Ice dams can form on any type of building structure; from unheated sheds, to any style of home, to large “flat” roof commercial buildings. The phenomenon occurs on a snowy or icy roof, when a higher area on the roof is warmer than a lower area in freezing temperatures. The resulting effects are the thick edges of ice and icicles that form on the edges of the structure. While ice dams them self are somewhat unsightly, the resulting icicles can be dangerous and water backing up under the roofing materials can damage ceilings and walls, cause mold and mildew inside the home and compress insulation making it less efficient. In worse case situations, ice dams can be so heavy as to break rafter tails or destroy and pull gutters and fascia away from the home. A heavy piece of ice or large icicle can fall causing damage to property or injury to someone standing below. It is also fairly common for icicles to fall and break ground level windows.
The way to prevent and or at least manage ice dams is to create conditions that attempt to even out the temperatures on all areas of the roof whenever it is below freezing. There are 4 things that affect the roof temperature and the resulting ice dams, those being: 1) Radiant heat loss 2) By pass heat loss 3) Solar heat gain 4) Improper attic ventilation
Radiant heat loss is common in homes built before 1976, when the building code had minimal requirements for insulation. The structural design of most bungalows, story and ½ and two stories prior to this date does not allow for adequate insulation and often makes proper ventilation impossible to achieve without a substantial amount of work. With unfinished interior areas, there are often creative ways to achieve the desired insulation levels by; a combination of furring out framing members, installing foam board stock or by applying various spray in place foams. In areas that are finished, the retrofits are more complicated and sometimes are better approached through the roof side of the assembly. If a house is in need of a new roof, this can be an ideal time to consider a roof insulation project as it may be more economical to install insulation and/or venting solutions from the exterior. One common area of radiant heat loss is on the exterior wall plates on the level soffit sides of the home. It is not uncommon for a storm or other high wind event to blow through the vents in the eave and blow the insulation off of the exterior wall plates, if insulation was ever installed properly in these often neglected areas. To fix this situation, attic chutes and wind wash materials can sometimes be installed from the attic but other times need to be installed by removing roof sheathing or soffit panels.
By-pass heat loss is caused by convection, where the warm air from the interior of the structure rises up and out through any type of holes or cracks in the walls or ceiling into the attic. This warm air rises quickly to the highest part of the attic where it melts the snow and ice on the peak of the roof first which then causes water to flow down to an area that is still below freezing and refreeze. The solution to stopping air by-pass is to physically find and block all openings. This is often accomplished by a using a combination of expanding foam for cracks and small openings, to pieces of plywood or drywall for larger openings. Recessed lighting fixtures can be a significant source of bypass as well as radiant heat loss. Building and installing insulated, air tight, boxes to cover the fixtures in the attic, and then carefully sealing them to the surrounding ceiling coverings and/or framing members can make a big impact on ice dams as well as heat loss and utility bills.
Solar heat gain is harder to control. Light colored shingles and lighter colors for siding that is installed in areas that are adjacent roofs can help minimize the effect of solar heat induced ice dams. If you are observant, you may notice that even unheated garages and sheds will often have ice dams, especially on the north sides, as the sun heats the south sides faster and the heated attic air rises to the peak and has a similar, if less dramatic ice dam effect. The only way that this can be stopped is to manually keep the roof cleared of snow. By its self this rarely causes a situation that causes water leaks to the interior of the structure.
Proper Attic Ventilation is the fourth component affecting ice dams that needs to be considered. As no amount of insulation or by-pass sealing will stop all heat loss, ventilation is the last piece of a healthy roof puzzle. Under the assumption of proper insulation and all openings in the attic being sealed, the proper amount, type and location of ventilation products will complete healthy home construction techniques. Most shingle manufactures and distributors have calculators and charts to help figure out the proper amount of ventilation needed. While the solutions for proper ventilation are typically easy when building new homes, retrofitting ventilation in existing homes can be a much more complicated challenge. Unfortunately, many roofers offer to add additional roof vents for nominal costs but if they are installed without a complete understanding of the existing framing and roof structure, they are often just “roof ornaments” with no functional value and in some cases can cause problems.
On the bright side there are more products and options than ever to address different types of ventilation challenges. Roof vents, ridge vents, soffit vents, wall vents, continuous vents, gravity vents, power vents and a variety of attic chutes and many “built in place” fixes might be part of the best answer.
Removing snow off of a roof will help to minimize ice dams and their effects no matter what type or how severe of a heat loss problem a building might have. This can be accomplished from ladders or by using specially designed “snow rakes” but can be very difficult on high and steep roofs. Sometimes weather conditions can make it nearly impossible to do until there is already significant ice buildup. If and when a structure has significant ice dam issues, it is best to use a steam type pressure washer to melt the ice away. It is common to have inexperienced people show up with hammers, axes and shovels to get ice of homes, which typically results in a project for the roofer or gutter installer in the spring. Pounding and chipping ice down to the shingles is not the preferred method to eliminating the ice dam.
The best long term solution for fixing ice dam problems is to have the structure evaluated by an experienced remodeling expert who understands each of the 4 ice causing components, as well as how everything must work together to create a healthy home.
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