While renovating a bathroom in their
22-year-old home, the owners were
shocked to find wet insulation, severely
decayed framing and sheathing, and live
carpenter ants behind the tiled shower
stall (Figure 1). Tucked into an outside
corner, two sides of the stall were against
exterior walls. The walls consisted of
floor-to-ceiling ceramic tiles set on mortar
and metal lath, standard gypsum
wallboard, unfaced fiberglass batt insulation
between 2x4 studs, plywood sheathing,
and wood shingles. The bathroom
had a window, but no exhaust fan.
The shower pan and drain tested
leakfree, and the owners recalled that
the tiles and grout had only a few
cracks. This told me that the cause of
the problem was not liquid water leaking
into