New algorithm for water leakages flow through rain screen deficiencies

Abstract

There is a need of more knowledge about the mechanisms of water leakage through façades exposed to driving rain to make reliable risk analyses. Therefore, we have studied it in more detail and the outcome include inter alia a new algorithm. The algorithm is developed for calculation of water leakages through rain screen deficiencies. The algorithm is based on empirical values from many measurements according to standardized test method and validation. Even though the leakage process is very complicated, simple correlations have been shown. The leakages flow rate through deficiencies are mainly limited by the runoff rate and the catch area above the hole and around the hole with dam. Apart from wind pressure as a driving force, the inlet of the holes is often on a higher level than the outlet at the rear of the façade, which creates significant hydrostatic pressure, which can be elevated by impoundment at the obstacle. This is the main reasons to comprehensive water leakages through façades without any wind pressure (pressure equalized façades). If precise information about defects data is not available, there are extensive measurements supporting the following assumption-a realistic leakage flow for a small or invisible spot leakage at a façade detail is presumed to be 0.5 to 2% of the runoff rate per meter of façade width. If there are multiple penetrations or obvious defects in the façade design in combination with the dams, a significantly higher proportion of the runoff flow can leak in.

Review of rainwater infiltration rates in wall assemblies

“…Van Den Bossche et al [41] and Calle and Van Den Bossche [42] have calculated the expected driving forces necessary for water to infiltrate through round openings and cracks represented by slits in a polycarbonate and PMMA panel. Olsson and Hagenthoft [43] have developed an algorithm to calculate the expected infiltration rates through an opening with a given geometry and validated the model by means of experimental data measured for openings in fibre cement panels and polycarbonate panels with and without a dam [44].…”