Preventing Bathroom Mold

Bathrooms are often hot, humid & stinky. This is why we put bathroom fans in them. While the stinky part may cause problems within your family dynamics, only the humid part really causes problems with the durability of the house. Durability problems can come in 2 varieties – bulk water and humidity. Bulk water problems can be obvious problems, either of the one-time-event variety (“OMG I forgot I was running the bath water”) or the recurring-problem variety (“hey, have you ever noticed that dripping noise whenever someone takes a shower?”) or they can be insidious, sneaky, stealth problems. The sneaky, stealth kind are especially worrisome precisely because you don’t know they’re problems for a long time. The biggest cause of the sneaky water problems are in cracks and joints, especially places where two types of materials come together. For example, the interface between your tub and the wall, or the around the gaps in your tile around the shower handle are places where water LOVES to enter your wall.

When Water Gets Behind Your Wall

What happens to that water when it gets behind your wall? If you live in a relatively new home, chances are good it’s fairly air-tight. This means air isn’t blowing through your wall cavities every time the wind blows. This is great for energy efficiency, but can be somewhat challenging for drying building materials that happen to get wet. When building materials get wet, mold & mildew problems develop. Mold develops when standing water is present on materials – like the sheathing behind your shower – for a long time. Once the water gets back behind your shower, the only way for it to escape is through evaporating into the air and then finding its way out through cracks in the wall. In a humid environment, like your bathroom – especially in places like Houston, that’s not likely to be a quick process.

The Solutions

Luckily, there is a two-part strategy that can prevent the majority of sneaky, stealth water problems. The first part of this strategy is to prevent the water from getting behind the walls in the first place. For this, a tube of caulk can be your best friend. It is important to completely seal the cracks, and to inspect them frequently for places where the caulk has separated from the wall. To properly apply the caulk, the shower must be completely dry and must stay dry until the caulk has fully set. Caution: find an alternate shower before approaching this project! This will likely take a few days.

Pinterest caulk

The second part of the strategy is to install and use a bathroom fan that exhausts to the outdoors, not your attic. The theory behind the bathroom fan is that when it is exhausting hot humid air from the bathroom, it pulls air in from the rest of the house, which is presumably less humid. This prevents mold buildup on the surfaces of the bathroom and also gives a better chance to any water trapped behind the walls to make it back out from behind the wall. It is important to ensure that the fan isn’t just moving the humid air to your attic, where it will just cause mold problems there (yes, even if it’s a vented attic).

Bathroom fans come in many varieties, but the most effective are fans with occupancy sensors and/or timers. The timer can be set to go off at a set time after the occupant leaves the room, which gives the room time to dry out without the risk that you’ll leave for the day and forget to turn it off. In general bathroom fans don’t use much energy, but Energy Star-qualified fans are quieter than non-qualified fans. This makes them more pleasant to have on more often, but may cause problems if the fans are often used for noise abatement.

Proper application of caulk and regular use of a bathroom fan should at least keep the sneaky, insidious water out of your walls and keep your bathroom dry. At least until you hear “mommy, my rubber ducky is swimming on the bathroom floor!”

carolinekostak GreenHouse Integration provides Green Building & Building Science services to Houston. Caroline performs energy testing of new homes and provides green building expertise to home builders and homeowners who want to build healthy & environmentally-friendly homes. GHI also provides deconstruction and reclaimed materials services to the Houston area. Caroline frequently speaks to audiences, both large and small, about a variety of topics, including Green Building and living sustainably.

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