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Does a 1.5 mm gap drain as well as a 10 mm gap? The short answer is yes. Gap size actually matters less than other factors such as water application rate, water absorption, drainage patterns, drainage distance, and gap continuity. This is especially true when assessing drainage efficiencies in accordance with ASTM E2273. The brainchild of the EIFS industry, this standard demonstrates how a lot of water poured down an orifice results in a lot of water being released at the base of the wall. In other words, this approach measures displacement more than it does free drainage under real in-service conditions. A truer measure is gained by assessing drainage at lower application rates. This graph shows drainage efficiencies of 10 mm and 1.5 mm gaps under standard flow, low flow, and high flow conditions. We tested two full-scale walls for each flow and gap condition. The 10 mm gap was achieved with HDPE furring strips, installed vertically. The 1.5 mm gap employed a commonly used drainage wrap. Under all three flow scenarios, the 1.5 mm gaps achieve the minimum criterion of 90% efficiency. Higher flows result in higher efficiencies, lower flows result in lower efficiencies. So, less water - not more - is the greater rigor. Built Environments #buildingscience #materialsscience #buildingmaterials #buildingproducts #buildingdurability #durability #buildingenclosures #buildingenvelopes #drainage #rainscreens #walls #testing #standards #producttesting