Before we get into that, let’s look at what mould needs to grow:

1. Moisture;
2. A food source; and
3. The right temperature for germination and growth.

The first one; moisture is the most important one. Like any other thing, mould requires water in order to survive and prosper. Water can take the form of liquid water as in a puddle or a fine film on a surface. It can also take the form of high humidity. If mould spores get water, the spores swell, burst and then put down roots and grow….into the 2nd requirement; a food source.

What About a Food Source?

Mould will “eat” any organic material, that is, one which contains carbon atoms. This organic material will supply the mould with enough energy to grow. Mould will grow rapidly given any source of food. Cellulose is a good food source, especially the paper backing on drywall. The paper-making process pre-digests the wood pulp. It is then easier for mould to break it down further.

Mould will also grow on leather, furs, cotton, linen, silk, wood, just about anything. Even dust will support mould growth. This is because dust is primarily of plant pollen, human and animal hairs, textile fibres, paper filers, minerals from outdoor soil, human skin cells, and many other materials. As such, even a seemingly clean surface could support mould growth. Think about the mould that you sometimes find at the bottom of your windows. I guarantee you it is surviving on dust which accumulates in this corners. So that brings us to the last criteria; temperature.

Ok, so it Must be Too Cold or Too Hot for Mould.

Mould thrives quite well from 32F (0C) to 120F (49C), but its activity is heightened between 70 and 90 F (21C to 32C). The temperatures in most homes are in the heightened mould growth range of temperatures. Let’s go back and look at the corner of that bedroom ceiling. What exactly happened there?

Well…normally there would not be enough moisture on the corner of the ceiling to allow mould to grow, even though the temperature at the top of the room would provide the heightened growth range temperatures.

What has happened though is that there is a very fine film of water there and the reason is out of our line of site. The average homeowner will never see it as it hides in the attic, and we know how people like going up into their attics.

Tell me About the Attic?

In these days of fast and efficient construction methods, often insulation installers miss that extra step to prevent mould. How can an insulation installer prevent mould you ask? Well….let’s see just how they do their job first then we can understand their impact on our health.

When the home is built there is a vapour barrier installed under the ceiling joists and then the drywall is installed. Once the rough-in wiring is completed and inspected the insulation can go in the home, including the attic, the exterior walls and the basement foundation above ground level.

Before blowing in loose fill insulation into the attic most installers will stuff fibreglass batts into the rafter cavities that won’t be provided with baffles to keep the loose fill insulation from going into the soffits. This is a critical step, and one where a simple mistake can cause a much bigger problem.  We will get to that later in this post.

Once all the baffles and batts are in place the insulation installers will blow in the required depth of insulation according to the local building codes. The depth and R-Values get recorded on an insulation install certificate and they are done. For most home and for a while this is ok. Everything hums along just fine.