Having the proper balance for a healthy building

Infiltration & the Stack Effect

It’s time to talk about a second way of heat transfer, convection. Convection can create a current when hot air or water rises and, consequently, cool air or water sinks.

In a building like your home, rising hot air creates an area of high pressure at the top of a building. That pressure is only lessened by conditioned air forcing its way out of any hole to the outside. Warm air escaping the building boundaries, or building envelope, then creates negative pressure at the bottom of the building and pulls in air from the outside environment.

You can visualize the process as like drinking a milkshake through a straw. This infiltration, or stack effect, means the air you’ve conditioned by removing moisture and heating or cooling is constantly lost at the top and replaced at the bottom by air that must be turned comfortable—costing you more and more in energy bills.


In a nutshell: Water vapor causes problems when it condenses in a vulnerable place.

A good roof can keep out water damage in the form you usually think of: liquid. But what about water vapor? When we talk about air movement—either intentional through ventilation or unintentional through infiltration—it’s important to understand water vapor always moves with it.

As long as it stays in vapor form, water’s ability to cause damage within a building is only its potential to turn into liquid again in the wrong place. Water vapor that meets a temperature at or below its dew point will condense into liquid water, causing harm to materials like drywall and insulation other than closed-cell spray foam, which is its own moisture barrier.

Every insulation option has pros and cons. When it comes to water damage, cellulose can lose its fire and pest resistance over time in the presence of excess moisture. Fiberglass can harbor mold or mildew. Other parts of your home or business are at risk, too. Inner wall cavities are vulnerable and prone to moisture problems like mold and rot.

At Koala Insulation, we know which building uses and climates call for a water vapor barrier, which type to recommend, and the proper way to install one for the maximum practical impact.


Natural ventilation may intially seem contratidctory to the purpose of insulation. However, although we're trying to keep most of the outside elements outside of a building, attic ventilation specifically helps keep the area dry and temperature regulated. 

To put it in perspective, outdoor air helps to keep the cieling of the attic cool during the winter when the heat is running. Otherwise, you would be at risk of ice damming, which is when the snow or ice melts off the roof because of a hot attic and re-freezes in the gutters to create an 'ice dam'. 

Additionally, attic fans contribute to proper ventilation during the hot summer months. The fans draw the cooler outside air from attic vents and push the hot air back outside. This is why it's very important to have proper insulation and air sealing, and to avoid blocking attic soffit vents. Otherwise, the attic fan will pull cooler air from the air conditioned building below, causing your A/C to work harder and increase your utility bill.