Effects of valved soffit vents on low-rise buildings with hip and gable roofs.

摘要

It is evident from various post-hurricane surveys that soffit failure has been a significant contributor to considerable damage in low-rise buildings. Soffit vents, which are frequently integrated into low-rise buildings in order to provide natural ventilation of the attic space, have been found to be points of particular vulnerability. In high wind events, soffit vents provide a point of entry for wind-induced pressure and wind-driven rain into the attic space. Internal pressurization from wind-induced positive pressure entering the windward soffit vents combined with external suctions on the roof can lead to the potential failure of the roof sheathing. In addition, once water enters the attic space, it accumulates, soaking the insulation and gypsum board, which can cause the full collapse of the ceilings.;This study presents a valved soffit vent technology that has the capability of depressurizing the attic space when strategically positioned in areas of wind-induced negative pressure, i.e. wind separation zones. Valved soffit vents (VSVs) facing the approach flow are activated by wind-induced positive pressure and close for wind speeds greater than 30 mph, thereby preventing air intrusion and wind-driven rain into the building.;Large-scale experimentation was conducted at the Wall of Wind (WOW) facility at Florida International University to investigate the effects of valved soffit vents on internal pressures within the attic space and on net pressures that are often responsible for damage to the roof envelope. In addition, the effectiveness of VSVs in preventing wind-driven rain (WDR) entry into the building was also studied. Four different roof models were tested: a large hip, a large gable, a small hip and a small gable. The large roof models were used to study a patented VSV product, the BPA Safety Vent, while the small roof models were used for a 1:6 model scale study.;Results showed that for various wind directions, the net mean pressure coefficients on the gable and hip roofs increased, generating less suction on the roof envelope in the case of soffit openings with VSVs than for soffit openings without VSVs. The hip roofs with VSVs yielded an increase in net mean pressure of more than 90% on the roof sheathing above the windward vents. Furthermore, the mean pressure coefficients on the interior roof surface of the different roof models at any wind direction were reduced when the VSVs were installed.;The net peak pressure coefficients generally remained unchanged for the different roof models, irrespective of wind direction. However, the hip roofs displayed an increase in net peak pressure coefficients at the vent locations. The VSVs also demonstrated their ability to prevent wind-driven rain from entering the attic. Testing was also performed to identify the wind speeds at which the VSVs begin to activate. The valved soffit vents show promise for future applications in the areas of wind-induced pressure and wind-driven rain damage mitigation.