-are there significant differences in the various ice & water shields on the market? -water & ice shield companies suggest coverage in areas like rake edges, non-living areas (garage eaves) and roof ridges what areas do you suggest and is 6' better than 3'? -does it form a vapour barrier? and what precautions are needed to completely cover 2 small sections of roof which actually have rooms below them ? -because of the valleys on the upper portion of the roof water flows down, almost like a drill, onto shingles on the lower roof section. as a result these shingles have lost most of the granules. on the new roof what can be installed in these areas to prevent this or diminish its effects? -is there value in using 25 lb tar paper in limited 4-12 pitch areas ? -do you do roof inspections ? what is the cost ? when could I schedule it
Answer:
As far as I can see most of the difference between ice and water shield brands is salesmanship and it is applied onto the whole roof in case of low slope but only high enough to be at least 9" past the exterior walls on others. Where there is ice and water shield, there is little point in using tarpaper and yes, it does form a VB. In the case of your valley imitating Niagara Falls, there isn't a whole lot to be done about it except to install some creatively designed eaves troughing. That may actually do you more harm on the upper roof than it prevents though. Like most other building inspectors, I do roof inspections.
