ISO 15927-3:2009规定了两种程序，用于估算可能影响任何给定方向墙壁的水量。它考虑了地形、当地遮蔽以及建筑物和墙壁的类型。 第一种方法基于一致的每小时降雨量和风力数据，定义了影响吸收性表面（如砌体）含水量的年平均指数和影响雨水穿透砌体和其他墙体系统接缝可能性的拼写指数的计算方法。 第二种方法基于平均风数据和降雨存在和强度的定性记录（目前的降雨天气代码），定义了一种方法，用于计算吸水材料（如砖石）受潮期间的持续时间，在任何一年（通常称为平均重现期为10年）超过10%的概率。 ISO 15927-3:2009对这两种方法进行了比较。 ISO 15927-3:2009给出了纠正地形、局部遮蔽以及建筑物和墙壁类型两种方法结果的程序。 ISO 15927-3:2009中包含的方法不适用于陡峭悬崖或深谷的山区、年降雨量25%以上来自强对流风暴的地区，以及降水中有很大一部分由雪或冰雹组成的地区和时期。

ISO 15927-3:2009 specifies two procedures for providing an estimate of the quantity of water likely to impact on a wall of any given orientation. It takes account of topography, local sheltering and the type of building and wall. The first method, based on coincident hourly rainfall and wind data, defines the method of calculation of the annual average index, which influences the moisture content of an absorbent surface, such as masonry, and the spell index, which influences the likelihood of rain penetration through masonry and joints in other walling systems. The second method, based on average wind data and a qualitative recording of the presence and intensity of rain (the present weather code for rain), defines a method for calculating the spell length during which an absorbent material such as masonry is moistened, having a 10 % probability of being exceeded in any year (commonly referred to as having a mean return period of 10 years). ISO 15927-3:2009 provides a comparison between the two methods. ISO 15927-3:2009 gives procedures to correct the results of both methods for topography, local sheltering and the type of building and wall. The methods included in ISO 15927-3:2009 do not apply in mountainous areas with sheer cliffs or deep gorges, in areas in which more than 25 % of the annual rainfall comes from severe convective storms, and in areas and during periods when a significant proportion of precipitation is made up of snow or hail.