A Roofer instructor explains what to watch for and how to handle trouble
It’s hard to say that one part of your home plays a more important role than others in protecting you from the elements, but your roof might top them all.
To deconstruct that pun, we asked Roofer instructor Scott Kennedy (Roofer ’07) to tell us why winter can put our roofs at risk, the damage that can occur and what we can do about it.
techlifetoday: What kind of damage can occur?
Scott Kennedy: Structural damage from snow loading is quite rare. Building codes in Canada use research from groups like the National Research Council to ensure that structures that comply with the code will withstand the environmental loads placed upon them during their lifetime.
Damage from meltwater, causing leaks inside the house, is far more widespread. In addition to staining carpets and other interior finishes, water leaking into a home can be absorbed by wooden structural members like studs and joists, causing the wood to swell, and contributing to deflection, or bowing.
Structural issues in a home will often appear first at load-bearing areas. Doors and windows that no longer open easily could indicate deflection. Also, cracks on interior plaster or drywall would be strong indicators of deflection.
Also, the higher humidity levels created [by incoming water] can lead to the spread of mold and mildew.
How does water get in?
Heat [from] your house warms the attic air, which rises and accumulates near the ridge. As this heat warms the roof deck and causes snow to melt, that snow runs down towards the eaves as water. It can refreeze, causing ice dams.
These dams begin to block the flow of water off the roof, causing it to back up [beneath the surface material]. Any roof that is not waterproof – and most sloped-roof systems (shingles, cedar, tiles, etc) are not – can begin to leak in these situations.
Are some roofs less susceptible than others?
Smooth-surfaced roofs like metal-panel roofing tend to shed snow better than asphalt shingles. Some are so efficient that we install snow guards to help prevent an avalanche of snow from the roof.
The steeper the slope of the roof, the less snow tends to hang on it, [and] the faster meltwater will run down the roof deck [without freezing].
Roofs with a slope, or rise/run, of less than 8/12 (i.e., that climb eight inches over a distance of 12) need a waterproof eave protection membrane installed from the eave to 12 inches past the inside of the exterior wall to help prevent meltwater from leaking in.
What can homeowners do to prevent water damage?
Most preventative work should be addressed in the summer months.
Ensuring proper ventilation of the roof is one of the keys to preventing ice dams. Air flow through the attic will help remove heat and humidity. Building code specifies a minimum 1:300 ratio of ventilation area to building area. For example, a 1,200 square-foot house should have at least four sq. ft. of ventilation. For buildings with vaulted ceilings, that ratio should be doubled, to 2:300.
This ventilation area should be split between the intake near the eaves and the exhaust near the ridge.
Insulating the ceiling will help reduce heat leaking from the house into the attic space. Ensuring a tight vapour barrier will help prevent moisture and warm air from entering the attic space from the house. If ice dams continue to be an issue, installing heat trace tape at the eaves can help to melt the ice.
Sometimes there are loud creaks and pops in the attic. Should I worry?
As roofs heat up during the day and cool off at night, the framing lumber will expand as it warms and contract as it cools. This thermal cycling can add to the stress the roof is dealing with. Framing members will bow and flex with the loads placed upon them.
Whether from snow loading, thermal cycling or strong winds, in most cases the noises you hear are just the structure adjusting to those forces as it has been designed to do. Much like the squeaks in my floor, the noises are very rarely cause for any concern if nothing else appears out of the ordinary.
What if I really need to get snow off the roof?
If snow must be removed to prevent leaks, there are roof rakes designed to work from the ground, but sliding snow can be quite dangerous. If working on the roof, start at the ridge to keep out of the path of snow and ice.
If the thought of climbing up on the roof or dodging snow slides doesn’t fill you with joy, there are many contractors who offer roof snow-removal services.
If snow removal is being considered for structural reasons, take a step back and think critically about the situation. If there are concerns about the structure of your house, this is a warning sign that you should consider calling a professional.
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