EN ISO 15927-3:2009

Foreword
Introduction
1 Scope
2 Terms, definitions, symbols and units
3 Calculation of airfield indices from hourly wind
  and rain data
4 Estimation of the effect of driving rain from
  average wind and present weather code for rain
5 Calculation of wall indices
Annex A (informative) Limits to the validity of the
        calculated indices
Annex B (informative) The nature of a "spell" of driving rain
Annex C (informative) The procedure for generating the
        driving-rain maps
Annex D (informative) Comparison of methods specified
        in Clauses 3 and 4
Bibliography

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.