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Thread: Fastener placement on metal roofing panels

  1. #1
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    Fastener placement on metal roofing panels

    On metal roofing panels with ribs, why would one drive screws through the flat part of the panel instead of through the top of the rib?

    The directions for installing metal roofing panels that are attached by exposed fasteners give different methods for nails vs screws. These panels have raised ribs. My natural inclination would be to insert fasteners through the top of the rib so that the hole in the panel would be as far above running water as possible. This is indeed the method that is recommended when nails are used. But when screws are used, the recommended method is to drive them through the flat area of the panel. Why would this be the superior way to use screws?

    Both the nails and screws used in this work have flexible washers to seal the heads. The nails are not to be driven so hard that they would dent the panel. I think screws could driven with equal delicacy.

    Example directions ( from http://www.fabral.com/installation/i...ation-5-09.pdf) :

    The correct way to fasten steel panels with nails is to drive the nail
    through the top of the rib so the washer is compressed securely
    against the metal. Nail placement must be in the ribs for roofing
    applications to minimize the potential for roof leaks. Over-driving the
    nail can split the washer and dimple the metal, causing leaks.

    Wood screws with combination metal and neoprene washers should be
    installed in the flat area of the panel adjacent to the ribs, and
    tightened such that the washer is compressed as illustrated above.
    This will ensure a lasting, leak-proof seal. See pages 4 to 5 for the
    correct fastener locations.

  2. #2
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    nails are more likely to back out than screws, i'd think, so they tell you to put them up high to reduce water leaks.
    i'm sure you could use longer screws run down thru the top of the ridges, but it would cost more money to buy the longer screws- which is probably the main consideration.

  3. #3
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    nails are more likely to back out than screws, i'd think, so they tell you to put them up high to reduce water leaks.
    i'm sure you could use longer screws run down thru the top of the ridges, but it would cost more money to buy the longer screws- which is probably the main consideration.

  4. #4
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    Hi, Most carpenters will tell you that a screw is worth ten nails. Today,
    good screws with the proper coatings or material vs the metal panels you are applying are affordable. But I seldom try to out-think the manufacturer.
    I'll repeat that. "Don't try to out-think the manufacturer." they are in the business of making a good product, and good performance of their product is their own best advertising. They have an interest in your roof performing as advertised. Try to talk with them or visit their web site. Very often, the additional information they have to offer will reveal just why exactly they do things the way that they do.
    Now, as to my thinking. Screws, properly applied, give you good control.
    A pan head screw with a compresive washer may be what is reccomended for your application. I have often used an old fashioned bit brace to set screws at exactly the pressure required. Think of a valve cover. people tighten valve covers too tight and they deform, defeating the good seal they might have had if they set them properly. Some electric drills have a clutch release alowing you to set screws at a common setting. Maybe that is a way to go. Fasteners are only as good as the wood they are going into. make sure that your roof is solid. Dry rot holds nothing. The first strong wind will tear it off.
    All of that said..... contact your manufacturer. Be patient. Have all of your questions written out in advance so that you get all the info you wanted.
    Speak slowly and distinctly. Anxious customers are difficult to satisfy.
    Good professionals keep it clear, and listen well, and are efficient with a good man's time. Nice people get what they need. This works.
    Ask them what is best. You paid good money for a roofing system. There is no savings using a cheap fastening system.
    It only costs a little more to go first class, and there are few jobs as important as a good, durable roof.
    Best regards, Dan

  5. #5
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    Hi, I should add that if you are using aluminum panels, you have to be very carefull in selecting the proper metal in your fasteners. This is why they use aluminum screws when fastening aluminum screen doors. Otherwise, metals interact with each other. It isn't good. And it only gets worse near salt water.
    Good luck.
    Dan

  6. #6
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    Interesting- I just checked both the house roof, the garage and the carport (all colourbond roofing panels) and they all have the screws in the raised ridge rather than the flats (all various ages and made by various companies)
    So I am assuming that is just the company who manufactured yours that did it (cost savings for shorter screws perhaps???)

    Personally I think its a bad idea as the rubber seals deteriorate over time and the expansion/contraction of the aluminium under them wouldn't help for sealing either

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  7. #7
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    I looked at my dads workshop roof today, it's about 50 years old and made from corrugated galvanised steel sheets. It is all screwed down and the screws are on top of the corrugations and has never leaked (mkind u it is tarred every 4 years.
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  8. #8
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    It is common to see directions that say to drive screws through the flat part of metal roofing panels. The example that I gave isn't unusual. I picked it since it is a brand that my local Lowes Hardware can special order.

    (As another example, the PDF with the directions for "Tuff-Rib" can be found at
    http://www.bestbuymetals.com/how-to-...l-roofing.html.)

  9. #9
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    sometimes this is done on cheaper panels to prevent over tightening screws and denting the ridges. dont know if this is the case here but i have come across this before in uk

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    I wonder if silicone washers are available for this application. They do well in external applications and are noted for sealing out water. Perhaps.

    Dan

  11. #11
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    http://www.builderbill-diy-help.com/...ng-fixing.html shows how all buildings I checked from the street in town have the screws ie on the ridges- not the flats

    The same site has a picture of standard roofing screws with ridgecaps as used on my garage
    http://www.builderbill-diy-help.com/...oof-screws.jpg available from Bunnings, Elders or any other hardware store.

    Even the walls on my garage have the screws in the ridges rather than the flats (maybe just to match the screw lines on the roof???) but without the ridgecaps
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  12. #12
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    In the USA, a distinction is made among metal roofs panels as to whether they are "structural or architectural" vs "residential". The former type can support themselves. A typical example of it is the kind that has a sine wave cross section and is often seen on sheds and barns. The "residential" kinds must have a support such as plywood set underneath. The directions for the "structural" kinds often show the fasteners applied to the top of the ribs or waves. The directions for the "residential" types usually say fasteners are to be applied the lower levels of the panels and sometimes (as in the last link that I gave) on the top of the ribs also.

  13. #13
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    Quote Originally Posted by tashirosgt View Post
    In the USA, a distinction is made among metal roofs panels as to whether they are "structural or architectural" vs "residential". The former type can support themselves. A typical example of it is the kind that has a sine wave cross section and is often seen on sheds and barns. The "residential" kinds must have a support such as plywood set underneath. The directions for the "structural" kinds often show the fasteners applied to the top of the ribs or waves. The directions for the "residential" types usually say fasteners are to be applied the lower levels of the panels and sometimes (as in the last link that I gave) on the top of the ribs also.
    strange...

    Here there is no structural distinction between `corrugated iron' (whatever its made of- steel/aluminium /gal/etc) ie the sinewave stuff and `colourbond' which is normally the flats with a ridge every 15cm or so (6"). Neither require plywood under them, just bearers spaced apart roughly 50cm to 80 cm or so apart

    (I was going to take a photo of my carport which has your `residential' style colourbond with bearers and ridge top screws but that will have to wait till tomorrow till I get to work where some brightspark left his data/charge cable for his phone...)
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  14. #14
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    In the USA, not all the "structural" metal panels are the sine wave type. In fact, most that are designed for commercial buildings have ribs with flat tops and fancy finishes.

    Perhaps the manufacturers don't want screws put through the top of ribs on "residential" panels because putting the screw down hard enough to seal the washer might deform the rib.

  15. #15
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    http://img.photobucket.com/albums/v2...arportroof.jpg

    Thats a colourbond roof (flat panel with ribs about 15-20 cm apart). You can even see the screws that hold it down in the ribs

    Quote Originally Posted by tashirosgt View Post
    In the USA, not all the "structural" metal panels are the sine wave type. In fact, most that are designed for commercial buildings have ribs with flat tops and fancy finishes.

    Perhaps the manufacturers don't want screws put through the top of ribs on "residential" panels because putting the screw down hard enough to seal the washer might deform the rib.
    http://www.builderbill-diy-help.com/...oof-screws.jpg - that's why you use these ;-)
    Last edited by boppa; 2010-Feb-04 at 04:18 AM. Reason: get quote
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  16. #16
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    The colourbond panel appears to have been used as a "structural" panel in the photo. There is no plywood sheathing under it.

    Two things are involved here. The question of how people install panels is one issue and the question of how manufacturers say to install them is another.

    It is interesting to see your examples of how people do install panels since I'm tempted to install some that way. It seems the most "logical" way to me. However, my original post is seeking any reasons why the "logical" method might not be the best one since manufacturers directions often show screws driven through the lower lying flat parts of the panels.

  17. #17
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    To tell the truth I have never seen any with plywood under it- sometimes there's sarking paper in house roofs under it - sometimes.... but even thats more for insulation than anything else. I'd say its more to do with building regs than anything else- for some reason you lot need plywood under it- it's not required here in Australia (at least in Qld and NSW anyways to my knowledge)
    Nearest I've seen is the stuff with the molded stryofoam backing on it for sunrooms and verandas where you want a bit of insulation and a `finished' look rather than exposed beams.

    It's interesting the differences in building codes and requirements around the world isnt it?

    (BTW even though we don't have plywood under the colourbond- nobody has any quarms about walking on it- I did regularly back when I was installing TV antennas- we even had a `roof party' on my house with deck chairs and a telescope a few years back when there was a spectacular meteor shower)

    One question - don't you get mould/rot problems with the plywood being pressed up against the tin?
    Last edited by boppa; 2010-Feb-05 at 06:40 AM. Reason: add question
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  18. #18
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    I think your "colourbond" must be heavier gage metal than the "residential" type of roofing panel. If I walked on "residential" type paneling that was only supported by joists, I would dent it. This type of panel is also used as siding.

    The normal installation for residential roofing panels is to have the same things underneath them that you would have for shingles. There would be plywood or composite sheets. On top of that would be tar paper or a plastic vapor barrier. Over that, the metal panels would be put down.

    I haven't had any metal roofs on my house yet. I'm told that the main thing that degrades them is that condensation forms underneath the panels causes them to rust. Another saying about metal panels: Don't mark on them with a pencil since this causes corrosion, use a felt pen.

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