Self-adhering underlayment sheets to form waterproofing joints, related building assemblies and methods

Abstract

As described herein, the invention includes a building underlayment sheet that comprises an underlayment lamina having a top surface and a bottom surface. The bottom surface includes an interior portion and a selvage portion that extends from the interior portion of the bottom surface to a terminal distal edge of the sheet and the interior portion of the bottom surface bears a self adhesive layer. The selvage portion of the bottom surface bears a bonding composition that is capable of bonding to a top surface of a second underlayment lamina to form a full lap joint. In some embodiments, the self adhesive layer includes an asphalt, a polymer such as poly(styrene-butadiene-styrene)(SBS), and a tackifier, and/or the bonding composition includes asphalt, a polymer such as poly(styrene-butadiene-styrene), ground tire rubber (GTR), and tackifier. Also included are building assemblies that include the application of one or more of the underlayment sheets to a building surface, such as a roof surface and methods of installing the underlayment and waterproofing a roof surface.