When it snows we are getting piles of snow throughout the attic from snow that filters its way in. There are no large holes or areas of daylight showing between the exposed slates, but somehow the snow works its way in. I've had other people in our area say the same thing happens to them, but no one has a solution.
I would like to finish the attic with insulation, etc and make it a living space. The entire house also lacks hvac and that too is planned to change. But I don't want to make these changes and have it snowing inside the house.

Any solutions? Or do I scrap an otherwise functioning roof that could have another 80 years of life left?
Thanks for any input!!
Jen