I am in the process of renovating my 1950s New England ranch. I am currently working on the attic and once the weather warms up I will be placing 4" of polyiso on the sheathing.

Because the house is board-sheathed I'm unsure about how to air seal it. One local architect, Bruce Coldham, is in the habit of wrapping the sheathing in Ice & Water. Is this a reasonable approach for me to take? The existing wall is 2x4 construction which will be dense packed with cellulose. Is this idea just nuts? Ice & Water isn't cheap or easy to work with.