Homestead Green Building: Straw Bale

When you first start thinking of building green with natural materials, straw bale is probably one of the first building styles you think of.  It seems to be the most commonly mentioned in green building circles.  There is good reason for that, as straw bale construction has a number of benefits.  Let's take a look.

Straw is a wonderful building material for a number of reasons.  It is, basically, a waste product.  This is not the hay that is used for animal feed.  Animals cannot digest straw.  In actuality, straw is the stalk that comes from pretty much any grain.  Once the grain itself has been harvested, the stalks are baled.  It can be used for animal bedding.  But a great percentage of straw is burned as waste.  By putting it to use in building, less is burned, making it great environmentally.  When it is baled, it is tightly compacted.  This is useful because 1) it provides greater strength, 2) gives it a higher insulating value, 3) animals, such as rodents, find it difficult to nest in it, and 4) less open space for oxygen, making it more fire resistant.  So now, let's break each of those down a bit.

Greater strength.  There are primarily two ways to build with straw bales.  One is using the bales in and of themselves, without any extra framework, and the other is by infilling a traditional type frame with the bales.  As the bales can be used without additional framing, even for load-bearing walls, and in two story builds, this testifies to it's strength.  The downside of this, is that it can make it a bit more difficult, although not impossible, to obtain building permits.  While more and more places are expanding building codes to be inclusive of straw bale construction, many of those do require some sort of framework.  This is one of those times when working closely with code officials will be necessary.  Know your information well, as it may very well be a relatively unknown subject to code enforcement officers.  But built correctly, it can easily last a hundred years or more.  They have even been known to withstand earthquakes.  They are tough buildings.

Higher insulating value.  In any climate, building a structure with good insulation is imperative.  Using standard insulation, anything with a rating of R=19 or higher is considered "super insulated". Tightly compacted straw bales average at about R=2.7 per inch.  And as bales are generally between 16 and 18 inches thick, that would put the overall rating between R=43 and R=48 (according to this).  As you can see, this is a superior insulating material.  That being said, there is practically zero thermal mass, meaning it won't hold heat or cold for extended lengths of time.  That is where a good natural plaster (such as cob or lime) come in.  Adding a good thick layer will give the walls great thermal mass, as well as seal the wall for protection from insects, animals, and excess moisture.  Moisture is the main thing that can be disastrous in a straw bale building.  Proper sealing is absolutely required.  And it must also be breathable.  Modern wall sealants don't allow for this breathing.  So if any moisture has been trapped inside, it won't be able to escape.  Natural plasters are breathable and more forgiving as settling occurs over time.  This prevents cracking in the walls that can, again, let in unwanted moisture.  So why not include a healthy layer of a natural material that not only protects the bales, but also provides thermal mass?

Rodents find it hard to nest in.  Ok, so it's not impossible for them to get in.  But they don't like eating it, as they can't digest it.  When the bales are tightly compacted, it's more difficult for them to get in.  And with a good and proper plaster finish, it greatly reduces the odds of one of these critters getting in there.  And the same goes for insects.  While there may be some already in the straw as your building,  once the plaster goes up, the ones in there cannot escape, and will eventually die.  And new ones will not be able to get in.  Now if you are utilizing a timber framework within which you will be placing the bales, you will have to do something for the possibilities of termites and any other critter that would find wood attractive.  So that is something to keep in mind.

Fire resistant.  This one almost seems like an oxymoron, doesn't it?  Straw?  Fire resistant?  Actually, yes.  Again, this comes from the fact that the straw is so tightly compacted into bales that there is little to no space for oxygen to flow.  And without oxygen, fire cannot live.  And, yet again, the final plaster further protects the straw in case something were to happen.  In fact, tests have shown that properly constructed straw buildings are actually MORE fire resistant than traditional built homes.

Straw bale construction is easily learned, and can be done by the do-it-yourselfer.  It goes surprisingly quickly.  The bales, being the size they are, makes the walls go up very quickly.  Bales can also be used as internal walls if you'd like.  Just remember that that size will take up a bit of floor space, unless you have already planned for that and make the overall structure larger to accommodate that.  Alternatively, one of the other natural building styles we've already discussed can be used for the interior.

Another great aspect of straw bales is that they are almost universally available locally.  If you can become well acquainted with a local farmer, that helps a lot.  You may, however, need to plan out in advance for the next year's harvest, to have the farmer set aside bales for you.  If you do happen to be in an area where they aren't locally available, and you end up having to order them from elsewhere, that might factor into your plans in cost of shipping.

Now the downside is that while it is easy to build, and generally costs much less than a traditional build, especially if you're doing most of the work yourself, it is absolutely essential that those final layers are done properly.  With straw bale, this cannot be stressed enough.  Those finishes protect from water, rodents, insects, aid in fire resistance, add thermal mass, and are what essentially keeps the structure standing longer.  If not done correctly, it can cause major issues down the road.  It can be done by you.  It is something that can be learned easily enough.  With enough patience to make sure it's done correctly, this isn't a problem.  But if you doubt your ability or patience, a professional may be necessary.  This is where the cost can start to add up.  Professionals in natural plasters don't generally come inexpensively.  But with a good footing/stem wall, an adequate overhang, and solid plastering technique, I believe anyone can do it.

Straw bale homes may not be for everyone.  But they are easily built, require readily available and renewable resources, provide excellent insulation, and as a bonus, absolutely incredible sound-proofing.  Definitely consider this as an option.  They can be built in just about any climate so long as proper precautions are taken for reasons of moisture and/or creatures that may try to claim the straw as their own.  A flood zone may not be the best ideal, but otherwise, they are definitely worthy of consideration.  For more information to begin your research, here are some valuable resources to check out.

https://www.strawbale.com/new-to-straw-bale/

http://buildingwithawareness.com/the-pros-and-cons-of-straw-bale-wall-construction-in-green-building/

http://pajaconstruction.com/advantages-and-challenges-of-straw-bale-construction/

http://www.greenhomebuilding.com/QandA/strawbale/varmints.htm

http://www.motherearthnews.com/green-homes/earthbag-cob-strawbale-zbcz1605

http://www.simple-living-today.com/straw-bale-house.html

Homestead Green Building: Cordwood

Let me tell you something about cordwood construction.  It is beautiful.  It is charming.  It is rustic.  There is a ton of information online and in books on this subject.  I will also tell you that to find specifics that actually work is a whole other story.  Your best best, hands down, is to find someone who you can actually talk to.  Someone who has experience.  And by experience, I mean years of experience in actually building multiple structures, possibly in multiple conditions, if at all possible.  Find a workshop, and go.  For me, I have not been able to find a workshop within a reasonable distance, so, unfortunately, the information that I am presenting here is coming from a number of sources, none of them personal.  But, in an effort to provide you with the best information that I can, I am going to tell you what I've found - all the contradicting info out there.  From there, it's up to you.  But again, on this one, I STRONGLY urge you to find someone with lots and lots of experience that you know you can actually trust to learn the best possible information from.  That being said, let's start down this somewhat crazy path of cordwood construction.

So what exactly is cordwood.  Well, basically, cordwood is really any wood that would otherwise be wasted or not able to be used for traditional construction.  A "cord" is a unit of measurement.  When the wood is well stacked and relatively compact, a cord is a volume of 128 cubic feet, or 3.62 cubic meters.  A cordwood wall provides both insulation and thermal mass.  Insulation is from the wood, and whatever other insulation you may decide to use.  Thermal mass comes from the mortar.  The basics of building with cordwood is actually quite simple.  Cut all your pieces to roughly the same length, stack and mortar the pieces like brick or stone to then build your wall.  Simple, right?  Well, it should be.  While pretty much everyone will say that is simple enough that a child can do it, that's about all that is agreed on.  At the end of this post, I will include a few site links with information, some chat threads, and whatnot for you to look through and make your own judgments.

Let's start with a foundation for your walls.  Some sources say that you can start building directly on your foundation, or even directly on the ground.  Other sources say that the cordwood should start no less than a foot above the ground, preferably, more like two or more feet, so as to keep rain, snow, or whatever other kind of moisture could possibly get into your wood, out.  Having it raised, the advocates say, also greatly limits the amount in insects you'll end up dealing with.  I would tend to agree with the later sources.  Again, I have no personal experience, but, quite frankly, it just seems to make more sense.  Build the wall, much as you would cob or adobe, with a stone, or other solid material, foundation.  If nothing else, I, personally, think that makes the exterior that much more interesting and attractive.

For the actual cordwood section of the wall, some say that you can simply use the wood and mortar, especially if you don't need much in the way of insulation.  Others say that when you lay the wood, the mortar goes on either end of the wood, and then the center portion, rather than more mortar, use an insulating material.  With the insulation, there is disagreement on what is best.  Some say simple sawdust is enough.  Some say a combination of sawdust and lime.  Some say modern foam insulation.  As for the mortar, there is debate on whether or not to use modern concrete mortar, or a natural mortar, such as cob.  Supporters of cob insist that using concrete will keep the walls from breathing properly, which, as we should all know by now, is one of the trademark characteristics of most natural walls.  Nor would the concrete allow for natural compaction and expansion of the wood over time.  On the other hand, if cob is used, then it takes extra work to take care of the wall, including a larger overhang in order to keep moisture from coming in from the top.

Now, let's talk about the wood itself.  What kind do you choose, and what do you have to do to it?  Is there any agreement here?  Nope.  No such luck.  Now there does seem to be one common theme, in that most sources do say that it's better to use softwoods rather than hardwoods.  The reasoning behind this is that softwoods hold up better over time, and are generally easier to season, or dry.  Another complaint I've seen is that hardwoods generally tend to have higher amounts of oil in them creating stronger scents that some people can find offensive.  I would say that's a personal opinion, but the other sounds logical.  The seasoning or drying of the wood is yet another topic for disagreement.  All say to remove the bark, which is primarily what attracts insects and disease, and also holds in moisture.  Beyond that, well....  Some say to remove the bark while the tree is dormant.  Some say to remove it in the spring while the sap is flowing, making removal easier.  How long does it take to dry?  Some say that only 3 - 4 months is ample time to season the wood.  Others say that a few months is no where near enough time, but rather you need at least 2 -3 years for the wood to completely dry out.  To use the wood after a shorter amount of time, according to the proponents of the longer time frame, is to vastly increase the chances that your wood will not be dried out enough to keep it from rotting.  Rot happens because of moisture.  Disease, insects, and all of the other things that can possibly happen to wood to cause it to degrade happen due to moisture.  So, according to these sources, when the wood is truly seasoned over a longer period of time, what that means is that there will be much less expansion and contraction of the wood (which will happen over time, to one extent or another, as atmospheric fluctuations happen), leading to less upkeep, and practically eliminates entirely any need for chemicals of any kind to seal or treat the wood.  They say that once the wall is built, there really is almost zero upkeep needed, if it is built properly to begin with.

Cordwood buildings are beautiful.  And the actual building, regardless of the method followed, does seem to be one of the simpler building methods.  It also lends itself quite easily to variations.  Use different shapes and circumferences of wood to create patterns and designs within the wood.  Integrate colored bottles into the walls for interest, added color, and extra light.  Use it for the entire building, or for only one accent wall.  Some areas do require some sort of post and beam frame in the codes, but even that can have it's charm.  The possibilities here are massive.  If you can cut through all the conflicting information and find some real information from a truly reliable source, this is a great option that can be adapted for just about any climate.

http://cordwoodmasonry.com/

http://cordwoodconstruction.org/

http://www.greenhomebuilding.com/cordwood.htm

https://www.niftyhomestead.com/blog/cordwood-construction/

https://cordwoodconstruction.wordpress.com/

http://www.greenhomebuilding.com/QandA/cordwood/misc.htm

https://permies.com/t/8654/cordwood-houses

http://www.motherearthnews.com/green-homes/ask-our-experts-shrinkage-of-wood-in-cordwood-construction-zm0z11zblon

http://www.masterjules.net/cordhous.htm

http://www.homesteadingtoday.com/general-homesteading-forums/homesteading-questions/118815-cordwood-masonry.html

http://www.minimalisti.com/home-garden-design/10/cordwood-house-cordwood-construction.html

http://cordwoodconstruction.org/img/Why_Cordwood.pdf

http://www.dirtcheapbuilder.com/Home_Building/Cordwood_Masonry.htm

http://www.greenhomebuilding.com/QandA/cordwood/seal.htm

http://www.lifeunplugged.net/greenbuilding/build-a-cordwood-home.aspx

http://www.appropedia.org/Cordwoodguy%27s_cordwood_guide

Homestead Green Building: Wattle and Daub

Wattle and daub buildings trace all the way back at least 6,000 years.  It is definitely one of the oldest building styles, found the world over.  There are some that say that more common techniques, such as cob and adobe, are developments that came out of wattle and daub building.  So what is wattle and daub?  Within  a timber framework, a network of lattice is made from some form of flexible sticks between the timbers.  This is the wattle.  An earthen mixture similar to cob is then "daubed" into the lattice/wattle.  While the mix is similar to cob, it can easily be adapted to whatever elements you have on hand that can create the same type of effect.  Generally speaking, the mix tends to consist of dirt, clay, plant material, straw, and animal dung.

Now, I've looked at many different sources, and there does seem to be some conflicting information, or at the very least, conflicting opinions, when it comes to wattle and daub.  While most agree on the basics, here is where the conflict arises.  Some say that there are two main downfalls to using wattle and daub as exterior walls.  Those downfalls are 1) that it simply isn't strong enough to be used for load-bearing purposes, and 2) that these walls are so thin that they don't provide any good thermal or insulating properties.  Others disagree with both of those.  I think the main difference between determining which side is more likely to be accurate would depend on what wood you are using for your primary timberwork framing.  If you use thin, flexible wood for the frame, then yes, you are going to have a lot of give if weight is added on top of it.  And being thin, no, it wouldn't provide much insulation or thermal mass.  You can easily make these walls as thick as you would like.  Just remember that part of the beauty of a wattle and daub wall is in it's flexibility.  The wall has to be able to give a little  if it needs to adapt to changing conditions.  And the wattle within the walls can actually help to stabilize the overall structure when other timbers may become impaired.  Also, the thermal mass and insulating properties can be increased based both on what mix you ultimately use as the daub, as well as how thick of a wall you end up with.  But because there are differing opinions from people who most likely know a whole lot more than I do, I will include a list of some of my references at the end of this post for you to read through, and come to your own conclusions.

One thing that is consistent is that you should not ever - NEVER - use anything such as cement or modern paints and sealants that create rigidity and hinder air flow.  Wattle and daub are designed to be flexible.  To include materials that would hinder that flexibility would actually cause the walls to degrade and crack.  It must also be able to breathe.  Any moisture that should get trapped in the wall needs a way to escape.  Otherwise, the wood inside will rot.  Lime plaster and and/or lime washes are what is recommended with this type of building.  Yes, it will mean the upkeep and reapplication may be more often.  But with regular and proper maintenance, these buildings can last several hundred years, at least.

Wattle and daub is not common in the U.S.  It is, however, still commonly used in other parts of the world.  It's easy to identify in most cases.  It has a rustic feel to it.  The walls tend to wave, and even the roofline can be uneven.  This can add to it's charm.  It can also be made smooth (relatively speaking) by plastering the walls with the same mix used as the daub.  This is recommended so as to encase the timber frames, giving them extra protection from the elements.

Another beautiful aspect to this type of building is that it can be used to make an entire wall, or to make individual panels that are then put into place wherever they are wanted/needed.  Again, it is very flexible.

The last thing I want to address is the use of animal dung.  For me, this was a big "HUH?!"  That sounds gross.  I use it in my garden as compost, yeah.  But to have it built into the walls of your home?  Does it smell?  Well, to address that,  I give you this site.  They explain it way better than I ever could.

Wattle and daub is a beautiful and natural building technique that should be considered in your research.  It has a long history.  And so long as you don't mind the upkeep, it can last for a very long time, and be beautiful and charming to boot.  For more information, here is the list of resources I mentioned earlier.  Happy researching!


https://www.britannica.com/technology/wattle-and-daub

http://www.buildingconservation.com/articles/wattleanddaub/wattleanddaub.htm

https://primitivetechnology.wordpress.com/2015/07/07/building-a-wattle-and-daub-hut/

http://www.earthhomesnow.com/wattle-daub-homes.htm

http://www.motherearthnews.com/green-homes/build-structures-using-ancient-method-zbcz1404

http://www.thatched-group.com/articles/building/UnderstandingOrganicBuildings.htm

http://permaculturenews.org/2013/04/26/bamboo-wattle-and-daub-structures/

http://www.energyauditingblog.com/wattle-and-daub-the-ancient-wall-made-modern/

Homestead Green Building: Earthbags

So I was planning on writing about a different type of building this week as kind of a continuation of sorts from last week.  However, I live in Florida, and we just experienced Hurricane Matthew.  I had a very interesting conversation with a friend of mine, and we were discussing the devastation that happened in Haiti from this storm.  That conversation brought this building style to the forefront of my mind.  Let me tell you why.  My heart breaks for the people down there.  In fact, it breaks for any and everyone who lost all or part of their homes.  This particular building style is something quite special.  Earthbag buildings have been said to be hurricane-proof, earthquake-proof, and even bullet-proof.  There were a number of earthbag homes built in Haiti after the earthquake there not too long ago.  And in the aftermath of the large earthquake in Nepal, those buildings that had been built with earthbags were found to still be standing intact, while traditional-built buildings had completely collapsed.  Also, they are much less expensive to build than standard housing.  The only real cost is that of the bags and barbed wire.  And those can be acquired inexpensively, or even through barter in some cases.  These homes are ideal for areas prone to these kinds of natural events.

So what is earthbag building?  Well, it's pretty much exactly what it sounds like.  Earthbags, also referred to as sandbags (yes, the same kind used for protection against flooding), are filled with natural materials, and used to construct the building.  The bags can be filled with pretty much any natural substance, readily found on the property.  What you fill them with can determine their ability, if you will.  When filled with gravel, they can be used as a foundation layer to keep moisture away from your structure.  When filled with pumice, vermiculite, or something similar, they can act as a great insulating wall.  And when filled with soil, they make a great thermal mass.  See here for more information on that.  When the soil is moistened before being put in the bag, it can be referred to as "superadobe", a term that is credited to Nader Khalili at the California Institute of Earth Architecture.  Learn more about him and superadobe here.  This technique is also generally used with longer, earthbag tubes.  It can, however, be used with smaller bags, as well.  As far as which type of bag you choose to use in your structure, there are a lot of people with a lot of opinions.  The simplest answer is use what you are comfortable with.  Longer tubes may be difficult for only one or two people to handle, whereas smaller, individual bags can be done by one person.  Tubes are generally recommended when creating dome like structures.

To build an earthbag structure, it's really as simple as laying a row of bags, tamping them down, lay barbed wire, which holds the bags together, then lay the next row, and so on.  There may be some extra engineering involved to help brace the walls if you are planning on building underground, earth-sheltered or earth bermed.  But they are very suitable to such building designs.  These buildings are also versatile in that they can be rectangular, as with a traditional home, or circular, like a roundhouse.  Also, remember to include any framework for windows and doors right into the walls as you build them.  For the most part, the bags are all you need, with the barbed wire.  That can change with some factors.  If you are planning underground, especially completely underground, you may want to include a good wood or steel framework within the walls.  That may also be warranted if you want a green roof or have the possibility of heavy snow loads.  Also consider the shape of your roof.  Traditional roofs are a good design for green roofs, whereas domes can work great in just about any other situation.  And as for electrical and plumbing, they can be built straight into the walls, just as with cob.

To finish, it's a simple matter of choosing what kind of plaster you want to use, both on the interior and exterior.  Some people opt for traditional plaster, some use a cement plaster, while others use cob.  Of course, you don't have to use the same materials on both.  It's all up to you.  Again, though, remember that you may also need to consider weather/water-proofing.

The next question will most likely be how to determine how many earthbags you will need.  The answer will vary depending on the size of bags you wind up getting.  There are a number of different sizes available.  But to get a basic idea on determining how many, check here and here.  Once you determine how many you will need, there are a number of places to get them.  Sometimes, you can find them on eBay for a decent deal.  Sometimes, you may be fortunate enough to find them on Craigslist or even for free on sites like freecycle.org.  If you cannot find them there, you can always purchase them.  On occasion, some home improvement stores may carry them.  At the end of this post, you will find a short list of a few companies which sell these bags online.

This is a great green building technique that can be learned quickly and easily, and has the advantage of being easily built by either a large group, a few people, or even a single individual.  It is economical, environmentally friendly, and inexpensive.  It is versatile enough to be worked into just about any other building design, or as a stand alone structure.  There are many many benefits to building an earthbag home.  It is well worth the time to research it, truly consider it, and even find a workshop, if at all possible.  For more general information on earthbag building, here and here are good places to start.  And never forget to search youtube.  There are tons of tutorials there.  Happy researching!

Bag suppliers:

http://bagsupplies.ca/

https://www.onlinefabricstore.net/18-x-30-polypropylene-bag-.htm?gclid=CNyDiYSDqc0CFQgaaQodmbwIgA

http://www.chkbag.com/

http://www.earthbaghome.com/node/2

http://www.allinsafety.com/sandbags.aspx

Homestead Green Building: Cob, Adobe, and Rammed Earth

Yes, I am including all three of these building styles into one post.  Why?  Well, the simplest answer is because there is very little difference between them.  They can vary, of course, with different things added into the mixture, but the basic underlying mix of each is the same.  These are, by far, the least expensive green building styles that you will come across.  After all, they are essentially just dirt.  You will have that in abundance pretty much anywhere you go.  You will, however, have to perform a test of sorts to determine the make-up of your soil.  Don't worry.  It's not a hard test.

To see how much sand and clay you have in your soil, do a simple shake test.  Dig down beneath your topsoil to get to what's underneath.  That's what you want to test.  Get a jar, and fill it about a quarter of the way up with your soil.  Top it off with water, and put the lid on.  Now, shake the dickens out of it.  You want to thoroughly separate the sand from the clay.  Once it's all shaken up, set it on a flat surface to let it settle.  The sand will settle first (unless you have heavier particles like gravel), and will do so pretty quickly.  The clay will take a bit longer, possibly even a week or more.  Once everything has settled, you can easily see the makeup of your soil.  The first layer is sand, then you may have a thin dark layer of silt, and then the top layer will be clay.  The best make-up of your soil for the greatest benefits will vary based on the type of clay (some are more sticky than others)  As a general rule, you want more sand than clay, but the ratios's can be anything from 1:1 to 1:25.  It just depends.  So after you know what you have, do a few small test bricks with different ratios, adding just enough water to make it like a yogurt consistency, to see which one works the best.  Too much clay, and you'll get cracks as the mix dries and shrinks.  Too much sand, and it will essentially crumble.  You can always purchase (or scavenge) more of either to add if needed.  Beyond that, the simplest thing is to leave the mix as is.  It can be used this way.  However, most experts will encourage you to add something else to mix for added strength if building a home or, really, anything much bigger than a small sculpture.  The most common additive at this point is straw.  This will help bind and strengthen the mixture, making it much more durable for bigger projects (like walls).  There are some who would suggest to add cement, ash, gravel, and even ground granite.  Granted, I am no expert.  But I would tend to believe that the straw would be enough for most projects, simply because that is what most experts focus on, and it's easy enough to obtain.

So what, exactly is the difference between the three building styles?  Simply put, cob is free-form.  It is built up onto itself without the use of forms.  It is easy to get creative here with curved walls, organic shapes, and even sculpture built right into your walls.  Adobe is the same mixture only formed into bricks, and laid out to dry in the sun.  Then they are layered, as you would masonry bricks, using the same base mix as the mortar.  If you like the look of a brick wall, but want it to be a little less expensive, this could be your bet.  Rammed earth is, again, the same basic mix, only this time, it is packed into wooden frames, one layer at a time, until the wall is completely built.  All of these options can be adapted to as thick or thin as you'd like.  However, thicker is generally better for supporting heavier loads.  Think of load-bearing walls needed to support the roof.

Another thing that all three of these options have in common is the basic care, both in the construction and maintenance.  In construction, it is important to remember that these are all made out of earth.  While they can very easily last a few centuries if properly taken care of, they will need a little protection to keep them from wearing away.  A little moisture won't do too much.  However, the idea is to keep excess moisture away from your structure.  You must start with a good foundation. In an earthen structure, it all begins with digging a trench around the perimeter of your future structure.  Your exterior walls will eventually sit on top of this trench.  The bottom should reach down to the frost line.   Fill the trench with gravel or small stones to help drain water through.  Some experts also suggest laying a polyethylene (pvc) pipe into the bottom of the trench, drilled with holes, in order to help the drainage.  Above this, will be what's called a stemwall.  This gives the wall above something solid to sit on, and keeps it from having direct contact with the ground.  You can use found stones, buy stones, bricks, concrete blocks, or even use recycled concrete pieces if you can find them.  Your cob/adobe/rammed earth sits on top of this.  Then, after you build the wall, you also need to protect it on the top with a good overhang.  There's not really a set size for the overhang, but the general rule is the bigger is better.  It needs to come out over the wall far enough to give it really good protection from any moisture that may come in from above.  I've seen everything from 10 inches to a few feet.  Just make sure it's solid and gives good coverage to the wall.

If you are building in a dry climate, you may be able to stop there.  However, it's always a good idea to put a good waterproofing layer on your earthen walls.  A lime-sand plaster is generally the most common, and it works very well.  There are currently some earth builders who are experimenting with something called waterglass (sodium silicate).  It's been known for quite sometime, but for this particular use, it has mixed results.  There is also a technique that is commonly used called tadelakt.  An ancient technique from Morocco, this is a lime plaster that is sealed with a black olive oil soap.  I'll get into this one a little bit more in a later post discussing interiors.  A good seal is important to any exterior wall, but remember to add an extra couple of layers to any portion that may have need of more protection.  For example, if you are building in an area that snows, you want to make sure that the bottom of your walls have that extra protection.  Of course, ideally, you'd want to set up some way in which the snow won't sit in direct contact with the walls.  These water-resistant methods can also be used for sinks and bathtubs.  Believe it or not, you can even have a cob swimming pool for much less money than a traditional pool.  Something to think about.  But again, I'll get a bit more into that later on.

You're probably now asking just how long will this take to dry, right?  Well, there's really no easy answer to that. There are few factors, such as climate, water in the mix, and thickness of your walls, that will alter the timeline.  In a very arid climate, it may dry so fast that you have trouble keeping up.  Whereas, in a wetter environment, it can seem like it takes forever.  But remember that while it may take longer to dry, this is going to be both the interior and exterior surfaces, and the internal structure of the wall, all in one.  Also, plumbing and electrical can be built right into the walls as you go.  So yes, it may take longer to build, but when you're done, you've already got all that other stuff already finished, too.

One thing that is very important to remember when using earthen materials for your walls, is that these are great for thermal mass, but are not insulation.  Whereas insulation keeps heat or cold in or out, what thermal mass does is it absorbs heat and then releases that heat slowly as the surrounding air cools.  It works beautifully in designs that include the use of passive solar.

These are easy techniques to learn and even master.  An earthen structure can be done by just about anyone with the will and time to devote to it.  Look to see if there are any workshops that you can attend to get good, hands-on experience, and you'll feel like a master in no time.  As far as building codes and guidelines, well, those are hard to pin down in one single post.  Some areas have strict guidelines, where other areas have practically none in regards to earthen structures.  So be sure to look up your specific area to find out for sure.

I will tell you that even if none of these building techniques seem right for you, mixing cob could still come into play in other types of green building.  It's great as a outer coat for straw bale and earthbag structures (which will be discussed in upcoming posts), and is also a great mortar for cord wood (also upcoming), and bottle brick walls we talked about  with earthships a couple of weeks ago.  There are so many uses, that it's just a good technique to learn.

There are a great number of resources out there for more detailed information.  The main source that I would highly recommend is here.  The lady who does this page is Sigi Koko, and I will tell you that she is so full of information, knowledge and wisdom, that you may not even need another source.  She is an expert in multiple types of green building and techniques.  Follow her on Facebook, Twitter, and YouTube.  I promise that you won't be sorry.