What should be installed at the top plate of a partition wall adjacent to an unconditioned space?

The most appropriate choice for installation at the top plate of a partition wall adjacent to an unconditioned space is sealed gypsum board. This material provides a robust barrier against air infiltration and moisture, which is particularly important in areas where conditioned spaces are adjacent to unconditioned spaces. The sealed nature of gypsum board helps reduce the potential for mold growth and structural damage by preventing moisture from entering unconditioned areas while also minimizing the transfer of air, which can lead to energy loss and discomfort in the conditioned space.

In contrast, while drywall can be a surface finish, it does not inherently provide an effective seal against air and moisture without additional treatment. An air barrier is crucial in maintaining energy efficiency and controlling air leakage but is typically used in conjunction with other materials. Moisture-resistant insulation is certainly valuable, especially in locations susceptible to dampness, but on its own, it does not address the necessary sealing function at the top plate as effectively as sealed gypsum board. Thus, sealed gypsum board combines both structural and thermal properties essential for this application, making it the most suitable choice.