In many cases, buttresses are not the optimum solution for bracing earthbag walls. Post and beam designs are often preferable and have many advantages. Besides being less obtrusive, post and beam designs are suitable for wider range of styles, require less plastering, take up less space, and are faster and easier to build in many cases. Plus, exposed timbers look fantastic! Using poles from a forest obtained with a low cost firewood permit, this option doesn’t have to cost a lot.

You could bury posts within the wall, next to the wall or even set them apart from the wall. One option is to use round posts of say 6”-8” diameter and cut 2” off one side. This provides a flat surface to go against the wall, making plaster work somewhat easier by eliminating recesses behind posts. This also enables you to stack uninterrupted earthbag walls, which is faster and easier than working around posts.

How to connect posts to the walls? Easy. Cut strips of expanded metal lath as ties. Nail one end to the back of the post, bend to 90 degrees and pin to top of bags. You could use the same technique using scrap metal. For pins, strawbale builders make U-shaped pins out of heavy duty galvanized wire.


Comments

Post and Beam Designs — 17 Comments

  1. As a newbie, I’m wondering if I’m understanding things correctly. The posts would be supported by the stem wall (bags of gravel or scoria). Then the whole of the structure would “float” on the rubble foundation. If I were to anchor the posts directly into the ground in concrete, it seems that in an earthquake the posts would move with the ground and be out of sync with the vibrations of the rest of the structure, probably resulting in damage.

    Also do you know where there is a description of how to install rebar vertically down the center of the wall? I see you can pound in the shorter pieces from the bond beam, but installing longer pieces this way looks difficult. I saw a description of doing it for straw bale walls by impaling the bales over short threaded rod sections, which are extended by coupling additional sections as the wall rises. However impaling bags of dirt before tamping and final placement also seems problematic.

    Thanks for all your help. This is invaluable to me and others, too.

    • The posts I’m describing are primarily for wall stiffening. This is particularly beneficial if you have long, unsupported lengths of straight walls.

      Rebar pinning for seismic areas: We’re making drawings in SketchUp right and they’ll be posted soon. Basically, you drive 3′ lengths of 3/8″-1/2″ rebar through the center of the wall in corners and on both sides of doors and windows.

  2. Hi Owen. Your article on post and beam looks interesting and relevant. We have purchased a large lot near Bishop, CA and want to build a home doing mostly our own work. With limited experience, earthbag building seems doable. We’re in a high risk seismic zone and have building codes in effect. At 4000 ft elevation we have moderately cold winters (4300 annual heating degree days) and very hot summer days with cool nights, and 4 inches annual rainfall. I’ve looked at the Cal Earth website. There isn’t mention of heating and insulation, which would be needed in our area. We do, however, plan on a visit there soon.

    Scoria and perlite are abundant here. There is a perlite mine nearby. Do you know of any earthbag buildings using these materials in a seismic zone? Would perlite have enough weight and be strong enough in compression for use in loadbearing bags, or should it be relegated to infill situations?

    I’m planning to build a gardening shed of 120 sf (the maximum non-permitted size) to get experience. Tentatively it will be yurt-shaped with 12.4 ft inner diameter, and have a bay window facing south for starting plants in spring. Glazing will be Kalwall ‘Sunlite’ flexible translucent fiberglass, probably double-paned. (It can be bent around to form a bay.) I was thinking of digging out the interior and wall area down a foot and filling with scoria for a combination insulated subfloor and rubble foundation. The walls would be bags of scoria set directly on the rubble. My impression is that scoria doesn’t wick-up moisture. I would use posts around the doorway and window per your suggestion, to avoid buttressing, but otherwise, walls would be loadbearing. Do you think a bond beam would be necessary for such a small structure?

    I welcome comments or suggestions. Thanks,

    • You would need to experiment with loadbearing perlite walls. It should work okay on small structures with lightweight roofs like the one you’re describing. Scoria will definitely work.

      You’ll likely need some temporary bracing to support the walls as they’re being built to keep them aligned. You’ll definitely need a bond beam to tie the walls together. Add vertical rebar pins down through the center of the wall on each side of doors and windows and rebar from the bond beam down into the top 24″ or so. Also, I would use plaster mesh or fishnet on both sides of the walls and tie it together. To do this, lay lengths of poly baling twine between courses as you’re building the wall. So to recap: the walls will be a little shaky as you’re building, but they’ll be strong if you follow these steps.

      The same thing can be done for larger structures in seismic areas if you add more posts.

      I read that scoria does wick moisture. You’ll need to confirm this. Kelly Hart’s house was in a dry, cold climate and so wicking wasn’t an issue for him. Add 6 mil poly as needed to keep water out.

      In freezing climates, gravel is best in rubble trenches to ensure adequate drainage.

  3. This is my first time I visit your site and I find it interesting with great tips and suggestions you share here. Posts and beams are quite hard to build actually. They require accurate measurements and architecture to make them perfect and a good stronghold for any building. What I liked even more with your post is that you have given some more ideas as to what materials can also be used for structuring posts and beams.

    • I agree that posts and beams do take extra work and care, but they are well within the capability of many or most owner builders. For instance, complex joinery is not required if standard fasteners are used.

  4. Hi! I am a senior student of BS Human Ecology in the University of the Philippines Los Banos and currently enrolled in a course “Housing”. Im writing a paper about an application of sustainable housing which may conform to the country’s need to improve the evacuation sites especially after the damaging natural disasters of the previous year. I have been reviewing about the Earthbag Bag Building system with the many write-ups and information about it on the web.
    Alert level 4 was raised before 2009 ended until first week of January 2010 when Mayon Volcano threatened to erupt which resulted into more than 10,000 families
    or 47,766 persons to be evacuated and designated in 45 schools in surrounding cities and municipalities. Unfortunately, the displaced residents
    experienced overcrowding, inadequate space to sleep and rest, missed income opportunities, and health and sanitation problems. These all caused the evacuees
    physical, mental and emotional hazards.

    This is a reflection of unplanned and unprepared disaster management, since these kind of situations expectedly and naturally occur in the Philippines. I believe
    evacuation centers are really important since these become the temporary shelter for the victims of calamity. Evacuation sites are supposed to house and protect the
    affected people. instead school buildings and its premises are always converted into evacuation sites.

    With these, I have been curious about the potentials of sustainable (durable,
    inexpensive and ecologically-friendly) houses to be built as evacuation houses
    in the areas which are often affected with natural calamities, like Albay in Bicol which is the location of Mayon Volcano (the most active one in our country).

    I think the Earthbag Building is one of the potential housing system that is appropriate
    for this purpose. There had been many
    information available in the internet, however, I want to elaborate more on its results since its application in the Philippines. The problem is there had been no follow through information after it was said to be built as school buildings in three provinces in our country. May i ask your opinion about the idea i am proposing and im wondering why this project had not been sustainable in the Philippines.

    Thank you very much for your help. its a useful site!

    • Earthbag building is ideal for just the sort of thing you are describing. As always, you need to use good design to prevent problems. I hope you pursue this idea further. Let us know if we can help.

  5. Are there any pictures or links to examples of this ‘post and beam with earthbags’ method. This idea is what I want to do, but I am unsure how.

  6. Hi Owen,

    Thanks for the reply. I think that perhaps I worded my post vaguely as what you outlined (laying bags end to end with layer of insulation on outside doubling as a moisture barrier) is what I intended to convey.

    What is the advantage to having a breathable wall? Will floor and ceiling vents not be enough to move moisture out of the dome? I am planning on having a rather large earth berm and moisture is a large concern of mine. I have read plenty about having proper drainage, but I still feel that a moisture barrier would be necessary especially during spring melts when water seems to be flowing everywhere.

    Also, with my large earth berm I am concerned about the structural integrity of the dome. Walls made with lighter bags (filled with say scoria or pumice) may not stand up to forces of heavy earthen banks weighing on them.

    Even with standard bags I wonder if I need further reinforcement. I am planning on having roughly 180 degrees around the dome bermed, with the berms reaching about 3/4ths of the way up the dome. I am planning on building a dome 14ft in diameter with the traditional “peace dome” type shape.

    Thanks for your continued feedback.

    • Moisture can get trapped in walls behind impermeable moisture barriers. This is less of an issue with scoria, since any moisture could travel down through the wall. I recommend quality exhaust fans for the stove and bathroom that are vented to the exterior. This will eliminate much of the moisture.

      Yes, you’ll want to use 1-2 layers of 6 mil poly for your berm.

      Domes are very strong and will easily withstand the force of the berm (including scoria filled bags) if they are symmetrical and built correctly (2 strands barbed wire, buttresses next to large openings, etc.).

  7. Hi,

    I have recently stumbled upon your blog. It has been very helpful in forming my plans to construct an earthbag dome of my own this summer.

    Living in northern NH, insulation is a large concern for me. I was wondering how practical it would be to insert a layer of insulation into the bag prior to filling it with dirt. I was thinking about the flexible bubble type insulation with the reflective coating (like prodex or reflextix). My thought is that if a wide strip of this insulation were placed at the outside (or maybe even inside) edge of the bag before it was filled it would create a series of overlapping layers of insulation around the dome.

    Has anyone tried applying conventional insulation to an earthbag house?

    Thanks for you help. I love the site.

    • What you’re proposing could work, although I”m not sure exactly where you’re proposing to put the insulation. It sounds like you plan to put the bags side by side. Most earthbags are placed end to end. Anyway, you could put strips of insulation under each course of bags. The end result would be a shingle effect of long horizontal strips that not only insulates but also helps shed water. You would need stucco mesh on top so the plaster has something to bond to.

      Have you read this article on insulated earthbag houses? This article offers three insulating options that are low tech and ‘breathable’ (allow moisture to pass through).
      http://www.earthbagbuilding.com/articles/insulated.htm

    • Hi Skenderbeg,
      I’ve been looking into building with earthbags here in New Hampshire. i haven’t had the chance to work on one yet or even to see one in person.
      I’m wondering how you’re coming with your project since january. i’d love to have some hands on experience if you’d like some help.
      Please let me know if i can help or if i could take a look at your earthbag dome in person.

      does anyone know of any other earthbag projects in New Hampshire?

      thanks

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