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Community and Q&A

Is this my best foundation choice?

Kendo64 | Posted in Plans Review on

First off, Green Building Advisor has been invaluable in my research to design my future home and have found it well worth the membership cost. So thank you, to all you who have made this site what it is.

I am planning on building a 1700 sq ft ranch style straw bale house near Cortez Co (climate zone 5B). Currently I am sketching up layouts, making lots of notes on building techniques, choosing home fixtures (doors/windows), HVAC systems and researching different build options, before I take my plans to an architect so he can refine and incorporate them.

The major issue with the very gently sloping building site is that the soil is moderately expansive. As I desire only a ranch style home (no basement as that would mean stairs, which can be a hindrance in later years) my foundation choices are much more limited. After looking at several options, I believe pier and beam foundation with a crawl space is the best option for my home. The positives of this foundation are:
– Pier and beam foundations have a proven track record in expansive soil
– I am able to easily insulate the raised floor over the crawlspace
– The crawl space gives me access to plumbing, electrical, and whole house vacuum piping, all of which can be more difficult to distribute when dealing with straw bale exterior walls.
– I can have an electrically heated radiant floor under bathroom tile floor without having a slab suck away the heat. Note: house will use ductless mini-splits.

I considered slab systems such as Wafflemat, which may be a great solution for my unheated steel outbuilding, but it seems everything I looked at just didn’t have the benefits of the pier and beam with a crawls space.

So my question; is there a foundation/flooring system better for my situation? I need it to handle expansive soil, it needs to be insulated, and of course I want it to be cost effective.

I have attached a drawing showing my proposed foundation arrangement. The 2×4 pony wall is there to support the wider and heavier straw bale wall.

Thanks, Ken

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  1. GBA Editor
    Martin Holladay | | #1

    No matter what advice you get on this forum, I urge you to take it with a grain of salt.

    If you are building on a site with expansive soil, talk to an engineer and follow the engineer's recommendations. This is not the type of topic where you want to get your advice from a web forum.

  2. user-4524083 | | #2

    Ken - 1.) The crawlspace does not appear to be insulated, and you plan to have plumbing down there. This may be a faulty plan. 2.) I'm not sure why there are piers below what appears to be a footing, that appears to be 4' down or so. Why not place a good sized footing below the frost line and eliminate the piers? 3.) Martin's advise is good. This site is great for energy efficiency questions, but not so much for the realm of soils and specialized foundation systems, though you may get lucky with some informative participants. Best of luck to you on your project.

  3. Kendo64 | | #3

    Thanks for the responess.

    Kevin you are correct I do need stem wall insulation to protect my plumbing.

    The footing is actually the beam and its mass rests on the piers which provides a stable base. The piers go much deeper than the frost line as the problem is not frost but moisture content causing the clay in the soil to expand and contract. The pier lengths were not drawn to scale in this drawing.

    I agree the Engineer advise is required, but before going there I would like to have some potential solutions to ask about.


  4. BillDietze | | #4


    I've been wrestling with this detail as well. I'll someday be building ~ 70 NE of you and have expansive clay as well. Second round of soils tests this summer, then get the engineers involved. The pier & beam foundation, with void forms under the beam, is the way I'll probably end up going, but in the resulting crawlspace I've been considering gravel then 4 - 5 inches of foam, then a 2" thick non-structural slab on the foam (the so-called rat slab). The air barrier is poly on top of the foam brought up to the beam/foundation walls (with 2" of foam between the slab and the beam). That brings the entire crawlspace into the conditioned envelope. The foam and slab can move up and down independently of the foundation and because nothing sits on the slab, that's ok. Easy access to the plumbing.

  5. BillDietze | | #5


    If you find a company you like for placing the piles please post the firm's name! I can easily use a firm based in Cortez, Durango or Montrose. In any event, when you get the foundation placed, take pictures and post an update!

    Thanks in advance.

  6. Kendo64 | | #6


    I have been talking to some more builders in the area and they are recommending just to over excavate, refill with good non-expansive base, and then make sure you have a good foundation drain installed around the perimeter. It would be nice if I can get away with this approach but I need to investigate more.

    Biggest problem I have right now is I currently live 7 hours away South of Dnever and many of the builders (especially the good ones) in the Cortez area do not advertise except by word of mouth. So when I come down to visit the property I spend much of my time talking to neighbors, building supply store employees and just people I meet, trying to find leads.

    IF I can get away with just the replacement of the base soil I would be tempted to use a monopour setup using fast foot and ICF stem wall. Then I would likely finish the crawl space in the same manner as you described.


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