Prevent Ice Damming with Proper Attic Care

Does your home have large icicles hanging off its gutters? If so, this could be a telltale sign of a much more serious condition called ice damming.

Ice damming  is caused by the refreezing of melted snow at the roof overhang which creates a “dam” that can trap water under shingles or other roof finishing layers, causing leaks through roof deck joints, nail holes which may appear inside as stains, cracks or bubbles within drywall and must be inspected for mold prior to repair.

The problem of ice damming is a much deeper issue than it may first appear, and may be indicative of poor construction, insulation or ventilation problems and possibly lead to serious health related issues in the home. Because ice damming can force water backward and underneath your roofing material it can damage the roof sheathing, cause the wood rafters to rot, and accelerate the deterioration of your insulation – leading to higher fuel bills, the development of mold growth, health problems and costly repairs.

The rule of thumb is that properly ventilated attic air should never be more than 15 degrees hotter than the outside air. If it is hotter, that is an indication of additional heat sources in the attic that should be eliminated, and/or an indication of unsatisfactory attic ventilation that must be corrected immediately. Purchase a good thermometer and test it yourself!

Health Hazards

One of the most common types of mold that thrives in a moist attic environment is black mold. Black mold spreads by spores, and there is growing evidence of serious health hazards associated with breathing in the black mold spores. This is an unhealthy home syndrome that must be corrected immediately. (Black Mold photo)  Remember, just because you are not allergic to molds today does not insure that you will not be allergic to molds tomorrow. If you are experiencing breathing and allergic type reactions, contact your doctor and then have your attic inspected for proper insulation, ventilation and heat sources. Visit the EPA for additional information on mold:

Excessive Attic Heat: The Primary Culprit

How does heat enter the attic? How does heat exit the attic? These are two very important questions that must be asked for every construction design. Without heat, there are no ice dams, no moisture condensation problems and no health issues to be concerned about. The following are examples of common ways unwanted heat enters the attic space, telltale signs of ice damming conditions and some reasons why heat can not exit that attic space:
• Attic air space should be considered unheated space. Thus, all walls adjoining that space must be insulated to help reduce heat entry into that attic space. Doors leading to unheated spaces should be addressed and trimmed as if they were outside doors, complete with saddles and weather stripping.
• While standing in your attic can you see down into the open space around the framed box of a fireplace? If so, this is a major heat source, open directly into the attic space due to unsatisfactory construction and will cause ice dams and must be corrected.
• Un-insulated walls or ceilings allow heat to penetrate into the attic and will result in huge utility bills for heating and air conditioning and create an ice damming situation.
• Some homes have been retrofitted with new energy efficient h.v.a.c. systems which may have been run through attic space. Big mistake! Un-insulated ductwork allows increasing heat build-up in the attic, leading to snow melt and ice damming.
• Has your home been resided? Be certain that the original wood-covered soffit overhangs were removed and that new perforated soffit vents (to assure inlet air flow to the attic) were properly installed. This is an important and necessary element for a healthy home.
• Check inside to see if attic insulation is covering the soffit vents if so, remove it. Soffit vent protectors should have been installed to help keep insulation from blocking these vents.
• Check the wood in your attic by looking for “white vertical lines” which would indicate that frozen water had infiltrated the home and then froze again when exiting through the siding weep holes and soffit vent holes. This condition could lead to major problem if not corrected.
• Did someone install” standard” recessed lighting fixtures in the ceilings? If located in very close proximity to the low sloped roof it can pre-mature ice melt and ultimately an ice dam. Note: Don’t cover a light fixture with insulation! Is it a double-walled insulated light fixture? Has insulation been installed according to local fire code? If you can’t answer these questions call for help.
• Another common way for heat to enter the attic involves installing the bathroom exhaust vent duct into the soffit vents, rather than correctly installing the duct to an outlet vent. Soffit vents are inlet vents, not outlet vents. Everything that exits the house at a soffit vent immediately re-enters the house in the attic space, because that is what soffit vents are designed to do. Not only will this add heat, but it will also add humidity and moisture to the attic, defeating the very reason for installing the bathroom fan in the first place. Even a home with functional attic ventilation can now develop molds on the roof sheathing cavities above these unsatisfactory ducts.
• Insulation is designed to keep heat within the living space in winter. All sidewalls facing an unheated surface must be insulated, with the vapor barrier facing the heated surface. Twelve inches of insulation, creating an R-38, is optimal. Remember, only have one vapor barrier and install it facing toward the heated surface. To attain a 12 inch depth use either un-faced insulation or blown-in insulation.
• Further compounding the very unsatisfactory conditions of this attic is the use of loose, blown-in, fiberglass insulation, lacking a vapor barrier, which now doubles the amount of attic ventilation needed. Normally, the ratio of net free-air vent space to attic floor space being ventilated is 1/300, meaning that for every 300 square feet of attic floor space, one square foot of net free-air vent space must be provided. However, that ratio of required vent space now doubles to 1/150 for this type of insulation. Let us not overlook the heating duct near the roof line, too, which also adds additional heat – there is that word again, heat!

Solutions – Proper Attic Ventilation

You now know what not to do to create attic heat. Let us now discuss things to do to get rid of unwanted and damaging attic heat. First, to avoid ice damming and other problems, make sure that every steep sloped roof has continuous soffit inlet vents. Many homes designed and built in the 1950s were constructed without any soffit overhangs, making the installation of conventional soffit inlet vents impossible. Fortunately, the importance of attic air flow, even for homes built without soffit overhangs, is now becoming better understood. There are many new products on the market that will provide inlet air at the eave of the roof by bringing in the air from behind the gutters, through the roof sheathing, and under the shingle materials. Both roofing and carpentry work are required to install these new inlet vents, which are available wherever most roofing materials are sold. Second, you must have ample outlet vents in the form of 9″ roof vents, gable end vents, or ridge vents. Since heat rises to the peak of the roof, the logical outlet vent should be located at the peak of the roof, were an opening to the outside would then let unwanted heat exit quickly and efficiently. If your home does have gable end vents or standard roof vents, do not cover them with plastic during colder weather, thinking that you are saving heat. Doing that is the equivalent of “smothering” your home’s breathing capability. Be aware that just because you see a ridge vent on the outside of your roof, it does not mean that it has been properly installed. Most manufacturers of ridge vents, including all of the major shingle manufacturers, require almost a 2″ cut away on each side of the ridge board (the reason it is called a ridge vent) to allow for the proper and needed amount of net free-air vent space to work properly. Unfortunately, many homes do not have their vents properly and correctly installed.

A note about power vents – many times they won’t do the trick. They are thermostatically controlled and thus do not work in the winter, when it is actually more important to ventilate your attic. Now should your insulation get wet or old, it loses some of its “R” value, or resistance to thermal exchange, thus increasing the work required by heating and air conditioning systems. After reading all of this data, a roofer might say, “All you need is one of the many self-sticking ice and water barriers installed to eliminate ice damming.” You they would be right – to an extent. This material eliminates water infiltration through the roof in most cases. However, it would not solve other conditions related to the “inside” of the attic space, and other problems which would still occur even with the installation of expensive self-sticking barriers. It’s a cold hard fact: If you do not have excessive heat in the attic, you do not need this expensive material. Unfortunately, most homes have excessive heat and now, most roofing manufacturers are insisting on the installation of self-sticking barriers.

• Reduce unwanted attic heat sources.
• Remove attic heat with proper ventilation and insulation.
• Survey your home for molds and mildews.
Ask Lon for additional information or support.
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Lon Thomas
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Resources: Bill Thomas – Ron Hungarter at Thor Systems Inc – Do it Yourself Community Forum – Scott Prior Construction