Deep Snow Lesson and an Easy Fix
There is two feet of snow on the roof. Big icicles hang from between the fascia board and the gutters along the roofline outside the bathroom window. Inside, when showering, even though the exhaust fan is on, the bathroom steams up and the mirror is coated with condensate. Leaving the door open tends to reduce the fogging. There is no heat in the bathroom, other than what enters from the rest of the house, but, need be, there is a heat-lamp next to the light in a recessed metal box in the ceiling. Last summer insulation has been blown into the walls.
Does this all mean that the contractor did something wrong? Probably not, but let’s investigate.
The icicles are a symptom of an ice dam along the edge of the roof, which can also damage your house, should the melt-water behind it back up between the roof shingles. Fluffy snow is full of air, making it a good insulator. And there is lots of it on the roof. Warm airborne moisture carries a lot of energy — as much as 970 BTUs per pint —, all of which is released as heat when the moist air cools.
It doesn't matter whether the bathroom is heated or not. It is at indoor temperature, which is warmer than the temperature of the attic. Heat flows from warm to cold — and warm air, being lighter, will rise into the attic. The layer of snow next to the roof surface is melted from below and the heat it keeps absorbing is prevented from escaping by the snow-insulation above it. Raking off the snow at least near the eves should help.
If the bathroom mirror fogs up while you shower, the ventilation does not work properly. Its outlet may be blocked by the accumulated snow or the fan may vent into the attic. Vents must never exhaust into the attic. Unfortunately, however, in many older houses they do, because a contractor who didn’t know any better, have cut corners to save money.
Even if the fan does vent outside, there could be leaks into the attic either from a leaky exhaust duct or directly from the bathroom through leaks in the ceiling. A likely culprit is the recessed light fixture-box.
Fortunately this is a fairly easy fix: 1.Turn off the power to the ceiling fixture by tripping the appropriate circuit breaker in the breaker panel of the house. 2. Note how the fixture and wires are installed in the box. 3. Remove the fixture and disconnect the wires. 4. Carefully fill all holes inside the box with silicone caulk, including where the wires enter the box. Use your fingers or a small tool. Be neat: There should be no excess caulk protruding into the box when you are done. 5. Caulk around the box to seal any gaps between it and the ceiling surface. 6. Reconnect the wires and reinstall the fixtures. 7. Turn on the circuit breaker.