Some Basics of Building Science and Necessary Components

So I’ve found it helpful in my class work to conceptualize the building process into necessary components. Once you understand what a building needs to stand structurally and perform efficiently, it’s easy to see how natural materials can be substituted for conventional ones and how experimentation can occur.

As a disclaimer, this is a very simplified explanation of construction and building science. My understanding of these concepts is still rudimentary and is continually evolving. I am putting this to text as a way of helping me better understand and remember and also to share my ways of understanding these concepts with others who have limited building knowledge.

So a building needs several things to work correctly:

Foundations – a very complex subset in of itself, won’t go into detail here, but conventional foundations are generally poured concrete, while natural foundations are either rubble trenches (rocks packed down into a trench) or variations on poured concrete that aim to use less concrete by substituting in less harmful materials. The ultimate goals of foundations are to stabilize the building, keep it connected to the ground, and protect it from the underground freeze-thaw cycle of moisture that can damage buildings structurally. Due to variations in the type of building and the water table and frost line of the area in which you’re attempting to build, different projects and different sites indicate different necessities of foundation work.

Structure – what holds up the building, bears the load of the building materials, the people and things inside of it, and natural factors like wind and snow.

Conventional architecture: stick framed stud walls, made of highly standardizable 2x4s.

Natural building: Stud wall system, timber frame system, or building materials that bear the load themselves, such as earthen structures or stone structures (and sometimes strawbale).

Insulation/Wall Mass – this is where it gets fun. All high performance buildings need insulation to keep heat (or cool) inside the house and the undesirable temperatures of the outdoors out doors. This reduces energy consumption and is in general a highly sought after feature of “green” buildings. This is generally also what makes up the thickness of the walls. Have you’ve ever wondered: what is this wall made of? Besides the structural framing, it’s mainly insulation.

In conventional architecture, this requirement is usually accommodated by foam, spun fiberglass, or some other industrial, petrochemically-derived, and generally toxic substance, along with drywall or other types of flat board to connect it to the structure and offer a surface for paint and finishes.

In natural building, it opens up a whole world of possibilities. Types of natural buildings are generally categorized by their wall systems/insulation types. It is important at this point to make a distinction between insulative wall systems and massive wall systems.

Insulative wall systems maintain a heat barrier between the indoor and outdoor environments by providing lots of tiny little air spaces in the materials. Air is the best insulator, so tiny air spaces create insulation without allowing heat to move through large holes or paths (which would happen if the air spaces were too big). So the main examples of insulative wall systems in natural building are straw bale (all that straw = lots of air space), straw-clay, woodchip-clay, and cellulose (recycled paper blown into wall cavity and compacted down). Most insulative wall systems require a structural system along side them, because they cannot support the building on their own. So for instance, straw bales will be wrapped around a timber frame, or sculpted inside a stud frame, straw clay and woodchip clay can be fit into a double stud frame using slipforms or wood lathe forms, respectively. The main exception to this rule is structural straw bale, in which straw bales are laid in such a way that they actually support the structure of the building, kind of like stones or bricks. Insulative wall systems are best used in colder climates, where through either passive solar or efficient wood stoves, heat is produced inside and then trapped inside, reducing fuel consumption.

An example of how a straw bale insulation system can relate to a wooden structure system.

The other type of wall system in natural building is massive walls. These are often characterized by earthen materials – cob, adobe, cordwood, and stone masonry are all examples of this. Massive walls are better suited for hot or more temperate climates that the Northeastern US. This is because they absorb heat steadily, keeping the inside of the house cooler, but will also release heat if the temperature outside drops below the temperature of materials, releasing heat back into the house if necessary. They are not insulative and would take a very long time to heat up in a climate like Vermont, making them more suitable to the Southwest or warmer climates such as that. However, massive elements such as stone and earth can be effectively utilized INSIDE of homes with insulative wall systems as a natural means of climate control. If the inside of the home becomes too hot at any point, they will absorb the excess heat and store it. Indoor massive elements are also essential components of passive solar design, in which large amounts of sunlight are allowed into the house, then absorbed by the stones or earth structures, which then release the excess heat when the house’s temperature drops at night. Massive wall systems also frequently multitask as structural systems. Just like a stone wall or a brick wall is able to hold itself up because of it’s massive strength, adobe blocks or cob (which is really just like unfired bricks sculpted into the wall instead of mortared) can generally support themselves and the indoor and roof structure of a house, if designed correctly.

A smaller but essential feature of some natural building materials is a surface for the plaster (which acts as the plywood/vinyl siding, etc. on the inside and outside of the structure) to adhere to. Plaster is forgiving and sticky on its own, but it still needs a rough surface for optimal adhesion.

There are other elements – such as roofing and final finishes (which can be beautifully substituted with natural materials), but we haven’t gone so much into those features in our class and it’s the elements of structure and insulation that interest me most with regards to conceptualizing these ideas. You can see (hopefully, maybe I’ve made it awfully confusing) how once you understand what a building needs and what natural materials provide these needs, the options for creativity are (basically) endless. This is especially so when you get down to the intricate details. What should I use for an air fin to seal areas when plaster meets a wooden edge? How can I stop thermal bridging in my structure? I won’t go into what all these terms mean. That was just me showing off my knowledge of more complex building terminology hehe.

So just some application of this knowledge:

In a cob structure, the thick earthen mix acts as the structure and the massive wall system. Plaster can be applied to the earthen wall.

In a strawbale structure, a wood frame (either stud or timber style) acts as the structure, wall the straw bales are the insulative wall system. Plaster is then applied directly to the rough surface of the bales themselves.

In a straw-clay building structure, a double stud frame is utilized was straw clay mix packed and tamped down into the cavity between the two studs. This is achieved using a slipform, which is a piece of wood board temporarily attached to create a form while the mix is being added, then removed and moved up, so that the whole wall structure can be created without excess wood. Small braces are needed into a straw-clay wall to connect it securely to the wall structure. Plaster can be applied directly to the rough surface once it’s dried.

You can see how this can lend itself to creativity. Straw bale wall systems can be combined with cob interiors for an insulative/massive dynamic. Straw clay is used as an extra insulator in straw bale structures in the lights grooves, wells, and corners that the straw may not reach (although ideally you have good enough straw craftsmanship to avoid this is the first place). Straw bales can go inside or outside structures or be their own structure! You can slather many different mixes on top of that and incorporate true craftsmanship in terms of stone work, timber framing, sculptural earth, and so much more.

Beyond these basics rules (as well as a lot of smaller details to keep in mind) there are two aspects of building science that are always essential to understand when designing a natural structure: thermal dynamics and moisture dynamics. I addressed the issue of thermal dynamics earlier with regards to insulation – you want a structure to be as well insulated as possible to perform efficiently in terms of heating. But super well insulated houses subsequently pose the problem of moisture. If we don’t build in moisture permeable surfaces and ventilation systems into our super airtight homes, moisture can get trapped inside, causing terrible problems like mold and rot, especially in natural structures made from straw (yikes). This is a whole different shebang – maybe I’ll get more into it as I learn more.

Sorry about this super long and dry post about building structure. I found it interesting and fun to write and hopefully you’ll find it fun to read. I have pictures illustrating some of these concepts from the building structure we’re working on, but it’s a little late to load those on. I’ll post them tomorrow, as well as some pictures I’ve been accumulating that have been inspiring me recently with regards to natural building design.

Thanks for reading!

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