My first thought was efflorescence or possibly white mold but I’m not sure. It is powdery in some parts This is a cedar exterior and also aluminum soffits. This is a very shady area of the house.
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I think you’re onto it with the white mold 
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Thanks @anon26752184. That was my hunch. The guy said that it grew almost overnight on the cedar.
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Some comparison pics are here:
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It appears mostly where theres possibly rain splatter and shaded areas, so white mold gets my vote too.
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