I’m going to be putting a new dormer on roof and have a question about the vapor barrier. My architect recommended the standard Tyvek. However, a friend who is an architect told me that he recommends the use of good ol’ fashion tar paper instead. He’s found over the years that a lot of moisture has, in fact, gotten trapped and has caused rotting of the sheathing. Does anyone have any experience/recommendations/warnings for the use of either Tyvek or tar paper? Your feedback will be appreciated.
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First off, neither Tyvek nor tar paper is a vapor barrier -- ignore any advice from anyone who refers to them as that. Beyond that, the Tyvek/tar paper argument is a religious one.
Agree w/ Dan ... your 'architect' hopefully didn't refer to Tyvek as a vapor barrier. Tyvek is an air barrier. I think felt paper would be considered similarly, but I think it's real job is more like a underlayer rain screen (i.e. bulk water) ... but I admit that the traditional function of felt paper elludes me (as it does many people ... it's just been historically always used).
Tyvek should NEVER trap moisture behind it ... if moisture does get trapped behind it ... I don't think it would be the problem of the Tyvek that causes it.
You are either interpreting what your 'architect' is saying or he doesn't know his materials like he should.
Since the advent of Tyvek, there have been proponents and arguments about the benefits of both Tyvek and felt paper. Legitimate arguments. So the jury is still out on that. For a small dormer (even a large one), I'd do the felt paper ... you might have to buy an entire roll of Tyvek ... quite expensive. One big argument against Tyvek ... if it isn't continuous across the entire house, it's benefit is greatly diminished ... you are doing only a dormer? Keep it simple ... go drag out some left over felt from your or your neighbors garage and do it!