The stem wall under a straw bale wall must rise at least 30 cm above finished grade, and 45-60 cm in wet climates or where snow is heavy, so splash and snowmelt cannot reach the bales. It can be dry-stacked stone, urbanite, adobe bricks or gravel bags, and it carries a moisture barrier on top, because masonry itself wicks water into the first course.
Part of Straw Bale Construction
The stem wall is the short masonry wall between the foundation and the first bale course.
Height Is Set By Splash And Snow, Width By The Bale
The stem wall exists to keep bales above the zone where rain bounces off the ground and where snow lies. The parent article’s minimum is 30 cm above finished grade, with 45-60 cm for wet climates or heavy snow. Width follows the bale: a standard two-string bale is about 90 x 45 x 35 cm, so a bale laid flat is 45 cm wide and one stood on edge is 35 cm wide. The stem wall should be at least as wide as the bale it carries; the arithmetic of how the courses stack on top is in Load-Bearing (Nebraska) Style.
What You Need
- Stem wall material: dry-stacked stone with earthen mortar (abundant, durable, free), urbanite (broken concrete chunks salvaged from ruins), adobe bricks made from local clay, or gravel bags (earthbags filled with gravel), which give drainage and elevation. See Adobe Bricks, Earthbag Building and Stone Foundation.
- A moisture barrier for the top: salvaged plastic sheeting, tar paper, or birch bark.
- A level, to make the top flat for the first course.
Method: Raise, Level, Break The Water Path
Step 1: Measure the finished grade where the wall will stand, allowing for the ground to be shaped away from the building.
Step 2: Choose the height: at least 30 cm above that grade, 45-60 cm for wet or snowy sites.
Step 3: Build the stem wall to the width of the bale or a little more.
Step 4: Level the top, since bale courses inherit the error.
Step 5: Lay the barrier over the full top, with laps, before any bale goes on.
Common Mistakes
- Measuring height from the trench, not from finished grade. The wall ends up too low.
- Stem wall narrower than the bale. The bale edge overhangs and sheds water into the joint.
- No barrier. Moisture wicks from the masonry.
- Porous stem wall in a wet site with no plaster or cap.
Safety
Heavy masonry and cut edges
Stone and urbanite are heavy and break with sharp edges. Lift with two people, wear gloves and eye protection when splitting stone, and keep the trench edges back while stacking.
What’s Next
- Learn next: Wall Systems
- Combine with: Roof Overhang and Rain Protection