Potential of self-drying siding with raised air cavities for building envelopes

摘要

Within building envelopes, air cavities behind a siding provide a feasible way to mitigate the moisture-related issues such as rain penetration and frost damage. However, for a common contact-applied siding system, the small gap directly attaching the siding with the wall sheathing greatly limits the drying functions of air cavity: capillary break, drainage, and ventilation drying. Moreover, the drying performance of the air cavities behind the siding remains unknown, and commonly a rectangular unicellular cavity is inexactly assumed to simplify investigating the hygrothermal performance of a siding system. After analyzing the irregular and complex configuration of air cavities composed of multiple same cavity cells, this paper develops a mathematical model based on the circuit diagram principle to quantify the air flow rate within the multicellular cavity behind a siding with respect to the air differential pressure and flow resistance. This model is then used to evaluate the drying performance of a siding system, which is found to be heavily dependent on the cavity depth between the siding and the wall sheathing. Further sensitivity analysis shows that the air flow rate within the cavity rapidly increases to a maximum value as the cavity depth increases, and then converges at a lower value. The cavity's air flow rate reaches its maximal value when the cavity depth is 48% of a siding panel projection, e.g., 0.31 in (7.8 mm) for a triple dutch lap vinyl siding. Based on the optimal cavity depth, several design improvements are proposed.