Replies

1. 
   UncleDunc | May 18, 2004 12:18pm | #1

   I don't have any idea about sulfur in bituminous materials, but if there is, and if it forms sulfuric acid in contact with liquid water, wouldn't the sulfuric acid wick right through the rosin paper and start eating on the copper? Or is rosin paper quite a lot more waterproof than I thought?

1. 
   DaveRicheson | May 18, 2004 12:48pm | #2

   Following your same logic.

   Wouldn't aluminum be reactive to sulfuric acid also?

   Seems like H2SO4 leaching from bituminus material would end up in aluminum gutters eventually. Same thing would be likely to happen with roofing tire and many foundation sealers. Even weak solutions of sulfuric acid leaching from them would have a long term effect on many building materials.

   Good question though.

   Dave

2. 
   KaneoheBay | May 18, 2004 09:20pm | #5

   Sulphur is present in petroleum. I was surprised to hear that the quantity or its form was sufficient to form sulphuric acid. I'm not a chemist so I really don't know about these reactions.

   Butch

2. 
   Piffin | May 18, 2004 01:42pm | #3

   This is one of those things based more on theory than on reality. how is that moisture going to get there in the first place? Modern building science works to control moisture and where iot goes - what it does. Older theories worked on assumptions that it might...

   I have been required to do the same on govt contracts long time ago. I am betting this rofer was an old timer with old habits.

   I have torn off thousands of roofs and hundreds with copper flashing. never, under any situations, have I seen the copper corrode before the roof material. I can't even remember seeing copper corrode to the point of failure. I have seen copper valleys washed out from the erosion effects of water and debris.

   My final point would be that there is likely to be far more corrosive action from the atmosphere itself than from beneathe the copper. I see much more corrosion of ALL flashing materials but AL especially in closer proximity to industrial areas and just down wind of factories where acids are spewed. Acid rain affects more than maople trees and trout. It shortens the life of roof metal.

    

    

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1. 
   KaneoheBay | May 18, 2004 09:24pm | #6

   The moisture in the air (water vapor) is supposed to condense on the underside of the copper sheet.

   I dunno know.

   Butch

3. 
   seeyou | May 18, 2004 02:30pm | #4

   Excellent question. Back in the days of terne metal, rosin paper was necessary for the reasons explained. The tars were corrosive to terne. The process of laying rosin paper has been held over from terne to copper as copper has been replacing terne for flat and standing seam roofs. It's not really necessary.  The only reason I see for it under standing seam is for a slip sheet. Sometimes the felt will stick to the bottom of the copper. I use it under flat seam roofs because the tar will occasionally bubble thru when soldering.

   The only failed copper I've ever seen (less than 80 years old) is from errosion rather than corrosion. 

1. 
   KaneoheBay | May 18, 2004 09:32pm | #7

   Thanks for all your answers. When I first saw the show, I was surprised. Thinking about it for a couple of weeks and visiting internet sites regarding galvanic corrosion yielded some info but did not address my concern directly.

   Your responses were much more informative since they were based on experience. Seems the roofer's (on the show) practice and "theory" is more smoke 'n mirrors.

   I guess I'll proceed with my original plan of installing copper flashing at the fascia and watertable and shingling it over with ice/water dam material to complete the waterproofing.

   Thanks again,

   Butch

2. 
   JohnSprung | May 18, 2004 09:37pm | #8

   > The only reason I see for it under standing seam is for a slip sheet.

   That's the explanation I've heard from the CDA.  Copper expands and contracts a lot with temperature changes, so if the ends of a pan get stuck down by the goo, expansion could make it buckle upward.

   -- J.S.