Abstract: A method including: obtaining a flexible underlayment, wherein the flexible underlayment comprises: a first sensor, wherein the first sensor comprises a first flexible circuit, and wherein the first flexible circuit is configured to: measure a first value representative of a first roofing system condition measurement, wherein the first flexible circuit measures the first value at a first location, wherein a first location identifier indicative of the first location is stored in a database in communication with the first sensor; determine a first roofing system condition in the first location based at least in part on the first value and the first location identifier; and generate a first notification representative of the first roofing system condition; installing the flexible underlayment on a roof deck of a steep slope roof of a structure; installing a first roofing shingle over the flexible underlayment and above at least the first sensor.