boards which support tiles on roof
笮 refers to thin wooden boards or slats used to support roof tiles, a specialized architectural component. Its meaning is narrow and technical, with no common abstract extensions.
笮 combines 竹 (bamboo) with 乍, which likely contributes a phonetic element. The character originally referred to bamboo slats or boards used in construction, particularly for roofing.
The top 竹 is bamboo, and the bottom 乍 looks like a stack of thin boards. Picture bamboo strips laid across a roof to hold tiles in place.
For サク, imagine a sack of bamboo boards being hauled up to the roof: sack -> サク, and the boards support the tiles.