- Q. It has become common practice in new construction around Nashville to vent bathroom fans into a nearby soffit. One problem is that the vent often gets covered with vinyl or metal soffit because the siding crew doesn't want to cut a hole in the finished soffit. Other than running the vent into the attic, which is not a good idea, what can you do? With the pitfalls of mold becoming more problematic, we need more options.
A.Harrison McCampbell responds: The International Residential Code (Section R303), referring to mechanical ventilation in the bathroom, requires that "the minimum ventilation rates shall be 50 cfm for intermittent ventilation or 20 cfm for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside."
This seems pretty clear: Venting to the attic is out of the question, as that is not directly to the outside. Venting into the area behind the soffit panel would be the same thing, while venting through a hole in the soffit is only a step away. While using a vent cap mounted in the soffit panel might be considered venting to the "outside," the moist exhausted air will most likely be drawn back into the attic through the soffit vents as soon as it hits the outside (assuming that the soffit and ridge vents are properly sized and installed and have good convective flow). So while this follows the letter of the code, it doesn't follow the spirit.
Although it may cost more and add another penetration through the roof, you should take the time to do this right: Install a roof vent and flash it properly.
Harrison McCampbell is a consulting architect in Nashville, Tenn., specializing in construction defects.