Although this goes along with my previous post on metal roofing panels over Avantech, I thought a new thread would be in order since my research on this reveals that there are at least two basic camps of thought on this, even by the manufacturers of the panels.

Some say that the panels should always be screwed down on the flats.
Others say that they should always be screwed down on the ribs.
Even others say a combination of the two.
Seems most manufacturer instructions say the flats, but I found one, at least, that says the ribs.

Some of the reasons for screwing through the flats are:
     * The screws can not be tightened enough through the ribs without squashing the ribs.
     * When through the ribs, the air gap between the metal and wood allow a leverage of the 'rocking' motion caused by the movement of the panels due to heat expansion/contraction.

Some reasons for screwing through the ribs are:
     * If/when the screw backs out and/or the gasket cracks/deteriorates, the leak will be much greater if the screw is in the flat.
     * If the screws are put through the outer ribs only (the ribs that overlap the adjacent panel), the screws can be tightened sufficiently without squashing the panels.

Of course, using standing seam panels would solve any fastener leak possibilities, but in my area it's twice the price or more.

I'm still undecided on this, but I'm wondering if the following method might be feasible on a plain roof with no gables:

Attach the screws along the eaves and ends of the roof (where the screws protrude into the open outside air and not into the attic space) through the flats every 12"
For the roof over the house itself, screw only through the metal outside ribs at 24" spacing. (In other words, screw only through the outer ribs where they overlap with the next panel's outer rib)
It just seems to me that if the metal panels were attached securely along the perimeter of the roof, then throughout the rest of the roof, that screws through the overlap ribs only should be more than sufficient to hold the metal down. And since the screws would be going through 2 ribs, you should be able to tighten them sufficiently without squashing the ribs.

I know that once I have the roof done, I sure don't like the idea of getting back up there to fix any future leaks (getting too old).

What are your thoughts on this subject ?

Arky

Arky I had a friend of mine help me with my roof.  He is a roofing contractor as well and has installed several metal roofs.  Your main concern with wind is along the outside edges and the eve portions.  I look at some of the owner/builder roofing jobs not only on here but through my travels and normally there are way too many screws installed.  The more screws the more chances for failure.  All the screws are placed in the flat areas.  The ribs are left to be self locking and expansion.  The screw placement is every 30-36" laterally.  Normally there is no (or very little)screws placed at the top edge as the ridge cap is secured on the sheets through into the sheeting or purlins.  

If you can locate they now have a "torx" head screw which I used. The head of the screw does not protrude as the 1/4" hex head do. They will not allow leaves and debris to hang up as bad.  I think it was a $2.50 additional charge for the more modern screws per 500 count but money well spent.

The rubber gasket should not be drawn down to the point that it mushrooms out. That will allow the gasket to split around the outside edges. Just torque it to the point that it starts and leave well enough alone.   I have complete faith in my install and do not foresee any leakage via the installation procedure. If I could just saw as much for the trees.


I looked for a decent picture of the roof of mine but this is as good as I could find.  The total run is approximately 12 feet and as you can see the screw placement only depicts two rows of screws in the middle of the panel. The ridge and eve screws are seperate.  There is only 1-(one) screw into the flat area in that horizontal line. On the eve I doubled the screws to one on each side of the rib rather than one per flat.



I had also measured up from my eve and predrilled the screw holes (drywall square) so that all would be in alignment and made the installation so much easier and faster.  I know they say they are self tapping but I just found it so much easier and a little safer being that I did not have to lean out over the sheet trying to start the screws off balance.  And it gave a lot cleaner look to the screw alignment. 

I hope this may help.

A good bit of screw placement is driven by the post frame industry specs, they are also using the metal sheathing to develop diaphragm action to brace the roof. That is another reason for calling for the screws in the flat, a screw with a gap under it has very little shear strength. If you are over a solid deck, that is providing the diaphragm. This is also one of the reasons you will see more screws than needed just to hold the metal down on many engineered commercial or ag buildings, the metal is replacing the ply for rack resistance and has been tested for specific screw placement. The post frame specs do call for stitch screws from sheet to sheet up on the rib in places to make that continuous skin. That said I always screw on the flat, double up on the bottom (that's where the trouble starts in a storm, bottom corners of the roof).

Use the sealer foam strips, if air isn't moving under there there is no humidity to reach dew point and condense. If the metal is in contact with a solid deck it will be below dew point fewer hours of its life.

I pondered the same thing before installing my roof. Luckily I got help from a friend with some experience installing metal. He, like Redoverfarm and Don P. recommended screwing on the flats, and also using less screws.

The roof I bought came with a manual and it said the same thing. We pretty much just followed their schedule and screwed on 4 ft rows, the recommendation for our wind zone. They also supplied different screws for "stitching" at the seam where the panels overlap. Also, the butyl tape they sent for the seam overlap was nice to use compared to caulk.

Will the standard screws supplied with most metal roofs poke through the inside of 3/4" sheathing? On the interior of my cabin that wouldn't be too much of an issue since it will eventually be insulated and covered with T&G, but the porch is decked with 3/4" boards and I hate the thought of hundreds of little screws sticking through.

My little metal roofing experience has been with corrugated roofing.  Just my preference thus far.  Corrugated roofing is self-venting, to a degree, whether it is installed on solid sheathing or purlins ... unless special efforts are made to seal the panel ends.  In the heavier ga's ... 26 and 24, the panels offer quite a bit of anti-racking.

My local Ace hardware sells the special soft-washered screws in various lengths.  I use a 1/4" hand drive rachet to install the screws ... usually, in pre-drilled holes, on the ridge-tops.  I also like to lay the metal panels in daubs of construction poly sealer/adhesive ... this seems to deaden noises quite a bit ... and may make the screws redundant.  A few screws are installed loosely until the poly cures, then I go back and finish installing the screws.  This allows the poly to "level" the panels compensating for some of the irregularities in wood work.  I have not been brave enough (foolish enough) to try an installation without the screws ... I'd hate to have my metal roofing rain down on my neighbors.

Quote from: davestreck on August 06, 2010, 08:26:09 AM
Will the standard screws supplied with most metal roofs poke through the inside of 3/4" sheathing? On the interior of my cabin that wouldn't be too much of an issue since it will eventually be insulated and covered with T&G, but the porch is decked with 3/4" boards and I hate the thought of hundreds of little screws sticking through.

You may have to run 1x4 strapping - flat purlins  on top of the sheathing -fasten them to the joists and the roofing to the strapping.  Run the strapping across the joists and under the roofing at the spacing required ...usually 2 to 4 foot spacing.

   Back in the day . . .    We nailed (roofing nails w/rubber washer) the "top" of the rib when building quonset hut type machine sheds.   Of course there are more choices of metal roofing material now.   

   Here is a pic of what we would use.

The palm nailers do a good job of nailing through the top of the rib - it may take the oversized adapter to get over the nail head and neoprene  washer.  I'm not sure as mine has the 60d spike adapter on it already.

No smashed fingers with the palm nailer.  [ouch]

I use that type metal - the rustier the better - makes my buildings look old.

Quote from: davestreck on August 06, 2010, 08:26:09 AM
Will the standard screws supplied with most metal roofs poke through the inside of 3/4" sheathing? On the interior of my cabin that wouldn't be too much of an issue since it will eventually be insulated and covered with T&G, but the porch is decked with 3/4" boards and I hate the thought of hundreds of little screws sticking through.

Dave with mine I used just 7/8" purlins and the standard length screw (  ) that I used penetrated the purlins about 1/2 - 3/4" which was not really a problem.  I spray stained the rafters , purlins ,underside of the roofing tin and covered the screws as well.  They are not really visible.  I think I posted a picture but I will have to go back and see.

I'm using 1/2" plywood on my roof and was planning to use metal. After reading this I'm wondering if thats a bad Idea. 
Is using 1x4 or something of that sort required for a satisfactory job or is the 1/2" plywood going to have enough for the screws to grip.
I'm not too concerned with the screws over penetrating the plywood as far as looks go, but if it's a bad idea then thats another thing.

Our house is roofed with ribbed metal panels over 7/16 OSB as is every other metal roofed building in the neighborhood. Screws on the flats through the OSB. Also self threading metal screws where a rib overlaps another rib or the ridge connects to the roofing rib. .  As was pointed out making certain the lower edges are well secured will go a long ways in preventing wind lift. Also check recommendations for your wind zone as Dug pointed out.

Ditto our cabin.

I've done some reading as this showed up on another forum as well. 1/2" is ok'd by at least some manufacturers with 5/8" in high wind areas, 24" between rows is commonly specced.

This is from the tech sheets of a panel I've used a fair amount of, they spec 5/8 ply minimum and don't care for osb, I've attached enough to 5/8 osb that it doesn't bother me;
http://www.fabral.com/technical/Residential.pdf
http://www.fabral.com/technical/Residential_condensation.pdf
http://www.fabral.com/technical/Fastener_location.pdf
their entire list of topics;
http://www.fabral.com/technical.php#details

As an aside...oak purlins can also be corrosive on a metal roof.

Edit,
Dave, when we have nice T&G porches I'll plywood over the top of the T&G, nailing that to the porch rafters and then screw the metal to that built up roof.

Dave on the house portion I used 5/8" sheeting and I was not worried about the screws protruding into the rafter cavity.  On the porch I just used purlins.  I was really not after the finished look since it was a porch on a rustic cabin.  Again I did not vary from the spacing on the installation so there were very few screws to see from underneath.  Now if you want that finished look then I would do as Don suggested and lay an extra layer of 1/2 ply to absorb the screw depths.  I can tell you that an open porch without some solid decking will sweat.  With that in mind I would use some type of vapor barrier between the metal and the wood.  

I did discover that the stain I used was applied with a sprayer and worked very well adhereing to the underside of the metal.  

I'm diving into the whole metal roofing scene, and man, the debate on where to screw those metal roofing panels down is a real head-scratcher. Some say flats, some say ribs, and then there's the combo crowd.

I've been mulling over this and thought, why not mix it up a bit? Along the eaves and ends, I'm thinking screws through the flats, every 12 inches. But when it comes to the main roof, maybe stick to the outer ribs, spaced at 24 inches. It's like trying to get the best of both worlds – less risk of leaks and still a solid grip.

Wood screws (with the metal and neoprene washers) through the flats to the sheathing.  Self drilling metal-to-metal shorter screws (with the metal/neoprene washers) through ribs where one rib overlaps the rib on the other panel. The screws do not penetrate the sheathing. Those same screws are used for securing rake end trim, snow guards, etc. .

When it comes to roofing materials and the debate between metal and wood, it ultimately depends on various factors such as durability, aesthetics, and environmental considerations.

Metal roofing has gained popularity for its longevity and resistance to elements like fire, rot, and pests. Additionally, metal roofs often come with longer warranties and require minimal maintenance. From an environmental perspective, metal roofing is often recyclable, reducing its impact on landfills.

On the other hand, wood roofing, particularly cedar shake or shingles, offers a timeless aesthetic appeal that many homeowners find attractive. Wood roofs can also provide excellent insulation properties, helping to regulate indoor temperatures and reduce energy costs. However, they may require more maintenance, such as regular inspections and treatments to prevent rot and decay.

In terms of screw placement, both metal and wood roofs require careful consideration to ensure proper installation and structural integrity. Improper screw placement can compromise the roof's performance and longevity, leading to leaks and other issues over time.

As for my personal preference, I lean towards metal roofing, particularly when considering sustainability and long-term durability. However, I would also suggest exploring environmentally conscious alternatives such as.... SPAM LINK REMOVED..... . ECM homes often utilize sustainable materials and construction methods, offering a blend of modern comfort and eco-friendly living practices.

Ultimately, the choice between metal and wood roofing should be based on individual priorities, budget, and the specific needs of the property. Consulting with a reputable roofing contractor and considering the environmental impact of your decision can help guide you towards the best option for your home.