A Study on Improving Weather-Tightness of Siding Finishes for External Walls by Pressure Equalized Design Utilizing Hollow Section Furring
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概要
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Siding has been extensively used as external wall finishing materials for housing buildings, but relatively low weather-tightness of the joints prevents its wider application. In this paper, a new construction method of siding finishes is proposed, in which siding are fixed to hollow sectioned furring, of which cavity is utilized as pressure equalizing spaces for improving weather-tightness of the joints. Wall models clad with four courses of commercial type horizontal siding were made, and their resistance to rain penetration under heavy rain and wind condition was tested using pressure box type rainstorm simulator. The top two joints of the siding were pressure-equalized joints, which were backed up by hollow sectioned furring, while the bottom joint was constructed in ordinary way as a control joint. Four different systems for connecting the space inside the furring with outside air for obtaining pressure equalization were tested. These are holes directly drilled through the siding near the joints, vent pipes, vent pipes connected by flexible tubing, and tubular studs inside of which were connected both to external air inlet and the furring spaces. Air inlet area, extent of air leakage from the furring, amount of run-off rainwater over the wall, and wind pressure were selected as experimental parameters. The air pressure inside the furring was measured and its relationship with occurrence of rain penetration was investigated. Tests were done in steady pressurizing method and in rapid pressurizing method, in which wind pressure was raised to a designated value within 0.3 second. In steady pressurizing tests, it was found that pressure equalized joints could withstand up to a wind pressure of 1600 Pa without penetration depending on the air intake method and the air tightness of the furring, while in the control joint rain penetrated whenever wind pressure exceeded 140 Pa. Also, the amount of water leakage was far less in pressure equalized joints than in control joint for the same wind pressure. Among the four air intake systems. hole venting was least successful, since rainwater began to migrate through the holes under relatively low joint pressure difference. In rapid pressurizing tests, pressure difference across the joints in pressure equalized joints showed transitory surge just after the pressurizing, due to the delay in following up of the internal pressure of the furring. But it was found that this has little effect in occurrence of water penetration through the joint. Calculations based on measured joint pressure differences showed that in wall models used, there existed considerable amount of air leakage at air seals between the furring and the siding, which has to be somehow dealt with when applying the proposed construction method into practice. Coefficients of discharge for the outside air inlet for each air intake system were given for estimating joint pressure difference utilizing a simple equation.
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