Best exterior insulation for a hot, humid climate?

[MattD]

I'm finishing a weekend cabin near Baton Rouge and planning the wall assembly for our hot and humid climate. The current plan is to wrap the sheathing with Tyvek, then add a layer of continuous exterior rigid foam insulation before installing fiber cement siding on furring strips to create a rainscreen. I'm debating between using 1 inch thick plain XPS foam vs using 1/2 inch foil faced polyiso to take advantage of the radiant barrier effect from the air gap. My main question is whether the added performance of the radiant barrier in our climate outweighs the higher R-value of the thicker, plain XPS foam. I'm trying to find the most effective system for reducing heat transfer over the long term.

 

[Fukien_Monk]

Don't overthink the shiny stuff. Radiant barriers only work when they face an air gap, and in humid Louisiana heat most of your gain is from raw R-value. Go thicker with XPS. Half-inch foil sounds clever, but you're giving up insulation depth for marketing buzz.

 

[Lauren G]

I'm finishing a weekend cabin near Baton Rouge and planning the wall assembly for our hot and humid climate. The current plan is to wrap the sheathing with Tyvek, then add a layer of continuous exterior rigid foam insulation before installing fiber cement siding on furring strips to create a rainscreen. I'm debating between using 1 inch thick plain XPS foam vs using 1/2 inch foil faced polyiso to take advantage of the radiant barrier effect from the air gap. My main question is whether the added performance of the radiant barrier in our climate outweighs the higher R-value of the thicker, plain XPS foam. I'm trying to find the most effective system for reducing heat transfer over the long term.

For your Baton Rouge cabin, go with ½ foil-faced polyiso and a ventilated rainscreen. It's better at blocking heat than 1 XPS in actual conditions. That radiant barrier mixed with clever wall design really helps in hot weather.

Still not sure? If you can afford it and have enough wall depth, try ¾ foil-faced polyiso. Otherwise, layer polyiso over a bit of XPS to get the best of both worlds.

 

[HeyRee]

I'm finishing a weekend cabin near Baton Rouge and planning the wall assembly for our hot and humid climate. The current plan is to wrap the sheathing with Tyvek, then add a layer of continuous exterior rigid foam insulation before installing fiber cement siding on furring strips to create a rainscreen. I'm debating between using 1 inch thick plain XPS foam vs using 1/2 inch foil faced polyiso to take advantage of the radiant barrier effect from the air gap. My main question is whether the added performance of the radiant barrier in our climate outweighs the higher R-value of the thicker, plain XPS foam. I'm trying to find the most effective system for reducing heat transfer over the long term.

Foil-faced polyiso in your rainscreen bounces back a ton of radiant energy (90–97%), cutting down heat getting into your walls. XPS has a higher R-value, for sure, but radiant heat is what you should worry about most in your area.

 

[MattD]

I went with 1" XPS and skipped the radiant barrier since I couldn't guarantee a proper gap. Install's underway and already noticing a difference indoors. Might try foil-faced board next season if I can build in the spacing. Anyone here ever test polyiso in humid zones like Baton Rouge?