Ice dams can be a huge problem here in New England. Not only can an ice dam rip off your gutters and damage shingles, but they frequently lead to leaky roofs, causing water damage, peeling paint, warped floors, sagging ceilings, etc… Plus if your attic insulation gets wet, it will lose R-value and invite mold & mildew to form.
To get a handle on ice dams, we first need to understand how and why they form. The primary cause of ice dams is usually a result of poor ventilation or improper insulation.
Your roof structure is vented (or at least it should be!) for a reason. Roof ventilation systems help flush out super-heated air help keep your house cooler in the summer. When air becomes super-heated in the summer (130 degrees), moisture in the air can (and will!) condense on structural members which is ideal breeding grounds for mold and mildew, but that’s a story for a different day.
The goal of attic ventilation is to keep your attic and roof temperatures as close to the same as outdoor temperatures at all times – even in the winter! As the attic temperatures rise due to thermal heating (sunshine), snowmelt runs down your roof and should drip off the edge. On most houses, the lower edge, or eaves, of a roof stick out beyond the walls, keeping water run-off away from the side of your house.
The roof overhang, if not vented properly,can be much colder than the rest of your roof, causing snowmelt to freeze before it can drop off the roof. The snowmelt slowly builds-up and an ice dam forms. Larger ice dams can build, to the point where water is dammed up at the top edge of the ice dam. Water is not happy unless it is flowing down-hill, so when an ice dam forms and stops the flow of water, water droplets will seek an alternate route – right in to your walls and ceilings!
The best way to get a handle on ice dams is to prevent them in the first place. A qualified roofing contractor can be great resource to discuss proper ventilation of your attic. For example, the total vent area of your attic should be roughly 1/300th of the floor space of your attic, with half of the vent area at the soffits, and the other half at the ridge, roof or gable vents. And of course you have to take into account the size of the louvers and screens that keep out insects, rain and snow. And yes, cathedral roofs require ventilation too, even though there is no attic space! Too much ventilation can create problems too – if your ceiling is not well insulation, negative pressures in your attic will pull warm, moist air out of the living space below. As we discussed, warm, moist air is not ideal for your home’s structure. External factors, such as prevailing winds and shade trees, and how much sun/shade around the house will come into play when planning out a ventilation system.
Insulation, or lack thereof, can be a contributing factor to the formation of ice dams. Your roof could have the proper vents installed, however insulation may be installed too tightly to the roof surface, preventing air flow along the inside of your roof. With soffit vents in modern construction, baffles (usually Styrofoam) are installed at the underside of your roof sheathing that keep insulation back just enough to allow cool air to circulate. To see if your soffit vents are unobstructed, take a peek in your attic on a bright, sunny day. With the lights off, you should be able to see a little daylight reflecting along the bottom edge of your roof sheathing around the perimeter of the roof. If you can’t see any daylight what so ever, it’s probably best to call a contractor to come take a closer look.
Conversely, if your ceiling insulation does not reach to the outer walls of your house, heat will escape up in to the attic space and cause the snow to melt unevenly. After a snowstorm, monitor your roof closely from outside and compare the snowmelt pattern to that of surrounding homes. A properly insulated house with correct roof ventilation should have uniform snow-cover (drifting aside). If you see different sections melting faster than others, or see patterns resembling your roof framing, it likely means your roof is being heated from heat loss and/or poorly functioning vents. If your neighbors have ice dams forming on their house but not yours, your insulation and vents are functioning properly!
Again, the best way to deal with ice dams is to prevent them in the first place. There are still options other than having a contractor tear in to your roof – they will require a little elbow grease and you need to pay attention to what is going on around your home – every day!
Buy a good extendable roof rake, long enough for you to comfortably (safely) reach 5 feet up your roof. Clean off at least the lower 3 feet of your roof every time it snows (even if it is only an inch!). Once and ice dam begins to form, you’ve lost the battle. Keeping the edge of your roof clear is the best way to stay ahead of this problem. If you get lazy for even one storm, expect the ice dam to return. We really shouldn’t have to say it, but keep you and your roof rake WELL away from any power and utility lines coming in to your home!
Some people prefer to use heat cables attached to the lower edge of the roof in a zig-zag pattern. We’ve all seen the zig-zag pattern melted in to the snow on houses in neighborhood houses. While somewhat effective, you are still faced with having to get electricity safely to the cables on the edge of the roof. And no, an extension cord is not safe wiring, even though the guy at the hardware store suggested it! Call an electrician to install an appropriate exterior circuit that can be turned on/off with a switch inside (preferably one that lights up) in a conspicuous place so you remember the heat cables are on. These cables should ONLY be used when the roof is snow covered. When the roof is dry, the cables will cook the roof shingles, significantly decreasing their life expectancy. And of course you need to make sure all debris is removed from the heat cables before use each season. It does not take much to start a fire with dry leaves and pine needles! The downfall to heat cables is when it snows and you are off on vacation in a tropical climate for a week, you will likely come back to ice dams and water damage. Not a fun way to end a vacation.
Another way to help prevent ice dams is to install metal snow slides along the lower edge of your roof. The lower two feet of your roof are covered in smooth metal, which allows snow to slide off the roof before water has a chance to freeze.
So, if you, or someone you know who has water leaking in to their house from ice dams, please realize it is not worth wasting time and money every winter focusing on how to get rid of ice dams. Instead, it’s well worth the time and resources to fix what caused it.
Have ice dam you need to get rid of? Here are some do’s and (more importantly) don’ts:
Do NOT us an axe or claw hammer to break up the ice. It’s not safe and will likely cost you much more to fix the damage you cause.
Instead, try filling a few panty-hose/stockings with ice melt (DO NOT use rock salt!) and tie a rope to the end. Toss the stocking filled with ice melt up on to the ice dam perpendicular to the edge of your roof. The goal is to slowly melt a drainage channel for any water to flow away. The rope allows you to pull the stocking down safely – no ladders needed!
DO NOT use a pressure washer! It will blast away the top layer of your shingles!
If you use a roof rake, pull small amounts of snow off, gently. Avoid scraping the shingle as much as possible. There are rakes available with wheels at the ends of the blade that will roll along the roof surface as you pull the rake.
When it’s time to replace your roof, make sure your contractor uses an impermeable underlayment, such as ice & water shield, along the lower edge of the roof to prevent any water from penetrating the roof sheathing. Never install a new layer of shingles over old shingles!
DO make sure your bathroom and laundry vents exit to the exterior of your house (not just in to the attic!) Monitor all connections regularly.
If you have pull-down stairs or a scuttle hole to access your attic, check insulation and/or weather-stripping
to minimize air-flow and heat loss.
DO NOT use a space heater in your attic to try to melt the ice dam. It will likely just make the problem worse!