I have a house that was built in 2008 with expanded polystyrene in the walls and roof. I was wondering how much longer that material is going to last before it starts to degrade or lose its properties. Is it normal for it to still be working well after almost 20 years, or should I be thinking about replacing it?
Expanded polystyrene holds up pretty well - it can typically last 50 years or even longer without issues if it's not exposed directly to sun and extreme temperature swings. What you had installed in 2008 should still be working perfectly at nearly 20 years in, so it's not odd at all that it's still insulating well. Real degradation starts when it gets a lot of UV radiation or constant moisture exposure, but tucked inside your walls like yours is, it's well protected. Unless you notice it's not insulating like it used to or you see it crumbling, you don't need to replace it right now.
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