- 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.
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
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