High vibration from severe wind loads or seismic activity occurs in many areas in the United States. Thybar seismic curbs for rooftop HVACs are specifically manufactured to the seismic category required by geographic location. Available options include built-in filters, extra height, built-in roof pitch, and pressure treated wood nailer. VISCMA member. Thybar Corporation, 913 S. Kay St., Addison, IL 60101. Ph. 800/666-CURB. Fax 630/543-5309. Website: www.thybar.com. E-mail: [email protected]. — Thybar