What air space shall be provided where wood girders enter exterior masonry walls, unless naturally durable or preservative treated wood is used?

When wood girders enter exterior masonry walls, providing a proper air space is essential for preventing moisture retention and potential decay of the wood. The correct specification for the air space required in this case is 1/2 inch.

This 1/2 inch space serves as a precautionary measure to ensure adequate ventilation around the girders, allowing any trapped moisture to escape and reducing the risk of wood rot, especially since untreated wood is vulnerable to such issues when in contact with masonry, which can retain moisture. Allowing for this air gap is crucial unless the wood is naturally durable or has been preservative treated, which are exceptions due to their enhanced resistance to moisture and decay.

In contrast, the other options propose air spaces that are either too small or too large. A smaller space, such as 1/4 inch, may be insufficient to allow for proper ventilation. On the other hand, air spaces larger than 1/2 inch do not offer additional protection and could complicate the structural integrity and support that the girder is designed to provide. Therefore, a 1/2 inch air space is the optimal requirement for maintaining the longevity and integrity of wood elements in masonry applications.