杮 also refers to thin wood shingles or splints, but is more commonly used in the context of traditional roofing (杮葺き). 折板 emphasizes the process of splitting or peeling.
板 is a general term for a board or plank, while 折板 specifically refers to a thin, split board used as a shingle or splint.
Etymology
Compound of 折り (へぎ, the continuative form of 折る, 'to split') and 板 (いた, 'board'). The spelling 折板 reflects the meaning of a board made by splitting wood along the grain.
