For fire-resistance purposes, 1/2" of unsanded gypsum plaster is equivalent to how many inches of Portland cement sand plaster?

The equivalency between unsanded gypsum plaster and Portland cement sand plaster is determined by their fire-resistance ratings, which are correlated to the thickness of the materials.

In this case, 1/2 inch of unsanded gypsum plaster is generally recognized in building codes and fire safety standards as equivalent to 1 inch of Portland cement sand plaster. This equivalence is due to the different material properties and the way they contribute to fire resistance. Gypsum plaster has inherent fire-resistive properties that allow it to provide effective protection even at a thinner application compared to Portland cement sand plaster. When evaluating these materials, the fire resistance of gypsum plaster can be more effective for the thickness provided.

Understanding this equivalency is crucial for architects, builders, and inspectors to ensure walls, ceilings, and other structural components meet the necessary fire-resistance requirements. Correctly applying these ratings helps in designing safer buildings that comply with fire codes, promoting occupant safety and minimizing fire damage potential.