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Reduced carbon footprint pier and beam?

Lacunatx | Posted in General Questions on

I’m designing an energy efficient tiny house (14’x26’ foundation, single story) in Central Texas on a zero-slope site with hard-packed gravel soils with a solid granite base at 6ft feet down. I am looking for an energy efficient foundation structure that uses minimal concrete and is cost-effective. I looked at helical piers, but cannot find a trade that will come out to our middle-of-nowhere property. Now I’m considering basic concrete pier and beam with a slip-form perimeter wall made from the copious granite fieldstone that we have on the property. This would give me the sealed crawl space I’m after while reducing the carbon footprint a bit over a solid concrete perimeter beam. I think it makes sense in our hot climate to vapor seal the ground and insulate the perimeter beam to take advantage of thermal coupling, but I cannot find much information about this approach and would love to get feedback. Is a vapor barrier helpful if I’m not below grade? Should I use closed-cell sprayfoam on the perimeter beam to seal the space or is a vented crawl space better to disperse heat? Any potential pitfalls? Thank you all so much!

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Replies

  1. brendanalbano | | #2

    You might look into ground screws. They are the tiny sized version of helical piles, and they might be something that an ordinary contractor can order and install, rather than requiring a specialized subcontractor like helical piles. Because they are smaller, you will probably end up using more of them. I've looked into ground screws and helical piles in an effort to use less concrete, but have not done a project with them yet.

    If you, your engineer, and your local code officials are all willing to get a little adventurous, you could do a wood slab on grade, like outlined in this article: https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-020-wood-foundations-picasso-does-foundations

    Less adventurous would be a concrete perimeter footing, with a concrete-free slab. I'd imagine that in central Texas, your foundations don't have to be particularly deep, so this would result in a relatively low amount of concrete compared to a conventional home. There are a number of articles on Green Building Advisor about that approach. Here are two:

    - https://www.greenbuildingadvisor.com/article/another-take-on-a-concrete-free-slab
    - https://www.greenbuildingadvisor.com/article/200832

    It's definitely worth reading all the comments as well.

  2. AdamPNW | | #3

    Lacunatx,
    The BEAM Calculator developed by Builders for Climate Action is a great tool for comparing carbon emissions of materials, such as a perimeter beam vs helical piles.
    https://www.buildersforclimateaction.org/beam-estimator.html

    It’s definitely helped me with my own home design, I’m planning a perimeter beam with a concrete-free slab (earthen clay floor over vapor barrier, over expanded foam-glass aggregate) so that I’m minimizing concrete AND coupled with the earth for energy-sake.
    Good luck with your project!
    Adam

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