What is the required airspace for wood girders entering exterior masonry or concrete walls if they are not naturally durable or preservative-treated?

When wood girders enter exterior masonry or concrete walls and are not naturally durable or preservative-treated, the required airspace is specified to help prevent premature deterioration of the wood due to moisture exposure. An airspace of 1/2 inch is considered necessary to allow for adequate ventilation and moisture drainage, thus minimizing the risk of decay.

This air gap helps to protect the wood from direct contact with the masonry or concrete, which can retain moisture and lead to conditions conducive to wood rot or insect infestation. By ensuring the proper airspace, builders can promote a healthier environment for the structural components of the building and enhance their longevity.

The fact that this requirement specifically pertains to untreated wood is significant, as naturally durable woods or those that have been treated with preservatives have different levels of resistance to moisture, thereby necessitating different construction techniques or spacing standards.