That doesn't mean that air-tightness targets aren't a good idea. Moisture accumulation in sheathing might be a problem in a wall without a rainscreen, but the same level of moisture accumulation might not be a problem if there is a ventilated rainscreen between the sheathing and the siding.Īs with almost everything in building science, the answer is once again, "it depends." Some wall components are very vulnerable to moisture - OSB being the classic example - while others are more robust. What’s a dew-point calculation?īuilders or designers perform dew-point calculations to determine whether a…Īlthough various energy-efficiency and green building programs have published envelope air leakage targets, I think it is impossible to generalize about the effect of air leakage on wall condensation problems.įor example, air leakage and condensation won't damage some wall assemblies (CMU walls, ICF walls). Moreover, they represent a theoretical one-dimensional model since the real world has three dimensions, this model has limited value. However, since these temperature profiles usually fail to account for air leakage, they are usually inaccurate. If we draw a cross-section of a wall, we can calculate the theoretical temperature of any point within the wall. The other wall components will be at temperatures ranging between these two extremes. If it is 72☏ indoors and 0☏ outdoors, the siding temperature will be close to 0☏, while the drywall temperature will be close to 72☏.
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