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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. 

The most insulative type of insulation for behind drywall is spray foam insulation, but this is the most expensive insulation available. The most common insulation—sometimes considered the best for the value you get for the money—is fiberglass roll or fiberglass batt insulation, which is significantly more affordable but also far less insulative. The best kind of insulation for your house will also vary based on the climate in your area, your budget, and more. A professional insulation company can help you decide which type is best for your home.

For standard 2x4 walls, the ideal insulation has an R-value between R-13 and R-15. This level of insulation, typically around 3.5 inches thick, fits well within the wall cavity. Common options include fiberglass batts and spray foam. The best choice for your home can depend on your climate; use R-value maps, like those from Energy Star, to determine the recommended level for your region. For colder climates, you might also consider adding exterior insulation for greater efficiency. Always check with your local building codes to ensure you meet any required standards.

The best type of attic insulation depends on where you live, your budget, and what stage of construction the attic is in. For example, if you're building a house, then structural insulated panels are a worthy investment since they're easy to install during construction and they're the most energy-efficient type of insulation.  

Additionally, if you live in a very warm climate, then you can potentially save quite a bit of money by opting for reflective insulation, which is more affordable than comprehensive insulation but doesn't work well for cool climates. Blown-in, loose-fill, and spray foam insulation are all great options for attics in moderate climates.