I was just reading some articles on the U Mass Building science website. Well he said that he liked felt better and for good reasons. He did perform some hydrostatic tests(I guess he sprayed the things with water) on felt and tyvek. felt lost 30% of water after 2 hours. tyvek lost none. he considered both good results, tyvek being superior in this instance. tyvek has better perm rating than felt 15#. 15 has 6 when dry and climbs all the way to 60 at 95 RH. Which is a good thing since you want air moving inand out. so in other words, felt has a much better perm rating, when it is wet. So,, his conclusion was that when water gets behind your building paper, felt will do a better job at drying out the sheathing. The article also pointed out that unprimed wood siding act as water reservoirs, and when the sun comes out, water vapor gets behind felt or tyvek. Well since felt performs better under damp conditions, it will allow more water vapor to espace from the wrong side of the “wrap”. Another article I read in FHB  said that paper gets wet from water on both sides and dries out the water. Which is good and not possible with tyvek.

A little refresher never hurts. So, use felt and back prime your wood siding. It will save us all from a lot of trouble.

On the last job i was at, the siding contractor was caulking all the hardie plank joints. Plus all the cedar shingle corners were not weaved. Well, those that don’t know this, you flash behind the joints, and you build your shingle corners by stapling your corners before hand. Later….