Week 2: Foundations

After enjoying a relaxing weekend, the students in the Natural Building Certificate Program at Yestermorrow greeted each other Monday morning and readied themselves for the week ahead. The days would be divided into two separate classes: Foundations and Stump to Sticker. The latter course would focus on the processes involved in milling local lumber, while the former would cover the basics of designing a good foundation. Both classes would relate directly with the project at Knoll Farm since the students would be pouring the foundation for the structure and using the milled lumber in the building.

Having established a visual foundation of the project, as well as an understanding of natural building materials and methods, the class set about understanding the physical foundation of the building on Monday. Led by the eccentric-jack-of-all-trades, Robert Riversong, the students learned about the many different styles of foundations in the world of building. From slab-on-grade to full cellar to frost wall, the class discovered the importance of a good foundation as well as the importance of choosing the correct style for a particular site. For the project on Knoll Farm, a rubble trench foundation was chosen for its lessened use of concrete, and hence, a reduced impact on the environment. Concrete happens to be the most widely used man-made product in the world and its manufacturing and transportation accounts for upwards of ten percent of total, global energy use. Therefore, it is of paramount importance that the reduced use of concrete occurs, while the research and development of alternatives continues so that more environmentally friendly options become available.

The rubble trench foundation was also chosen for its superior draining capability. Vermont is known for its very wet soils and the site at Knoll Farm proves the point quite well! A layer of bedrock at the site keeps rainwater near the surface and offered a challenging design aspect for the foundation. To remedy this situation, filter fabric was laid at the bottom of the trench below the frost line. Then, a few inches of small rocks, also known as rubble, were backfilled on top of the fabric. This was followed by the placement of a perforated, drainage pipe over the layer of rubble. More rubble was then poured over the pipe and then the filter fabric was wrapped over the “rubble-pipe sandwich”. The rubble trench was then completed by backfilling more small rocks into the trench to bring the level up to grade, or ground level. This design allows the inevitable flow of water to go through the foundation, while keeping the drainage pipe free of debris. Since the water is always on the move there is very little chance of freezing, or frost-heaving, which can cause a foundation to move and consequently wreak havoc on the structural integrity of a building and/or its components.

With the rubble trench in place, the students began the task of leveling out the top of the rubble in preparation for the pouring of a concrete grade beam. The grade beam distributes the weight of the structure onto the rubble trench, while also forming the “footprint”of the building. Additionally, the grade beam serves as a barrier for any water that might make its way into the structure. By using a contractor's level, the students were able to sight the level of the rubble within an 1/8 of an inch all around the footprint. This would assure an even and level pour of the concrete for the structure to sit upon...and this was just Monday.

Tuesday found the class putting together the form boards for the grade beam. While some concrete contractors often throw away the form boards after a pour, instructor Robert Riversong came up with a method of reusing them within the floor of the structure, which would be built later. By wrapping plastic around the top, inside, and bottom of the 2x12 boards, the students were able to keep the forms free of concrete. Simple ideas such as this one can save a lot of money, as well as reduce the resources used in a project.

Having squared off the form boards to the correct dimensions for the footprint, the students used Wednesday morning to lay three, parallel runs of rebar inside the forms. In a foundation, the rebar is usually set about two inches off the bottom and adds structural integrity to the concrete beam. In terms of a more natural material for this application, bamboo is often used since it possesses a similar tensile strength to the steel found in rebar. With the everything set for the pour, the students sat down to lunch and awaited the concrete truck to roll up the hill.

A concrete pour could be compared to the chaos that ensues when a raindrop hits an anthill: once the first drop hits, it is a scramble to make sure everyone is in the right place and doing their job properly. Depending on factors such as the weather and the amount of water in the concrete mix, the material can set up quite fast and being prepared is the key. As the driver of the truck guided the chute over the forms, the students quickly went to work spreading the concrete inside the boards. Once an area was filled, the truck would move on down the line the process would repeat itself. Meanwhile, other students used “skree boards”, two foot long 2x4's, to smooth out the top of the beam and ensure even coverage throughout. In perhaps the most satisfying aspect of the pour, still other students used metal trowels to finish the beam with a silky-smooth texture.

As the truck neared the last section of the beam, the final ooze of concrete crept out of the chute. In a humanistic twist of fate, the amount of concrete ordered barely missed filling out the form. Such is the nature of the beast in the world of building, be it natural or conventional. While the truck driver cleaned out the chute of the truck, a second order of concrete was placed. However, the minimum order for delivery far exceeded the amount needed for the empty area. So, in a creative twist of fate, the students brainstormed for some alternative uses for the extra material. These are the types of real-life situations found in Yestermorrow classes that would not be found in the conventional classroom. The result, after the second truck came and went, were several concrete-block stairs which were imprinted with the shapes of leaves from around the site and a concrete bench to commemorate the site.

By paying careful attention to the design of the foundation at Knoll Farm, the use of concrete was minimized without sacrificing the structural integrity of the grade beam. This attentive planning also provided the ability to reuse the form boards that helped to shape the beam. Thinking about these logistics also helped make for an easier pour, despite having to order more concrete. In the end, the problem quickly turned into a creative solution. The natural beauty infinitely imprinted on the concrete stairs will serve as a reminder of the ability to turn an unwanted situation into a lasting, loving memory.