GB/T 328.13-2007 "Test Methods for Building Waterproof Sheets - Part 13: Polymer Waterproof Sheets - Dimensional Stability" specifies the method for determining the dimensional stability of polymer waterproof sheets, which is applicable to the performance testing of various types of polymer waterproof sheets. The testing requires the use of an electric blast drying oven with a temperature control accuracy of ±2°C, a steel ruler or tape measure with a division value of 0.5 mm, and a bracket that meets the requirements for specimen placement. After conditioning in a standard environment, the specimens are subjected to constant temperature treatment at a specified temperature for a certain period. After cooling, the dimensional changes are measured, and the dimensional change rate is calculated to evaluate the dimensional stability of the sheets under high-temperature conditions.