Here's a close look at the roof sheathing from inside the attic. The sheathing is plywood that spans the roof trusses or rafters and the shingles are nailed to it.

Look at the ice crystals...the ones on the sheathing, just above the pink insulation. The crystals on the nails that poke through from holding the shingles down are normal. Ice crystals are frozen water...hmmmm....

Must be the wood is wet. But if its wet inside the attic, it must be the shingles (and underlayment beneath the shingles) are degraded to the degree that moisture is getting through them and saturating the wood.

Time for a new roof before the damage gets worse!

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