The Role of Roof Design
Much of the typical advice on ice damming overlooks the role played by home design. For example, it's clear that complex rooflines increase the likelihood of ice buildup. Dormers, valleys, and other breaks in the roof plane are all places where insulation has to be cut, seamed, and fit into place. Plus, these areas are frequently difficult or impossible to adequately ventilate. The solution isn't to get rid of these features, but to do a better job with air-sealing, insulation, and ventilation in the original construction.
Skylights. Any penetration through the ceiling is an opportunity for heat to escape into the attic, and skylights are no exception. Wells connecting the skylight with the ceilings are usually wrapped in fiberglass batts, which tend to settle and sag over time, resulting in heat loss. That's why I use spray foam around all such penetrations, even if the rest of the house is insulated with batts. Closed-cell spray foam seals any air gaps and provides an R-value of 6.5 per inch.
Inadequate insulation (manifested here as lines of snowmelt along the rafters), a narrow, poorly ventilated soffit, and heat loss around the skylight all contributed to ice dams on this house.
Low-slope roofs, like the one on this shed dormer, are commonly plagued with ice dams.
In this retrofit job, the author has used two-part spray foam to thoroughly seal and insulate a pair of skylight wells.
Cathedral ceilings. With a cathedral ceiling the chance of ice damming rises exponentially, particularly if there are skylights or recessed lights. Even with insulation installed to code, cathedral ceilings by their very nature allow interior heat to get closer to the roof deck. There is also far less space for efficient ventilation, making them a great breeding ground for monster ice dams.
Shed dormers. In some older homes, shed dormers with 2x4 or 2x6 rafters make it impossible to get enough R-value from fiberglass. Here I use closed-cell spray insulation to create a hot roof with no roof ventilation. Although some people have theorized that hot roofs aren't a good choice for snow country, I have had no problems with these installations.
Eaves. In general, the smaller the eaves, the more likely the home will have ice dams. Small eaves have less room for vents, and the smaller vents are more likely to clog. A few paint jobs can be all it takes to choke off adequate air flow. To test soffit vents, we use a yard blower to move air up through the vents, with someone stationed in the attic to make sure the air paths are clear. (Bring your dust mask!) If the lights are off, the person stationed in the attic should also see daylight coming in at the eaves or through the insulation chutes. While we're at it, we also look for daylight coming through the upper half of the vent system - ridge vents, gable vents, or box vents.
While in theory soffit vents should allow enough cold outdoor air into the attic to prevent snow on the roof from melting, they are often too small.
Soffits also may be blocked by insulation.
Daylight at the eaves is a sign that there is at least some airflow through the soffit vents.
I seldom see an overventilated attic. You want as much airflow through the attic and truss spaces as is reasonably possible. Unfortunately, most homes we see have minimal attic ventilation. On homes troubled with frequent ice dams, I recommend adding more ventilation whenever possible, especially on a complex roof. One way to do this is to add gable vents, which in my opinion are underused. When it's architecturally appropriate, we install gable vents in addition to soffit vents. As a rule, houses built after 1955 tend to have better roof ventilation than older homes.
Roofing types. On very shallow roof slopes we try not to use asphalt shingles, even if it's allowed by code. Where it fits with the home's design, a single-ply roof system like EPDM is a great choice. If the roof is visible from the ground or from inside the home, I prefer metal roofs, either standing seam or soldered flat seam. Architecturally, metal roofs look great on low slopes, even if the rest of the roofing is a different material.
Removing Snow and Ice
Besides being a profitable side business in our climate, snow and ice removal is a great way to connect with prospective clients. If your company doesn't do roofing, you can probably contract with your favorite roofers to do the snow removal. They will have the necessary insurance and safety equipment, and will probably be happy to have work during the winter. As for us, we perform all of our work under rope and harness to keep things safe.
When to remove snow from the roof depends on the house: Some homes can handle 10 to 20 inches before we worry; others can start having problems at 2 inches. It also depends on what we can negotiate with the client. In some cases they might want us to come out only when there's a snowfall of more than 4 inches. Or they might like to receive an e-mail whenever conditions are right for ice dams.
Snow can be removed with roof rakes, a stiff broom, and a plastic shovel. It's important to use plastic rather than metal to lessen the chance of damaging the roof shingles. In most cases - though it's more expensive up-front - I recommend removing all the snow from the roof rather than just the bottom few feet. After all, it's the snowmelt from the upper half of the roof, where the warm air in the attic collects, that feeds the ice dam.
Removing ice dams is a bit tougher. We have repaired hundreds of roofs that have been damaged by homeowners and even well-intentioned professionals using hammers, picks, and hatchets to attack the problem. No matter what anyone says, never trust those kinds of tools for removing ice dams; companies that use those methods due so only because they can't or won't invest in professional equipment.
Our company has been using commercial steamers for over 20 years. When used properly, steamers are very effective and totally safe for roofs. Even so, I've seen terrible damage done to homes by inexperienced users. Steamers are powerful but finicky machines. The problem is that you're running cold water outside in a hose, and unless you know what you're doing, that water is going to freeze and ruin your $5,000 steamer. Over the years we've modified our machines to keep everything running in the cold, using a system that allows us to flush the steamer with anti-freeze between jobs. We collect and reuse the anti-freeze with each cycle.
Another simple modification we made was to clamp a piece of oak to the bottom of the steamer wand. Though the wand can heat up to 300°F, the oak keeps it off the roof surface so that it doesn't mar the asphalt shingles. We use the steamer to undercut the ice dam and to slice it into blocks about 12 to 18 inches long, depending on the thickness. Then we gently pick up each block and throw it off the roof, making sure there is nothing or no one below (the blocks weigh 40 to 60 pounds apiece).
Steve Kuhl owns Kuhl Design + Build and The Ice Dam Co. in Hopkins, Minn.