Moisture Flow

Controlling moisture flow into and out of the building is essential in the effort to ensure that they stay healthy and structurally sound.

Moisture comes in three phases: as a solid, as a liquid and as a gas. Moisture can move in four ways: by gravity, by capillary action, with airflow and by diffusion.

In order to limit the volume of water that enters the building we must understand the phases and characteristics of its movement.

Gravity: A typical example would be rain falling on a roof. With properly installed shingles, flashing, and overhangs, we can prevent the vast majority of water from coming in contact with the buildings structure.

Capillary Action: Is the tendency of water to be drawn up a material. This material is usually somewhat porous in nature. An example would be the effect seen by placing just the corner of a paper towel in the kitchen sink. The water, via capillary action, draws itself up the towel, eventually soaking the entire piece. Water can do this to building materials as well wicking its way upwards, downwards or sideways, accessing places not intended to ever be wet, and causing them to rot or mould.

Air Flow: Is the process where moist air or humid air passes by the air barrier entering the buildings structure. While this can happen, a well-designed wall should allow for the then condensed air to drain or evaporate in a controlled manner. If it is not, rot and or mould may take hold in this location.

Diffusion: Is a process whereby water passes directly through a material. Water vapor not unlike air pressure will pass from an area of high to an area of low pressure. Diffusion cannot be stopped only accounted for. As only a very small amount of water can get through most materials over a given time, wall systems must be designed to allow them to dry properly. Allowing water to enter the system is not really the problem, it’s ensuring that the water does not become trapped in the system that is the real concern.