What Causes High Humidity in a House

Taking a steamy shower, throwing your clothes in the dryer, wallpapering a room, or boiling a cup of tea are all surprisingly menial day-to-day tasks that can have a real impact on humidity levels in your home. The ability to balance your home humidity levels is essential in maintaining a safe, functional, and comfortable living space. 

Therefore, in this article, we discuss the causes of high humidity levels in the home. We have also provided solutions to maintaining both your health and the structural integrity of your house as a result of those high humidity levels.  

What is Humidity?

You might have heard the phrase “it’s not just the heat, it’s the humidity!” exclaimed before, but what’s the difference? While heat refers to temperature, humidity is the concentration of vaporized water in the air; it can be high or low and depends mainly on climate.

Because hot air can contain more moisture than cold air, higher percentages of water vapor exist in warmer places, especially near water sources such as oceans or lakes. When the temperature dips, the air might become entirely saturated with all the moisture it can hold and will then “drop” those water vapors as they form into precipitation.

Think of a chilly night in San Francisco, with rolling fog too thick to see through, versus a clear and muggy evening in Austin, Texas: in the warmer climate, the water vapor hangs around longer in the air instead of liquifying. When the temperature outdoors is higher than within a house, grains of moisture can begin to collect on surfaces.

If you’ve ever enjoyed a cool drink of lemonade on a scorching summer day, you might have noticed a similar phenomenon of dewy condensation forming on the outside of the glass. In your home, when water vapor touches colder surfaces (such as windowpanes), it is cooled back into liquid form.

Why Should I Care About High Humidity?

Humidity is more uncomfortable than dry heat because it leaves us sticky and unable to self-regulate our temperature through perspiration; on the flip side, very low humidity can cause overall dryness and make you more vulnerable to respiratory illnesses.

For good health, ideally, your home will retain a relative humidity level between 30-50%. Aside from the natural wetness of your climate, there are other sources that might raise or lower humidity levels in your home, but — unlike geography — these elements can be controlled. Like your body, your house might also suffer the consequences of unbalanced humidity levels.

“When humidity passes 50%, mold growth inside of the walls can become a problem,” says Bob Stockton, owner of Stockton Mechanical, a heating and air conditioning business locally operated in Santa Fe, New Mexico. Even in the high desert, mold and mildew can grow in damp places, such as basements or the bottom of a clothes hamper.

9 (Controllable) Causes of High Humidity in Your House:

Taking a Shower

Perhaps the most obvious humidity culprit, if your bathroom is not properly ventilated then taking long, hot showers might be causing mold or mildew growth on plaster, tiles, wood, or any other bathroom surface. Dehumidifiers can be purchased for specific rooms, like the bathroom, to pull moisture from the air.

Drying Your Clothes

The dryer in your laundry room produces moisture when wet clothes meet with high heat in the drum. If you have the space, hanging laundry on a line outside instead of using a tumble dryer will help reduce humidity (bonus: it’s an energy-saving method, your sheets will smell fresher, and sunlight can help to disinfect laundry without the use of heavy bleaches).


Boiling Stock, turning on the Kettle, frying veggies, etc., and especially boiling water, can raise the humidity of your kitchen. The heightened humidity that comes from cooking uncovered foods at high temperatures can be mediated by turning on fans while sautéing or using the range hood over the stove when making a big vat of delicious turkey stock.

Lack of Weatherstripping or Caulking

The actual build of your house is important in regulating air temperatures between outside and in. The plumbing and HVAC (heating, ventilation, and air conditioning) experts at Home Climates suggest weatherstripping around doors and windows to create an airtight seal, along with caulking fixtures that are often exposed to moisture, such as faucets and tubs.

Poor Insulation

Implementing proper insulation ensures that neither warm nor cool air (depending on the season) can escape through cavities within your walls, and this goes for pipes, too. Proper insulation works to slow heat flow throughout your home to control heat loss, and because cold water pipes absorb heat it will be more cost-efficient in the long run.

Incorrect Wallpapering or Painting

Speaking of walls, painted surfaces are less likely to trap moisture than wallpaper or vinyl, and if your home is mostly carpeting the likelihood of dust mites and mildew growth are higher than with tiled or hardwood flooring. Be careful when renovating with plaster or paint, though — if your humidity levels are too high, the material might not dry properly or quickly, risking the growth of mold.

Poor Ventilation

Older buildings are often old-school ventilated, meaning cracks in facades, windows, and doors are what keep fresh air moving through the space. The problem with this is when humidity comes into play, and hot, damp air makes contact with cool surfaces, resulting in water formation that can lead to damage.

If you’re using natural ventilation, the US Department of Energy recommends supplementing the latter with spot ventilation, a more localized form of ventilating that usually takes the form of fans and range hoods. If neither of these methods is efficient enough to lower the humidity in your home, whole-house ventilation is the next best option, in which a system of fans and ducts works to control the flow of fresh air throughout the entire house.

While air purifiers (devices that use fans and filters to remove contaminants from the air you breathe) have become increasingly popular in recent years, most are not designed to dry out the air, and therefore have little effect on humidity. When it comes to killing mold and bacteria that thrive off of dampness, a dehumidifier to suck moisture from the air is a better option than a purifier.  

Structural Damage

The existing structural integrity of your home, such as the porousness of the walls, the possibility of burst pipes or dripping leaks, rot from damp wood, crumbling concrete, or rusted steel beams are all factors to be considered when it comes to bettering indoor humidity. Heavy rains or rising damp might be hurting your home, so it’s a good idea to check for signs of dampness. 

 If you don’t want to purchase a humidity gauge from your local hardware store, here are other ways to tell if your house is compromised: are there any stains or discolorations along the ceilings, walls, or floors? Do any wooden or plaster surfaces, such as shelving or decorative moulding, feel soft to the touch? Are your windows fogged? Do the stairs creak when you step on them? Use your senses to see if you can’t detect the smell of old socks or rotten wood, which might be signs of mold growth. If you uncover any of these elements, it’s time to contact your nearest HVAC service.

Inefficient Heating & Cooling Systems

A final consideration for in-home humidity is the central heating and cooling system of your home, especially if your HVAC system does not already include a dehumidifying component. Using forced air heating via a gas or electric furnace in the winter can lower your indoor humidity, but if levels fall below 50% (as they often do in areas that experience cold winters), the lack of warmth-retaining moisture in the air can cause your furnace to work harder and less efficiently.

Home Humidity Considerations

Understanding the balance of relevant humidity levels is important; you don’t want to completely eradicate all of the water vapor in the air, but you also don’t want to suffer through muggy, sweaty summers. In particularly arid climates, a humidifier might be necessary to replenish moisture, which can soothe dry skin and aid in breathing by hydrating your mucous membranes and throat. Small humidifiers can be purchased to spot-treat specific areas, such as the bedroom. Humidifiers work very similarly to air conditioners; common models will use a fan to blow air through a filter moistened by cool water.

What of the summer months? Ideally, an air conditioning system will help to dehumidify your home when it’s hot enough outside to jump in the pool and grill burgers in the sunshine. The general gist of AC systems is that they suck warm air out of the room, cool that air over pipes of coolant fluid, and dehumidify simultaneously.

An issue arises when the air conditioning unit is too large for the home; conditioners too powerful for the space they occupy will neither cool nor dehumidify effectively. Because large units turn on and off frequently as a means of regulating energy when they are placed in smaller homes or offices, they become less effective at keeping moisture down and cool air flowing steadily.

 To keep your wooden furniture from cracking or warping and to stop the growth of mold, regulate your home with the change of the seasons: for the winter, invest in portable humidifiers or whole house humidifiers (some house plants also help to keep the air moist), and for the summer you should use fans and properly sized air conditioners. 

Final Thoughts

If you’re not yet convinced of the need for humidity balance in your home, consider these other little-thought-of issues: your denim jeans, new leather belt, Sam Edelman flats or Nike sneakers can grow mold if not stored in low-humidity spaces. That bottle of Decoy you were gifted for Christmas is in danger of losing its label if the relevant humidity is above 70%, and the cork can begin to dry out and crack if it goes below 50%. If you have a beautiful oil painting hanging in your living room, it’s the same story; protecting your house and belongings from humidity damage is simple and cost-effective in the long run. To start, hang your laundry outside, turn on the fan when you shower, or maybe pot a fern or two in the living room.

Latest Articles

Related Articles