This project is located in: Köppen–Geiger Zone Am, ICC Climate Zone (SIM) 0a, in an area with 0 Heating Degree Days and 6093 Cooling Degree Days.
After the wonderful experience of attending the 2016 International Straw Bale Conference (ISBC) in New Zealand, I attended a workshop that Steve Richards held on an exciting new way to build with straw called “Light Straw Construction” (LSC). This is a process similar to rammed earth, but using only a light straw and clay mixture tamped in around solid framing members. Several qualities made it more intriguing to me than straw bale construction:
• LSC is a space saver. The walls are between 6 and 8 inches thick, which is much thinner than the 16-18 inch wall thickness of conventional straw bale walls.
• We were living in Bali and baled straw wasn’t available. Bypassing the DIY baling process was a real time saver.
• LSC still has many of the wonderful qualities of straw bales with only slightly smaller insulative and sound absorption values.
•LSC takes a natural plaster finish more easily than bales do because the exterior straw finish is very smooth once the forms are removed.
The LSC workshop opened up a whole new world of possibilities that I couldn’t wait to try out.When my husband left town for three weeks, I decided I would surprise him with a new bathroom upon his return. I tore down the old termite-infested bathroom walls and began experimenting with Light Straw Construction at home. Overall it took about one and half months to complete the bathroom for less than $400, which was basically the cost of the finishes. The walls were free. It pays to go natural!
1. We chose to use bamboo framing inside the walls and a plywood formwork to shape the straw. Bamboo and straw are both readily available in Bali and we can treat the bamboo with borax to make it resistant to bugs. We also added bamboo pegs horizontally on the framing members to help lock the straw into the walls. We used two pegs per bamboo segment, extending the pegs approximately 3 inches into the wall cavity on each side. Wooden shims were added to the bamboo for attachment points for the plywood forms. The space created by the shims allowed the straw/clay mixture to fully cover the bamboo frames.
2. Next we prepared our clay slip and our straw mix. For our straw mix we used a combination of rice straw and chopped up old grass roof panels that would have gone to the dump. Our roof was getting replaced and we had piles of roofing material to use. For our slip we mixed clay with enough water to make a nice soup, just enough to coat our fingers. We added a few pails of our soup to the straw mix and tossed it like a giant salad, ensuring every piece was lightly coated with the clay slip. We carefully avoided overly wet areas by adding more dry straw, and we kept tossing until it felt slightly dry and a bit tacky. “The trick is to toss the mixture until the dry crunchy sound goes away,” noted Steve in his workshop.
3. We pushed our mixture into the framed cavity wall with a broomstick and were careful to really work the corners. With the amount of compression, it took a surprising amount of material to fill. We then added another layer of plywood once we filled the first section, and then did it all again.
4. Once the walls had dried we removed our plywood formwork and added a layer of wire mesh to the wood blocks on the bottom half of the wall. The mesh would fortify the bottom half exposed to rain splashing from the ground and the top half would be protected under the eaves.
5. We plastered the walls with a mixture of locally dug clay, black volcanic sand, and chopped straw. To our delight the earth plaster went onto the rammed straw wall just as easily as it did over the wire mesh.
6. For our finishing touches, we added a “Truth Window” made with custom shaped glass. It’s a treat being in Bali where glass panels can be readily sculpted to any design. Just sketch it out and the glass shop down the road carves a plaster mould; a glass sheet is set on top, covered, and then set into a kiln where it melts into the moulded shape. The glass was inlaid into a small slab of wood and lined with a strip of black wood and framed with coconut shells set in resin.
Jeni is an architect living in Bali, Indonesia for the past 15 years. She has a passion for natural buildings but it wasn’t until living in Bali that she was able to experiment with the rice straw, bamboo, and clay that are abundant there. She can be reached at jenikardinal@gmail.com
