Here in the cold northernmost island of Japan, apartments and houses are very different when it comes to how their rooms react to the cold weather, and the issues of excessive moisture and mold tend to arise as an indirect result of this weather.
If there is one thing I’ve found is a fairly large problem in my apartment during the winter it is condensation, mainly on the windows and the entrance door which is made of steel. In houses with proper heating and ventilation which keep “room temperature air” circulating through all of its rooms (in addition to the use of dehumidifiers), this problem is almost non-existent.
There are a wide variety of reasons that condensation occurs, ranging from room temperatures that are too low (the cold air can’t hold the moisture so it deposits on the windows) and high temperature showers, boiling water, etc. that contributes to higher humidity levels indoors.
For people like who have a modest-at-best income and live in an apartment without central heating, having a heater every room is not a very efficient option money-wise. As expensive electricity bills make for an even more difficult winter, we have to be a bit more creative with our solutions to avoid this.
For starters, a 除湿器 (joshitsuki, otherwise known as a dehumidifier) is important for rooms that are cannot be heated most of the time. I personally reserve the joshitsuki for our bedroom so that water does not deposit heavily onto the windows, which then drip onto the walls and floor and lead to an even worse enemy than unwelcome excessive moisture: mold.
For other rooms that get neither the heater nor the joshitsuki, a bit more maintenance is required to prevent excessive moisture and mold. Every morning I wake up and use a 結露取ワイパー (ketsuro tori waipaa, or “condensation removing wiper”), an ingenious invention that lifts water from smooth surfaces like glass and stores it in the handle to be dumped later.
As the condensation also builds up around the window frame and the surrounding walls, a daily wipe with a rag is also necessary.
During the winter, windows are rarely opened because of the cold temperatures. This leads to stagnant, motionless air which is a large contributing factor to the development of mold. At the very least, you should open your windows at least once every couple days for a good 20-30 minutes to cycle in fresh new air and hopefully get a nice breeze through your rooms as well. Since this can be quite cold, I recommend closing off these rooms during the process.
For worst case scenarios where moisture and stagnant air have led to mold, you need to act quickly as the presence of mold in your home is detrimental to your health. My personal recommendation is to pick up a mold killing spray made for walls like カビキラー (kabi kiraa) or “mold killer”. It is recommended to spray on moldy areas until the spray gets all bubbly and leave it for 20-30 minutes before wiping it clean.
You additionally need to have a nearby window open to keep the area well ventilated as the chemicals in the spray include bleach, the fumes of which should be inhaled as little as possible.
You should always confirm that it is the correct kind of mold spray. Some types are only for bath areas and some are meant for the walls of your house, so walls could end up damaged if you choose the wrong kind. Asking a store employee これは壁の為ですか？ (kore wa kabe no tame desuka) meaning “is this for walls?” while showing them the product should get you the confirmation you need.
No matter how you choose to deal with excessive moisture and mold, always keep these two basics in mind:
1. Temperature and humidity regulation is important for controlling moisture, so make sure your rooms either have a heater and/or dehumidifier. If this isn’t possible use the moisture removal methods listed above.
2. Mold likes moist areas with little to no air flow, so make sure you find these mold prone areas and keep them dry with moving air.