BS EN ISO 15927-3:2009

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

Describes two procedures for providing an estimate of the quantity of water likely to impact on a wall of any given orientation.

This part of ISO15927 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, given in Clause3 and based on coincident hourly rainfall and wind data, defines a means of calculating 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, given in Clause4 and based on average wind data and a qualitative recording of the presence and intensity of rain (the present weather code for rain), defines a means of calculating the spell length during which an absorbent material such as masonry is moistened, which has a 10%probability of being exceeded in any year (commonly referred to as having a mean return period of 10years). A comparison between the two methods is given in informative AnnexD. Procedures are given to correct the results of both methods for topography, local sheltering and the type of building and wall. The methods included in this part of ISO15927 do not apply in mountainous areas with sheer cliffs or deep gorges, areas in which more than 25%of the annual rainfall comes from severe convective storms, areas and periods when a significant proportion of precipitation is made up of snow or hail.