As a result of recent research, the effects of rain wetting on perpendicular to the grain compression strains experienced by boundary joists under load bearing walls are now better understood. A significant increase in the amount of "squash" can occur in deep boundary joist members that are subjected to perpendicular to the grain loading from load bearing walls above, if these boundary joists are allowed to get wet during construction. This “squash" is made up of both timber drying shrinkage and a significant amount of squash under load attributed to a lower MoE perp for the wet timber than for dry timber.

This article offers a method to keep kiln dried boundary joists dry during the construction period prior to the building wrap and cladding being erected.

From TDJ 13-2