Why is my Home Drafty Downstairs in Winter?
Heat escapes from the conditioned living space pressure barrier.
Existing Insulation Evidence : find a perfect black line corresponding with the seam between the drywall and framing called the bypass. This seam is accompanying the gap between the trim / baseboard / drywall / floor of the living space below. This is a direct result of skin dust and hair which is pulled up through stack effect to the attic from temperature differences between the attic and the living space. The black lines of the photo are not mold ( commonly confused and misdiagnosed) it is skin dust and hair from the living space. The fiberglass insulation does not stop air movement. No loose fill insulation stops air movement.
To verify this process of finding skin dust and hair in the attic, shake out your blanket in the morning with a bright light and notice the dust that fills the air. This dust is pulled between gaps in the room up and out to the attic. This is the same air that leaks and escapes from the heated bedroom resulting in unintentional air exchanges, a drafty lower level, higher bills, mold food in the form of condensation, premature snow melt, icicles, ice dams and more.
