[sky's]

Originally Posted by DickR

Indeed, Grace's Ice & Water Shield or a similar product must be applied at the roof edge, going at least to a point two feet past where the wall is underneath. The rolls are three feet wide, so that a single roll will suffice for an overhang up to a foot past the walls. A wider overhang will require a second roll. The material also should be applied over valleys in the roof surface.

Whether or not to apply the material over the whole roof requires some thought. It may be appropriate for a roof with very low pitch. For a more normal roof pitch of, say, 5/12 or steeper, total coverage is not required. There also is the matter of permeability; the stuff is a complete vapor barrier, meaning the roof deck will not dry to the outside and thus must be able to dry to the interior. This is not a problem if there is a vented attic space underneath, hopefully with continuous ridge and soffit vents. If you have a cathedral ceiling below, with vapor retarder and insulation applied directly to the rafters, then you really should not have Ice & Water Shield applied to the whole roof surface.

If you don't have ridge and soffit venting, a reroof is a good time to have such venting added. Simple gable end vents really don't do an adequate job of venting. If you have gone into the attic in winter and found that there is a lot of dampness under the roof deck, this tells you two things. First, there is too much leakage of air (and humidity) from the house into the attic space, costing you a lot of heat and creating conditions favorable to rot and mold on the roof deck. Losing heat to the attic also can result in a lot of ice dam formation and the damage that can cause. Second, the moisture that gets into the attic is not being vented properly. Continuous ridge and soffit venting takes care of this.

all of the points mentioned above are very good. Never let a roofer talk you into a "go over" or add a second layer, reduces the life of the top layer by as much as 10+ years. Ice and Water Shield is a very good product and yes depending on your roof pitch will determine on how much to use. A roofer that recomends only 3 ft course on the bottom may also be using a cheap underlayment like felt paper or tar paper a good undelayment like IKO Roof Guard is a very good underlayment combined with Ice and Water Shield or IKO Gold Shield. and most importantly is roof venting can't express that enough. soffit vents combined with a ridge vent is very important. i worked on a home this summer that has no venting what so ever the home owner thinks they have a great house maybe but the last roofing company failed to inst a venting system, the current roof that is less than 10 years old looks like it is 20 years old because of lack of air flow. and last but not least don't take the lowest bid and make sure your contractor is INSURED. sorry if this seems overwhelming but there is a lot homework that needs to be done and this forum is a good start. best wishes if you need help you can call me or send me a e-mail.