Weaver-Hovemann timberframe and straw/clay home by EcoNest

Weaver-Hovemann timberframe and straw/clay home by EcoNest


Timberframe and straw/clay house in Crestone, Colorado (click to enlarge)

Timberframe and straw/clay house in Crestone, Colorado (click to enlarge)


Mixing straw/clay for filling gaps between straw bales

Mixing straw/clay for filling gaps between straw bales


Straw/clay has been in use for thousands of years with great success. The focus of our blog is obviously earthbag building, but we’ve decided to include coverage of other natural building methods to broaden our horizons and reach a wider audience. It’s good to know a whole range of building ideas so you can obtain the best possible house. For instance, maybe you want to use earthbags on exterior walls and straw/clay on interior walls. This is a very good option that requires no formwork. You could stuff straw/clay inside pallet walls for soundproofing between rooms. Most often straw/clay is combined with a timberframe that carries the loads.

“One of the best low-cost insulating materials is clay-coated straw (or other lightweight plant materials). A light coating of clay acts as both a binder and preservative. Clay-coated straw has been shown to last over 700 years as a non-deteriorating insulation! As the clay dries, it binds the straw together in a surprisingly rigid mass. It’s a “natural styrofoam”.

Materials
Any stiff agricultural waste similar to straw will work. Hay is too flimsy and has seeds, so it doesn’t work very well. Barley straw, wheat straw, and other grain straws work well. Clay can be gotten from the earth. Many subsoils are primarily clay. River bottoms and river banks are usually clay. Clay is also used by brick and tile manufacturers and can be bought from them cheaply. (in our area, about $16 per ton)
Even soil which has a moderate amount of clay such as commonly used for adobe, about 35-50% clay, will work. The slurry is not as sticky, compared with pure clay, but even ordinary mud works well enough. This is not rocket science. Use a dry wall stirring paddle and electric drill to mix the clay or mix in any kind of mixer. Mud mixed in a box with a hoe works.

Method
1. Break the clay into small particles so that it will mix with water easily.
2. Make up a slurry of clay and water. Any soil that is mostly clay will also work. The consistency should be like cream or a thin milk shake.
3. Spread the straw out on the ground. Dampen the straw with a spray nozzle if available.
4. Pour (drizzle) the slurry over the straw, then toss and mix the straw so that it becomes lightly coated. Ordinary garden rakes work well. The clay should only very lightly coat the straw. This is NOT adobe. Maybe 5-10% clay, 90-95% straw. When dried in the wall, you can hardly see the clay, but it binds the straw together very well.

Uses
In addition to being an insulator, it can be used as a wall forming material. In the middle ages, even up to the present time, the method works like this:

1. A post and beam structure is first built.
2. Two boards are temporarily nailed to the posts, one on each side.
3. The resulting cavity is filled with straw-clay.
4. The material is tamped down (a 2×4, 4×4, or small post will do). The idea is not to compact it into a solid mass, you couldn’t do it easily anyway because the straw will remain springy until it dries.
5. The two side boards are moved up immediately and stuffed again and again until the wall is as high as desired. No need to wait for the straw-clay to dry before moving the boards up. (A moveable, sliding form could also be used to make walls.)
6. A saw is used to cut out windows, or window frames are placed first.
7. The wall is allowed to dry and is hand plastered inside and out. The soft undulating plastering adds a charm that cannot be found in modern buildings.”

Source: Planetary Renewal.org
Image source: EcoNest
Image source: Windy Ridge Woodworks
Image source: Our House of Straw


Comments

Straw/Clay Houses — 25 Comments

  1. I live in East Tennessee. I’ve seen what the weather here can do to a straw bale home. Would a earth bag built home work or would it still be to wet of climate here?

    • There are lots of earthbag buildings in the tropics and I’ve never heard of a bad problem. That’s one of the key advantages. Build a good roof with wide overhangs and cement or lime plaster.

    • This post is about light straw/clay. To make houses of clay and bamboo I recommend wattle and daub. This is one of the simplest, most primitive building methods in the world. Wattle and daub is still widely used around the world. But it’s not favored by modern natural builders because it tends to create rather crude, thin walls. It’s also prone to water and insect damage. You can learn a lot more by researching wattle and daub.

  2. My wife are renovating, slowly, an old clay house in central Poland. Nobody builds with this any more, and the older generation are dying or dead. It’s hard to find advice locally.
    Poland’s climate is similar to Ontario, or Wisconson for US folks. What’s the best outer coating for the clay. My wife’s now deceased dad used a home-recipe of cement, sand, and god-knows what else. It’s falling off the clay like old bark. In recent years past someone has attempted to cement oarts of the outside, it too falls off, in large hunks.
    Any advice for winterizing the exterior?

    • The most common plaster in the US for adobe houses is a layer of foam board insulation and then cement plaster. A layer of insulation will greatly improve thermal performance. Otherwise the earthen mass will suck the heat out in winter.

    • Termites, ants and water are all major factors. Sooner or later roofs always seem to leak. While straw/clay could certainly work, no one I’ve seen uses it here. Even adobe (which has minimal straw) gets attacked by insects. Earthbag has no organic material and is compacted enough that insects aren’t interested. It’s far easier for these critters to live elsewhere.

  3. Clay slipped straw is great–it fits borderline conventional building. You can put it between existing studs in a remodel (although I would want it thicker than 3 1/2 inches). It fits around roundwood timbers and into corners. It uses less straw than “normal” strawbale and can use roundbales, which can be MUCH cheaper. A roundbale is usually one tenth the cost of square bales per ton.

    It is important to cover all different kinds of building. Most sites talk about their favorite kind of building, which may actually be the best for where they live–but not for everyone. Thanks for taking it to the next level again.

    Build with what you can find local that lasts (what did the indigenous people use?) and substitute modern materials/methods when they make sense. Like earthbags instead of rocks and tin roofs instead of thatch.

      • Maybe a tenth is an exaggeration. I looked it up again locally and it is currently running about one-fifth the price in a big bale. That is off-season, dry-stored wheat straw, loaded yourself. It takes much less time (and fuel) to make and move round bales with modern machinery. Even the Amish community down the road hires “english” farmers to make big round bales for them.

        The price difference can be less if you pick up the square bales yourself from the field right after they are made. The price difference can be more if you have them delivered from dry storage during the off season. The price may come back down as spring rolls around and there are leftover bales from last season (which are actually better for building).

        Big bales are 600-1200 pounds (vs. 30-60 for smalls), so they are not the easiest for just anyone to deal with. But all you need is a small trailer and a farmer willing to help load (most will). Two people can roll or tip it off the trailer on-site and then break it open to use for slip or cob. But most farmers that make round bales have trailers that will haul 4-6 at a time and dump them off in a few seconds. If you need several bales, it is usually cheaper to have them delivered in one trip than you spend gas on several.

  4. Maybe natural builders need to improve their marketing. (I’m speaking generally, not about one company.) Walk up to 10 people and ask them to visual a house made with straw/clay. If they say “what’s that?” then explain it’s straw and mud mixed together. Ask them to describe the house they envision. Then show them the top photo (EcoNest home). How many people would imagine straw/clay could be so beautiful? Probably none. The same holds true with trying to explain earthbag houses and other similar alternative building materials. Most people just can’t imagine it. [Or maybe it’s not marketing. Maybe there are a lot of stupid people out there? ha ha] Seriously though, it seems like millions of people would want a home like that photo, yet only a tiny fraction choose this option.

    • It’s all about education and deprogramming. I was never impressed with new construction and was always drawn to older, well-built homes with a lot of character. However, when I came across your blog – many months ago – it really opened my eyes to the wonderful world of natural building. While I love earthbag building, I am finding that the mixtures of different natural building styles can really expand the idea of each individual “perfect” house. Thank you very much for your never-ending search of beautiful, warm homes created using natural materials. I’m excited about building our future “perfect” home!

      • Thanks, glad to hear you’re enjoying the new look. It’s much more fun covering a broader range of topics, and in the long run I think readers will end up with better homes. Often the ultimate home is a mix of different building techniques.

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