You’ve really done your homework here, and honestly, I think you’re asking all the right questions. That “what’s under there?” concern is something I see a lot, especially with homes from the 50s. Even with a thorough inspection, there’s just no way to know for sure what’s going on beneath old shingles until you pull them off. I’ve seen cases where everything looked fine from the attic and the surface, but once the tear-off started, there were hidden spots of rot or even some pretty gnarly mold patches that would’ve kept growing if left covered up.
The weight issue is another big one, especially in areas like upstate NY where snow loads can get intense. I’ve come across rafters that were never designed for the extra layer, and over time, you start to see subtle sagging or even cracks in the plaster below. It’s not always catastrophic, but it’s definitely something you don’t want sneaking up on you.
Warranties are a bit of a minefield, too. Most manufacturers are pretty strict about their terms, and I’ve seen claims denied just because there was an overlay. If you’re planning to stay put for a while, having that peace of mind is worth a lot.
On the landfill side, I get the hesitation. It does feel wasteful, but you’re right—if you ever have to do another replacement, you’ll be dealing with double the debris. Some places have recycling programs for asphalt shingles now, so it might be worth checking if that’s an option in your area. Not a perfect solution, but it takes a bit of the sting out.
If you do go for the full tear-off, brace yourself for a few noisy, messy days, but most folks I’ve worked with say it’s worth it for the peace of mind. Either way, sounds like you’re making a well-informed decision. Sometimes there’s no perfect answer, but being proactive goes a long way.