Driving rain tightness, intrusion rates and phenomenology of leakages in defects of façades: A new calculation algorithm

Doctoral thesis, 2018

This thesis presents the driving rain tightness of façades with façade details as well as the water leakage flows that can be expected. Furthermore, it describes the key mechanisms for water leakage in defects in the outermost layer of external walls. A new algorithm has been developed and validated based on the empirical measurements of water leakage. In order to produce accurate calculations for water leakage, the geometry and dimensions of the defects need to be precisely defined. Extensive data is presented in this thesis that facilitates relatively reasonable assumptions of the water leakage flow, even though the geometry and dimensions of the defects are unknown.

The aim is to improve knowledge, generate more data and developing a calculation algorithm for water leakage flow. This would increase the ability to produce more accurate two or three-dimensional moisture calculations and reliable probabilistic risk moisture analyses.

The research is mainly based upon laboratory testing and experiments, and field measurements.

The results point out that water leakages are almost always expected in small concealed or invisible defects in façades with façade details such as window-wall interfaces, etc., regardless of the façade type and façade systems such as unventilated, ventilated and pressure-equalized façades.

Four of the greatest importance for the water leakage flow in experimental trials were; façade material, the size of the hole, the size of the dam and hydrostatic pressure derived from the building. Additional two factors are pressure difference across the façade layer and water flow on the façade due to driving rain which derives mainly from the prevailing weather conditions.

In order to use the algorithm, the important factors, as mentioned above, need to be considered together with a table that has been prepared with the constituent constants.

Based on an assessment of all the results and assuming carefully completed assembly, it is reasonable to assume that the water leakage flow through each point leakage corresponds to 0.5-2% of the vertical water flow cross a unit width of the façade at the given height.

The lower proportion within the range only refers to holes/slits, while the higher proportion refers to holes/slits with dams.