Abstract
A counter-balanced mass measurement system was constructed to allow measurement of water loss from a full-scale wood-framed wall assembly. Water was injected onto a localized area of paper towel adjacent to the oriented strand board (OSB) wall sheathing. Moisture pins in the OSB and relative humidity/temperature sensors inside the insulated wall cavity monitored conditions as the wall dried out. The wetted OSB area’s moisture content dropped at a faster rate than the total mass of the wall, indicating moisture redistribution within the wall. A simple model was used to calculate overall moisture redistribution, which was characterized using a near-exponential decay function. This simplification of the inherently three-dimensional physics of moisture redistribution could be incorporated into the one-dimensional hygrothermal models often used in research and engineering practice.
Highlights
Long-term moisture durability of exterior wall assemblies is a design requirement
The success of the diffusion model which tracks the total mass was not surprising, but the ability to track the local oriented strand board (OSB) moisture content demonstrates the usefulness of the engineering approximation for the moisture redistribution
The model was optimized by adjusting Rosb, with diffusion through the framing assumed to be negligible due to the polyethylene covering, in order to minimize the difference between measurement and model prediction for both the moisture content (MC) within the wetted area and the total mass of injected water remaining in the wall
Summary
Long-term moisture durability of exterior wall assemblies is a design requirement. Improper design can lead to problems with moisture accumulation and subsequent degradation of materials, which defeat the primary purposes of any exterior wall. Moisture control strategies for exterior wall assemblies are well known [1]. A significant goal, no matter the source of the water, is for wall assemblies to have the ability to dry out if they get wet, either during construction or during their service life [4,5]. Drying potential, which is this ability to dry out, is often a concern for wall assemblies that are insulated and air-sealed to levels required by current model energy codes [6,7]. Considerable research has been conducted on wood-frame walls, further work is still needed in order to provide a quantitative basis to minimize the risk of moisture damage and quantify drying potential
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