What is Wind Washing (and why every homeowner should know)?

by Erik North on July 8, 2011

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One thing customers often ask about during energy audits is wind washing…Oh, wait…customers NEVER ask about wind washing. But they almost always ask about the freezing kitchen, bedroom or bay windows. They know SOMETHING is wrong. Their master bedroom is freezing, the heating bill is through the roof and every time the wind gusts the curtains and drapes flutter or the door into the knee wall crawlspace pops open.

As January temperatures plunge below zero, your home’s insulation problems and air leaks become more obvious. One of those problems, which compromises insulation and whisks heat out of the home, is wind washing.

It’s the very rare customer who knows about wind washing (I suspect if they did, they wouldn’t have called in the first place). But it is something that affects many homes especially in states (glances at Maine) with sharp coastal winds and winters that beat them around like a punching bag. Homeowners may not know the expression but are very well acquainted with its home chilling effects.

So…what is wind washing?

Wind Washing…The Boring, Wikipedia-style answer

Simply, wind washing is wind/air movement through insulation that strips the heat from it and in the process lowers the insulation’s effective R-value. Or more a more alarmist way of putting it would be: Wind washing is listening to wind sweep $4.00 per gallon heat out of your house.

Wind washing is wind driven air pressure that enters a building (read, your house) and moves through the wall and attic insulation. This often occurs at building corners or in attic spaces where the house directly faces a prevailing wind source. Wind will drive air into one attic soffit, through the attic insulation and out the opposite soffit. Fortunately in coastal Maine we rarely have relentless gusts of ocean wind or pounding Nor’easters ripping the warmth from your home so we can safely ignore this.

Wait…this happens ALL THE TIME in Maine and is one of THE MOST COMMON reasons people feel extremely uncomfortable drafts in their home.

And Wind Washing Affects My Insulation How?

Insulation is installed to prevent heat loss. Unless you have fiberglass, in which case, the intention was to prevent heat loss. Most insulation work by trapping pockets of warm air and slowing the movement of heat. The more fibrous insulations such as fiberglass and rockwool are very porous and easily 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.

The Answer To The Washing Of The Wind?

So what to do?

If you have excessive chilly drafts, a blower door test by an experienced energy professional would be a good first step. Blower doors simulate the equivalent pressure of a 20 mph wind and are great for diagnosing exactly where wind driven air drafts are occurring.

Once the biggest sources of air heat loss are identified (and, why not, addressed), some further general steps can be taken. One job of your home’s building shell should be minimizing air movement. Keep the outdoors out and the indoors in. And in Maine, unless you indulge a lingering fondness for mosquitoes capable of piercing Kevlar, this means no gaping holes in the side of your house.

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, oil deliveries, cable lines, telephone lines, around window frames, etc.) and proper weatherization can help minimize wind driven drafts.

The problem with attic and kneewall spaces are the open, unsealed soffits in vented attics. Wind will gust into the attic (or into living space if the soffits are adjacent to bedrooms), pushing into the building frame and insulation. This wind washing kills your insulation’s ability to retain heat and warm your home. Over time this can permanently damage the insulation, necessitating the ever popular insulation project.

This can be solved by a few different methods. One is installing foam blocks flush against existing attic baffles and sealing with foam gap sealant. Another 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.

Here is a link to a customer’s post-audit retrofit blog write up, where they installed foam blocking flush against the attic venting.

Being more conscious of how wind driven air pressure affects your home (poorly) and how to improve it will make your home warmer and more comfortable.

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