Our front door has an aluminum alloy threshold, and we have just noticed
that ice is forming on the indoor side of it; this, when it melts, will
not be good for our wooden floor.
What must be happening, I am sure, is that, because the outdoor
temperature is now well below freezing, water-vapor from the indoor air
is condensing an freezing on the surface.
Short of (a) replacing the threshold by a wooden one or (b) cutting the
aluminum one lengthwise and interposing a "thermal barrier" between the
two sections, what's a good way of solving this problem?