Managing moisture in buildings - naturally

Managing moisture in buildings - naturally

by Dave Ogle

It’s hot. You’re sweating all over the place. So the most obvious thing to do is… zip yourself up in a plastic suit wearing a shower cap right? Hhhhmmm, nice. Or do you prefer fabrics that let your skin breathe, the evaporating sweat cooling you down? Why would we treat the buildings in which we live and work any differently?

Buildings have to be energy efficient, durable, fit for purpose – yes, but they also have to be comfortable to live, work and play in. So what is a comfortable building? A comfortable building has a steady indoor environment, with a small range of temperature and relative humidity variation with optimum levels of relative humidity (RA) of between 40% and 60%. In other words, the building manages its moisture: it is not damp or clammy.  Levels outside of the optimum range of humidity can cause occupier discomfort, health risks and the degradation of the building. In particular, relative humidity levels above 60% can lead to condensation within a building, resulting in the growth of microorganisms, whilst relative humidity levels below 40% are associated with discomfort and respiratory conditions. (Maskell, Thompson, Walker, Lemke, Shea, Lawrence. 2015).

What is moisture in buildings?

The most obvious signs of uncontrolled moisture in our buildings is seen when condensation drips down the inside of windows or the sight and smell of mildew on walls and in bathrooms. This is the evidence of moisture that we can actually detect. However, of much greater concern is the unseen moisture that collects inside the wall spaces, crawl spaces, attics and ceilings cavities, breeding harmful mould and decay that cannot be easily cleaned or repaired, leading to chronic health ailments and structural damage.

Where does it come from?

The most obvious sources of moisture in buildings may be cooking and hot showers/baths, but the greatest contributor is far less obvious - the air itself within a building holds a lot of moisture.  So when moisture is locked in a space with impervious walls (painted, concrete or fired brick walls) and not released through ventilation, the air can become poisonous, causing health damage and the stagnant moisture causing structural damage.

It’s important to note that warm air can hold more moisture, or vapour, than cold air.  Therefore, in cold climates, where the air outside is cold and the air inside the home is warm, the inside air holds much more vapour than the cold outside air. This is fine, as long as the warm air doesn’t come in contact with anything cold, such as a window or a cold wall. If contact does happen, then that moisture-laden air cools quickly and all the moisture forms condensation.

Why is it so important to manage moisture in buildings?

The main reasons for managing moisture within buildings is to protect our health and the longevity of the building.  The U.S. Institute of Medicine (Leardini & Raamsdonk, 2004) identified that unmanaged building moisture contributes to microbial contamination, which includes problematic fungi. Fungi require a suitable substrate (such as wood, paper, gypsum board, or other materials that have a high cellulose content) and water to form and grow. Once formed, certain species of fungi produce mycotoxins which can cause a toxic response in humans.  Humans are exposed to these toxic chemicals by inhalation of spores or material that has been contaminated by mould. Moulds also contain alcohols and ketones which are irritants to humans.  Therefore, unmanaged moisture contributes to the development of mould which has been found to contribute to respiratory infections, allergies, asthma, eczema, and can also affect the immune system.  Furthermore, repeated exposure to small fungal particles can also cause hypersensitivity pneumonitis in certain people which can cause headaches, fevers, excessive fatigue, cognitive and neuropsychological effects, gastrointestinal symptoms, and joint pain (King & Auger, 2002).

How to manage building moisture and create healthy and comfortable spaces

The most sustainable ways to create a healthy environment in which to live are naturally available to all of us.  One the simplest – and most natural - ways to manage interior humidity is by using materials that absorb vapour when it’s in excess, and release it when the air is too dry.  This can be achieved through the use of hygrothermal materials such as exposed clay surfaces and raw timber.  “There has been growing interest in the use of exposed clay surfaces for the passive regulation of indoor temperature and humidity levels. This is largely due to the exposed thermal mass and hygroscopic properties that help buffer the temperature and relative humidity of the internal environment. There is also scope for the inclusion of mineral and organic aggregates to help improve these hygrothermal properties. (Maskell, Thompson, Walker, Lemke, Shea, Lawrence. 2015).

Another method of embracing nature to help manage moisture in our buildings is through natural ventilation. Much more than just opening a window, this method harnesses pressure differentials between outside and inside air to create a simple, cost effective managed ventilation system. Natural ventilation is important because it can provide fresh air without mechanization, therefore is more energy efficient and kind to our earth than mechanical systems. This continual, controlled movement of air maintains freshness within a building and helps to manage any residual moisture within the space.

The ideal time to consider methods to manage building moisture is during the design and specification process. In a future blog post we will look at the benefits of clay in modern buildings in more detail.



Alsmo, 2014: Ventilation and relative humidity in Swedish buildings

King & Auger, 2002: Indoor air quality, fungi, and health

Maskell, Thompson, Walker, Lemke, Shea, Lawrence. 2015: Improving the hygrothermal properties of clay plasters



Improving the hygrothermal properties of clay plasters, 2015

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