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Has anyone used spray foam insulation on an earth bag home?

Posts: 5
Location: Central Maine
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Hey everyone,
I am in the planning phase of our future earth bag house and had a question regarding insulation. Has anyone used spray foam insulation on the exterior of their earth bag house? We will be in central Maine and will need to insulate it in one way or another. I've come across a few different ideas, but this one seems easiest. Just curious if anyone has done this before and what you used to cover it (just earthen plaster or stucco or ?). Also if anyone has any other advice or suggestions on insulating earth bag houses in general would be appreciated as. Thanks!
Posts: 1398
Location: cool climate, Blue Mountains, Australia
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Spray foam is PU foam and very enviro-unfriendly and unhealthy on the top of it. And it breaks down in UV light as there is always a bit of light it will break down after a few years.
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I'm not aware of any projects doing this, but I think that it is an awesome combination. The closed cell spray foam blowing agents being used in the last few years (solstice and similar) have a much much lower footprint. By grabbing a complete air and vapor barrier on the exterior, and seamlessly insulating the exterior of all that mass, that house, properly designed and built, should have a tiny heating/cooling load for a very long time. Stucco over spray foam over Adobe is very popular and successful in northern NM. Stucco over SPF would keep all insect, UV, fire away from the  SPF. In your climate, I'd just keep the inside as your breathing side. If you can afford it, it'd be awesome. I do know of exterior rigid foam over EB.
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Location: Ashhurst New Zealand
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I wouldn't use it, for a few reasons:

1. Environmental footprint of manufacture + transport...the stuff's hardly a poster child for earth friendly materials.

2. Offgassing into living space. Most PU for direct application (as well as adhesives like Gorilla Glue) contains methylene diphenyl diisocyanate, which has all sorts of toxic effects, many of which are known to the state of California.

3. Breakdown under UV exposure, as mentioned above.

4. The stuff traps water amazingly well (lesson learned the hard way when I used it as a teenager to fill rusted quarter panels on my beater first car). This makes me doubt that it's breathable, which is a red flag for something that will be part of the building fabric.

According to this article there are some possible green alternatives: https://www.scientificamerican.com/article/better-home-insulation-needed-to-ward-off-chemical-exposure/  I have no idea about pricing, availability or long-term performance on these but they look attractive at first glance.
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