30 lb felt will last much longer then 15lb its thicker and offers more protection especially if you loose a shingle. cost might be the factor sometimes 15lb would be less expensive, but after all it is your home you have to make that decision, in my honest opinion the roof is the most important part of a home
I would only use use the best quality material that offers the longest life,cheers!
In my opinion, felt paper is out of date (old school). There are much better products than felt paper. I use synthetic underlayment which is tear resistant and if nailed properly, slip resistant. Synthetic underlayment is also much much lighter. You also get 10 Sq per roll in most cases. In my area I usually pay $70 per roll. Which is much more cost effective compared to felt. I’m not sure why they still even make felt paper anymore (for roofing that is)
I have been installing roofing systems with asphalt felt for many years. The rule of thumb is to install 15# asphalt felt on pitches under 7/12. 30# felt is normally used on roof pitches over 7/12. The reason for the thicker felt is because the thinner 15# felt can rip from foot traffic during the installation.
Overall the market is changing to synthetics. Depending on the shingle (check product specific underlayment requirements) the Rhino 15# synthetic is close in price to an asphalt felt and can be used with almost all asphalt shingles.
I agree. Stay away from felt underlayment. They are old school and the alternatives are far superior. Roofing is not an area where you want to skimp to save a few bucks. A little more now is cheap insurance for the long haul.