You realize that require climbing to the roof
twice a year?

Christopher A. Young
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wrote in message
...

- I could put coarser screen over it, to keep birds out. But, I'm
concerned that might just make it more appealing to (say) yellow
jackets. double yuck.

Alas,
George

I tend to agree it was frozen moisture. Snow could not get on the
underside too easily. 1/4" hardware cloth is all I can suggest. In
summer, add fine screen, and take it off in winter....