Presently, I have been dealing with this very same issue. Due to delays (i.e., weather, stucco application, etc.) in adding the top material (Spanish Tile) to our Mediterranean house build, we have noticed our 30 lb. felt exposed since Oct. '13. It is now March 2014. Much of what I am about to say has been purely from self-education and persistence in uncovering the truth. The original plan was to apply Ice & Water Shield (Guard). This product does contain a published exposure rating of approx. 3-6 months. However, the reason why felt does not is because it isn't meant to be exposed, period. There is supposedly both installed, but why the felt was not delayed in being laid is beyond me, as this was the plan. I was curious what was used on my roof. This roofer it had been expressed by our Architectural Consultant who works for a premiere tile company representing not only them, but others, of being reputable & in business for eons. He went on to say do not think that their bid being the lowest is short changing either you nor them. They were confirmed, as being top-notch. They only do hard roofing. Having picked up debris, trash, etc. along the way given we have poured our heart and soul into the build on a farm I searched for something to identify what felt was used. It was Tamko 30 lb. from a torn wrapping found near the property. Holding this up to what is shown on-line confirmed the product. The roofer had mentioned to me, that they usually like to have the felt covered within 30 days, yet what was discussed with the builder was different. Both GAF and Tamko (mostly Tamko) confirmed your question. GAF suggested it, but they did not state for certain, as they do not deal in the product as much as others. After having called Tamko's Technical Division I asked, "Is the reason why felt doesn't list an exposure time is because it isn't meant to be exposed and covered in approx. 30 days." His reply was as follows. "Your answer is partially correct. It isn't given an exposure time because it isn't meant to be exposed, however, it's top finishing material should be placed immediately." As far as the blogger who's client did not budget for roofing as being a priority is just poor planning. As far as, the blogger who mentioned he would not leave the felt exposed at all stands to be the only individual with correct thinking. I hope this helps, though is far beyond the time the original post was made. Sorry so tardy....better late, than never. Perhaps Custom Home Building could be referred to as a Cold War. Because even Ronald Reagan said, "Trust, but Verify", Ronald Reagan As and aside, for those who borrow the funding choose a reputable lender, as those involved with your project will sit more straight in their chairs when it is reminded, that the client doesn't technically own the house, the Bank (Granddad) does. Ciao!
