It's wintertime in Chicago! Yay!
The annual test of our mettle is at hand. All the fun in the snow we have to look forward to. ... unplowed side streets and alleys, shoveling buried cars, shoveling walks, sub-zero temps, big heating bills, big snow, howling wind, dibs.
Last winter, a frozen gutter fell from a neighboring house onto my truck, causing about $3,000.00 damage. Luckily, no one was near when this happened as they likely would have been killed or seriously injured if otherwise. But, sometime in the middle of the night, the entire gutter, somewhere around 20 feet long and weighing in at probably 200 to 300 pounds, detached from the house and came crashing down on Li'l Taco and the Hula Girl. ("She's dead, Jim!") As one might imagine after learning that I've named my truck and it's mascot, I was devastated.
Ice Dam Dynamics
Ice damming causes, among other things, injury, property damage, roofs to collapse, basement seepage and accelerated roof covering deterioration. It can result in interior finish damage and contribute to mold growth in your home, which in turn can affect indoor air quality and occupant health.
The cause of ice damming is pretty straightforward. Snow-melt from the upper, warm portions of your roof deck drain down to the roof's overhanging eave ends, where your gutters are. The eave ends and gutters are exposed to the elements, making them much colder than the roof deck. The runoff hits the gutters and these cold areas and begins to freeze. The ice builds up, resulting in a dam that catches more runoff, which also freezes.
The cycle continues. The ice gets thicker and backs up under your roof shingles, where it can cause leaking and damage in your attic and wall cavities, as well as providing a moisture source that can contribute to mold growth. What runoff does get past the dams and gutters drains to the ground. Ice accumulates at your home's perimeter which, come warmer weather, will thaw, possibly overloading already saturated soil adjacent your foundation walls, resulting in basement seepage.
Luckily, the traditional fix for all this is also straightforward and time proven. The first step is air sealing. Any penetrations through your attic floor or through your top floor ceiling must be sealed. This includes recessed light fixtures, junction boxes, conduit, duct and plumbing runs, etc. The objective is to prevent any conditioned air from entering these areas. All duct work in an attic or plenum space should be sealed and insulated to at least an R-8 level.
Attic Ventilation 101 (The Basics)
Step two is ventilation. Proper ventilation is critical in preventing ice damming. During the wintertime, ventilation helps to keep the roof sheathing's temperature below freezing. Do this and there will be no ice damming. Optimal attic ventilation is accomplished by providing three things. These are low ventilation, high ventilation and an clear path for air circulation in-between. The style of the components may vary, but they should all have one thing in common. They should run continuously along the lowest point of the roof assembly (soffit vents) and the highest (ridge vents). Buy the best you can afford 'cause this should be a once and done thing. Better components last longer.
Insulation Baffles (Importante!)
Another thing typically you'll need to install are insulation baffles. These are placed between your roof's rafters, way down at the ends of the eaves. Their purpose is to prevent insulation from blocking the rafter channel at this location and maintain that -low-to-high ventilation path.
Step three is insulation. Any number of products work. Fiberglass batts, loose-fill fiberglass, mineral wool (batts or loose-fill), loose fill cellulose, rigid foam insulation. (I lean toward loose fill cellulose for its good- R-value, ability to manage moisture, and greenness.) The important thing is to provide a sufficient amount of attic insulation. In our climate, that's R-49. Whatever you choose, the insulation should neatly and completely cover the entire attic floor, all skylight shafts, all interior knee walls. Make sure the attic hatch is insulated to the same level.
There are some additional tweaks that will help optimize your new insulation and ventilation. But, you'll have to like my post for me to share them. --KW
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