The lifespan of crawl space insulation depends on how well you maintain your insulation and the type of insulation. Fiberglass will need replacing every 15 to 20 years on average if you don't have a vapor barrier in place. If you do have vapor barriers in place, then your insulation could last much longer. Spray foam insulation can last anywhere from 80 to 100 years. 

R-30 insulation is better for higher thermal resistance, but whether it’s "better" depends on the application. R-30 is much thicker and suited for areas like attics or floors in cold climates, where more insulation is required. R-13, on the other hand, is thinner and works well for 2x4 walls or milder climates where less insulation is sufficient. Choosing between R-13 and R-30 depends on the area being insulated and the climate. For example, R-30 provides more insulation but may not fit everywhere in your home.

Yes, you can install insulation behind drywall yourself, but only if your walls are not finished. If your studs are exposed, installing fiberglass insulation in roll or batt form is very straightforward and just requires a few tools and some safety equipment. If your walls are already finished and you’re looking to add insulation, it’s better to hire a professional, as you’ll likely need blown-in insulation, which can be dangerous to work with and a challenge to get into the proper areas in your wall voids.

Reflective and high R-value batt or roll insulation are often considered energy-efficient, offering significant thermal resistance benefits.