{"id":3095,"date":"2013-10-02T09:21:43","date_gmt":"2013-10-02T13:21:43","guid":{"rendered":"http:\/\/www.constructionspecifier.com\/?p=3095"},"modified":"2017-01-18T15:51:00","modified_gmt":"2017-01-18T20:51:00","slug":"investigating-sheathing-durability-infrared-surveys-in-hot-climates","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/investigating-sheathing-durability-infrared-surveys-in-hot-climates\/","title":{"rendered":"Investigating Sheathing Durability: Infrared surveys in hot climates"},"content":{"rendered":"
\"All<\/a>
All images courtesy Building Diagnostics Inc.<\/em><\/figcaption><\/figure>\n

by Brett T. Fagan, PE, and Adrian Gerard Saldanha
\n<\/strong>Sheathing decay caused by trapped water in building walls is a leading cause of construction damage. Unfortunately, because sheathing is concealed after construction, this only becomes evident after consequential distress develops in the structure or finishes.<\/p>\n

<\/a>Sheathing\u2019s hidden location makes it difficult to evaluate its condition. Countless investigations have demonstrated it can be consumed by rot without detectable signs or symptoms, such as leaks to the building interior, odor, or cracks in interior and exterior finishes. Therefore, the ability to detect trapped moisture within the assembly is essential in evaluating an exterior wall\u2019s durability. Although excavations are usually necessary, finding hidden water using non-destructive techniques such as infrared thermographic (IRT) surveys can be useful when the techniques are used correctly.1<\/sup><\/a><\/p>\n

It is possible to perform infrared surveys in hot climates (i.e.<\/em> the South, traditionally, but an ever-growing portion of the country), but there are limitations. The authors have tested wall panels with wet sheathing in a laboratory environmental chamber to demonstrate the difference in infrared measurements between hot and cold weather. In both cases, water was applied to the sheathing; in the hot-weather simulation, however, the water was not readily detectable by the infrared survey and could have been missed.<\/p>\n

\"Insulated<\/a>
Insulated demising wall in environmental chamber with wall specimen in opening (viewed from stud side). When the chamber doors are closed, one side of the chamber will be heated, and the other ventilated to force heat to flow through the wall specimen.<\/span><\/figcaption><\/figure>\n

IRT development<\/strong>
\n<\/a>Infrared thermography is an investigative tool widely used to perform energy audits for buildings and other structures in the built environment. It uses the infrared spectrum of light to detect thermal anomalies, such as inefficient insulation or air leaks. During World War II, great strides were made in the field of infrared technology with the registration of several patents.2<\/sup><\/a> Post-war declassification of IRT technology made it available for various applications in industrial and domestic markets.<\/p>\n

The use of IRT technology for building diagnostics picked up pace when federal agencies recognized the impact of the huge cost of energy losses in the built <\/a>environment. Rising fuel prices in the 1970s strained national energy budgets, leading to the roll-out of the Department of Energy\u2019s (DOE) Weatherization Assistance Program (WAP) in 1976.3<\/sup><\/a> This program provided support for low-income families to investigate the effectiveness of the building envelope\u2019s insulating properties and resulting energy loss reduction.<\/p>\n

More recent \u2018green\u2019 certification programs have provided further encouragement to building owners to improve energy performance of their properties. In general, a drive toward eco-friendly design, energy efficiency, and long-term cost savings has created a strong market for IRT professionals and equipment.<\/p>\n

Although there is no single authority governing the training and procedures, ASTM International, the American Society for Nondestructive Testing (ASNT), and others have established standard practices. However, the authors did not find among their publications adequate warnings about the pitfalls of performing IRT surveys in hot climates.<\/p>\n

Lab tests of wall panels<\/strong>
\nIn a durability lab, the thermal performance was evaluated of wall panels representing different types of construction. They were subjected to conditions simulating a hot and a cold exterior, similar to the conditions to which a building envelope is subjected in different climates.<\/p>\n

A demising wall was built in an insulated environmental chamber to serve as a partition between two spaces with different temperatures (Figure 1). This limits heat transfer between the two sides of the chamber, consisting of a wooden frame and 178 mm (7 in.) of polyisocyanurate (polyiso) insulation with an R-value of 42. Wall panels were installed in a 1.2-m (4-ft) square opening at the center of the demising wall. By separating the test chamber into two sections, it was possible to create heat flow through the wall panels.<\/p>\n

Heating elements were placed on one side of the wall in an attempt to obtain a temperature difference of at least 10 C (18 F)\u2014the minimum \u2018delta\u2019 recommended by ASTM C1060-11a, Standard Practice for Thermographic Inspection of Insulation Installation in Envelope Cavities of Frame Buildings<\/em>. (Interestingly, some wall specimens could not maintain this temperature difference, even though they represent current construction practices, because they had insufficient insulation.) Connected to a data logger to measure the temperature at key locations over time, thermistors were installed at three locations on each side of the wall (six in total):<\/p>\n