As I posted before I have tar paper on the sidewalls of my house thats been up for a month or two.  Its been kind of beat up and now I’m ready to side the house. I’m putting 3/8 inch foam on the walls then siding with vinyl.  Would it be ok to put another layer of tar paper right over the first as I side or would two layers be a problem? When I get to the windows which have been flashed with self stick membrane to the tar paper what should I do with the second layer.  I know the self stick can’t be freed at the sill and jambs from the original tar paper so should I just go over it with the second layer and any moisture that does get there will run out over the first layer? Thanks. Also , I noticed that wood exposed to the weather for a while turns grey (even PT wood). Does this effect the wood structurally or is it just cosmetic. Thanks again.