IMG_2929.JPG Cob Home Eco-construction

After gathering information and studying two books on cob construction (see on cob book page). An old collapsed ruin in the garden was studied for restoration, but finally another site was chosen. A small round cob room was designed with possibility for future extension. A drainage trench under the wall, was dug, filled with gravel and terracotta pipes were installed. A few meter outlet was made. The ground around the house was leveled to conduct the water outward. A stemwall, with rocks from the ruin, is actually under construction (01.09.12).
  • Design the Construction

    • Cob Building Choice

  • IMG_3045-mini.jpgIMG_2628-mini.jpg
  • The goal is to build with common materials that can be found on the site or locally, and the building easy to reproduce. Apart from the classic advantages of building with cob, such as aesthetics, connectedness with nature, breathability or ecology, the choice of this type of building was essentially motivated by three reasons specific to the site. First, cob is fireproof, a real hazard when surrounded by a forest in a dry climate, with precaution from locals. Second, clay for cob is abundant on-site, as it has been spread when the well was drilled, years before project start, into a thick 15cm layer that is asphyxiating the soil and should be removed. Third, cob insulation is very good, an important aspect in this climate with summers over 30°C for 3 months and a month over 35°C, and should regulate the high summer temperatures and rainy and cold winters. Additionally, many surrounding cities in this region cultivate wheat which makes straw abundant for cheap.=
    • Existing Ruin Examination

  • IMG_2624.JPGFirst thing that was done is to examine an existing small ruin, with remaining wall of 60cm, and assess if it is appropriated to build over it with cob. The ruin was a dry stone construction that collapsed one day. A lots of rocks inside the ruins was removed and the walls were examined, but two major problems were found, apart for not being able to choose the shape of the house. First, the ruin, situated at the highest point in the land, was also placed on the steepest place, and the ground level is at the height of the wall uphill. This a real problem for drainage, as if the strong rain soak uphill, the interior would be flooded, and the only solution was to significantly lower the ground level uphill or raise the floor level inside, which is a very large task. Second, at the lowest point, the wall was built by placing simply stones on a sandy soil. Stones at the bottom of the downhill part of the wall was not buried, with no foundations, and threatens to compress the sand and move under cob wall weight. These two reasons prevent us from using the ruin wall to build our cob home, and can explain why it collapsed years ago.
    • Siting the Construction

  • The choice of the exact position and orientation of the house, several alternatives that allow to not remove any tree, were compared by taking into consideration access and feeling and for their relation to the four elements - i.e. Sun, Wind, Water; Earth. Orientation relative to the sun can moderate summer heat, especially with southern trees shadows, while in the winter when these trees are deciduous the sun can heat the house. Wind, strong in this area, is influenced by house altitude and surrounding trees, and can similarly cool the house in the summer but be difficult to stand in the winter. Rain water, is essential for cob building, in a country with regular annual floods, and rain runoff can be abundant and threaten house cob walls, if it is placed at the bottom of a long slope. Earth quality and access to clay is also important, as on the higher half of the site, 10cm of clay cover the original sandy soil that can be found on the whole site. The final site choosen (see the the picture below), in the upper half, on a moderate slope, had a mulberry at south east tree to protect it from morning sun in the summer, and cypress trees as wind break that may be pruned later to offer more winter sun.
  • Almond House
    Almond House
    • Shape and Interior Design
  • A round shape was choosen, on the picture above, well suited and cob building and very stable. The space of the construction is limited by trees and only a small room about 15m² is needed for a start. A second room can be later built as a future extension. The trees all around helped to find the contour of the room. By keeping a small distance from the trunk and canopy, a contour is traced and looks like an almond, the most frequent tree on the site. The ‘almond house’ has a lot of similarities with almonds: it is small, it won’t be flooded by rain water. This room will function as a place to rest, to chill out and also as a storage for materials. Its design has a quite separated sleeping space and living place that look toward the windows, instead of looking toward the bed when entering the room or when sitting in the small living place. Finally, this design is simple and transformable to future needs, therefore no built-in benches or furniture was planned.
  • Drainage

  • Drainage is an an essential part of Cob construction, as it prevents the cob walls from being soaked and the interior from flood, even even in the event of a very abundant rain, which happens annually in this region (i.e. 100mm of rain in 24h). The choice of drainage system is threefold: a Rubble Trench drain under the cob walls, a Berm around the house and an uphill Swale. A French Trench drain can be later added if the drainage is proven insufficient.
    • Rubble Trench Drain
Digging: After tracing the contour, we dug the rubble trench at almost 50cm of deepth and 50 cm large. We also dug a smaller trench to lead the drained water 5m far from the construction, large enough for the pipes. Our ground is slitly slopped with the first 10cm of clay, 10 cm of sandy loam soil, a sand layer and a final layer of very thin sand and rocks. We excavated layer by layer and stocked the different materialsfor later use. We put the clay in the center of the house and the sand nearby, while the sandy loam we moved it a little further near the planting beds areas. We haven't flattened the area before starting, even though it could be a good idea after later consideration. We compacted the trench several times with a tree tronc as tool and water.

Pipes: We posed the pipes of 10cm dimetre on a compacted layer of 3 to 7 cm of big sized gravel. The pipes followed the slope of the site with lower point the smaller trench where the water will exit. The clay pipes following the almond shape were fixed one with another and covered with gravel.

        • Filling
        • Mismatch between Design and Realization: While digging the planned dimensions of the trench varied from place to place and as a result the trench and the wall will be thiner than planned initally. The use of sticks to mark would be helpfull to follow the initial plan.
    • Berm
    • Uphill Swale
  • Stem-wall

    • Moving Stones
    • Puzzle Stones
    • Stabilize Stones
    • Ditch Adjustment