It is relatively common practice to lay new sheathing over old, but I don't like it, and whenever we are faced with this, we remove the old and install the new. I'm going a reroof in two weeks time, where we are removing all the old roof covering, and the old sheathing (delaminated and rotted 3/8 plywood) and replacing it with new 5/8 T&G plywood.
My reasons were: 1) the old stuff has no more structural integrity, and at best, it is a spacer between the new sheathing and the rafters onto which the new sheathing is fasted. 2) The old stuff is full of mold. Why build a new roof with the mold-starter built in? 3) If and when you will sell the house, someone will go into the attic and see all the old rotten and delaminated wood. How are you going to convince them that you've got good stuff hidden away behind it?
While we've got the sheathing off, we are also going to ensure that the ventilation channels (from soffits to the main attic area) are clear and open. The homeowner wanted to have a proper solution, since the two roofs he installed in the twenty years he's lived in the house have failed prematurely. |
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