I opened up my shed and in the back corner was one big pile of white, sand type, stuff. There was also the remains some wood that was pretty much deteriated.
My neighbor told me that termites were building a nest there.
I cleaned it all out and removed the wood and sprayed it with an insecticide.
I don't know if what he said was true or not but, I have 5' of snow in front of my shed doors and in the spring I'll see if it happens again.
I would take a sample to your local hardware store and see if someone there knows what it is.
You are sure it's not blown-in insulation?
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