We read your article this morning and my wife suggested you might have some suggestions for our ice-dam problem.
We’ve lived in our house for 22 years and we’ve never had this problem before. However, two weeks ago some stains appeared on the sloping wall of the closet in our bathroom, and when I checked the roof, we had an accumulation of about 8 inches of ice on the roof. I chipped the ice away, but the stains haven’t disappeared, and when I checked again today, some additional ice had accumulated, which I have again chipped away. The house was built in 1929, has ‘litter and lime’ insulation, and the ice-dam formed on the west side, south of a dormer and on a steeply pitched 12/12 portion of the roof.
Any thoughts on the best course of action?
Neil Trembath, e-mail
With the heavier than normal accumulation of snow on roofs this year, I have seen hundreds of homes with ice damming and huge icicles, in my travels. These issues are readily apparent even from the street. I am quite surprised that yours is one of the few inquiries that I have had on the subject. It is very likely that many homeowners, like yourself, are seeing this problem for the first time. The reasons for the ice damming on your home can be quite easily explained, but might be much more difficult to remedy. I will try to offer you some useful suggestions.
Ice damming occurs on a roof due to melting of snow on the higher part of the roof, which cools and freezes as it runs down toward the eave. The cause of the snow melting may be from a combination of factors, but mainly is due to heat escaping the home and causing the roof sheathing and roofing to be too warm. A steeply pitched roof, like yours, will make the situation more likely and the presence of the dormer is also a contributing factor. To simplify the answer to your question, anything that can reduce air movement and heat loss into the attics or increase ventilation will help prevent the ice damming.
From your question, I am assuming that your home is a 1 ½ story home. It may be a 2 ½ story, which will make little difference to the approach we take, but I doubt you would have ventured that high to chip the ice from the roof. I normally begin an inspection of an older home of this design by telling the client that these houses had an inherent lack of ventilation when they were built. This is due to the minimal attic insulation and ventilation practices used at the time and the multiple attic spaces. When insulation levels and air sealing techniques were improved in the later part of the 20 th century, increased attic ventilation became necessary. Most of these homes with dormers and knee-wall attic spaces had little to no ventilation, except at the upper attic. Many knee-wall spaces were improperly insulated between the rafters and these small attics used as closets. This situation dramatically increases the chance of ice damming and moisture intrusion through the roof.
The fact that you have never seen stains in the area mentioned, before this year, does not mean that the problem has never occurred before. What is new, this year, is that the extra heavy accumulation of snow has built up over the entire winter in multiple thin layers. This appears to cause the snow to remain on the roofs in very thick and dense amounts, without being blown off by the wind. The thicker snow will insulate the bottom layers of the pile, warming it and increasing the chance of ice dams. The ice dams will be thicker and heavier than normal and may find new points of entry into the roof, walls and eaves that didn’t exist with the thinner ice of previous winters. The roofing on the home may also be increasingly worn every year, which will be accelerated by the ice damming. This may be the first time that a hole or opening in the shingles or flashing has appeared.
The first thing to check is the method of insulation, and presence of any vents, in the small knee-wall attics on the upper floor. The “closet” in the bathroom may be one of these converted spaces and is likely to blame for the air leakage. Bathrooms are particularly bad for causing ice dams due to the high temperature and moisture content of the air from the shower and tub. If these small attics have insulation between the rafters, and the gable ends or are warm spaces, they must be changed.
Removal of the insulation from between the sloped rafters and insulating and air/vapour sealing the knee-walls, access hatch and floor in these spaces is the first step. Next, roof vents and/or gable vents should be installed to allow cool air to enter the space. This will return the knee-wall area to its proper use as an unheated attic, reduce the temperature of the roofing and sheathing, and prevent the ice damming and moisture intrusion.
It may be difficult to accomplish this entirely until spring, but the inside work may be done anytime. Once the snow and ice has melted from the roof, it can be inspected and repairs made to damaged roofing, flashings or siding on the dormer. Roof vents can then be installed and the moisture damaged area in the bathroom repaired before next winter.