On Mon, 22 Dec 2008 18:27:58 -0500, "Percival P. Cassidy"
wrote:

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?

Perce

Place a rolled up blanket, sand bags, or door draft stopper at the
bottom of the door. Consider a storm door.