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Community and Q&A

Insulating storm shelter

Jking008 | Posted in Green Building Techniques on

Hello I am in the process of building a storm shelter / office. I live in the panhandle of Florida close to the southern Alabama line so we are lucky to be high enough in elevation for storm shelters and basements.

I am not building your typical underground shelter but I am using a more environmentally friendly approach by using the earth bag method using an adobe clay mixture in netting type sand bags with 10% Portland added to the mixture for the walls. The issue I am having and trying to figure out is how to insulate the structure to prevent moisture build up.

I was looking into the closed cell foam spray for the exterior of the structure before back filling.

• would this work for my application?
• if so how thick should the structure be sprayed?
• should I also spray the foam down under the slap before pouring to?
• do I need a vaper barrier (6mil plastic?) in conjunction with the exterior foam spray?
• should the vaper barrier, if needed, be on against the walls then the foam or Vise-verse?
• should I spray foam the interior of the exterior is spray foamed?

Sorry for all the questions, this will be the first under grade project I have done and want to make sure to get it right the first time around.

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  1. GBA Editor
    Martin Holladay | | #1

    If you are building an underground office that you hope will stay dry, and you are using earth bags to build your walls, you have your work cut out for you. That's a challenging project.

    It's always hard to keep an underground room dry. Using earth bags complicates your work. For one thing, it's harder to insulate and waterproof an earth bag wall, because it isn't smooth and flat. You'll need a lot more (expensive) closed cell spray foam than you would need with a conventional concrete wall. And I'm not sure how "green" all that spray foam will be.

    The best approach is to use a poured concrete wall, and to skip the earth bags. Consult with a reputable architect or builder familiar with waterproofing details.

    Closed-cell spray foam can be used to insulate the exterior of a foundation wall. It can also be used to insulate under a concrete slab. But in almost all cases, rigid foam is a better choice (especially if you have a smooth, co-planar surface like concrete rather than a bumpy wall made out of earth bags).

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