Estimated reading time: 1 minute
When the wind blows against your house and leaks air inside, it loses the battle with the wind.
The idiom “clean your plow” can refer to outwitting someone or something, or winning a contest. Leaky buildings lose the wind washing battle, and correcting the issue post-construction is challenging.
The most common type of wind wash that a typical home inspector observes occurs near the eaves. Areas of thin or missing ceiling insulation indicate this issue. The wind blowing through the soffit vent pushes the attic insulation away from the edges of the ceiling, near the outside walls. As a result, patches of drywall become exposed and lack insulation. This leads to hot and cold spots in the home, particularly in rooms along the outside walls.
Wind washed loose-fill insulation is a thermal bypass on steroids. Here’s a common example:
Have you worn a sweater with a light shirt underneath and experienced a cold wind blowing through the weave? You’ve been wind-washed! The DoE estimates that average wind washing costs homeowners around $120 per year.
Start With Better Framing
To compound the issue, even without wind washing, many homes lack adequate insulation along the outer edges of their exterior walls. Why? Because of limited space. The heel cut of a 2 x 6 rafter won’t allow us to fit R-38 insulation (climate zone 3) above the ceiling.
We can address wind washing at the eave by implementing two solutions (see photos).
(click/hover to zoom photo)
Raise the roof by installing a raised heel rafter. The extra room won’t pinch the insulation. Note that we can now extend the wall sheathing and create an air barrier that protects the insulation from being displaced.
Install a baffle between the rafters. Its job is to channel the air up and over the insulation. Baffles are included in our building code. Most new homes have baffles. Eave Baffle: Energy Code N1102.2.3, IRC Energy Chapter (R402.2.3)
What about existing construction? Batt insulation isn’t displaced as easily, and adding an air barrier on the outside perimeter of the wall proves difficult. For a retrofit, install the baffles to the underside of the decking and cut 16-inch sections of batt insulation. Push them out near the outside wall between the ceiling joists. If needed, install extra insulation in the attic at your discretion. This helpful chart will assist you in determining your climate zone and provides a link to a relevant article.
Applicability of Code Language
Code enforcement during construction is contingent on local adoption. If the local authority having jurisdiction (AHJ) has not adopted this specific code version or has amended it, the provisions of N1102.2.3 may not be legally binding for compliance. This use of model code standards as a benchmark is a well-accepted approach in building science and consulting work, especially when helping clients understand deficiencies in non-code-compliant but existing structures (aka – old buildings).
Climate Matters
If you live in a cold climate, adequate insulation and ventilation over exterior wall top plates are especially critical. The heat gain in the attic through thin insulation can melt snow-covered roofs and lead to the risk of ice dam formation.
The Building America Solutions Center has detailed information about framing and battling wind wash.
What About Cost?
For new construction, your savings start the day you move in (if built with raised heel rafters).
For retrofits, the cost of air sealing, installing baffles, and adding batt insulation to combat wind washing in a 2,000 sq. ft. attic in Climate Zone 3 varies significantly due to factors such as home age, regional labor rates, and material choices. For a 25-year-old home, professional air sealing typically ranges from $400 to $800 to address pervasive drafts. Meanwhile, attic baffles, crucial for ventilation in humid climates, add $100 to $400. The return on your investment will vary.
Don’t let the fear of an upfront cost overshadow the consistent drain on your resources that wind washing presents. A professional inspection can help you understand the specific issues in your home and provide a clear path to reclaiming your comfort and your energy savings.”
The Inspection
The biggest challenge to an inspector is that wind-washing affects more building components than a typical inspector will see, such as cantilevered floors and open porch ceilings adjacent to second-story floor cavities. While in the attic, look for daylight penetrating the soffit. Compare the insulation levels at these points. Consider the effects of wind washing using a thermal camera. Shoot the ceiling near the outside walls. Report it in a narrative format using as much detail as needed.