By Jenna Harris
Ice dams form on your roof through a process that involves accumulated snowfall, the differing temperatures of the outside air and your roof, and heat loss from your home. Picture this scenario. It is an ordinary winter day, and there is a buildup of snow on your roof. In and of itself, this is probably not a significant problem. A home that was constructed in adherence with building codes was designed to support expected snow loads. If your home has air leaks or your ceiling or attic are insufficiently insulated, escaping warm air will rise and warm the higher portions of your roof to above 32°F. This means that the snow on these warm apportions will quickly melt. However, as the water runs down your roof and reaches those portions of that are still below 32°F, it will re-freeze, forming ridges of ice, or ice dams. These ice dams trap the water that continues to flow from the still-melting snow on the higher areas of your roof.
That is how the damage is caused: the dammed-up accumulated meltwater overhead will flow into your attic, through your ceiling, or down and inside your walls — anywhere there is an opening or crack. Everything that can happen from that point — sheet rock or ceiling damage, wood rot, mold, mildew, etc. — all started with accumulated snowfall, which you can’t control, and heat loss from your home, which you can.
How Can I Prevent Ice Dam Formation at My Home?
Although some home contractors will tell you that you should heat your attic to prevent ice dams, the opposite is true: warm air leakage is the source of the problem, so the solution lies with sealing air leaks and adding proper insulation, while at the same time providing adequate attic ventilation to dissipate heat.
First, make your ceiling airtight. This will prevent warm air from escaping into your attic. These air leaks can be found in several places:
- Around water heater or furnace vents
- Wiring bypasses
- Uninsulated “whole-house” fans
- At the point where any home additions were constructed
Finding these air leaks can be difficult for you as a homeowner to find. For example, there may insulation covering a gap, or they may be too small for you to notice. But even a seemingly insignificant opening can be a major source of heat loss, reducing the effectiveness of your attic’s insulation by as much as 70 percent. For that reason, your best bet is a professional home inspection that includes infrared thermal imaging. This will help identify any problem areas, so you will have a better understanding of how to proceed.
After sealing any leaks, the next step is to install insulation if necessary, keeping the following considerations in mind:
- You must fix any air leaks before installing installation.
- Depending on the manufacturer, you may need between 10 and 16 inches of cellulose or loose fill fiberglass insulation.
- The desired R-value should be between R-38 and R-44. This number measures thermal resistance; the higher the number, the slower the heat loss.
- Make sure to maintain an airspace between any insulation and the roof deck. This prevents a buildup of condensation, which can delaminate your roof tiles.
- If your insulation is wet due to roof leaks, it needs to be dried out completely, and possibly replaced. Wet insulation has virtually no R-value, and even when dry, may still be compromised due to compression. Cellulose insulation is particularly vulnerable to water damage.
- Install rafter air channels that are made of polystyrene.
- Place insulating batts or blankets over your furnace’s heating ducts.
- Have a cover installed over the hatchway to your attic.
Finally, reduce heat buildup and keep your attic dry by ensuring that you have adequate natural ventilation. In areas where there is heavy snowfall, mechanical ventilation is not recommended, because it can cause unwanted negative pressure and moisture problems in your home.
Do I Really Need a Professional? Can’t I Just Do the Inspection and Repairs Myself?
Properly inspecting your attic for leaks, inspecting your roof and the interior of your home for damage, and correcting any problems is often beyond the skill level of most homeowners. It can be dangerous, and in some cases, even against the law.
- Walking on your roof during the winter puts you at extreme risk of falling.
- Trying to “chip away” accumulated ice from below can cause injury from falling ice or debris.
- You could cause extensive damage to your home.
- Old-style “knob and tube” wiring needs to be redone before sealing your attic.
- Certain types of insulation may contain asbestos. If this is the case, State and Federal guidelines must be followed to avoid asbestos contamination.
- If your bathroom vents into the attic, the venting must be rerouted to the outside.
- If your furnace or fireplace is unvented, it must be vented or removed.
- If your roof has already been damaged, it must be repaired before any other work is done.
As you can see, there are several considerations that must be taken into account if the problem is to be properly corrected. Failure to do so can result in further damage to your home.
Here’s the good news. If you take the time to make sure these modifications are done right at the beginning, long-term follow-up maintenance is relatively easy and inexpensive. Most importantly, you will potentially save thousands of dollars in utility charges, avoid costly repairs, and protect your biggest investment: your home.
Jenna Harris writes for Snap Construction in Minneapolis. For more information about ice dams or other construction topics, please see www.snapconstruction.com.