Enrique Cano-Suñén

Assessment of water penetration risk in building facades throughout Brazil

ABSTRACT The penetration of atmospheric water (rain) into facades creates problems for building habitability and the durability of construction materials. This study analyses the exposure of Brazilian facades to the two main climate factors responsible for this penetration: wind-driven rain and driving rain wind pressure. Daily weather records (spanning 2005–14, from 171 weather stations) were analysed. Both exposure factors were combined to assess the risk of water penetration at each site. The relationships between the different exposure indices calculated from daily, monthly and annual records were determined and compared with results from other countries. From this analysis, detailed isopleth maps are provided that allow a graphical characterization of the moisture exposure conditions of facades anywhere in Brazil. A comprehensive characterization of the water penetration exposure in Brazilian enclosures is created and can be used to establish normative design requirements for actual climatic conditions in each area of the country. In general, an increased risk of penetration was identified in the flat areas of the South and Northeast regions of the country. The sites located in the Amazon basin present comparatively lower risks, despite a greater amount of rainfall, because the wind intensity is less in these inland areas.

An extended method for comparing watertightness tests for facades

Watertightness tests for building facades attempt to simulate the most relevant climatic exposures for water penetration by reproducing standard conditions. Such conditions do not represent all possible climatic exposures, hence a new method was recently presented that relates test severity to watertightness performance of a facade under any operating conditions. In addition, test conditions vary for each regulatory framework (i.e. the results generated for one test cannot necessarily be extrapolated to other tests). A process is presented for considering the influence of exposure time. This allows a comparison of the severity of the conditions imposed by different watertightness tests independently of the exposure parameters. This comparison, which is based on a performance criterion, can enable a global certification of watertightness of any facade design under any operating conditions using results from only one watertightness test. The method developed herein was applied to facades under various operational conditions at a reference location, comparatively evaluating the conditions recreated by different international watertightness tests. The results suggest that American tests are more appropriate for recreating high climatic exposures, while European tests are more suitable for evaluating moderate and protected conditions of wind-driven rain and wind pressure.

Improvement alternatives for determining the watertightness performance of building facades

The accurate determination of a facades watertightness performance is important for optimizing design. Different micro-climatic conditions can affect water penetration. The recently developed Bayesian method allows this performance to be estimated for any operating condition and location, based on the results of standardized watertightness tests. This performance-based method uses semi-empirical calculations for wind-driven rain, estimates of wind velocity based on the wind profile power law and analyses of the annual maximum climatic data. This method determines the return period of climatic conditions that each facade system can withstand. Alternative approximations are studied that may be implemented using the Bayesian method to obtain more precise or functional estimations: improved friction coefficients, peaks-over-threshold analyses or catch ratios from computational fluid dynamics (CFD), among others. The effects of these alternatives on the results of the Bayesian method were evaluated by analysing different case studies in two cities in Spain. This analysis suggests that the original formulation of the method underestimates watertightness performance and highlights the fundamental importance of wind velocity to estimate the performance of any facade accurately. This will provide greater precision for estimating facade performance and provides potential for introducing performance-based codes for watertightness.

On the significance of the climate-dataset time resolution in characterising wind-driven rain and simultaneous wind pressure. Part II: directional analysis

Both semi-empirical methods and CFD simulations use real climate datasets as a basis for determining the building facade exposure to wind-driven rain and simultaneous wind pressure. The time resolution of these datasets and the number of variables considered (commonly rainfall intensity, wind speed and wind direction) determine the required calculation effort and the accuracy of the result. Omitting the wind direction, a former article (Part I of this research) has analysed the effect of this time resolution on two scalar exposure indices obtained by semi-empirical methods: driving rain index (aDRI) and driving-rain wind pressure (DRWP). However, the wind direction during precipitation events also causes significant exposure variations between possible facade orientations. Thus, it is also necessary to clarify the influence of the time resolution of the dataset, on the accuracy of the directional semi-empirical calculation of aDRI and DRWP. To meet this challenge, the article examines 10-min climate records collected between 2001 and 2016 at 6 Spanish locations, uses them to obtain hourly, daily, monthly and annual datasets, and analyses the accuracy of the directional exposure indices associated with each time resolution. The results show that a daily dataset would allow identifying the most exposed orientation with an error less than 45°. However, even the hourly datasets cause errors close to 10% in the exposure values identified on each facade orientation. Finally, adjustment relationships that allow estimating the maximum value of directional exposure from simple scalar indices are obtained.