Basement Humidity: Levels, Variations, Impacts and Controling

Written By Adam Paul - Waterproofing Expert

The basement humidity is the amount of vapor water in the basement. Humidity is expressed as percentage where 100% humidity means the air is fully saturated with moisture and cannot hold any more, and zero is no moisture in the space. The 3 types of Humidity levels are absolute humidity (AH), relative humidity (RH), and specific humidity.

These are the 8 main categories of basement humidity levels.

The ideal humidity level in the basement is between 30%-50% RH (relative humidity).
The lower humidity level in the basement is considered as between 30-40% RH.
The correct/normal humidity level in the basement is 40-50% RH.
The optimum humidity level in the basement is 50-55% RH.
A good humidity level (health and structure) in the basement is 40-50% relative humidity (RH).
The higher basement humidity level in the basement is between 50-60% RH.
More than 60% RH is considered as the extremely high humidity level in the basement.
The healthy humidity level in the basement is between 30-50% relative humidity (RH).

You can monitor the basement humidity by using a hygrometer, smart sensors, and dehumidifiers, and checking moisture levels frequently. The basement humidity can be varied in 4 seasons Spring, Summer, Autumn, and Winter.

When a basement has prolonged humidity problems it causes to mold and mildew growth, structural damage to the house, health hazards, damage to the belongings, pest infestation, and increasing energy costs. The basement humidity level can be increased due to waterproofing failures, basement cracks, groundwater seepage, poor ventilations, inadequate drainage systems, and underground pipe cleanings.

You can control the basement humidity by waterproofing the basement, installing dehumidifiers, installing ceiling fans, improving basement ventilation, insulating the basement, and using moisture-absorbing materials.

Table of Contents

What is the Ideal Humidity Level in the Basement?

The ideal humidity level of the basements is between 30%-50% RH (relative humidity). The advantages of having the ideal humidity level in the basement are preventing mold and mildew growth, improving the quality of the indoor air, and increasing the comfort of the inhabitants. Humidity over 50% can lead to condensation on surfaces and mold growth. Lower humidity levels cause gaps between windows and doors in the basement, leading to structural damage.

What is the Lower Humidity in the Basement?

The lower humidity level in the basement is considered as between 30-40% RH. Lower humidity levels in the basement reduce the mold and mildew growth in the basement walls, floor and fixtures. It helps avoid damage to furniture, wood, electronics, and walls from excessive moisture and wetness.

What is the Normal Humidity in the Basement

The correct/normal humidity level in the basement is considered the comfortable and safe humidity level for the basements. The normal humidity level in the basement is 40-50% RH.

What is the Optimum Humidity Level in the Basement?

The optimum humidity level in the basement is considered as the maximum humidity level without damage to the structure and health. The optimum humidity level in the basement can be considered as 50-55% RH.

What is the Good Humidity Level in the Basement?

A good humidity level in the basement is considered as the humidity level in the basement that is good for both human and structure. The good humidity level in the basement is around 40-50% relative humidity (RH). It reduces the risk of mold growth, maintains air quality for breathing, and reduces health impact due to dust mites.

What is the Higher Humidity Level in the Basement?

Basement humidity between 50-60% RH is considered as a higher humidity level. A higher humidity level in the basement tends to grow mold and mildew, increasing dust mites, and creating condensation on windows. Prolonged higher humidity levels in the basement cause paint peeling, wallpaper bubbling, wood rotting, and material decaying over time.

Is 57 Humidity in the Basement High?

Yes, 57 (57% RH) humidity level in the basement can be considered as a higher humidity level but it is not extremely high. 57% RH will not be alarmed. But moisture-related issues can be visible when it is prolonged.

The relationship between temperature and humidity is inversely proportional, which means when the temperature increases, the humidity decreases and when the temperature decreases, the humidity level increases.

What is the Ideal Temperature in the Basement?

The ideal temperature for the basement is in the range 60-75˚F(15-24˚C), which is different with the country and the location. There are many advantages of having the basement at an ideal temperature, such as preventing moisture and Mold by keeping the ideal temperature consistent, offering a comfortable living environment, protecting structural integrity, and contributing towards the overall energy efficiency of a house.

What is the Healthy Humidity Level in the Basement?

According to the National Asthma Council, Article “Indoor humidity and your family’s health” in 2016 the healthy humidity level in the basement is recommended between 30-50% relative humidity (RH). This range helps to prevent dust mites, and musty smells due to mold and mildew growth which cause to many sever health problems such as allergies, asthma, and uncomfortable breath to the user.

How to Monitor Basement Humidity?

You can monitor basement humidity levels by following 4 ways.

Use a hygrometer: Place a digital or analog hygrometer in the basement. It can measure the humidity levels and get the accurate readings in the basement moisture.
Use smart sensors: Smart humidity sensors can sync with apps and give real-time humidity data and alerts if levels go beyond the ideal range.
Use dehumidifiers with built-in sensors: Dehumidifiers have humidity sensors that can measure the humidity and automatically adjust to maintain the desired humidity.
Monitor humidity level frequently: Check humidity levels frequently, especially in changing weather or after heavy rains.

What Are the Humidity Levels in the Winter, Summer, Spring, and Autumn?

Basement humidity levels can be varied in four seasons: Spring, Summer, Autumn, and Winter. Basement humidity levels can be varied with temperature in every season.

Basement humidity in the Winter: The basement humidity in the winter is around 25-40%. The basement humidity level increases due to reduced ventilation, heating systems, as well as cold outdoor air temperature. It is essential to keep the basement humidity level to a certain level during winter, as if the level drops too low, the users can experience adverse effects on their health.

Basement humidity in the Summer: The basement humidity level in the summer should be around 30-50%, and the humidity level increases because in Summer, the outside air is more humid and warmer. Many homeowners use dehumidifiers to keep the basement humidity level to the above-mentioned level. The reasons for the increase in the basement humidity level are, warm outdoor air, and warm humid air can condense the cooler basement surfaces. Therefore, condensation is another factor. Summer brings heavy rainfall, leading to an increase in moisture.

Basement humidity in Spring: The basement humidity level changes during spring because of an increase in rainfall, thawing ice, and snow, and indoor activities. As the Winter passes and the temperature level soon starts to rise, so will the humidity level; for that reason, it is advised to keep the humidity level below 50%.

Basement humidity in Autumn: The recommended basement humidity level in autumn is between 30-40%, not too high and not too low. The same as the Spring season, Autumn also has variations but typically a decrease in humidity level, with climatic changes such as cooler temperatures, a decrease in rainfall, and stable weather conditions compared to Spring and Summer.

What are the Reasons for Higher Basement Humidity?

Basement humidity level can be increased by these six factors such as, waterproof failure, basement cracks, seeping of groundwater and rainwater to the basement, poor ventilation, inadequate drainage systems, and underground pipe leakages.

Basement waterproofing failure: The basement humidity level can increase due to basement waterproofing failures. The basement waterproofing layer fails due to poor installation, lack of maintenance, poor quality materials, and poor surface drainage.
Basement cracks: Basement cracks increase the basement humidity by allowing moisture to seep in from the ground, eroding the wall’s structure. The basement cracks are formed by poor construction.
Groundwater and rainwater seeping into the basement: Basement humidity increases by the seeping of groundwater and rainwater. Groundwater seeps in by cracks in the walls and floor or through thick soil settlement around the basement, especially in areas with annual rainfall over 40 inches a year.
Poor ventilation or lack of airflow: The basement humidity increases because of poor ventilation. The lack of airflow is caused by the lack of exhaust systems, clogged vents, neglect of maintenance, and insufficient windows, creating a lack of ways for water to escape, making the basement cool.
Inadequate drainage system: Insufficient drainage system is another reason for increase in basement humidity. Erosion of pipes, landscape issues, poor construction, and hydrostatic pressure are some reasons for inadequate drainage systems. With the lack of drainage systems, water has no way to drain away, increasing the moisture.
Underground pipe leaks: Underground pipe leakages increase the basement humidity. Due to clogged gutters, clogged drainage, and hydrostatic pressure, underground leaks occur. So the water accumulates in the soil around it and slowly gathers around the foundation making it’s way inside the basement, creating a damp environment.

What are the Negative Impacts of Basement Humidity?

The 6 negative impacts of basement humidity are mold and mildew growth, structural damage to the house, health hazards, damage to the belongings in the basement, pest infestation and an increase in energy costs.

Mold and mildew growth in the basement: Due to higher humidity levels in the basement, mold and mildew can grow. It tends to deter carpets and wood materials, cause property damage and create allergies and respiratory issues for the users. These are the results of mold and mildew growth in the basement.
Structural damage to the house: Higher and lower humidity basement levels cause structural damage to the house, which results in the place being unsuitable to live in and raises safety issues. Sagging or uneven floors, doors, and windows decrease the property value of the house.
Health hazards from poor quality: High basement humidity and poor air quality produce serious health issues. It triggers allergies, coughs, headaches, and irritations to the nose, skin, and eyes.
Damage to belongings stored in the basement: Fluctuations of the basement humidity levels damage belongings stored in the basement. It can damage the fabrics and materials, paper documents, and books stored in the basement, make the environment unsuitable for living and decrease the value of the entire house for potential buyers.
Pest infestation: Higher humidity level in the basement helps to grow pests like termites and ants. Those harmful insects destroy wood, furniture, papers, and valuable things with spreading diseases, damaging the interior of the basement, and reducing the structural strength of the house.
Increased energy costs: Excess humidity levels in the basement leads to higher energy bills. The user tries to maintain the temperature using air conditioning systems, which increase energy and utility bills, putting the user in financial strain, and the constant running of the system reduces the efficiency and affects the performance of the system.

How to Control Basement Humidity?

These are the 6 ways to control the basement humidity

Waterproof the basement
Install dehumidifier
Install a ceiling fan
Improve basement ventilation
Insulate the basement
Use moisture-absorbing materials

Waterproofing the basement: Basement humidity can be controlled by waterproofing the basement. Basement waterproofing can prevent mold growth, increase usable space, and preserve the property value. You can use both liquid and sheet waterproofing membranes to waterproof the basement.
Install a dehumidifier in the basement: Installing a dehumidifier in the basement is another way to control the basement humidity. Using a dehumidifier improves the air quality, preventing musty odours. To install a dehumidifier, first choose a location that is easily accessible to a power outlet, then set the humidity level to 40-50%, which is the best setting that feels comfortable.
Install a ceiling fan in the basement: Basement humidity can be regulated by installing a ceiling fan in the basement. It is a cost-effective solution that improves the overall ventilation of the basement. Install a ceiling fan to keep the environment ventilated as less humid air blows onto the basement, quickly diffusing the rising moisture.
Improve basement ventilation: Improving the basement ventilation manages the basement humidity as it regulates the temperature level making the environment comfortable for the occupants by getting rid of the musty smell. You can improve the basement ventilation by installing windows, ceiling fans, and exhaust fans.
Insulate the basement: Basement insulation helps to control the basement humidity. Insulation also absorbs sound, which results in reducing noise, and it promotes a comfortable environment with stable temperature and humidity preserving the structural integrity. Insulating the interior walls with materials like rigid foam, installing vapour barriers along with insulation and sealing air leaks are the methods used to insulate the basement.
Use moisture absorbing materials in the basement: Basement humidity can be reduced and controlled by using moisture absorbing materials in the basement. By using moisture absorbing materials in the basement can reduce the growth of mold and mildews and prevent condensation. Moisture absorbing materials like “humydry, silica gel, calcium chloride, baking soda and activate charcoal” are placed in small open containers or distributed throughout the basement to reduce the humidity level.

Can Basement Humidity Affect the rest of the House?

Yes, higher basement humidity can affect the rest of the house. When the basement humidity is high, it produces mold and mildew growth that cause to musty odor. It can spread over the house and fell unpleasant experience in the house. As well as it cause to dust and mites which cause to respiratory problems and allergies. More than that higher moisture can damage the structure by rotting, deteriorating and decaying over time which cause to reduce the structural integrity.

Can Only Basement Waterproofing Stop the Humidity Problem?

No, only basement waterproofing does not stop the basement humidity problem. You should use other methods such as installing sump pumps, installing French drains, using dehumidifiers, maintaining gutters and downspouts, and maintain the grading of the land to stop the basement humidity.

Does the Finished Basement have less Humidity than the Unfinished?

Finished basements have less moisture than unfinished basements. Finished basement consist of minimum cracks, a waterproof system, possessing an inside drain system, which means ensuring there is no excess water in the soil around the foundation. But unfinished basement is not consist of these functions. Therefore it is necessary to implement moisture control measures in the unfinished basement.