Ice dams form after snowstorms and are caused by the heating and refreezing of melting snow. Protecting your home from their damage requires preparation and proper maintenance after snow falls.
What is an ice dam?
An ice dam is created when snow at the top of your home’s roof melts during the day and refreezes at night along the roof edge. This buildup of ice blocks water from draining off the roof, causing it to seep under the roofing material and into the house.
How do ice dams damage a roof?
After several days of melting and refreezing, the ice dam can work its way under the shingles, allowing water to enter the attic and damage ceilings, walls, and interior contents. If not addressed, it can lead to structural damage (including failure), mold and mildew growth, loss of insulation, and damage to gutters and downspouts.
How to protect your home from ice dams
The National Weather Service recommends the following actions both before and during a snow event:
- Clear all debris from your roof, gutters, and downspouts.
- When safe to do so, remove as much snow as possible from your roof. Use roof rakes to pull the snow off your roof. Don’t go up on your roof and shovel the snow off. You could slip and fall.
- Remove snow and icicles from gutters and downspouts.
The best way to prevent ice dams is to ensure proper attic ventilation and roof insulation. Proper ventilation and insulation prevent heat from rising from the home’s interior to the roof, preventing snow from melting. If the attic space stays cold enough, the snow won’t melt and potentially cause an ice dam.
Attic ventilation requirements
In Wisconsin, attic ventilation requirements are set by the Uniform Dwelling Code. The code requires a minimum of one square foot of attic ventilation for every 300 square feet of attic floor space. For example, if your home is single-level and 1,500 square feet, you would need five square feet of ventilation area.
Net free ventilation area is the unobstructed ventilation space a venting product provides, measured in inches. To determine the required quantity of a specific ventilation product, the code-required area must be converted to square inches. Multiply the required area by 144 to get the number of square inches. In our example, 5 x 144 = 720 square inches.
The ventilation area must be evenly split between air intake and exhaust to create a balanced system. Dividing the square inches by 2 yields the net free area required for the intake and exhaust systems (720 / 2 = 360). You can then select the best roof ventilation products based on your roof design. It’s best to distribute both types of ventilation (intake and exhaust) evenly between the high and low sides of your roof.
Roof insulation requirements
The Wisconsin residential building code requires R-49 to R-60 insulation for unheated attics. R-value is a measurement of a material’s ability to prevent heat absorption, and the higher the number, the better the insulator it is. To achieve this level of insulation, most homes need around 18 inches of fiberglass insulation. If your attic doesn’t have this level of insulation, you may be able to add more depending on the depth of your roof joists. Contact a roofer for a comprehensive assessment of your roof insulation and recommendations to improve it.
Ice/water shield
The code also requires that homes in Wisconsin have ice and water barrier protection on shingled roofs over heated spaces. This applies specifically to roofs with slopes of 4:12 or less. The barrier is installed directly to the roof deck, from the roof edge up the slope about 24-30 inches, depending on the location of the exterior wall line.
This shield protects the roof deck from water infiltration caused by ice dams, wind-driven rain, and snow. It seals around nails and helps protect eaves, valleys, and chimneys.
When installed correctly, your attic ventilation, insulation, and ice and water shield should protect your home from damaging ice dams. It’s better to address these issues proactively to help prevent damage to your home and belongings. A professional roofing company, like New Roofs, can help you assess your home’s existing roof system and make recommendations to improve its performance, keeping you and your family safe, warm, and dry.