BACK PAGE BASICS: Wind-Washing

Intermediate

As outside temperatures start to drop, your home’s insulation problems and air leaks may become more obvious. You may feel more drafts in certain rooms or hear the furnace kick on more often as it struggles to maintain a certain temperature setting. Contributing to these problems is wind-washing, which compromises insulation and whisks heat out of the home. While you may not be familiar with the expression, you may be well-acquainted with its home-chilling effects.

Wind-washing is wind-driven air pressure moving through the wall or roof assembly, which lowers the insulation’s effective R-value. This often occurs at building corners or in attic spaces where the house faces a prevailing wind. Wind can drive air into attic soffits on one side, through the attic insulation, and out the soffits on the opposite side.

Most insulation works by trapping pockets of warm air and slowing the movement of heat. Fibrous insulations, such as fiberglass and rock wool, are porous and allow wind to flow through their fibers. Denser insulations like blown loose-fill cellulose are less prone to wind-washing, and solid insulations like XPS foam board or most spray foams are barely affected.

If your home has drafts, a blower door test by an experienced energy professional is a good first step to identify exactly where drafts are occurring. Home facades with open exposure (in a field or on a waterfront) or facing a persistent wind (in New England, Nor’easters) should be paid particular attention. Caulking wall penetrations (electrical boxes, cable lines, telephone lines, around window frames, etc.) and proper weatherization can help minimize wind-driven drafts.

Unsealed soffits in vented attics and kneewall spaces can also be vulnerable—wind will gust into the attic (or into living space if the soffits are adjacent to rooms), pushing into the building frame and insulation. This can be solved by installing foam blocks flush against existing attic baffles and sealing with foam gap sealant. Another method is installing attic baffles/proper vents with a built-in wind barrier. Both of these methods ensure that the wind travels up the venting rather than into your house or the insulation.

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