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Straw bale house in San Miguel de Allende Mexico (C) Daniel Friedman Straw Bale House Construction & Inspection Methods

  • STRAW BALE CONSTRUCTION - CONTENTS: Photographs of a strawbale constructed home show construction details, areas where problems occur, history of repairs, durability characteristics. How to Recognize & Assess the Condition of Straw Bale Constructed Buildings - Straw bale construction methods, costs, durability, advantages, risks. Where do problems on straw bale constructed buildings most often appear? - Strawbale house inspection and common defects. Sources of guidebooks and "how-to" books on strawbale construction.
  • POST a QUESTION or READ FAQs on repairing cracks in straw bale constructed homes
  • REFERENCES
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Straw bale constructed homes:

This article describes a straw bale constructed home that is more than twenty years old, commenting on its construction method, durability of straw bale construction, and where strawbale home defects are likely to be observed. Our page top photo shows the exterior of a load-bearing strawbale constructed home in San Miguel de Allende, Mexico. Strawbale homes are not common in San Miguel, but are popular in many areas of the Southwestern United States.



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Straw Bale House Building Construction Defined & Illustrated

Straw bale house (C) Daniel Friedman

Strawbale construction is a construction method ascribed to early settlers in the United States in Nebraska in the 1890's, and a method popular in the U.S. into the 1940's with a continuing following of straw bale enthusiasts to the present.

Prior to about 1890 straw, hay, and similar grasses were used for thatch roofing but it was the advent of the mechanical bailer using wire or twine and producing rectangular straw bales that permitted straw to be used as construction building blocks.

According to the U.S. DOE,

Straw bales were a fairly common building material in the United States between 1895 and 1940. Interest in straw-bale home construction began to re-emerge in the mid-1970s. But it wasn't until the mid- to late-1990s that building codes began to acknowledge it as a viable approach. The rising cost of conventional construction materials, techniques, and concern for our environment has fueled the growing popular enthusiasm for straw bale home construction.

There remains much we do not understand about appropriate ways to build with straw bales in different individual building assemblies, climate zones, and weather conditions. Two of the current straw bale construction methods include non-load-bearing or post-and-beam, which uses a structural framework with straw bale in-fill, and load-bearing or "Nebraska style," which uses the bearing capacity of the stacked bales to support roof loads.

Proposed straw bale structures still face considerable barriers, including the following:

  • Local building code approvals
  • Building loans
  • Mortgages
  • Homeowner's insurance
  • Community acceptance.

The non-load-bearing construction method is the approach most regulatory authorities accept today.

To find out the building code standards for your state, contact your city or county building code officials. Your state energy office may be able to provide information on energy codes recommended or enforced in your state.

How to Recognize & Assess the Condition of Straw Bale Constructed Buildings

But how easy is it for a home buyer or home inspector to quickly recognize a straw bale built home? A glance at our page top photograph of a straw bale house in San Miguel de Allende, Mexico, may not immediately show how this house was constructed. But look again more closely: notice those thick walls that can be detected by the thickness shown at window and door openings? And if you (click to) enlarge the photo you might notice the "lumpy" building sides. Look again at our straw construction house wall photograph just below.

How are Straw Bale Homes Constructed

Straw bale constructed home wall details (C) Daniel Friedman

STRAW BALE CONSTRUCTION uses bales of straw tied with string or wire as the modular building blocks. Straw bales are stacked vertically in a running bond pattern - each straw bale is placed so that its center is over the end-butt joint of two bales in the course below.

The strawbales are laid either on their base (a wall thickness of about 18-22") or on their sides (a wall thickness of 14-18"). For narrow wall sections the straw bales may need to be cut and re-bound to the required length. Small and irregular wall gaps that do not fit a straw bale may be filled with hand-packed wire-mesh or wire lath forms cut to fit the necessary shape.

"Straw" is defined as the stem portion of a grain plant such as the stalks of barley, oats, rice, rye, or wheat, but without the grain (seeds) or grain "heads" of these plants.

Strawbale walls are normally, reinforced with through-driven or surface-tied wood, bamboo, or steel re-bar rods, and then coated on all sides with a stucco of earth, clay, or a cement mixture, applied either directly to the straw bale wall surface or applied to a "chicken wire" mesh or to clay-coated burlap that has been tacked to the surface of the bales or to the reinforcing bamboo on the wall exterior surfaces.

Strawbale wall plastering may be performed entirely by hand, or the builder may use a textured-paint sprayer to first prime the straw wall, making subsequent plaster coat application easier and providing a better bond. During plastering of the strawbale wall, a "cob" mixture of straw, sand, clay and water may be packed into any small remaining gaps between the bales. The straw bale wall plaster recipe varies by location and available materials.

The plaster first coat may be an 80-20 mix of sand and clay with chopped straw added for additional strength.

The final plaster coat, hand troweled, may also be an 80-20 sand/clay mix with an addition of 4% lime water. This coating will contain less chopped straw or none at all in order to give a smooth hard finish on the wall. Finish coating with lime plaster or similar materials may be applied depending on the climate and building use. For building durability proper curing of the plastered or stucco coatings and final lime or pigmented coatings is very important as hairline cracks can invite moisture into the structure, destroying it.

Post and beam-constructed straw bale homes use straw bales to fill in the wall spaces between wood, reinforced concrete, or steel posts and beams that form the structural frame for the home. The frame supports the weight of the building roof and upper floors. In post and beam strawbale construction the courses of bales may be pinned together using vertical lengths of bamboo (two to a bale) placed on the inside and outside of the straw bale wall, then tied together using a stiff wire "needle" to force twine through the bales where necessary.

Load-bearing-wall-constructed straw bale homes are built using courses of straw bales that themselves form the supporting wall structure for the building. Strapping over the top course of straw bales is (or should be) carried to connections that pin the wall to the building foundation (if a foundation is provided). Some straw bale homes are built without a masonry foundation, resting the first course of straw bales on compacted earth or gravel.

Our photograph (left) shows the sides of a straw bale built home. The "lumps" visible on the building wall are about the size of a bale of hay or straw - we call this modulo-straw-bale lump size, an obvious indicator of the materials of which this home was constructed.

Some advantages of straw bale construction include

Some disadvantages of strawbale constructed homes include


Straw bale house interior (C) Daniel Friedman

This straw home photo (left) shows the interior of part of this two story home. Here, too, when the angle of illumination is just right, it's easy to see the straw bale texture of the home's walls. Of course other straw-bale constructed homes may be parged to a smooth wall surface, hiding this straw bale shape.

How durable are straw-bale built buildings?

We have read assertions that well-constructed straw bale houses in Nebraska have lasted for more than 100 years. But as with any construction method, the life expectancy of a strawbale home will depend on both the quality of its original construction and the quality of maintenance over the life of the building.

The type of straw used to produce bales used in strawbale construction may make a difference in the durability of the building. Straw may be comprised of the stalks of barley, oats, rice, rye, or wheat. But the higher silica levels in rice straw make it easier to dry and more resistant to decomposition from moisture.

In the home shown in these photographs, the strawbale constructed home uses load bearing straw bale walls. The load bearing design may be a significant factor in the appearance of the wall cracks and leaks shown in our straw bale wall damage photographs (below).

Our OPINION is that non-load bearing straw bale construction (in which straw bales are used as infill between the posts of a wood, concrete, or steel post and beam structure) may be less likely to experience these problems. The walls of a load bearing straw bale home must carry not only the weight of the wall material itself but also that of the roof and of the live and dead loads of upper floors in the building. Any condition that increases the chance of cracks in the stucco coating of the straw bale wall increase water, insect, and rodent penetration risks and thus the chances of further rot, settlement, or infestation in the structure.

Where do problems on straw bale constructed buildings most often appear?

The window in our photo (below left) shows the wall thickness - a clue that this is a straw bale home. The outside of the window jamb was painted green, the inside white. A good outdoor construction detail on a straw bale home of this design is the inclusion of a slope on the window sill so that it drains without risking sending water into cracks in the straw bale stucco coating. Our second photo (below right) shows one of the places to look for cracks, leaks, and water entry at a straw bale constructed home - at the window and door openings.

Straw bale  home window detail (C) Daniel Friedman

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Straw bale house window details (C) Daniel Friedman

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Straw bale constructed home wall cracks (C) Daniel Friedman

Our photo at above left shows a thin vertical crack in the stucco covering of this straw bale home, at the center of this picture.

Straw bale wall crack details and repair history (C) Daniel Friedman

Our second photograph of a straw bale home (above) shows both cracks and evidence of previous repairs in that same location (click these photographs to enlarge and make the crack details more visible). Just below are closeup photos of cracks in the stucco coating of this straw bale constructed house wall.

Straw bale constructed home wall cracks (C) Daniel Friedman

What special steps should be taken to preserve a straw bale home?

Straw bale wall crack details and repair history (C) Daniel Friedman

Reader uestion: How easy or hard is it to repair small cracks in a straw bale home? How easy or difficult is it to cut in a new window or door in a straw bale home wall?

It has been very useful to have stumbled upon your website as I had no knowledge of straw bale construction and its special care requirements. Since you offered some support, I would like to ask you two things. As you know the house is old. It was built specifically for rental and the quality of most materials, such as window and door framing, and furnishings is below what I prefer in a home. It has potential, though.

Last summer I noticed that a small section (maybe 10 cm.) of an exterior apartment wall had cracked and was open to the elements. I did ask my property mamager to repair it, but I don't know if she is aware of the construction material. So question one is how easy or difficult is it to repair a small section like that?

The second question is how easy or difficult is it to cut a new door or window into an existing wall, as I someday want to put a room addition on the lower, one-story apartment. - N.G., Myanmar

Reply: Advice About Straw Bale Home Crack Repairs and Adding Windows or Doors to Existing Walls

Think of the straw bale wall structure as a thin masonry shell plastered over bales of hay or straw. If water gets into the interior of the shell it invites decay or pests that over time can damage the bales, leading to hollow areas that are structurally weak compared with the as-built design. So my opinion is that it would be smart to inspect the house from time to time and to try to keep any cracks you see sealed.

How we Patch Cracks in Straw Bale Wall Stucco Coating

Straw bale constructed home wall cracks (C) Daniel Friedman

Typical repairs to straw bale house cracks are simple re-plastering, or chipping open a crack wide enough that the plaster repair will be mechanically sound, then re-plaster and re-paint the wall.

By "re-plastering" I refer to using a cement mix, not actual "plaster". The crack may need to be opened a bit wider and cut to an inverted "vee" shape to get the best mechanical adhesion of the patch. Very fine cracks in the straw bale stucco coating, say less than 1/16" in width, might seal up ok if kept painted.

If you find actual damage that is resulting in movement of the structure - say crushing under a floor joist or beam - then it would be appropriate to open the wall to see what's going on.

It would be simple to add a post and pier if necessary, you don't have to chop open the whole wall and try replacing bales. But if you are not seeing structural movement, that more extravagant repair should not be necessary - just keep cracks sealed as best you can.

How we Cut Openings for Windows or Doors in an Older Straw Bale Home

Straw bale wall cut for window (C) Daniel Friedman

I'm more nervous about cutting openings for windows or doors, especially when both of us are just thinking by email and are not on-site to see exactly what's going on and exactly what is inside of a wall that we cut open. In general, a too-glib answer is that you can do just about anything to any building - that is it's possible.

The devil is in the details: just how much trouble and expense are we going to face, and are we sure we're handling the change with enough thought that we're not messing up the rest of the structure.

If you cut a door where there is already a window, often that's pretty easy as there is already a header over the window opening to carry the weight of the wall above. So if the top of the window is high enough to fit a doorway, just cut the bottom wall out below the window. It's not going to change the structure.

But if we need to make a new opening where there was none, most likely you'll want to frame in a header beam to be sure there is no sagging or cracking in the wall above. The header is carried on posts to concrete piers poured into the soil deep enough that there won't be any sinking and thus there won't be any cracking in the wall. Then the door or window jamb is framed into that opening.

Find Out More About Your Straw Bale Home Construction

Finally, if by chance a neighbor can tell you who built the straw bale home, we might find out if the original builder is still around, as s/he will also be familiar with hidden structural details in the home and somewhat familiar with straw bale construction. A clue would be whether or not we can find any other such homes in the neighborhood.

Straw Bale Construction Guides & Codes

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