CEILING IN ROOM BEHIND CHOIR ROOM
The original church roof ridges, valleys, flashing, downspouts, and hidden gutters were tin (painted with compatible lead paint).
The hidden gutters were replaced a while ago with copper. We have noticed this on all the older sections of the church building.
However, the rest of the tin (valleys) remained original.
The dissimilar metals were soldered together and this creates a galvanic reaction.
They don't necessarily have to be in contact to create a galvanic reaction. All you really need is water to run over bare metal and collect in the gutter of another uncoated metal. However, if the dissimilar metals are touching each other, you need much less time and much less moisture for one of the metals to begin to deteriorate.
The photos will show that holes have developed in the copper gutter directly below the valley and inside the top of the downspout connector. These areas have the greatest amount of water exposure.
1. Longest duration: Replace the hidden gutter and valley with new 20 ounce copper. Replace the downspout. It can either be copper or Nordic steel (as long as it is separated from the copper downspout adapter).
2. Mid duration: Replace the hidden gutter and separate it completely from any contact with the tin valley. Paint the valley to reduce the moisture exposure.
3. Short duration: Apply a sealant over the holes and expect it to fail in a few years.
Unfortunately, replacing hidden gutters is very time consuming for skilled workers. The first 3 rows of slate need to come off in order to do it properly. They did not do this during the first replacement and old tin is still underneath the starter slate on some sections of the church. This accelerates the deterioration of the copper.
Once the slate and hidden gutter have been removed, the rotten wood needs to be replaced and the wood inside the gutter box must be in excellent condition and sloped to the downspout. Then, the copper can be formed and installed over a slip sheet (sometimes a "waterproof" membrane). The seams must be riveted and soldered together by someone who will adhere to copper association guidelines. The new hidden gutter should not be nailed or fastened down in any way other than with the weight of the slate holding it in place. If it is nailed down, as it tries to expand and contract with changes in temperature, the seams will bust and it will begin leaking. The current hidden gutter has been nailed down in many locations. If you look closely, you will notice sealant that has been applied over seams ... because they leaked.
Expect to spend $20,000 for solution number 1.
The cost of solution number 3 is almost nothing ... until the copper deteriorates so badly (causing damage down below) that you are compelled to do solution number 1 or 2. In my opinion, solution number 2 is spending a lot of money to have the problem appear again.
The link in the button below tells the story a little better, if you would like to learn more.