Detecting decay in masonry-supported wood framing

by tanya_martins | July 24, 2024 11:44 am

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Wood structural framing supported by multi-wythe exterior masonry walls is common in buildings constructed up to the early 20^th century. Since wood elements embedded in exterior masonry walls are more susceptible to decay due to repeated moisture exposure, understanding the potential for deterioration of these hidden member conditions is vital in evaluating such structures and mitigating conditions that could lead to future failures or collapse.

Multi-wythe (or mass masonry) exterior walls manage moisture through a combination of shedding rainwater at its outer surface and temporarily storing water that migrates into the assembly until that moisture can be released back to the atmosphere—a process that typically does not degrade the wall’s integrity. However, if the condition of the masonry becomes compromised—due to improper detailing, construction, and/or maintenance—its resistance to water penetration may result in increased saturation of the masonry and repeated wetting of the embedded wood, promoting decay.

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The assessment of the embedded wood framing in masonry walls requires an understanding the condition of the exterior walls, noting any signs of poor weather resistance. Exterior issues such as masonry or mortar deterioration or cracking are indications of higher susceptibility to water infiltration. Interior issues such as water damage to finishes, staining, or efflorescence on exposed masonry surfaces indicate frequent water penetration to the building interior. If decay of the embedded wood framing is suspected, it is difficult to visually inspect the bearing ends of members without localized removal of the surrounding masonry—a process that is generally destructive, time-consuming, and costly.

Resistance drilling is a non-destructive option commonly used to detect decay in wood members. This technique uses a proprietary drill that measures and graphs the wood’s relative density by recording the resistance of a needle penetrating the wood. Wood in advanced decay offers little to no resistance to the needle.

Wood members with significant structural decay typically require repair through partial or full replacement or by adding supplemental support. Modern codes mandate protecting wood in contact with exterior masonry walls from moisture to lessen decay risk. This protection can be achieved by using preservative-treated lumber, protective coatings, or wrapping the member’s end with an impervious moisture barrier.

Given the many potential issues, a qualified assessment of wood framing members supported by exterior masonry walls is essential in any renovation or repair project of this construction type, especially if moisture exposure is suspected.

Author

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Alexandar J. Mlynarczyk, PE, is a senior associate with the Princeton, N.J., office of Wiss, Janney, Elstner (WJE) Associates Inc., specializing in investigation and repair of building structures. He can be reached at amlynarczyk@wje.com.

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect that of The Construction Specifier or CSI.

Source URL: https://www.constructionspecifier.com/detecting-decay-in-masonry-supported-wood-framing/

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