In the Skin

 BUILDING SKINS 01Building skin failures can be avoided.   

By Jeffrey C.F. Ng, Jennifer Keegan and Matthew Ridgway

Building skin failures generally stem from materials, components or assemblies that do not comply with project requirements, building codes or industry standards. They are objective, observable and measurable, becoming apparent throughout a building’s use and operation or through simulated testing. This means failures can be assessed, predicted, managed and mitigated.

The design of high-performance building skins demands more forethought than building codes or zoning can anticipate. Studies of failures in newly built skins suggest the causes can be traced back to conventional practices in design, value engineering and construction that lower quality and limit innovation. Rethinking the approach to assessing failures and managing risks can limit exposure, saving time, costs and reputations.

Conventional thinking around building skin failures relies on a compilation of experience and research, resulting in a large collection of information, multiple competing standards, lengthy checklists, unwieldy product literature and quality control and assurance practices during construction. Failures are categorized by typologies, based on various phenomena: water infiltration, air infiltration, thermal performance, condensation resistance, structural performance, glass performance, finish performance, acoustic effectiveness and fire protection continuity. Assessing and classifying failures this way can become difficult to manage. 

High-performance building skin design is often modified through value engineering. Sessions are usually conducted in high-stress conditions when the project is about to go to bid or has started construction, meaning they are often given lower priority and insufficient time. Evaluations are often performed piecemeal and focus on cost reduction. This can compromise quality assurance and long term performance.

Under this approach, building skins are designed with good intentions, but often succumb to performance failures. They are fixed with patch solutions that fail to address life cycle considerations and system durability. Better remedies and maintenance options, informed processes and better management of design and construction allow new building skins to perform at a higher level. This starts with employing a better way to organize the information around failures to better predict performance outcomes and establish design criteria and testing protocols to mitigate risk.

Building failures can be understood and categorized in relation to the three spatial dimensions and the fourth dimension — time. This approach explains relationships in building skin failures — specifically how failures in one material or component can lead to failures in other materials or components — and, in turn, provides insights into potential solutions.

Order of Failures

First order failures consist of linear openings, discontinuity or non-uniformity within a component or contiguous components of the building skin assembly. Examples include holes in a sealant joint, unsealed penetrations in a barrier membrane or damaged structural members. Generally, these failures are local defects, typically found at a discrete point in the component’s surface, running from the exterior to the interior. They can be repetitive and may be the result of deficiencies on site or in the fabrication plant.

Inspectors can observe first order failures on site or the manufacturing line. After installation, they are challenging to identify without the aid of probes and diagnostic testing. Using specified, approved components and quality control programs can help manage and resolve first order failures.

Second order failures generally consist of a defect or deficiency in assembly components within the skin, such as planar gaps or joint discontinuity. Examples include lack of sealant adhesion to incompatible substrate, improper lapping of flash materials allowing water to enter in an uncontrolled manner or lack of provision for differential movement at structural connections. 

Qualified installers, pre-installation meetings, construction supervision, coordination between trades, mockups, testing and third-party inspections can help manage and alleviate second order failures. Better attention to engineered drawings and documentation, and the use of well-maintained equipment operated by staff trained in state-of-the-art methods can also help.

Third-order failures are ones of size, volume or design capacity. Improper material selection, omission of pre-installation laboratory testing or improper engineering or design may lead to a failure to comply with performance requirements of the building skin system. Examples include improper flashing assembly height for required water resistance, inadequate insulation thickness and excessive deflection of oversized glass panels. These failures may be due to forces not anticipated by building codes that overload design capacity, like extreme wind loads or weathering, or they may be the result of conflicting or unanticipated performance requirements.

Computer simulation modeling, physical scale model testing and lab testing of building skin mock-ups can help to manage and resolve third order failures. Additionally, implementing alternative designs or using innovative materials, assemblies or fabrication technologies also can help.  

Fourth order failures cannot be avoided; they are related to progressive degradation of assemblies and components over time, caused by repeated use, exposure to elements, seasonal changes, weather and environmental conditions. Examples include UV degradation of exterior materials and corrosion of metal components. Changing codes and standards also can lead to fourth order failures, requiring skins to be adapted to meet the new codes and standards. 

While fourth order failures cannot be avoided, they can be mitigated by using durable, high-performance materials and assemblies. Design redundancy, post-installation performance verification testing, proper maintenance programs and timely repairs are important for reducing fourth order failures. Consideration of future building codes and industry standards in the design of adaptable high performance building skins will help assure long term performance.

The four orders of building skin failures allow us to spatially correlate multi-dimensional interfaces of building skin components with failures. They help pinpoint relationships between failures by identifying common characteristics and remedies. 

This classification system can be used as a communication tool during the design, value engineering and construction of building skins, by organizing relevant information in a clear, succinct, hierarchical manner, limiting short-sighted decision making at the expense of long-term performance. 

Jeffrey Ng is an architect and LEED AP, with more than 35 years’ experience integrating building design and technology.Prior to joining Intertek-ATI, Ng was VP and lead facade consultant at Thornton Tomasetti.

Jennifer Keegan has 19 years’ experience as a building enclosure consultant specializing in assessment, design and remediation of building enclosures. She has investigated failures, provided construction administration, condition surveys, design peer reviews of residential and commercial facades, and expert witness and litigation services.

Matthew Ridgway is a licensed architectural engineer specializing in assessment, design and remediation of building enclosures on historic and modern buildings. He has successfully managed technical requirements on historically sensitive buildings and National Historic Landmarks.

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