Combine yeast and lukewarm water, stirring to dissolve; let stand 5 minutes or until bubbly. Set aside.
Combine flour, baking powder, and salt in a large bowl; cut in shortening with a pastry blender until mixture resembles coarse meal. Dissolve soda in buttermilk; add to flour mixture, stirring with a fork. Stir in sugar and dissolved yeast; mix well. Cover tightly; refrigerate 8 hours or overnight.
Turn dough out onto a lightly floured surface, and knead 4 to 5 times.
Roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place biscuits in 3 greased 8-inch square baking pans. Cover and let rise 1 hour or until doubled in bulk. Bake at 400° for 12 minutes or until biscuits are lightly browned.