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How to waterproof a copper roof over a bay window

July 15, 2015

Q. Hi, I found your blog online and am hoping you can point me in the right direction please. I have a house in the SF Bay area that has 2 copper roofs with sections joined by seams, over bay windows. When the windows in the bays were replaced this month, I was told that there is not a waterproof membrane lining under the roof itself, and that I should have them painted with elastomer paint or silicone sealant in order to seal them.

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I love the look of the aged copper and would love to find a way to keep it (rather than paint it). Other than the fact that the windows had dry rot and needed to be replaced, I don't have specific evidence that the copper roof, per se, is leaking. Do you have ideas? Please let me know. Thanks in advance for your help.
Kate Chenok

Kate Chenok
homeowner - Orinda, California

A. Hi Kate. Copper is surely waterproof unless it has holes in it. Assuming it doesn't have rivet holes or other holes, the question becomes whether the joints are waterproof or can be made so. It's difficult for a reader many miles away to comment on that, but you might at least take a look at --

https://www.copper.org/applications/architecture/arch_dhb/arch-details/basic_details/joints_and_seams1.html

-- where the Copper Development Association acquaints us with some of the issues of joints in a copper roof.

I would try hard to find a roofer with significant experience in copper roofs, rather than a generalist more used to asphalt shingles. If you have already found one, I think you'll have to trust his opinion. Good luck.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2015

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