What is the required vertical spacing for wall ties in multiple wythe masonry?

The requirement for vertical spacing of wall ties in multiple wythe masonry is based on the need to ensure proper structural integrity and lateral support between the different layers of masonry. The standard spacing of 24 inches allows for effective load transfer and prevents issues such as cracking or separation between the wythes. This spacing also aligns with industry best practices and standards, which focus on maintaining structural soundness and accommodating thermal expansion and contraction.

Choosing a spacing that is too close or too far apart could lead to inadequate support beneath lateral loads or excessive movement between masonry layers. This could compromise the wall's overall performance, leading to structural failures or aesthetic issues.

Therefore, a vertical spacing of 24 inches emphasizes the balance between adequate support and practical construction methodologies in multiple wythe masonry systems, making it the correct answer.