Battling Building Envelope Corrosion

Rusting steel can expose structural timber, which can then rot. Photo courtesy of Australasian Corrosion Association.

Concrete is usually the foundation of a good building, and efficient management regarding the effects of concrete corrosion can extend its life. However, concrete is not the only part of a building that can be threatened by corrosion, the Australasian Corrosion Association (ACA) (Blackburn, Victoria, Australia) explains.

The ACA is a trade organization that works with industry and academia to provide a base of research that supports best practices in corrosion management for situations such as leaky buildings. This collaboration helps ensure all impacts of corrosion are responsibly managed, leading to the protection of the environment, enhanced public safety, and improved global economies, the group says.

On any building, both the cladding and fasteners holding it in place are exposed to varying degrees of corrosion. Less obvious parts that corrode are the polymers used as sealants, as well as the protective coatings applied to other materials.

Leaky Building Syndrome

One cost that may not be obvious, however, is unbudgeted capital expenditures to replace damaged frames, walls, and façades resulting from “leaky building syndrome.”

A leaky building is one that, as a result of defective design, materials, or construction—usually a combination of all three—allows water to enter through the external building envelope. In turn, this causes decay and damage to the internal structure of the building, the ACA explains.

The situation arose from a combination of factors in the late 1990s and early 2000s, when a large number of buildings were constructed using substandard materials. Those problems were compounded with design flaws and insufficient maintenance, leaving the buildings vulnerable to moisture ingress.

“Leaky building syndrome has become a serious problem in New Zealand,” says Les Boulton, a principal consultant and corrosion expert with Les Boulton and Associates (Auckland, New Zealand). “It is becoming a global issue for many governments, as there have now been court cases in New Zealand, Australia, and Canada where developers and manufacturers are being sued.”

There can be many contributing factors to the problem of leaky buildings, including poor-quality metal flashings. These allow water to get behind the façade of a building and corrode materials, including the building framework and cladding fastenings. In some cases, bare steel has been used for internal structural elements and left exposed to harsh coastal climates.

Additionally, more than reinforced concrete is impacted by corrosion. In fact, any part of a building is prone to some type of corrosion over time and at varying rates.

Impact on Construction Polymers

Moisture, heat, and UV radiation often lead to corrosion issues on exposed assets, such as this mast. Photo courtesy of Australasian Corrosion Association.Polymers are used extensively in the construction industry, including seals around windows and doors, guttering and downpipes, and corrugated polycarbonate (PC) panels. These are all affected by moisture, heat, and the sun’s ultraviolet (UV) radiation. In addition to structural use, polymers are also often used as sealants over other materials, including concrete.

UV radiation interacts with polymers at the molecular level, where the radiation has enough energy to modify chemical bonds. At this time, the majority of testing of polymers and other construction materials has been carried out in European countries and in the climatic conditions of the Northern Hemisphere. But research by other organizations and government bodies has shown that at equivalent latitudes, New Zealand and Australia experience even larger amounts and more intense UV radiation.

Even if stored in a dark cupboard, polymers still interact with their environment. When used as an additive to materials such as concrete and exposed to conditions such as thermal and wet/dry cycles, polymers can leach out chemical binding agents, according to the ACA.

Geography Matters

Boulton notes that while leaky buildings are not unique to New Zealand, the geography and climate of particular sections of that country seem to exacerbate the problem. In the past decade, corrosion on fixings of aluminum composite panels has caused a range of failures in commercial buildings clad with this material, resulting in panels becoming loose and allowing water to enter the building envelope.

“However, because it is not seen, building owners have been slow to recognize the problem,” Boulton says. “Asset owners need to be proactive about checking their buildings and cladding to ensure there is no water ingress.”

Inspection reports have shown that leaky buildings were often built with monolithic cladding systems, which provide little or no margin for error if moisture penetrates behind the cladding and into the building envelope. Usually, the untreated, kiln-dried framing timber—once approved by many regulators for use in construction—was particularly susceptible to any moisture ingress.

By the time an asset owner realized that there was a problem, it was already too late to fix it without rebuilding significant parts of the building’s structure.

Another contributing factor was that for many years, developers had no incentive to pay for the best design of their buildings, or the appropriate level of supervision of construction to ensure the buildings were constructed properly.

But today, the New Zealand Building Code (NZBC) Clause B2, Durability, is one example of a policy requiring all building components to be fit for purpose and provide a stated service life. Durability appraisals of building products are required before a new product is deemed as fit for installation in a new building.

This requires an independent assessment of the building product, system design, material corrosion resistance, and installation practices. It is also important that testing reflects the geographic environment where the building materials will be used, the ACA says. “Thorough appraisals give the construction industry and asset owners confidence that new products have been subjected to a robust technical examination by experts before the product is released into the market,” Boulton says. “Some failures in the ongoing leaky building crisis have been caused by water ingress behind inadequately designed or installed cladding systems, which resulted in corrosion of hidden metal fixings.”

Protection Strategies

When plastics eventually become brittle due to UV exposure, they no longer afford the protection for which they were designed, the ACA explains. Some cases have been observed where objects fall through PC canopies and injure people below.

While the most visible degradation effect on polymers is an aesthetic one—a grey-white powdery substance can form on the surface—there can be many other less obvious effects, such as polyvinyl chloride (PVC) guttering and downpipes developing cracks and leaks that could allow water to get inside the building envelope.

Owners of high-value assets should understand the cost implications of ignoring the effects of corrosion. There are many advantages of planning for corrosion control and mitigation such as extending the life of an asset and reducing maintenance time and costs.

Monitoring the impact of corrosion also serves as a critical aspect of ensuring asset integrity. A key method of minimizing corrosion is to employ appropriate corrosion protection technologies, the ACA explains. Proactively testing and inspecting building structures can provide a clearer understanding of where to spend limited resources on the maintenance of assets.

In order to effectively and comprehensively explain the benefits of incorporating maintenance planning into the design process, the ACA says companies and practitioners in the industry should ensure they understand new advancements in building products, construction technologies, processes, and legislation.

Source: Christine Filippis, Teraze Communications—e-mail:

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