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