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Galvanized Rainwater Goods on Barn of Larch & Douglas Fir
Q. I am a self builder undertaking a barn conversion. would like to use galvanized steel rainwater goods because of their environmental credentials but am being advised that it is incompatible with the timber I am using, i.e., Douglas Fir and Larch. Would it make any difference if the rainwater goods had a powder coating? The rainwater goods themselves don't come into direct contact with the wood because they basically sit on the breather membrane. The only point of contact is the holding screws into the wood. I realise I can't use stainless steel as this is also reactive with galvanizing. Is there any other solution?
Mike Alcockself builder would like to use galvanized rainwater goods - St Andrews Fife Scotland
April 29, 2019
A. Hi Mike. Thanks for bringing this to our attention. Although I was aware of the incompatibility of galvanizing with copper-bearing pressure treated wood, I was unaware of it's incompatibility with some types of untreated lumber, but I now see it discussed at
https://www.vmzinc-us.com/zinc-basics/compatibilities.html
I don't think stainless screws are a big problem, although galvanized ^ hot-dip galvanized should be fine too. But apparently runoff from fir and larch is a problem due to the pH. I'm not quite clear whether rainwater can hit and runoff the lumber on its way to the gutters.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 2019
May 8, 2019
A. "Galvanized", i.e., coated with zinc, is an almost meaningless term. Look through the fasteners at Home Depot or Lowes and you will find thin electroplated zinc, probably less than .0001" thick which will last barely a half year outdoors under mild conditions.
You'll also find some fasteners with drippy thick hot dip zinc which is twenty or thirty times thicker, and will last for many years under fairly adverse conditions.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
A. To me and lots of others "galvanized" implies "hot-dip galvanized" and has never meant zinc electroplated or 'electrogalvanized' ... but it's true that any word or phrase we use without a detailed specification can become slang, or become co-opted by copywriters, and start meaning anything the speaker intends, and therefore meaning nothing :-(
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 2019
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