The JSA JIS A 1438 Test Method for water resistance of exterior panels of buildings specifies the test method for evaluating the water resistance of exterior panels. The standard tests the waterproof performance and durability of exterior panels under long-term exposure conditions by simulating the moisture erosion that may be encountered in the actual use environment. The content includes the test equipment, operation procedures, setting of test conditions, and specific requirements for result evaluation to ensure the scientific and repeatability of the test process.