hut
橧 centers on a simple dwelling: a hut or small shelter, often made of wood.
橧 combines 木 (tree/wood) with 曾, which likely contributes the sound. The character suggests a wooden structure, fitting the meaning of a hut.
A wooden 木 structure with a layered roof like 曾: picture a small wooden hut with a thatched roof made of stacked layers.
For ソウ, imagine sewing a thatched roof onto a wooden hut: sew -> ソウ, and the hut is finished.