them across will be fine.

    Flashing works if you can fix it to plastered sides on the parapet wall. Facebrick doesn't work so lekker.
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    Default Re: IBR roofing requirements

    Do not go less than 0.5mm th IBR
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    Default Re: IBR roofing requirements

    Not sure if my sketch will make sense....

    If uncle Spike was here, he would have explained it nicely.

    In short, this is how I have always done it after my stepfather showed me how many moons ago.

    The problem with any metal roof is the expansion and contraction with any temperature change.
    Having grown up in the Helderberg, where the winds will push water up hill and lift flashings.

    The idea is to allow the roof to expand and contract without water eventually ingressing .

    If you look at the sketch, you will see the flashing consisting of 2 parts.
    The first top flashing has a 10mm lip at the top. The idea is that that part is inserted into a groove cut into the plaster. Use a good quality butyl mastic to seal. You can also screw it to the wall afterwards.

    The bottom flashing is atatched to the roof with the usual roofing screws into the purlines. You also have to bend the top of the IBR roof sheeting upwards before installing the IBR sheeting. Use polyurethane closures under the flashing to further help with sealing.

    This way, the two flashings work together to create a seal even if the IBR roofing wants to expand or contract.

    What ever you do, I will not recommend the use of 'Lap & Pap'. It works...... only for a while.


    Last edited by jdjoubert; 2020/08/12 at 12:00 PM.
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  6. #5
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    Default Re: IBR roofing requirements

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    Default Re: IBR roofing requirements

    Exactly as jdj explained above.

    Decades old procedure that will last for more decades when done properly.
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    Default Re: IBR roofing requirements

    Thank you all

    What is the opinion on using LandyLove's suggestion of just using metal lip channel purloins instead of a wooden frame.. I like it.
    0.5 or thicker IBR- Yes definately. I get family priceing on chromadek and may also slip in a clear pannel.
    Flashing- Just love the "lap en pap" . Never had any luck with it on metal, but on well prepared brick and concrete tile, if you take your time and dont have air trapped, it works OK. Anyway, its brick and plaster and the flashing will work well.


    G

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    Default Re: IBR roofing requirements

    Quote Originally Posted by jdjoubert View Post
    I wish I knew this last year....Now I'll have to rework....Ai, ai...

    I had my old zinc carport IBR replaced by insurance, it was 0.5mm, the contractors replaced with IBR that is like tinfoil!
    Last edited by NewLandy; 2020/08/12 at 05:59 PM.

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    Default Re: IBR roofing requirements

    Building permit and engineer's design/signature.
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    Default Re: IBR roofing requirements

    Building permit and engineer's design/signature. Ja, worth thinking about I guess, but on the other hand

    Concerning the structual timber requirement, is there a table giving beam profile sizes vs span for IBR??

    G

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    Default Re: IBR roofing requirements

    From memory...... and please take this with caution.

    An IBR roof with a clear span of 6m needs to have rafters of 228x76 space at max c/c of 1000mm

    You can have a longer span if you are going to use laminated beams. They can go up to 8m.

    Again, this is from memory of more than 10 years ago. Things have probably changed by now.

    Are you putting a ceiling in?
    If so, put 1 x 350mm Whirleybird as high up as possible in the middle and then put 2 x small vents in the ceiling as low as possible one closest to each side wall.
    White roof sheeting.
    Sisolation layer underneath the IBR sheeting helps too. The one which is silver to the top and white underneath. It is the bubble type.

    If no ceiling then you only might need the one Whirley at highest point in middle. Still put the sisolation in.
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  15. #12
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    Default Re: IBR roofing requirements

    Quote Originally Posted by Gengis View Post
    Thank you all

    What is the opinion on using LandyLove's suggestion of just using metal lip channel purloins instead of a wooden frame.. I like it.
    0.5 or thicker IBR- Yes definately. I get family priceing on chromadek and may also slip in a clear pannel.
    Flashing- Just love the "lap en pap" . Never had any luck with it on metal, but on well prepared brick and concrete tile, if you take your time and dont have air trapped, it works OK. Anyway, its brick and plaster and the flashing will work well.


    G
    Go ask your steel supplier. A 150 lip channel does not need a rafter / truss to support it over 6m. You can safely get away with only the lip channel resting on / in the side walls. You will gain the extra head space where the rafters would have been.

    I am doing a 9x12m carport next week. Will be using 150 lip channels and only 1 centre support of another 150 across down the centre to keep the roof up during a hail storm because the roof needs to be "a little too" flat.
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  16. #13
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    Default Re: IBR roofing requirements

    It is better to do this kind of projects properly. If the property is sold and no building plans it might be necessary to take the roof off. An other issue is related to insurance issues if something happens. Wind blows the roof off and insurance company checks if the roof was certified...

    Very many structures are not fully legal. We have that case also. In one case issue is with the municipality and the other to do with the builder.

    But do not trust the "engineer" either. I used "architect" to design garage extension. She could not take measurements, her trainee son could not draw and the "engineer" was not an engineer. He made design error on the tin roof design and also on foundation reinforcing. He could not sign so his partner was signing but not checking.

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    Default Re: IBR roofing requirements

    Quote Originally Posted by jdjoubert View Post
    From memory...... and please take this with caution.

    An IBR roof with a clear span of 6m needs to have rafters of 228x76 space at max c/c of 1000mm

    You can have a longer span if you are going to use laminated beams. They can go up to 8m.

    Again, this is from memory of more than 10 years ago. Things have probably changed by now.
    Good memory!

    228x76 @ 1000 c/c
    228x50 @ 750 c/c
    Last edited by LCamper; 2020/08/18 at 08:59 PM.

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  19. #15
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    Default Re: IBR roofing requirements

    You guys are brilliant.

    Thanks.

    Pic is flipped. The black is the vertical wall. Silver sits on roof horizontally.
    Attached Images Attached Images  
    Last edited by WillysCJ; 2020/08/14 at 12:01 PM.
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    Default Re: IBR roofing requirements

    Quote Originally Posted by Jouko View Post
    Building permit and engineer's design/signature.
    This ^^^

    Click image for larger version. 

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  21. #17
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    Default Re: IBR roofing requirements

    Quote Originally Posted by PRA View Post
    This ^^^

    Click image for larger version. 

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    The spacing is required with this table.

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    Default Re: IBR roofing requirements

    Quote Originally Posted by LCamper View Post
    Good memory!

    228x76 @ 1000 c/c
    228x50 @ 750 c/c

    Gengis, if you want to avoid going the route of getting an engineer to do a proper design then just use one of the 2 options above. It's straight out of the building regs sans 10400 and complies with NHBRC. Attached is the extract.

    If you want to used lipped channels (LC) the roof sheeting normally dictates the spacing of the LC for best economies. Take a look at the sheeting brochure and use the 'end span' dimension which is usually around 1000 to 1500mm to determine the spacing.

    If using LC, the wider spacing will mean higher uplift loads per end and will need better tying down.

    As Jouko says, if you go this LC route just note the consequences.
    This table from SANS 10400 Part L is out dated. Grade 4, 6 & 8 does not exist anymore - only 5 & 7. But the result is still the same - for a 6m span you will need a rafter of 228x50mm and for Purlin beams the same.
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