Metas roof to wood, screw placement, which camp are you in and why?

[texasjohn]

I'm up on my roof annually putting caulk on hex head screws that have backed out and they are in the flats..causing multiple leaks all thru the house. I have traveled to central america and noticed there on a BUNCH of metal roofs that EVERY ONE was screwed on the ribs..and they get LOTS of rain there.... daily, year round.

My conclusion: The recommendation to screw on the flats is because this is easier to install and will not deform the metal. This allows for inept and careless installers and less install cost. Initial appearance is good and short screws cost less. It works for about 10 years, then problems begin (my case) and when you go to the builder, they mumble about having followed manufacturer instructions, and you are left on your own.

Final conclusion... physics says that if you install on the ribs with long screws then even if a screw backs out, the resulting metal penetration hole filled by loose screw allows only extremely small amounts of water to enter during rainstorm. Water runs downhill and thus quickly leaves the penetration hole. However, on a flat, the same hole allows a torrent of running water in. Trust me, I know:drool:

Personally, I can't see how screwing on the ribs ever creates more risk of problems over the years than on the flats.

 

[jimmyj]

I've done all of the options, nails and screws, ribs and flats. I stick with screws on the ribs now. It just "seems" the right thing to do and it's what the majority of installations around here are.

 

[chopped]

(Through a lifetime of working in technology fields, I have had numerous occasions to observe that some engineers are somewhat lacking in the knowledge of how their engineering actually works out in real life conditions. Therefore, I don't automatically assume that written instructions for a product necessarily represent the optimum method.)
Well said. and this can be said for alot of other applications today..

 

[Big Bri]

i have 2 large 6 year old comercial buildings that are screwed in the flats and my house which is 60 years old w/ a 20 year old metal roof that is screw in the flats. I have zero leaks and have not been up on the roof to tighten a single screw. I live in southern Louisiana and we get a small amount of rain and wind

 

[tallyho8]

Having built many barns and garages and a house or two with metal roofs, let me give you my general observations.

First, it depends on the gauge of your metal. The most common sizes used are 29 gauge and 26 gauge. 29 gauge is too thin to tighten a screw or nail down on the rib and compress the washer enough, The rib will just dent or collapse. Screws on the flat are the only way to attach 29 gauge metal. (We are not talking about corrugated metal)

Second, there is one major difference in using nails and screws for attaching metal and leak prevention. Knocking a nail in the metal will cause a small dimple that will tend to hold water and eventually leak past the nail into the wood causing rot and loosening the nail.

When you properly tighten a screw in the metal, the screw will pull the metal around it up, creating a small levee around the screw hole preventing water from entering the hole even if the screw is loosened. For this reason, screwing metal on the flat is not as liable to cause leaks as using a nail and also assures you of being able to get the proper tension on the screw without denting the metal.

You can not attach a 3' sheet of metal by using attachments just around the perimeter. This would allow the panel to flex and flop in a wind storm, raising and lowering in the middle until it creates a break in the metal by the attachments and then tears away from the roof.

My opinion, (take it for what it is worth) using 29 gauge metal, always screw on the flats. Using 26 gauge metal, you may screw the overlaps on the ridge but screw the centers on the flats.
Screws always, nails never.

 

[/pine]

The key to fastening metal roofing through the ridges (recommended by some manufacturers) is pre-drilling...

stacking the panels and laying out the (purlin) pattern (based on measurements taken from the framing) then drilling pilot holes makes for an almost perfect looking job (appearence wise) it also makes it very easy and fast to set the screws...

Granted, the frame should be as square as possibe...the pilot holes also make it very easy to get the metal started off square and true also...(if the lapped over holes do not line up...something is not square)

When finished, the screw heads should line up diagonally arrow straight from any direction...it makes for a very sharp and professional looking installation...

 

[mwb]

The key to fastening metal roofing through the ridges (recommended by some manufacturers) is pre-drilling...

stacking the panels and laying out the (purlin) pattern (based on measurements taken from the framing) then drilling pilot holes makes for an almost perfect looking job (appearence wise) it also makes it very easy and fast to set the screws...

Granted, the frame should be as square as possibe...the pilot holes also make it very easy to get the metal started off square and true also...(if the lapped over holes do not line up...something is not square)

When finished, the screw heads should line up diagonally arrow straight from any direction...it makes for a very sharp and professional looking installation...

I did my house this way. Part way through I found drilling to be a pain and found that if you tried to drill more than four sheets at a time that the pilot hole might wander from the center of the rib (I had help doing this ). What I found worked just as well and much faster was to center punch them. With a whole stack (say twenty sheets) I could measure and punch the top sheet, the center mark would penetrate at least three more sheets. Use the top three and refresh the fourth (you could still see the center marks although faint). This was very fast and there was no difference from the first to the last sheet.

I also skipped punching one of the outer ribs; at the joints the top sheet would be center punched while the bottom one was not.

The recommendation from my steel source was to screw through the ribs.

 

[tallyho8]

The recommendation from my metal manufacturer was to screw through the flats. It was recommended to put metal to metal screws through the overlaps to hold them together but to use short screws that would not reach down to the purlins.

The panels were to be pre-drilled on the laps with the sides of the panels that go on top pre-drilled with larger holes than the sides of the panels that go on bottom but for all holes to be smaller than the screw size so the screw would pull the edges of the hole up around the screw.

If your metal panels are the same length and if you put the first panel on straight, then using pre-drilled holes, all drilled at once, your panels will all line up straight and even on the top and bottom without even having to check them first.

If your first panel is put on crooked, then the panels will start to run either up or down the roof and will all have to be unscrewed and the first panel adjusted straight.

If you are using narrow, crooked purlins, or if your purlins are not straight, do not pre-drill as the holes may miss the purlins in spots.

 

[6thgpSF]

I did my 100year old barn 15 yrs. ago with corr. steel.I used self tapping screws and screwed them in the valleys,no leaks so far.I'm doing an add on right now to the barn and am using the same materials and same methods. Last year I built a small building over my cave and roofed it with flexable corr. panels,red in color I bought at Lowes.The manufacturer sold their own ring shank nails approx 3" long and states to nail through the rib.although I'm not a big fan of using nails I did on this roof because that's what the manufacturer advised. russ

 

[CharlieS]

Years ago when we built pole barns and steel buildings i was always taught, predrill the panels, nails in the ridges, screws in the flats, and short screws in the ridges to hold the laps together.
When nailing use ring shank nails and heaven forbid if you ever need to pull one.