Indoor Humidity: What it is, Levels, Impacts, and Managing

Written By Adam Paul – Waterproofing Expert

The humidity is the amount of water vapor present in the air space. It is expressed as a percentage. Humidity is measured by the hydrometer, and its SI unit is g/m3. Humidity is mainly of 3 types such as absolute humidity, relative humidity, and specific humidity. As well as the humidity level is 3 main types such as too dry humidity, optimum (ideal) humidity, and too much humidity.

The ideal indoor humidity of a house should be between 30% and 50%. It helps to maintain good health and comfort for the residents without any structural issues or water damage. If it falls below 30% considered a too dry humidity condition, while it increases more than 60% considered too much humidity level in the home. Both of them affect the residents and the home structure by increasing damage to the home structure and increasing health effects to the residents.

You can identify a humidity problem in the home by condensation, musty odors, mold and mildew growth, paint peeling and bubbling, warped floors and swollen doors, clammy or sticky indoor air, and visible water stains on drywall and ceiling tiles. These humidity signs occur due to plumbing leaks, groundwater intrusion, improper ventilation, improper dryer vent discharging, daily activities, and leaky doors and windows in the home.

Higher humidity negatively affects the house interior. It accelerates mold growth, metal corrosion, paint damage, pest infestation, higher energy consumption, and damage to wood and furniture over time. To prevent these problems, you can use materials like ceramic tile, PVC, fiberglass, stainless steel, and moisture-resistant drywall.

To control the higher humidity in the home, Aqviz highly recommends installing a waterproofing membrane on the basement, foundation, roof, slabs, balconies, and other possible water-leaking and penetration areas. In addition, you can use a dehumidifier, sealants, and exhaust fans, improve insulation, repair leaky plumbing, and maintain the proper temperature in the home.

What is Humidity?

The humidity is the amount of water vapor present in the air. Humidity is usually expressed as a percentage. It is measured by using a hydrometer. The SI unit of humidity is g/m³. The humidity is mainly of 3 types: absolute humidity, relative humidity, and specific humidity. The humidity level can vary with the weather, temperature, and location.

The humidity level can be increased or decreased. If the humidity level is too low, it can cause dry skin, irritate the nasal passages and throat, and make the eyes itchy. If the humidity is too high, it can make the air feel stuffy or damp and can cause condensation on walls and floors, which can lead to mold growth. Hence, it is important to maintain a normal humidity level in the house.

What are the 3 Types of Humidity?

The humidity is mainly of 3 types: absolute humidity, relative humidity, and specific humidity.

1. Absolute humidity: Absolute humidity is a measurement that describes the mass of water vapor per unit volume of air. It is expressed in grams of moisture per cubic meter of air (g/m3). This measurement is not affected by temperature or pressure, unlike relative humidity. It’s used in weather forecasting and understanding climate.
2. Relative humidity: Relative humidity is a measurement of the amount of moisture in the air compared to the maximum amount of moisture the air could hold at the same temperature. It is expressed as a percentage (%). For example, if the air is holding half the moisture it could potentially hold, the relative humidity is 50%. High relative humidity indicates that the air is saturated with water vapor and can often create uncomfortable dampness.
3. Specific humidity: Specific humidity is a measurement that represents the actual amount of moisture in the air, irrespective of the temperature. It is usually expressed in grams of water vapor per kilogram of air. Unlike relative humidity, the specific humidity doesn’t change with temperature or pressure; it only changes when water is added or removed from the air.

What is the Dew Point?

The dew point is the temperature at which air becomes saturated, and water vapor condenses into liquid water (dew, clouds, or fog). A higher dew point (typically over 65°F/18°C) indicates more moisture and a “muggier” feel, often a better indicator of comfort than relative humidity alone. 

What is Comfortable Indoor Humidity?

The comfortable indoor humidity level is between 30%-50% RH. These are the 6 advantages of maintaing the humdity in the comfortable level.

1. Increases comfort and health for residents, reducing allergens and dust mites
2. Prevents mold and mildew growth on surfaces and within walls
3. Improves the energy efficiency of heating and air conditioning systems like Trane and Carrier
4. Enhances the durability of building materials such as plaster, tile, and hardwood flooring
5. Reduces condensation-related damage, minimizing water droplets on windows, ducts, and cold concrete surfaces
6. Protects indoor air quality, limiting airborne moisture that causes musty odors and microbial spread
7. Stabilizes structural components, preventing wood swelling, shrinkage, and joint separation

How to Measure Indoor Humidity?

To measure the indoor humidity, you should follow the below 3 easy ways.

• Digital hygrometer: Uses electronic sensors to display real-time relative humidity and temperature with typical accuracy of ±2-3% RH; we use this method on most Aqviz residential inspections.
• Thermo-hygrometer built into HVAC thermostats: Measures humidity alongside temperature using integrated sensors, allowing quick checks through systems connected to brands like Honeywell and Ecobee.
• Wet-bulb and dry-bulb method: Uses two thermometers and a psychrometric chart to calculate relative humidity manually; this method works reliably when digital devices fail and needs no power source

What are the 6 Reasons for Indoor Humidity?

These are the six major causes for higher humidity levels inside residential buildings.

1. Humidity level increases due to leaking plumbing lines under sinks, inside walls, or beneath concrete slabs.
2. Indoor humidity level increases due to groundwater intrusion from the unsealed basement walls and foundation cracks
3. Humidity level increases due to improperly vented bathroom exhaust fans and kitchen range hoods. These can trap the steam and vapor due to improper fixing.
4. High humidity often builds up when dryer vents discharge moist air indoors or become clogged with lint.
5. Humidity level increases due to everyday activities like cooking, boiling water, and showering without proper ventilation systems
6. Another way of measuring humidity level is leaky windows and doors, and an uninsulated attic space.

What are the 7 Signs of Indoor High Humidity?

Here are 7 common signs of higher indoor humidity and where each typically appears in the home.

1. Condensation on windows and glass doors in bedrooms, bathrooms, and kitchens signals high humidity accumulating inside.
2. Musty odors in basements, crawl spaces, or behind walls indicate moisture buildup that supports mold activity due to high humidity.
3. Mold spots and black mildew patches on bathroom tiles, ceilings, and basement corners thrive in saturated humidity conditions.
4. Peeling paint and bubbling wallpaper on the interior walls of living rooms and stairwells reveal persistent moisture caused by elevated humidity levels.
5. Warped wood flooring and swollen doors in living areas or hallways are signs of excess moisture content absorbed from humid air.
6. Clammy or sticky indoor air in closed bedrooms and poorly ventilated kitchens reflects high absolute humidity, making the space feel warmer.
7. Visible water stains on drywall or ceiling tiles in basements or upper-level bathrooms suggest long-term exposure to high humidity values.

Read more about these signs

• Musty Smell in House: Meaning, Places, Reasons, Impacts, and Elimination
• Paint Peeling: Everything You Need to Know
• All About Wood Warping: Types, Reasons, and Solutions
• Wood Rotting: Everything You Need to Know

What are the Effects of Higher Indoor Humidity?

Here are 6 major negative effects caused by higher humidity inside a house

1. High humidity accelerates mold and mildew growth on surfaces like drywall, wood beams, and insulation.
2. Extreme humidity levels can corrode metal fixtures, HVAC ducts, and electrical components, shortening their lifespan.
3. High humidity levels cause paint peeling, plaster cracking, and the weakening of structural materials in walls and ceilings.
4. High humidity increases the dust mite infestations, worsening allergies and respiratory illnesses for residents.
5. Uncontrolled higher humidity raises indoor temperatures, forcing air conditioning systems like Lennox and Goodman to consume more energy.
6. Prolonged higher humidity causes leads to wood warping and floor buckling in hardwood floors, damaging the home’s interior aesthetics.

Read More About: 8 Severe Water Damages in the Home: Causes, Impacts, Preventions

What Materials are Best for Higher Humidity in the House?

Here are 5 materials we recommend for homes with higher humidity values, based on our extensive field experience.

1. Ceramic tiles: Ceramic tiles resist moisture absorption, making it an ideal choice for flooring and wall surfaces in areas exposed to fluctuating humidity content.
2. PVC trim and molding: PVC trim and molding withstands warping, swelling, and rotting even when exposed to high relative humidity inside bathrooms, basements, or kitchens.
3. Fiberglass insulation: Fiberglass insulation, like Owens Corning, maintains thermal performance without absorbing moisture, helping stabilize indoor humidity values.
4. Stainless steel: Stainless steel fixtures resist corrosion and staining in environments with persistent high humidity levels, especially in laundry rooms and basements.
5. Moisture-resistant drywall: Moisture-resistant drywall (often branded as Greenboard or Purple Board) has a special coating that prevents mold growth even when humidity attributes peak.

These materials are highly recommended for basements, bathrooms, and coastal homes where the humidity level is high.

How to Manage Indoor Humidity?

Here are 6 effective ways to manage indoor humidity.

1. Install a whole-house dehumidifier like Aprilaire or Honeywell to automatically regulate humidity values across all living spaces.
2. Seal basement walls, crawl spaces, and foundation cracks with waterproof coatings such as Sika or Drylok to prevent groundwater vapor from increasing indoor humidity content.
3. Use exhaust fans in bathrooms, kitchens, and laundry rooms to immediately remove excess moisture and stabilize relative humidity after moisture-producing activities.
4. Improve attic insulation and add proper ventilation systems like ridge vents and soffit vents to block outdoor humidity infiltration during humid seasons.
5. Repair or replace leaky plumbing fixtures and drain lines to eliminate hidden sources of water that elevate absolute humidity over time.
6. Maintain consistent indoor temperatures using smart thermostats like Nest or Ecobee to reduce dew point issues and discourage condensation inside wall cavities.

Aqviz experts always recommend that basement waterproofing, foundation waterproofing, and crawlspace encapsulation are the best solutions to manage the indoor humidity.

Are Humidity and Moisture Different?

Yes, humidity and moisture are different. Humidity is the amount of water vapor present in the air, while moisture is the presence or amount of liquid water.

Humidity is the amount of water vapor present in the air. It is usually expressed as a percentage. It expresses the amount of moisture the air is holding compared to the maximum amount it could hold at a particular temperature.

On the other hand, moisture is the presence or amount of liquid, especially water, in a substance, object, or environment. It can be present in different formations, such as in the soil, in the air, or within objects like clothes or food.

What is the Relationship Between Humidity and Temperature?

There is an inverse proportional relationship between humidity and temperature. When the temperature increases, the air’s capacity to hold water vapor also increases, so the humidity may decrease even if the amount of water vapor stays the same. When the temperature drops, the capacity of the air to hold water vapor decreases, and the humidity increases

As a result of this, high humidity often makes people feel uncomfortable, especially in hot weather, while low humidity can cause dry skin and other discomforts. In summer, the air’s capacity to hold water vapor is higher than in winter, so the humidity is often lower in summer than in winter.