November 19, 2021
by Star Building Systems
Winter is on the horizon, and while most of us are looking forward to some cooler weather and holidays, it’s also important to look ahead to the hazards cold weather brings. Many of us are in the habit of winterizing our homes and vehicles as winter approaches – and might use this time to take care of other annual chores like emptying the water heater or replacing storm windows. But here’s a word to the wise: one more autumn chore is likely to save you from many more. Take advantage of the temperate Fall weather to prepare your structures for heavy snow and ice – and dreaded ice dams.
The formation of an ice dam relies on a few common cold climate conditions. First, snow piles up on the roof. Next, some of that snow – usually higher on the roof – melts into water, which runs down the slope of the roof underneath the snow until it reaches a colder area, usually on the eaves or edges of the roof. There, it re-freezes and accumulates as more water runs down the roof and refreezes. The ice dam continues growing as long as these conditions persist.
While ice dams are certainly unsightly, they also can cause costly damage. Roofs are designed for water to flow over and off their surfaces. Even the best-made roofs often have tiny holes or gaps, but these are so small that rainfall typically can’t get through them. However, ice dams grow from the edge of the roofline, causing all that ice, snow, and water to push backwards and upwards, underneath shingles and inside seams. These obstructions cause water to back up and form a reservoir – hence the name, “ice dam.” This reservoir creates hydraulic pressure, and suddenly those tiny pinholes that were never a problem become like pinholes on a soda bottle, spewing water inside the roof. There, the moisture can eat sheetrock, ruin acoustic ceiling tiles and lead to mold growth.
We know several variables must come together to form ice dams, but which can you control? Most ice dams are the result of building air barrier flaws – flaws that are not normally noticed or considered problematic. When there’s snow buildup on the roof and warm, indoor air escapes through the rooftop or into the attic, it warms the roof sheathing. This rise in temperature melts the underside of the layer of snow on top, allowing it to run down the roof slope. Snowmelt can also be caused by areas of the roof that are naturally warmer, such as darker colored portions, areas exposed to more sunlight, or locations of flues, chimneys, and other heat sources.
The best way to prevent ice dams is to design for them in the first place. In heavy ice and snow country, likely culprits for ice dam formation should be avoided. These include large eave overhangs – which will always be much colder than the rest of the roof in winter. Dormers, valley gutters and parapet walls also contribute to the problem. In cases where such architectural features are unavoidable, use heat tape on the areas most likely to refreeze, and make doubly sure the roof is well-sealed. Likewise, dark-colored roofs are a good choice in cold climates because they allow the sun to evenly warm the roof.
Check the attic or roofline for air leaks. These are the most common cause of ice dams, and simplest to rectify. They can easily be sealed with two-component polyurethane spray foam. Exhaust fans that run the risk of warming an area of the roof are also worth investigating. It may be necessary to extend their reach to keep them from melting rooftop snow.
Your local building codes are a good guide for how much insulation you need. If the design doesn’t allow for adequate insulation, use closed-cell spray polyurethane foam. If you decide to replace the roof, that would be a good time to install additional rigid foam insulation. It’s critical that your attic insulation completely covers exterior wall top plates.
Increasing cold airflow through the attic may seem counterintuitive. It makes sense in the summer, but why would you want more cold air in the winter? Ice dams can only form when there are different temperature areas on the roof – one area warm enough to melt snow and another cold enough to refreeze that snowmelt into ice. The goal is an evenly cold roof. This is accomplished by equalizing air inflow and outflow, bathing the whole roof with that cool airflow.
Soffit and ridge vents can help improve ventilation, but there are a few things to keep in mind. First, improving your ventilation will not prevent air leaks and should not be your first or only defense against ice dams. In fact, increasing ventilation while air leaks remain unsealed can increase your heating costs and make ice dams worse. Also, ensure you have an insulation dam (blocking) between the trusses and ventilation baffles at your attic’s perimeter, facing the soffits, so that the ventilation channel from the soffit to the attic is consistent and protected from wind-wash.
Two or more layers of rubberized membrane underlayment on top of your roof sheathing is another simple protection method, but like improving ventilation, this should only be done after air leaks are sealed and the roof is properly insulated. The underlayment should extend from roof eaves to a point three feet higher than exterior wall.
It’s not advisable to wait to do something until you already have tons of snow on the roof, but if that’s the case, removing it can help alleviate ice dams that might form. If you decide to shovel it, please be safe and careful, and only use plastic shovels. Metal shovels are likely to scratch paint or damage galvalume finishes, exposing raw steel, which will rust. Check out more Snow Removal Tips.
Ice dams are only one problem caused by accumulated snow. When tall piles of snow and ice finally slide down a roof, they can shear off roof vents and both PVC and cast-iron plumbing pipes. They can even tear large holes in a roof. Snow retention devices can be helpful to avoid such problems.
If you have more questions about ice dams or anything else regarding your roof, please get in touch with a Star Representative near you.
Become part of the powerful Star network. We invest in builders who understand the value of results and provide support that develops strong relationships between you and the entire Star team.
Your building is the cornerstone of the community where people live, work and play. Find a local Star Authorized Builder and let us help you bring your vision to life.
