1/21/2017
I mentioned in a previous blog about installing a cold roof to solve ice problems. I thought I should go into more detail as to when this is necessary and the benefits from it. The first thing that we need to understand is what causes the ice in the first place. Large ice sickles and ice dams are caused by a lack of insulation or a lack of ventilation or a combination of both. Ice is formed on a roof when the temperature outside is below freezing, there is snow on the roof, and the temperature in the attic or rafter space below is above freezing. The above freezing temperature in the attic causes the bottom layer of snow to melt and run down the roof. It then freezes again as it reaches the eves where the temperature is much cooler. There are several solutions to this problem but they will not all work in every situation. Hopefully this article can help determine which option is best for you.
Proper Insulation and Ventilation
In a properly insulated and ventilated roof system there will be enough insulation (minimum R38) to keep as much of the heat in the living space as possible and enough ventilation to exhaust any heat that escapes into the attic. There should be venting at both the eves and at the ridge. This will allow the cold air to enter at the eves and exhaust the warmer out at the ridge.
Ridge Vent
Probably the easiest and cheapest way to reduce ice damming is to cut in a ridge vent if there is not already one installed. This will allow the heat that is rising in the attic to escape. Many older homes did not have ridge vents or soffit vents originally installed. A ridge vent is easy and inexpensive to install at the time of reroof or as a repair. It may also be necessary to add soffit venting to increase air flow if there is not already one installed. This will probably add a fair amount of cost to the project, but having a properly vented roof will save on cooling cost in the summer as well as increase the life of your shingles.
Additional Insulation
If it is possible to add more insulation in the attic without restricting ventilation this is the next thing to look at. You should have a minimum of an R38 attic insulation and, all types of insulation are not equal. The three main types of insulation are fiberglass batts, cellulose (blown in), and spray foam. Fiberglass batt insulation is my least favorite in attics. It works fine in a wall stud cavities where it is sealed on all six sides but in an attic where air can flow through it, it may reduce the R value by up to half. Fiberglass also does not seal up well around wiring, plumbing vents, and other penetrations. My next least favorite attic insulation is also the most expensive, spray foam insulation. Most spray foam insulations expand and seal around penetrations very well and have good R values with minimal thickness. There are situations where this will work very well. The problem that I see with spray foam is more of an installation issue. A lot of insulators are installing foam directly to the under side of the roof sheeting in an unventilated system. While the R value is good enough to keep ice from forming, the problem is that heat is going through the ceiling and into the unventilated attic. The humidity in this trapped, stagnant air cannot be controlled and can cause problems. The foam should be applied to the top side of the drywall on the ceiling and the attic vented like normal. My favorite attic insulation is cellulose. It is cheap, it seals around penetrations, and it can be dense packed into rafter spaces as well as loose filled into attics. If there is room in the attic to get the R value you need cellulose is really the way to go. If you have soffit venting and ridge venting and it is either not adequate or you do not have enough insulation and cannot add more, a power vent may work very well. A power vent is a fan that can be installed either in the gable end of the house or in the roof itself. The power vent will draw cold air up from the eves and exhaust it out. The fan should run continuously during times when the outside temperature is below freezing and there is snow setting on the roof. It can also be used to exhaust heat in the summer and reduce cooling costs. Power vents work very well as long as there is good air flow from the eves.
Older Homes
In many older homes (80+ years) in the Traverse City area there isn't enough room to add more insulation and ventilation due to 2x4 or 2x6 rafter construction. In this situation, I would recommend a cold roof. A cold roof can be constructed a couple of ways. But it is basically installing new sheeting over new 2x4s on the flat screwed through new ridged foam insulation on top of the existing roof deck. The ridged foam adds insulation on top of the existing roof, while the 2x4s running eve to ridge create an air space that allow air to flow. It then gets ½" OSB sheeting over the 2x4s, a vented drip edge, a ridge vent and it is then dried in and shingled as normal. The benefits to a cold roof are that you add insulation and ventilation which will reduce both heating and cooling cost and eliminate ice buildup which can cause your roof to wear out prematurely.
Cold roofs are good way go to under the right circumstances, but there may be cheaper options to solve your ice problems. If it is time for a new roof and you have ice issues get a quote today or call us at 231-263-8300. We would be happy to help determine the best solution for your specific problem.
