simple natural home design,natural building materials,green architect,ecological building,eco-building,Darrel DeBoer

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Strawbale Thoughts

L a t e s t      N e w s

November 2005:

Author David Pearson was nice enough to include one of our houses in his most recent book, Designing Your Natural Home, (the cover is in the upper left corner of this page) just released from Harper Collins.  The book is done well and David has had a great track record in finding ways to get ideas about ecological design to reach mainstream readers.  So, once again, I think he has really achieved something here.

The July/Aug 2005 issue of what's now called Natural Home and Garden has a list of the Top 10 Eco-Architects, and they were kind enough to include us.

Check out the March/April 2004 issue of Natural Home magazine.  We're on the cover!

nathome.bmp  For more pictures, you'll have to buy the issue as it's not available online.

T h e     S y s t e m

Wood construction has had a few hundred years' head start on straw bale construction.  Now that most people have at least heard of building with straw, we're trying to refine straw facing southan intuitive system of building that just makes obvious sense.

I like building with straw because -- even after working on relatively few buildings -- it's clear that it works better than wood.  It's pure insulation with no energy leaks through the framing; with plaster, it just doesn't burn (try throwing your phone book into a fire), there are no openings for rodents and insects to run around, AND there's nothing there for them to eat anyway.  Done right, the system is amazingly strong, putting plywood to shame (see testing results), but the most crucial advantage over conventional construction is that straw walls have quite a capacity to hold lots of water before any kind of rot can begin.  In any building system, water will inevitably get into the assembly sometime, even if just from the breathing of the occupants or high humidity.  But if composting can only begin once moisture reaches 28%, or if almost a third of the contents of that two foot thick wall of solid cellulose needs to be water, you have to REALLY be trying to get that wall so totally saturated that there are problems.  Though I haven't worked in an extremely humid climate, I think straw is better suited for those conditions than wood framing with moisture-resisting fiberglass insulation because the moisture has no option other than sitting on the relatively small surface area of the wood framing.

The most important idea is avoid vapor barriers so the moisture can get out.

earth plaster Some of the gorgeous colors we've been getting just from the local clay.

One of the authors of the Straw Bale House Book, Athena Steen, was visiting awhile ago and casually mentioned that of the many experiments she and her husband Bill have done with bales, she has never found rot under an earthen plaster.  DING!  My favorite assembly is to put a lime wash over earthen plaster on the bales because the clay constantly attracts vapor out of the bales and the lime hardens the surface of the plaster to prevent erosion.  Water vapor molecules are 100 times smaller than liquid water, so this assembly keeps the water molecules out of the wall but still allows vapor to escape.  The problem with cement-based plasters is they are much less permeable, and moisture gets trapped between the wall and the plaster.

L o a d   B e a r i n g ?

When you first think about it, having the straw carry all the weight of the structure makes sense.  It settles evenly, and very little wood is needed.

load bearing strawbale     southeastThis project was possible because of the Owner/Builder exception to the building code that exists in two counties in California: Humboldt and Mendocino.  A person who lives in a place for at least 5 years can build whatever they want, and they don't need to explain anything to the building department.  But they ARE condemned to stare at their mistakes daily.  My personal opinion is that there must be a happy medium between over-regulation and NONE, but this project was allowed to explore the load-bearing possibilities.  And other than anchor bolts, there were no metals used in the walls to attract moisture on cold nights (a fishing net mesh went over the outside and inside)

N o n   L o a d    B e a r i n g

But there is an argument for a separate structure.  First, the discussion with the building department is usually not so simple when you announce that straw is going to hold up your whole house.  Second, during construction, the structure is subject to rain for some period while the roof is built.  And third, there are often times when you'd like something solid to nail to (like door frames, electrical boxes and exterior reinforcing mesh).

straw wall

So, lately we have taken to this system of building boxes out of 2x4's and plywood, making surprisingly strong composite posts and beams.

Then make sure that you really want a strawbale WALL.  Turns out most of us want a bunch of windows with a little bit of wall over in the corner.  Be honest and decide if you really need a big, solid, continuous chunk of insulation. straw wall with triangle Then, just put the straw walls on the sides of the house that really demand them: north and west in our temperate climate of northern California.  Since the south should be full of windows, just put in some small wood framing and don't bother with straw there.  Just put the straw in a long, flat wall if you can.  Where there's a sloping wall, frame it out of wood. rammed earth And if you are tempted to build a big mass wall, like rammed earth -- put it INSIDE the building where it will do some good and hold onto your precious heat rather than drain the heat right out.

R e s i s t i n g     E a r t h q u a k e s     a n d     W i n d

With mesh on the inside and out, tied through the bales about every 1.5 feet, and nailed all around the perimeter, the whole assembly is working as a unit.  The only way for the wall to collapse is when thousands of nails shear off simultaneously. UNLIKELY.

Some people think I talk about this just because I live where the building codes consider the most extreme earthquake risk.  But, the engineers tell me that WIND almost always outweighs the earthquake forces.  And don't ever relax when you live where they say the words "hurricane" or "tornado."  I'll take my earthquakes any time, thanks.

So, with the box post/beam system, you can complete the framing, with "studs" as far apart as 12 feet, put the roof on and get it totally waterproofed before you even need to bring a bale onsite.  But the great thing about the box post/beam system is that it's still very malleable.  For example, if you want to round a corner or angle a window opening, just hold the box post back a bit and just cob around the curve or turn the post at an angle. (oh, and these posts will also put hair on your head, make your toast in the morning and attract impossibly beautiful people to you daily!)

box post.jpg      south wall

Above is a fairly complex plan.  Notice the white ghosts in the wall that are the box posts.  I feel like we're now at a system that's more intuitive and shouldn't be as hard to build as some of the early projects which had a much higher percentage of head-scratching. 

very little wood

The bales can be left out until the roof is on, and the framing still doesn't use much wood compared to what we're used to seeing on most jobsites, yet the building department looks at this as a wood frame building, and they stop worrying.  I'm amazed how strong this assembly is... I watched the builder, Johannes Stimming run across the box beam at the top of the above picture and jump up and down in the middle of the 16 foot span.  It didn't move.

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