Controlling the amount of moisture in your home is achieved through vents in the bathrooms, utility room, and kitchen, as well as opening windows. The ducts for the mechanical vents are often not in the best of shape during home inspections, since they are easy to forget.
As we come to a better understanding of how to create comfort in a house, and as we come to a better understanding of how to make a home las longer, we have focused on the idea of controlling moisture within the building envelope. Walking into a kitchen built in the 1880’s, you will find windows arranged in such a way to provide a cross breeze when open. This did help cool the space down, but the moisture from cooking was also removed. We continued with the idea of removing moisture from our bathrooms and kitchens by opening windows, but we realized that this did not always work effectively. Enter the mechanical vent for the bathrooms and the range hood for the kitchen (surprisingly, it is still hit or miss if a builder will place a mechanical vent in the utility room, where the washing machine and dryer are located). The idea with these vents was to have the moisture out of the interior of the home, but often this moist air was dumped into the attic. The problem was moved from one space inside the envelope to another, not good. Currently, we do consider how to exit this moist air from the building in new construction; however, this is not always done in retrofits in existing homes.
This photograph is of a duct for a mechanical vent in a utility room. Unlike the ducts for your air conditioning system (forced air system), the ducts are not insulated, and they are smaller. The range hood duct going through the attic is a solid metal vent, whereas these ducts are the flexible metal type. They are often either 3″ or 4″ in diameter. In newer construction, you will have several of these vents come together in a bundle to go out of the roof. In a little bit older construction, or in retrofits, the ducts are oriented to go out of the home at a soffit vent. If you have a two story house, the vent from the first floor may have a duct that goes directly to an outside wall with a cover similar to the one used for your clothes dryer. The real problem with these vents is visible in this photo. The duct lays over a path to equipment and storage space in the attic. The duct has been crushed by a person walking on it. This has caused cracks in the line, which means the moisture can escape into the attic.
During my home inspections, I find tears, breaks,or cracks in these ducts all of the time. Unlike the ducts for the air conditioning, these flexible metal ducts cannot withstand all of the abuse that we dish out in our adventures in the attic. We also do not plan out how the ducts should be installed to ensure a clear path. One such duct looped down in front of the attic entrance in one home. Since the attic was designed to be a major storage space, there was traffic in and out. The previous owner had cut the duct in half to give himself room when entering the attic. We simply do not think about the damage that is possible over time with moisture being added to our attics. The repair of the ducts is simple: duct tape. Please make this the duct tape that is meant for your air conditioning units though. The solution to not having these ducts damaged is to re-route them through the attic, so we do not cause accidental damage.
I am always surprised how little things can turn out to be big problems over time. Moisture in the attic can effect the framing or equipment in that space, but the moisture does begin to cause a problem for the insulation first. A little damaged insulation can be cost you a good deal of money in utility bills. Just wanted you to have something to think about the next time you are up in the attic to haul down those holiday decorations, and you are sliding that box over this duct.