I've noticed similar results with felt underlayment myself—had it on my garage roof for about 10 years now, and it's still holding strong. But I do wonder if climate plays a bigger role than we realize. Maybe synthetic really shines in harsher climates or extreme temperature swings? Felt seems fine here, but perhaps in areas with heavy snow or intense sun exposure, synthetic might justify the extra cost...
I've seen felt underlayment hold up surprisingly well in moderate climates, but you're definitely onto something with climate being a major factor. In my experience, synthetic underlayment really starts to justify its cost when you get into extreme weather conditions—especially heavy snow loads or intense UV exposure. Felt can become brittle or degrade faster under harsh sunlight, and in snowy regions, the freeze-thaw cycles can cause it to deteriorate quicker.
I worked on a roof replacement last summer where the homeowner had synthetic installed about 12 years prior, and honestly, it looked nearly new underneath the shingles. On the flip side, I've also torn off felt underlayments that were barely recognizable after just 7-8 years in harsher climates. So yeah, felt can be perfectly fine if your climate is mild, but synthetic is probably worth considering if you're dealing with more extreme conditions or want that extra peace of mind...
That's interesting, I've always wondered how much attic ventilation affects underlayment lifespan.
"Felt can become brittle or degrade faster under harsh sunlight..."
Makes me think, could inadequate attic ventilation trap heat and moisture, speeding up the degradation even more? I replaced mine recently and noticed some areas were way worse than others, even though the climate's pretty consistent here. Maybe ventilation plays a bigger role than we realize...
You're definitely onto something with ventilation. I've inspected quite a few attics where poor airflow led to uneven underlayment wear—some spots practically crumbling, others holding up fine.
Seems like it does, from what I've seen."Maybe ventilation plays a bigger role than we realize..."
Had a similar experience last summer—was helping on a reroof job, and when we peeled back the shingles, the underlayment was toast in some spots but surprisingly decent in others. Turns out the homeowner had installed extra insulation a few years prior, but didn't bother with soffit vents. Basically created a mini sauna up there... moisture trapped, underlayment cooked. Definitely made me pay closer attention to ventilation details after that job.
