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 cost to install a radiant barrier ranges from $700 to $2,800, depending on the size of your roof and the type you choose. Most people pay an average of $1,700 to install a radiant barrier. Foil options, both single- and double-sided, cost between $0.10 and $0.90 per square foot, while spray-on options start at $0.60 and go all the way up to $1 per square foot—which can add up quickly.

Unfaced wall insulation is easier to cut and install, making it the better choice for a DIY project. It’s also more affordable. But if it’s unfaced, you’ll likely need to add a vapor barrier to reach your desired R-value and efficiency, as it doesn’t offer any moisture barrier.

Faced insulation uses paper or foil to create a built-in barrier and doesn’t require an extra step. It’s also more fire-resistant and safe. But it’s quite a bit more expensive and a little bit harder to work with as a DIYer.

Yes, cold walls are a common indicator of poor or inadequate insulation, especially if the walls feel significantly colder than the air in the room. This suggests that heat from your furnace is escaping rather than being retained. The issue could be that the walls have no insulation, or that the existing insulation is old or has been damaged by water, moisture, or pests. Your best course of action is to hire a professional to investigate. An insulation contractor can determine if you need to add or replace insulation and can often perform the work without creating large holes in your drywall. If you suspect the problem might also be related to your heating system's performance, an HVAC technician can take a closer look.