As builders and contractors seek more ways to create quality air and thermal barriers in their building envelopes, it has become increasingly clear that in order to successfully accomplish this, the right insulation material must be chosen from the start of the process. The expectation of your chosen insulation is that it not allow airflow or moisture to pass through or around the barrier.
Two popular insulation choices are spray foam and fiber insulation. A key objective of both systems would be to achieve low air permeance, a resistance to airflow. Air movement through fiberglass insulation is referred to as wind washing, which serves to diminish the effective R factor of the insulation, and creates the potential for condensation. Spray foam insulation by the nature of its cell structure prevents wind washing, and can create an air and vapor barrier dependent on the assembly and spray foam application method.
An attic often provides the best wind washing opportunity as air enters the venting system and travels through the insulation. Fiber insulation is susceptible to this as it cannot provide a 100% barrier based on limited contour ability to prevent air and moisture movement around its edges. Spray foam has a clear advantage based on its conformity and density properties that creates a wind wash barrier.
It is imperative that your barrier successfully manages the flow of heat, air and moisture. Failure to do so in key areas such as the roof and wall cavities can cause early deterioration in building materials and moisture buildup in walls, which can lead to mold and corrosion — driving repair costs literally through the ceiling.
In addition to experiencing the effects of energy and long-term repair costs, as the insulation protection decreases you will also notice a diminishing comfort of your home in areas such as less noise control, inability to maintain proper indoor heating and cooling environment, along with the danger of circulating allergens.
In a study of two-story homes by the U.S. Department of Energy, Technology Solutions for new and existing homes, wind washing affected energy use, peak demand, comfort, potential for moisture damage, and elevated humidity in hot and humid climates. Wind washing can also cause water pipes to freeze in cold climates
When choosing insulation, always make a point to inquire if it provides wind washing insulation. In short, all types of insulation are not created equal.
The phenomenon of air movement driven by wind pressures passing through or behind the thermal insulation within enclosures, causing significant loss of heat flow control and potentially causing condensation. Typically occurs at exposed building edges, such as at the outside corners and roof eaves because of the large pressure gradients at these locations. This can be thought of as the “wind blowing through the insulating sweater” effect.
Wind Washing Article Source:
U.S. Department of Energy Study: Investigating Solutions to Wind Washing Issues.