Another Metal Roofing Question

   / Another Metal Roofing Question #1  

Beltzington

Platinum Member
Joined
Oct 4, 2008
Messages
959
Location
Appling, Georgia
Tractor
JD 3720
I am amazed, not really, on the disagreement amongst installers on the best way to install metal roofing panels on top of sheathing. So what does TBN folks have to say. Existing construction not changing so not allot of value in this thread to discuss why it is better to not use sheathing under metal roofs in the first place.

1/2" ZIP OSB sheathing, metal panel approved 1st layer moisture barrier.

I was going to just screw the panels to the roof, hitting the 24" OC rafters if needed, however this method seems to cause a great amount of gas buildup if you google on the internet. Their preferred solution is to screw 1x4" strips to the sheathing to keep the metal off the roof which they believe will prevent moisture damage from condensation. Thinking this through, a problem of mine, any condensation will still end up on the sheathing so I do not see how this is a solution any better or worse than screwing it directly to the sheathing. Actual experience greatly appreciated, opinions will be tolerated. :rolleyes:
 
   / Another Metal Roofing Question #2  
Well... I put a galvanized roof on an old dairy barn over 20 years ago. laid it over and directly on both mineral paper as well as on shake shingles. No sign of rust or corrosion....:D
 
   / Another Metal Roofing Question #3  
I would do it the way they offer you to.
1x4 on 16" centre nailed or screwed in the farm trusses.
Then screw your thin to the strapping 1x4.
The metal roof needs to breathe...air movement between your sheating and thin...corrosion will form on the under side, it won't be visible from the surface until too late.
The way I do it here on a 32x210' barn , 60x40 shed and my house.
 
   / Another Metal Roofing Question #4  
I've allways put it on (ag type) buildings directly on the purlins. About 6 years ago I had a shed roof below a much larget roof and I used sheathing for concerns of the "upper" snow coming off might damage the lower shed roof that had barely a 3/12 pitch. Tar paper & screwrd it to the osb, So far so good, but any poblems would take a long time to appear. Fingers crossed. I like Man in black's (above) procedure. I think that is what's called a "cold roof" as it's fully vented directly under the panels.
 
   / Another Metal Roofing Question
  • Thread Starter
#5  
I would do it the way they offer you to.
1x4 on 16" centre nailed or screwed in the farm trusses.
Then screw your thin to the strapping 1x4.
The metal roof needs to breathe...air movement between your sheating and thin...corrosion will form on the under side, it won't be visible from the surface until too late.
The way I do it here on a 32x210' barn , 60x40 shed and my house.

I will be doing this myself it is a small roof, however I have been using materials I plan on using building my house to see if they meet advertising claims.

Agree air circulation is a proven method of removing moisture however help me understand where the air will circulate to and from when I have installed a grid of enclosed 1x4" cells across the entire roof? The top and sides will also be enclosed by a ridge cap and flashing. I appreciate your feedback just don't see the science in this concept.
 
   / Another Metal Roofing Question #6  
I see no problem screwing right to the shting. the only place that will get air is under the ribs and they'll be vented from bottom to top. Ridge cap doesn't block the ridges from venting.
 
   / Another Metal Roofing Question #7  
Where "I" live, all the pro's (tin installers) put down the 1x4's and screw the tin to them...

All the guys doing it on the cheep or that don't do a LOT of it, just screw it down!

There's NO way I would install, or would I let ANYONE install metal without the 1x4's on a roof of mine...

SR
 
   / Another Metal Roofing Question
  • Thread Starter
#8  
Where "I" live, all the pro's (tin installers) put down the 1x4's and screw the tin to them...

All the guys doing it on the cheep or that don't do a LOT of it, just screw it down!

There's NO way I would install, or would I let ANYONE install metal without the 1x4's on a roof of mine...

SR

But why do the "pros" do this, is it the best method or just means they don't waste anytime having to be concerned of hitting the rafters when attaching the sheets, thus saving money?

Also suspending the thin metal between firing strips can allow the metal to bend or deform as opposed to a nice flat roof screwed directly to the sheathing.

The cost of installing the 1x4" is too small to factor into my decision, only looking for the best construction method.
 
   / Another Metal Roofing Question #9  
Commercial here put down grace membrane then stand seam on top, no 1x4s.
 
   / Another Metal Roofing Question #10  
So the metal with breathe, THEY say, both the roof and metal will last longer... Good installers won't install it without the 1x4's...

Perhaps it's done differently where they don't have much winter...

SR
 
 
Top