A lath is a thin, narrow strip of wood used in building construction, especially in older homes. Before modern drywall became common, builders would nail hundreds of laths across the wooden frames of walls and ceilings, creating a grid-like pattern. Then they'd spread wet plaster over these strips. The plaster would squeeze through the gaps between the laths and harden, holding everything firmly in place. When you see an old wall being torn down and notice wooden strips behind crumbling plaster, those strips are laths.

You might see it written as lathe, though that spelling more commonly refers to a completely different tool: a machine that spins wood or metal so a craftsperson can shape it.

Laths weren't just for walls. They were also used under roof shingles and for lattice fences. Today, most builders use sheets of drywall instead, which is faster and cheaper. But understanding laths helps you appreciate how carefully homes were once constructed, piece by piece, and why those old plaster walls feel so solid and thick compared to modern ones.