Ice Dams: How to Beat Them
How to Prevent and Remove Ice Dams
The Roof Ice Dam
Ice dams are a pervasive and damaging winter roofing problem caused by poor roof ventilation and a warm attic space. Left untreated, ice dams can cause serious damage to your roof, gutters, paint, insulation, drywall, structure and even contribute to mold. Dam! (Pun intended, sorry).
Ice dams form when melting snow on a roof runs off and refreezes at the edge of a roof. This condition occurs when the snow is melted by a warm roof, creating water running between the snow and the warm roof surface, then freezing and turning to ice when it gets past the exterior wall and hits a cold unheated roof edge or gutter.
As the bottom of the snow pack continues to melt, water continues to flow down the roof surface until it hits the ice, thereby creating a larger and larger ice dam.
Ironically, ice dams occur most commonly after a heavy snow because snow is a great insulator. I’ll discuss why in the next section “What Causes Ice Dams?”
In this tutorial we’ll address the following Issues:
What Causes Ice Dams?Illustrated Guide
Ice dams form when melting snow on a roof refreezes at the edge of a roof. Why does snow melt on your roof when it’s freezing outside? OK, fair question. Well, it melts because the underside of the roof in the attic above 32 degrees Fahrenheit enough that it warms the outside roof surface to the point that snow melts. Now here’s the weird part. Ice dams start or get worse after a heavy snow because of its insulating properties. Since snow is such a good insulator (R-0.5 to R-1 per inch) the outside roof surface is able to warm up easier from the warm attic space, thereby melting the snow faster.
Warm attic spaces occur because of inadequate outside air circulation (ventilation) through the attic (soffit to roof ridge), which is necessary to keep the roof deck cold. Attic warming from poor ventilation is made worse with the introduction of heat from the occupied floor below the attic including sources such as lighting, air leaks, ductwork, etc.
As mentioned earlier, when roof snow is melted by a warm attic space, the water runs between the snow and the warm roof surface. The water then freezes and turns to ice when it gets past the exterior wall and hits a cold unheated roof edge or gutter. The ice dam grows as the snow pack continues to melt, and as water continues to flow down the roof surface. When the water flow hits the ice it creates a larger and larger ice dam.
Ice Dam Damage
If this situation continues, the ice can work its way back up the roof edge, get under roof shingles, melt and leak into the exterior wall, home or attic. Damage from ice dams may not be readily apparent.
As the ice melts and possibly drips into the wall or attic, insulation can be become wet and lose its ability to perform. In some cases if the right temperature and humidity exist, mold may begin to grow in the attic. Often paint will peel or blister weeks or months after the ice dam has melted as moisture from the leak in the wall or ceiling cavities tries to leave and pushes outward.
How to Prevent Ice Dams
The most effective long term solution is to reduce or eliminate any sources of heat in the attic and ventilate the attic space of the roof. The underside of the roof deck must be close to the temperature of the exterior side of the roof. Ideally ventilation should be installed using a continuous soffit-and-ridge vent system with baffles at the lower side of the roof. Provide at least a 2-inch space between insulation and sheathing.
By providing adequate ventilation as illustrated in this diagram, the temperature of the attic will be lowered thereby lowering the underside roof deck temperature.
It is also critical to eliminate all sources of heat in the attic space. Make sure to eliminate sources of heat such as:
Determining Proper Roof Ventilation Areas
The four model building codes, BOCA National Building Code, International Building Code, Standard Building Code and Uniform Building Code, determine required attic ventilation rates (not the FHA or HUD).
For example, Section 1505 subsection 1503 of the UBC states that 1 square foot of net free ventilation per 150 square feet of attic floor space be provided if you cannot attain a balance of soffit and upper roof area ventilation or there is no vapor barrier installed on warm side of the attic insulation.
This requirement is reduced to 1 square foot of ventilation per 300 square feet of attic floor space if the lower and upper vent areas are balanced and a vapor barrier is installed on the warm side of the attic insulation. It is this 1 per 300 rule that is most commonly used.
Calculating required ventilation area is easy:
Battling Ice Dams Before Winter
The most effective time to battle and win the war against ice dams is before winter. Here are some recommendations on how to beat ice dams:
Since ice dams are the furthest things from our minds in the summer, most people battle ice dams in the winter. Unfortunately your options at this point are limited, at least the safe ones.
But there are still some effective actions you can take by yourself.
Here are some recommendations on how to beat ice dams in the winter:
Some tools and approaches to ice dam removal are often discussed but are also very dangerous. I do not recommend any of these approaches because of risk of damage to your life and your home. Please do not try to remove an ice dam with any of these approaches. THEY ARE NOT SAFE!
There may be a time when either the amount of snow or ice dam buildup is too much for you, or you just do not have the inclination to try and remove the ice dam. In that case you may need or want to call in an ice dam removing roofing contractor.
Professional steam removal of ice dam:
If you end up with an ice dam and need it removed, you always have the ultimate tool in a toolbox, your checkbook. There are professional companies available that are insured and will remove your ice dam using professional equipment such ashigh temperature / low pressure steamer (do not hire a contractor that uses a high pressure power washer with a steam box).
Although this low pressure steam approach may cost a few hundred dollars, the prevention of damage to your home may be significant.
The Roof Ice Dam
Ice dams are a pervasive and damaging winter roofing problem caused by poor roof ventilation and a warm attic space. Left untreated, ice dams can cause serious damage to your roof, gutters, paint, insulation, drywall, structure and even contribute to mold. Dam! (Pun intended, sorry).
Ice dams form when melting snow on a roof runs off and refreezes at the edge of a roof. This condition occurs when the snow is melted by a warm roof, creating water running between the snow and the warm roof surface, then freezing and turning to ice when it gets past the exterior wall and hits a cold unheated roof edge or gutter.
As the bottom of the snow pack continues to melt, water continues to flow down the roof surface until it hits the ice, thereby creating a larger and larger ice dam.
Ironically, ice dams occur most commonly after a heavy snow because snow is a great insulator. I’ll discuss why in the next section “What Causes Ice Dams?”
In this tutorial we’ll address the following Issues:
- What causes ice dams?
- How to prevent ice dams.
- Determining proper roof ventilation areas.
- Battling ice dams before winter.
- Battling ice dams during winter.
What Causes Ice Dams?Illustrated Guide
Ice dams form when melting snow on a roof refreezes at the edge of a roof. Why does snow melt on your roof when it’s freezing outside? OK, fair question. Well, it melts because the underside of the roof in the attic above 32 degrees Fahrenheit enough that it warms the outside roof surface to the point that snow melts. Now here’s the weird part. Ice dams start or get worse after a heavy snow because of its insulating properties. Since snow is such a good insulator (R-0.5 to R-1 per inch) the outside roof surface is able to warm up easier from the warm attic space, thereby melting the snow faster.
Warm attic spaces occur because of inadequate outside air circulation (ventilation) through the attic (soffit to roof ridge), which is necessary to keep the roof deck cold. Attic warming from poor ventilation is made worse with the introduction of heat from the occupied floor below the attic including sources such as lighting, air leaks, ductwork, etc.
As mentioned earlier, when roof snow is melted by a warm attic space, the water runs between the snow and the warm roof surface. The water then freezes and turns to ice when it gets past the exterior wall and hits a cold unheated roof edge or gutter. The ice dam grows as the snow pack continues to melt, and as water continues to flow down the roof surface. When the water flow hits the ice it creates a larger and larger ice dam.
Ice Dam Damage
If this situation continues, the ice can work its way back up the roof edge, get under roof shingles, melt and leak into the exterior wall, home or attic. Damage from ice dams may not be readily apparent.
As the ice melts and possibly drips into the wall or attic, insulation can be become wet and lose its ability to perform. In some cases if the right temperature and humidity exist, mold may begin to grow in the attic. Often paint will peel or blister weeks or months after the ice dam has melted as moisture from the leak in the wall or ceiling cavities tries to leave and pushes outward.
How to Prevent Ice Dams
The most effective long term solution is to reduce or eliminate any sources of heat in the attic and ventilate the attic space of the roof. The underside of the roof deck must be close to the temperature of the exterior side of the roof. Ideally ventilation should be installed using a continuous soffit-and-ridge vent system with baffles at the lower side of the roof. Provide at least a 2-inch space between insulation and sheathing.
By providing adequate ventilation as illustrated in this diagram, the temperature of the attic will be lowered thereby lowering the underside roof deck temperature.
It is also critical to eliminate all sources of heat in the attic space. Make sure to eliminate sources of heat such as:
- uninsulated recessed ceiling can lights installed in the floor below,
- poor attic floor insulation (Use this DOE insulation calculator to see what insulation levels you should have for your home based upon your zip code location),
- uninsulated folding attic stair openings,
- heating ducts,
- furnace or water heating equipment in the attic,
- bathroom vent fans that improperly vent to the attic, and
- other similar problems.
Determining Proper Roof Ventilation Areas
The four model building codes, BOCA National Building Code, International Building Code, Standard Building Code and Uniform Building Code, determine required attic ventilation rates (not the FHA or HUD).
For example, Section 1505 subsection 1503 of the UBC states that 1 square foot of net free ventilation per 150 square feet of attic floor space be provided if you cannot attain a balance of soffit and upper roof area ventilation or there is no vapor barrier installed on warm side of the attic insulation.
This requirement is reduced to 1 square foot of ventilation per 300 square feet of attic floor space if the lower and upper vent areas are balanced and a vapor barrier is installed on the warm side of the attic insulation. It is this 1 per 300 rule that is most commonly used.
Calculating required ventilation area is easy:
- Determine the square footage of the attic floor area to be vented by multiplying the width by the length in feet.
- Divide this number by 300. This is the MINIMUM TOTAL square foot area of ventilation required for total ventilation of the upper ridge and lower soffit or eaves.
- Divide that number by 2. This is the MINIMUM square foot area of ventilation required (each) for the upper ridge area and lower soffit or eaves.
- Multiply these numbers by 144 to determine the net free area of ventilation required in square inches.
Battling Ice Dams Before Winter
The most effective time to battle and win the war against ice dams is before winter. Here are some recommendations on how to beat ice dams:
- Keep gutters clean: Make sure to have your gutters cleaned completely before winter and also make sure your downspouts are functioning properly. Melted snow cannot go anywhere if your gutters are clogged.
- Eliminate or reduce direct sources of heat in the attic: Proper ventilation alone will not solve the ice dam problem if you have active heat rejection into the attic. Heat from uninsulated, recessed can lights in the room below will add attic heat when they are on and when off the warm room air will still migrate through the cans into the attic via convection. Other sources of heat in the attic to eliminate include uninsulated ductwork or improperly vented bathroom exhaust fans. If you have a furnace or water heater in your attic, that’s a problem. You’ll need to add supplemental or powered ventilation to properly ventilate the attic.
- Increase attic floor insulation: The only way to keep warm air from your heated living space from warming your attic is by having proper amounts of insulation in the attic floor. Older homes are notorious for having inadequate insulation and usually have far less than required by current codes. Use this DOE insulation calculator to see what insulation levels you should have for your home based upon your zip code location.
- Properly ventilate roof, attic and eaves: The major action you can take in proactively battling and potentially preventing ice dams is through proper ventilation. As described in the previous section “Determining proper roof ventilation areas,” there needs to be an equal (balanced) amount of open free ventilation area in the eaves or soffits and the top of the roof at the ridge. If ridge ventilation is not possible, then high ventilation can be provided with numerous vents or powered ventilation. It is essential that attic rafter vents or insulation baffles are stapled to the underside of the roof deck providing clear cold outside air flow from the vents in the soffits and out through the gable vents, roof vents or ridge vent.
- Install heat tape: OK this is on the list because it can help in limited situations with light snow. However, in heavy snows, all this expensive “solution” is going to do is either move the ice dam further up the roof or make it worse, especially if your gutters are not cleared. A proper installation of heat tape will involve a serpentine installation at the roof edge and installation of the tape in the gutter as well. Your money is much better spent on the previous three recommendations which address root causes of the ice dam problem.
Since ice dams are the furthest things from our minds in the summer, most people battle ice dams in the winter. Unfortunately your options at this point are limited, at least the safe ones.
But there are still some effective actions you can take by yourself.
Here are some recommendations on how to beat ice dams in the winter:
- Act fast with a roof rake during a heavy snow: As I mentioned earlier, ice dams happen quickly after a heavy snow because of the insulating properties of snow. If you can get out and rake your roof with a special tool called a roof rake to remove at least the lower 4 feet of snow from the roof edge, you’ll do a lot to prevent the ice dams from even forming. A roof rake is like a shovel that is turned on its side so that you can pull snow off the roof toward you. It has a long handle about 16 to 21 feet long, and is safer than many other approaches since you use the tool from the ground, not on a ladder.
Roof Rake
- Calcium chloride or ice melt product: If you have an ice dam forming, one action you can take is to put a calcium chloride or similar product on the ice. (Forget any urban legends you may have heard about putting salt in pantyhose, it does not work well, takes a lot more salt and results in the pantyhose ripping apart). When you put the calcium chloride directly on the ice, be careful if you are on a ladder, icy conditions and ladder usage are not recommended so please be careful.
Calcium chloride or ice melt product
Some tools and approaches to ice dam removal are often discussed but are also very dangerous. I do not recommend any of these approaches because of risk of damage to your life and your home. Please do not try to remove an ice dam with any of these approaches. THEY ARE NOT SAFE!
- Hatchet or axe
- Ice pick or screwdriver
- Propane torch or heat gun
- Chainsaw
- Hammer and chisel
- Duct tape (OK, well I’m not actually aware of this being used but I figured someone tried it somewhere…)
There may be a time when either the amount of snow or ice dam buildup is too much for you, or you just do not have the inclination to try and remove the ice dam. In that case you may need or want to call in an ice dam removing roofing contractor.
Professional steam removal of ice dam:
If you end up with an ice dam and need it removed, you always have the ultimate tool in a toolbox, your checkbook. There are professional companies available that are insured and will remove your ice dam using professional equipment such ashigh temperature / low pressure steamer (do not hire a contractor that uses a high pressure power washer with a steam box).
Although this low pressure steam approach may cost a few hundred dollars, the prevention of damage to your home may be significant.
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