Bathroom Fans and Proper Venting

Why do we need bathroom fans?

Moisture in the home can be a real issue.  We are all familiar with wet basements, roof leaks, window and door leaks, but what about damage caused by water vapor and poor ventilation?

The bathroom can be a large contributor to moisture vapor in the home.  Condensing warm moist air on surfaces in the home can be a cause of mold growth.  But have you thought about what this same air can do to an attic without proper bathroom fan exhaust ducts?

How should they be ventilated from the interior?

Proper vent placement is critical.  Venting the exhaust pipe through the roof is the best way.  This helps ensure that the warm moist air is not recycled back through an open soffit vent to the attic.  It is important to locate bathroom exhaust vents away from any INTAKE air vent as well.

What happens when fans are not ventilated properly?

Terrible things can happen when vents are not ducted to the outside AND vents not properly placed.  As shown in the photo mold can develop as a result of poor placement.  In this instance the vent fan ducts were laid in the soffit space instead of properly vented through the roof.  The warm moisture laiden air was sucked back up the soffit vents and through the styrofoam chutes in the adjoining rafter spaces and have started to rot out the roof sheathing.  

Mold eats wood.  Have you ever wondered why every tree that ever grew and died in the forest isn't still visible on the ground?  I will say it again - MOLD EATS WOOD.

The picture is from a recent home inspection in Cedar Falls, but I have seen this on home inspections in Waverly, Waterloo, and other places.  This staining was visible on all of the other stryrofoam chute spaces as well on this side of the roof.  The worst ones were where the bathroom vents were located. 

The bathroom remodel in this case was done in 2007.  This problem developed over time and is only getting worse each year.

How can this be fixed?

Before the mold will stop growing, the roof staining sealed and the deterioration of the roof sheathing stopped the bathroom fan ducts will need to be rerouted, attached to a vent with a damper at the roof surface and the ductwork insulated.  The mold will continue to grow until the moisture source is eliminated. 

​The area will need to be properly cleaned and remediated by a certified mold remediation contractor.  Letting this condition caused by an improperly vented exhaust fan continue can have a very expensive repair bill if left uncorrected.  It would have been best to properly install the duct and vent in the first place.  Cutting corners like this by a builder and lack of thorough inspections by the area building officials does no one any good in the long run.