Glossary

Natural building materials are age-old, but the terms we use to describe these materials are relatively new to the dialog about construction.  As a result, I often notice some confusion in the use of different natural building terms as well as confusion about how each material is used to its best advantage.  This page is meant to help dispel some of that confusion.  Please post a comment if you'd like clarification on these or any other natural building terms or if you have suggestions on other materials to include.

CLAY BUILDING MATERIALS

sculpted cob bench at Black Ankle Vineyards
Clay minerals have very small, platelet-shaped particles, that create sticky little suction cups when wet and keeps a strong internal bond when dry.  That stickiness and plasticity is what makes clay such a great binding "glue" for a variety of natural building materials.  Because clay expands when wet (making it sticky) and then shrinks as the water evaporates, clay-based building materials include an aggregate, such as sand, to increase strength and reduce shrinking (and thus reduce cracking).  There are many different types of clay, with different capacity to absorb water, different expansion, different stickiness.  So use of clay as a building material requires testing of the specific clay that will be used to determine the best ratios of clay & sand (as well as any other ingredients).

Clay building materials are classified as "thermal mass", which means they act as a battery or fly-wheel for heat energy...absorbing heat energy when the environment around is warmer than the clay and releasing heat energy when the environment around is cooler.  Clay walls work well as solar heat storage walls (trombe walls) for passive solar designs.  Clay materials do not have insulating value, so should be used where high thermal mass, not insulators, provide the best thermal efficiency.  (For more information on where to use clay-based materials, see http://buildnaturally.blogspot.com/2010/12/strawbale-vs-cob.html.)

ADOBE refers to blocks, bricks, formed from a wet mixture of clay, sand and long straw or other fibers.  Enough water is added to the mixture so that the clay is slightly soupy, the consistency of sour cream, allowing the mixture to be poured into molds without leaving any voids.  The top is smoothed over, the forms are removed, and the bricks are placed in the sun to dry.  The sun-baking hardens the clay (more than if they dried in the shade, but not quite as hard as firing).  When dry, the bricks are mortared together using a clay mixture similar to the original adobe recipe.

COB is sometimes called "sculptural adobe", because it uses the same ingredients as adobe bricks (clay, sand and straw or other fiber), but it is formed, or sculpted, in place...building a monolithic wall system from the bottom up.  The main difference between cob & adobe, is that the walls are built while the clay is wet.  Wet clay has a limited capacity to support weight before it begins to flow like a liquid, so walls need to dry in place as you build in order to be strong enough to support additional weight above.  The dryer your cob mixture, the quicker you can continue to build vertically; the wetter the mixture, the longer you need to wait for it to dry before continuing to build.  Cob walls are generally built in a battered form, which means they slope inward as you go up, getting thinner and thinner at the top.

RAMMED EARTH uses a mixture of clay and sand tamped into formwork to create a monolithic wall system.  The compression of the tamping mimics natural geologic forces that form sedimentary rock...so rammed earth construction resembles hand-formed sedimentary stone.  Rammed earth is denser than adobe or cob, so is stronger and has higher thermal mass per volume of material.  Tamping is traditionally done by hand, though modern rammed earth often uses pneumatic machines.  It takes surprisingly little effort to hand tamp!  Because the stickiness of the clay platelets is achieved through force, the mixture is not wet, as cob or adobe are...the mixture is more damp and crumbly.

COMPRESSED EARTH BLOCKS are blocks made from rammed earth, often using a hydraulic machine that extrudes the blocks.  The blocks are often shaped to interlock with each other so they can be assembled without the use of mortar.


STRAW-BASED MATERIALS

stacked strawbales with bamboo pins
Straw has been used in construction for thousands of years, mostly as an ingredient in clay-based building materials.  The invention of the baling machine in the 1880's, however, created the innovation of strawbales building blocks, that could be stacked into walls, like big fuzzy, highly insulating bricks.

Straw is best used where you benefit from high insulation.  For example if you heat a space in Winter, you want insulating walls to keep the heat inside, saving on energy costs.  The variation depends on the quality of installation.  Straw is cellulosic, like wood, so it will rot if persistently over 20% moisture content.  However, like wood, it can be easily detailed to ensure that it remains dry & durable...bottom line is that if you can build in your area with wood, then you can build with straw.  (For more information on how to build durably with strawbales in any climate, see http://buildnaturally.blogspot.com/2011/01/yes-you-can-build-with-strawbale-in-wet.html.)

INFILL STRAWBALE refers to a method of construction where strawbales are wrapped around or fitted between a skeletal structural system.  All of the structural loads of the building are supported by the skeleton, not the strawbales.  Tests for the insulation value of strawbale walls show a range, between R-1.75 per inch on the low end and R-2.67 per inch on the high side, which converts to R-31.5 to R-48 for an 18" deep strawbale wall.  Which makes strawbales about the least expensive way to build a highly insulating building.  Strawbale walls are typically plastered on both sides with breathable plasters, like clay and lime.  Infill strawbale construction meets all current building codes, including requirements for smoke development, fire rating, wind loading, etc.

LOADBEARING STRAWBALE refers to a building where the weight of the roof and any floors are held up by walls made of strawbale.  The bales are stacked like bricks and pinned together for stability.  A box beam runs across the top of the strawbale walls to distribute any roof or floor loads evenly onto the strawbales.  To ensure structural stability, structural strawbale walls should have a ratio of height to width that does not exceed 5.6 to 1 (ie, the height should not be more than 5.6 times the width of your bales) and the ratio of unsupported length to bale width should not exceed 13 to 1 (ie, an un-buttressed wall should not be more than 13 times the width of your bales).

LIGHT CLAY STRAW/SLIP STRAW is a centuries-old material used for insulation between half-timber (fachwerk) buildings.  (The name light clay straw is a translation from the German term "leichtlehm", which means "light clay".)  Light clay straw is made by coating loose straw fibers with a light coating of clay slip and then packing the coated straw tightly between formwork.  The clay dries and binds the straw into a tight, insulating wall, rated at about R-1.5 per inch.  Once dried, the walls are often plastered on both sides.


HYBRID MATERIALS

cordwood & bottle wall with lime mortar
Several natural building materials are actually hybrids..combining two or more other materials.  Some of these are described below, along with appropriate applications for each.

WATTLE & DAUB is an ancient technique where a sticky clay mixture is pushed though and around woven lattice work.  The lattice, or wattle, is formed by weaving thin wood or bamboo around vertical stakes.  The daub material is made from a binder (usually clay or cow manure), aggregate (such as sand), and a reinforcing fiber (such as straw).  Wattle and daub walls can be quite thin, since their strength is reinforced by the internal lattice work.  They are suitable for interior walls, or where exterior walls provide enclosure but do not require high thermal mass or insulating properties.

CORDWOOD construction uses short, debarked pieces of wood plus a mortar to build a monolithic masonry wall system.  The wood is stacked, like firewood, so that the cut ends because the face of the wall.  Each piece of lumber is cut to a uniform length (usually around 16" to 24"), which then determines the thickness of the constructed wall.  The mortar used between the wood can be lime-based or clay-based cob.  Cordwood walls perform with a combination of insulating and thermal mass properties.  The R-value is around R-1.5 per inch thickness.  Cordwood can be appropriate for exterior walls and loadbearing walls.  This method of construction should only be used where wood is in abundance, especially where log-ends or salvage wood are available for repurposing.


PLASTERS & PAINT

durable clay plaster
Natural paints and plasters use a variety of non-toxic ingredients to make beautiful, durable, and incredibly forgiving finishes.  All paints and plasters use a binder, or glue, to make it sticky.  The binder is what keeps the paint/plaster glued to where you apply it.  Plasters are distinguished from paint in that they are applied in thicker layers...usually 1/8" thick or more.  Because plasters have mass, they also generally include an aggregate material to improve strength and reduce shrinkage as the plaster dries.  Sometimes plasters also include fiber reinforcing, such as chopped straw or animal dung.  Natural paints and plasters offer beauty and durability, and invite DIY experimentation and creativity.

CLAY-BASED PLASTERS use sticky clay binders to adhere to walls.  Clay is sourced from the earth, often found locally in the soils nearby the building site, meaning the materials are literally dirt cheap and non-toxic.  Since clay increases in volume when wet, and then shrinks when dry, sand is added to control cracking (since sand is the same volume wet or dry) and to strengthen the plaster.  Clay creates a breathable finish with the natural capacity to regulate moisture and temperature in the surrounding air.  Clay plasters are simple to make and extremely forgiving to use, even for beginners.

LIME PLASTER can be confusing, because the term 'lime' can refer to various chemically different (but related) materials.  (Not to mention the citrus fruit!)   Lime has been used for thousands of years as a fabulous binder in mortars, plasters, and paints.  It wasn't until the post-World War II housing boom that quick-setting cement products eclipsed lime in construction.  Lime does cure more slowly than cement, but it holds many advantages as a workable, self-healing, breathable, nearly carbon neutral material, making it much more suited to natural building.  First, because it has a lower environmental impact.  (Cement production creates 1.25 pounds of CO2 for each pound of cement produced, whereas lime is nearly carbon neutral.)  Lime plasters are suitable finishes over nearly every natural substrate, and create a breathable (vapor permeable) surface that is weather-proof.  I use it for exterior plasters on strawbale as well as in shower enclosures.

TADELAKT is a Moroccan technique for finishing lime plaster that creates a smooth, sensuous, nearly waterproof surface.  The traditional application involves polishing olive oil soap into a lime plastered surface, while the the surface is still "green" or plastic, using smooth stones.  The polishing process tightens the pours in the plaster.

NATURAL PAINTS describe a variety of paints for a range of applications, all of which are made from natural, non-toxic, non-off-gassing ingredients.  Natural paints start with a binder, such as clay, casein (the protein found in milk), egg, beeswax, lime, and others.  The binder provides the glue that allows the pigment or color to stick to the surface you are painting.  Pigments are generally mineral- or plant-based, so also natural and non-toxic.  Not all natural paints are appropriate for every application...for example, clay paints need absorbent surfaces (like unpainted drywall or clay walls), lime paints & washes can be used outside where weather resistance is important, egg yolk paints work on furniture, etc.


FLOORS & FOUNDATIONS

installing finish layer of an earthen floor
Buildings start with a good foundation, and the ultimate durability of a structure is often linked to the quality of the type and installation of that foundation.  But foundations aren't that sexy, so they often get overlooked.  (Not here!)  I'm also including earthen floors in this section, since they are a great substitute for concrete slab-on-grade installations.  (See above for notes on the characteristics of clay-based materials.)

RUBBLE TRENCH FOOTER is simply a continuous trench footer around the structural perimeter, dug as deeply as the ground freezing point in winter.  The trench is lined with filter fabric and filled with stone.  A structural (usually concrete) grade beam (a beam that rests on the ground) is poured on top of the stone-filled trench, and distributes the structural loads of the building across the surface area of the trench below.  This type of foundation uniquely provides both structural bearing as well as water drainage in a single foundation system.  Drainage is important with most foundation systems, since water is the single largest culprit for foundation failure.  Liquid water can erode the ground bearing around a foundation footer, and frozen water expands when it freezes, which causes the ground around your foundation to also expand and contract with freeze-thaw seasonal cycles.  When installed correctly, a rubble trench results in a resource-efficient, high-performing, eco-friendly, and low-cost foundation footer.

ADOBE FLOORS/EARTHEN FLOORS are made with the same ingredients as adobe and cob: clay, sand, and straw.  The clay is the binder that holds everything together.  The sand is the aggregate, that makes the floor strong and helps to control shrinking (and thus cracking) as the floor dries.  And the straw provides tensile strength, which knits the material together and also helps to prevent cracking. Earthen floors work well where a high-thermal mass (heat absorbing) material is beneficial, such as for passive solar designs.  The adobe is installed in one, two, or three layers, depending on the finesse of finish and on construction timing.  And is installed over a moisture barrier, several inches of sand or stone to create a capillary break (prevent water from rising into the floor), and usually some insulation to allow for temperature control inside the space.  The surface is sealed when the clay is completely dry, usually with linseed oil or beeswax (or both), to create a beautiful, durable, and wear-resistant floor surface.

DRY LAID STONE refers to stone walls that are built without mortar.  Eliminating the mortar heightens the importance of fitting each stone to the ones below.  No mortar also means no wicking points for moisture to enter the stone wall.


ROOFING

living roof in Pennsylvania
The primary purpose of any roof is protection from the weather.  The most desirable type of roof for any particular application depends on the materials available locally, the performance characteristics that would best benefit your building, whether rainwater will be collected from the roof, the pitch of the roof and other aesthetic considerations.

THATCH is a highly insulating roofing system made by lashing bundles of reeds or straw (or some other appropriate, locally sourced plant) to battens on the roof.  Quality thatch is superbly durable, lasting decades, with the ridge sometimes requiring repair or re-thatching each decade or so.  There is a perception that thatch roofs are highly flammable (most because of movies, I think), but in fact, the surface can burn, but then it chars and slows the flame (I've read it described as trying to burn a closed book).  Thatch is appropriate in any climate, especially where a highly insulating roof helps keep heat inside during Winter, but should be used on roofs with a good pitch on them (to help shed water).

LIVING ROOFS/GREEN ROOFS are roofing systems that allow plants to thrive on the surface of a rooftop, without access to groundwater...so creating an ecosystem that relies on rainwater alone).  Plants used are generally rock garden plants that thrive in your particular climate, and specifically often include succulents, like sedum plants.  The two main benefits of planting your roof are absorption of rainwater (especially useful in urban and suburban areas) and a net cooling of the roof surface (to help keep your building cool in summer).  Living roofs can also work in any climate, especially where a cooling roof will help keep you nice and cool in Summer.  Installation of a living roof is easiest when the pitch of the roof is shallower than 30-degrees.

7 comments:

  1. This is incredible Sigi, thank you!
    I am in the process of developing the website for a 501 C 3 Green Haven Homes. greenhavenhomes .org
    very early stages as I have hired a firm Accents Interactive to develop it. Hope to make it public within a month or so. I would love to have the ability to promote you and the information that you share through this site. I have studied most of what you offer and feel compelled to work with you at some degree in the near future. As funding becomes available I plan to hire you as our chief designer, consultant, or any other role that might be of use in making a positive difference for human beings in general. Please check out the start of my site if you have the time. Understand that it's a work in progress please, and I would really appreciate any critique that you might be so gracious to share...natural building is a wonderful process that needs to be taught and shared for many great causes..
    Thank You again for all of the wonderful work that you accomplish and share,
    Buck Harmon

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    1. Hi Buck,
      I'm so glad this is helpful to you! I want to expand it and make it more interactive over time...linking to images and more detailed info and videos... But here it is for now. :-)

      Your site looks like it will be great! I love your mission, especially how you write about education being the key to transformation. I completely concur! And it would be my absolute honor to partner with you in some way whenever you are ready. Maryland, look out!!!

      Enjoy the rest of your weekend, Sigi

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  2. AAahhh!! Thank you! This glossary is indeed incredible work, thank you very much!

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  3. Thank you Sigi for explaining & summarizing the materials here. Very helpful!

    Diane

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  4. Hi Sigi! I gonna ask something very silly but is a big doubt I got and i cannot found answer in the net. For build with cob you can use the soul of your land if it have enough clay. Ok my question is how I can prepare the soil? I mean, it have little stones and roots. Do I need to clean the soil of this things before I mix it with the sand and straw? Thank you

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    1. Hi again Barbara,
      It's a great question! So I sift the soil, like is shown in this video;
      https://www.youtube.com/watch?v=JwDHLOGK7RY&list=PL888E4B9BABB67AD0

      The sifting takes out big rocks and breaks up the clay. You shouldn't really have lots of roots...because you should be under the topsoil layer and don't dig into tree roots (or you can kill the tree). Hope this helps!

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  5. Thanks a lot for the answer!! Is very helpful. I just subscribed to your youtube account so I can keep learning! Xxx

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