Houses with bags of soil isolated
Energy performance in most buildings can be improved with insulation, including those made of earth, such as adobe structures and earth bags. Although most earthen structures are located in hot, dry climates, there is a growing demand for low-cost and environmentally friendly earthen construction techniques in cold climates. This article explores three innovative methods for insulating buildings with earth bags, which extend their construction range to cold regions.
Most soil bag buildings use soil filled polypropylene grain bags. The bags are filled, stacked in level rows, and then solidly packed. One or two strands of barbed wire between the rows bind the bags together and add tensile strength. The construction process using insulation filled earth bags as described here would be almost the same, although the bags would weigh significantly less and speed up construction considerably.
Unlike other earthen construction methods, earthen bag construction has the unique advantage of providing thermal mass or insulation and can therefore be adapted for cold climates with an insulated fill material. Slag, pumice, perlite, vermiculite, or rice husks are all suitable insulating materials. These materials are natural, lightweight, easy to work with, and non-toxic. They do not burn or rot and do not attract insects or vermin. Additionally, slag, pumice, perlite, and vermiculite are not adversely affected by moisture and can be used as part of earth-filled structures.
The table below compares the approximate R-values of three sustainable insulation materials that could be used in bags of soil. (The first column in the table is the insulation value per inch; the second column shows the R-value for a typical 15 “thick earth bag wall.)
Material – R value / inch – R value / 15 ”
Rice husks – R-3 – R-45
Perlite – R-2.7 – R-40
Vermiculite – R-2.13 – R-32 to 36
(Source: Wikipedia Encyclopedia). Http://en.wikipedia.org/wiki/R-value_(insulation)
1) The first method of insulating buildings with earth bags uses bags completely filled with insulation. The main advantage of this method over the other methods described below is the ease of construction. The walls are bagged wide and completely filled with insulation. The thick plaster of earth or lime inside provides thermal mass to help stabilize the interior temperature.
A demonstration house using this method was built in Crestone, Colorado, with bags of dirt filled with slag. Slag is also known as volcanic rock or lava rock. Due to its volcanic origin, slag is filled with small air spaces, which makes it a good insulator. Although the R-value of the slag is debatable, the owner claims that these earth bag walls are comparable to straw bale walls of around R-26 to R-30. This estimate includes 5 “of papercrete at approximately R-2 / inch.
2) Another method of insulating buildings with earthbags uses tube sandbags, also called pull tube sandbags, which are typically used to improve traction of cars on snowy or icy roads. (Bags are sold to add weight for vehicle traction). This method involves stacking tubular sandbags filled with insulation on the outside of the walls of the soil bags, thus creating a double wall.
Filled tube sandbags provide approximately 10 “of insulation, which is perfect for many climates, not too much, not too little. Again, slag, pumice, perlite, vermiculite, or rice husks can be used as Insulation Perlite would be my first choice due to its high R-value (R-2.7×10 “= R-27) and resistance to moisture damage, although the final decision must be compared to other low-cost, locally available natural materials.
3) A third possibility is to add a seam along the soil bags to divide them into two compartments. The outer part could be filled with insulation; the inner part with earth. Like the other systems described here, this would create an insulated wall with thermal mass on the inside. For many situations, especially structures in moderately cold regions, this is an ideal wall system.
The location of the seam may vary depending on the weather. In a temperate climate like New Mexico, about 4 “-5” of insulation outside would suffice. This would provide approximately R-10 insulation. In slightly cooler weather, the seam could drop down in half (50% insulation / 50% soil). In extremely cold or extremely hot climates, you would fill the bags with 100% insulation (or all the soil in hot weather if insulation is not available).
