Why Moisture Control is Important in Subfloors


Consistently high moisture levels can affect the structural integrity of a home, apartment building, workplace and commercial premise. Cracked walls, timber decay, and warped and expanded timber floor are just some of the signs of possible uncontrolled moisture levels. We also have to consider that termites can thrive in such environments.

More importantly, consistently high moisture levels can affect our health. That’s because this kind of environment encourages growth and multiplication of moulds. These moulds multiply by releasing spores which are carried in the air. If these spores or mycotoxins are inhaled, it may cause allergic reactions or even a mould infection. Blocked nose, eye and skin irritation, wheezing and an asthma attack are just some of the observed health effects caused by moulds.

How high moisture levels occur

Moisture is being generated all the time. Our daily activities (cooking, bathing, doing the laundry or even our normal breathing) all introduce or add more moisture on walls, ceilings, floors and other surfaces. That’s because some of the water vapour will condense on those surfaces.

That’s where the problem starts. Earlier we mentioned that consistently high moisture levels can affect the building’s structural integrity. Wood materials are often vulnerable to this aspect. After all, wood is good at absorbing water because the trees have evolved or adapted to holding water in their structures. As a construction material however, it’s not good because the wood will expand and attract pests (especially termites) and microorganisms (moulds and other fungi).

It’s normal to have high humidity and moisture levels from time to time. It becomes a problem if the levels are consistently high. This gives enough time for moulds to multiply in significant numbers and provide conditions conductive to termite infestation.

How does it all happen? Why could there be a consistently high humidity and moisture level in a building? Often, the culprit is lack of ventilation. There’s poor air circulation below the home which is why sooner or later, some of the water vapour will condense on solid surfaces. Also, there’s not much chance for the condensation to dry out. This then provides an ideal environment for moulds and termites to thrive.

Often, when we hear ventilation and air circulation we think about the visible areas in our homes and perhaps the area above the ceiling (the roof cavity). However, most of us don’t pay enough attention to the building’s foundation and subfloor.

Why moisture control is important in subfloors and foundations

It’s not about totally eliminating moisture. It’s about managing the humidity and moisture in acceptable levels. This is also about giving less time and fewer opportunities for moulds and termites to do their work.

Adequate ventilation is a huge factor to make that happen. The most common advice you’ll hear on improving ventilation are:

  1. Opening the windows whenever the weather permits (allow cross ventilation)
  2. Turning on the exhaust fans especially when cooking, showering, doing the laundry and drying the clothes

The first one allows for humidity levels to be the same both inside and outside of the building. This gives a better chance for lower humidity levels to be achieved inside our home or commercial premise.

It’s a similar case with the second advice. The exhaust fans will help in lowering the interior humidity levels by accelerating air circulation inside the building. The result is less chance for condensation to occur and a faster drying out of moist from various surfaces.

These are both excellent measures in moisture control. However, there’s often one forgotten or neglected advice in achieving adequate ventilation. It has something to do with subfloors and building foundations.

That’s because these areas often have high moisture and humidity levels. Also, they often have cooler temperatures and poor ventilation. As a result, condensation is more likely to occur and there are great opportunities for the moulds and termites to thrive. The entire setting even gets worse because these areas are inaccessible and hidden from our view. By the time we notice the problem, the damage has already been done. We’ll see the signs of the problem in the form of warped and expanded timber floor or cracks on the walls (due to expansion and contraction of the soil below your building). More importantly, the high moisture levels have already affected the occupants’ health because of mould growth and mycotoxins.

The issue also becomes serious because of the decay of timber foundations and floors. Moist wood often invites structural vulnerabilities (the wood becomes soft) and fungal decay. Given enough time (sometimes just a few months is all that’s needed), soft spots will manifest on the floor and the flooring and foundations might even sag and bounce. As more time passes, the timber might deteriorate prematurely and even collapse, which results to costly repairs and more importantly, exposes you or the occupants to safety risks.

We don’t even have to wait for timber floors and foundations to collapse (or the walls and brickwork to crack because of uneven moisture levels) before the case becomes serious. Consistently high humidity and moisture levels in the subfloor and foundation will readily encourage mould growth. The spores and mycotoxins from moulds will endanger people’s health, especially those with pre-existing respiratory conditions such as asthma and lung infections. Young children and elderly people are also at high risk because of their weakened or compromised respiratory tract and immune system.

It’s especially the case in most areas of Sydney wherein the relative humidity may reach up to 70% at 9am and 60% at 3pm. This consistently high humidity level brings a lot of water vapour, which can condense in cooler surfaces inside of your home or business. High subfloor humidity levels can also result if there’s a lack of ventilation (or there’s poor drainage).

The numbers mentioned above are perhaps just averages. There will be hours when the relative humidity will climb higher especially inside our homes or businesses. High and persistent human activities such as showering, cooking and drying the clothes will introduce more water vapour in the air. High relative humidity levels in the subfloors and building foundations may also increase the soil’s moisture, which can then be picked up by the upper structures.

What to do?

Because of the importance of moisture control in subfloors and foundations, subfloor ventilation systems are now being installed in both new and existing buildings. Many heritage buildings and structural renovations now also incorporate subfloor ventilation systems to improve moisture control.

These mechanical systems work by using ventilation fans to facilitate and improve air circulation in subfloors and building foundations. As a result, there will be fewer opportunities for moulds and termites to survive and thrive. This can have a positive impact to your health because you’ll be exposed less to mycotoxins.

In addition, effective subfloor ventilation systems will also help in extending your building’s lifetime. Earlier we mentioned that timber decay and wood rot happen because of high humidity and moisture levels. Lowering these levels can then extend the lifespan of your timber floors and foundations. This also helps you avoid costly structural repairs associated with the repair or replacement of the timber material.

We also mentioned earlier that walls may crack because of the uneven moisture levels of the soil beneath your building. This makes the soil expand and contract, which introduces stress to your walls, brickwork, render and internal lining boards. To release or alleviate the stress, cracks will manifest. This scenario could have been prevented in the first place if there’s effective subfloor ventilation that stabilises the soil’s moisture levels below your building.

In summary, having adequate moisture control in your building’s subfloor and foundation is a worthy investment. It’s especially the case when thinking about your health or that of the occupants. Also, the structural integrity of the building will remain intact because there’s less chance for wood rot and decay. You then avoid the costly structural repairs and get more value out of the building.

As a result, many residential and commercial clients contact us here at ExtractAir. We specialise in installing subfloor ventilation fans for new constructions, existing buildings, renovations, heritage buildings and unit blocks. We install mechanical ventilation exhaust fans, mechanical ventilation intake fans, high flow cement mesh vents, louvered grill vents & heritage vents.

For more than 15 years, it’s been our solid commitment here to deliver high-quality services. Through those years we’ve helped extend the lifetime of many buildings in Sydney. Our work has also contributed to significantly improving indoor air quality and the standard of living in many homes, apartments and workplaces.

Contact us today and tell us your requirements. Our technical team will then create a tailor-made and cost-effective solution for you.