Using light straw clay (slip straw) as interior wall fill — 18 Comments

  1. I am looking at packing light-straw into walls that have bathrooms on one side. Any thoughts on putting green-board (water proof drywall) on one side and plastering the other side of light-straw interior walls?

    • I have almost no personal experience with that product. However, an internet search reveals that green-board is not really waterproof, just water-resistant. See, for example: I cannot find a vapor permeability rating for it, which is the most important thing to know as far as how it will affect the durability of straw-clay.

      My guess is that rather than the greenboard itself, it would be what you put on top of it that really restricts vapor permeability. For example, latex paint has very low permeability and can lead to moisture problems. However, if you are able to prevent liquid water from getting into the wall, and if water vapor is able to dry to the other side, and if you live in a good drying climate, I expect you would be fine. Make sure that the straw-clay is fully dry before you install the greenboard, if you decide to go that way.

      Also you should know that straw clay and earthen plasters are unlikely to be damaged by water vaopr alone as long as they can dry. I know people who have used clay plasters over regular drywall over straw-clay in bathrooms with no problems. Of course I would use something more water-resistant, such as tile or a sealed lime plaster, in the shower and around sinks and tubs.

      Michael G. Smith

  2. Light Clay Straw construction is now allowed in the 2015 International Residential Code Appendex R. Starting 8 Feb. I have used this method with a earthbag foundation to make a solid chicken coop. Its a mess to do but FUN!!! Plan to build a small Bio shelter to raising fish. It will be passive solar and collect water.

    • Great news! Please send 1-2 good photos and a few paragraphs for a blog post if you can. And send a link to the formal news source if possible

  3. Is there any reason that you need 16″ spacing on studs for this form of construction for anything that isn’t a bearing wall? Seems to me that this lends itself to timber frame construction and filling in 4 to8 foot bays at a time.

    To the others who commented on exterior walls: You need to take the same care cladding it as you do with strawbale, and the same care with things that go through the plaster. (Window frames and electrical outlets. In a cooling climate you want the interior plaster to be about 1/10 the permeability as the outer plaster. This allows the wall to disperse water vapour faster than it’s accumulating it.

    For those of you who have to live with the house while you are doing this, a layer of clay and lime whitewash will give you a lot of temporary fire resistance until you get the plaster up.

    • I recommend using thin bamboo or something similar in the center of the wall to reinforce the straw clay. The wider the stud spacing the more important this is..

      Straw clay was used as post and beam infill for centuries in countries like Germany. Maybe you could locate an old book in the library to learn exactly how they did it.

  4. Hi
    Great video thanks.I’ve been building super adobe domes lately and have really got into bioconstruction in general.I’m in the process of renovating my very small stone cottage here in Spain and I want to put a fully roofed wooden porch on the front.Question is can this system be used for external walls or should i leave the outside shuttering on and clad with wood or something to protect it from the weather, and only use the clay render for the inside ? Also how long do you leave the straw before removing the shuttering?
    Look forward to your answer,saludos Paul

    • Europeans have been building with straw/clay for centuries. It’s even in the German building code, and possibly elsewhere like France where earth building is popular. You should have no trouble finding local resources online who can answer the specifics. I love recycled wood cladding. But some also plaster straw/clay.

  5. I’m not up on the term “slip straw” What exactly is this? The straw I’m familiar with looks a bit different than this type. Thanks Owen.

    • Two problems with that method: 1. awkward to cut (try it and see), 2. straw/clay mix is stronger and more resistant to moisture damage

  6. BTW, what exactly are the benefits of this method compared with other methods or with using cut straw bales?

    Is slip straw a good sound insulation material?

    • Straw is a good sound and heat insulator. Thin walls don’t take up as much space as straw bales and are less susceptible to damage. It’s do it yourself friendly. You can stuff preexisting wood framed walls or build new walls out of recycled wood. The materials can last hundreds of years as we’ve reported on earlier. (See article about straw/clay houses in Germany.)

  7. Well I was actually thinking of a stick-framed second floor with straw clay infill rather than bales. On the other hand, bales are appealing from the point of view of sound insulation. A wrap-around veranda would be ideal all right.

  8. Great video. I’m thinking of trying to build a small two-level dwelling: earthbags for the ground-floor level, with straw-clay infill walls for the upper level. I know you’re not a huge fan of straw (bales in particular) in buildings in Thailand, Owen. I’m hoping that with adequate roof-overhang and termite barriers it would be a cheap, long lasting option. Any thoughts?

    • If the bales are on the 2nd story and have large 4′ or larger overhangs (wrap around patios are best) then I see no problem. But the insulation is not needed and they take up a lot of space. Why not use thinner walls on the 2nd story?

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