Page 304 - Forensic Structural Engineering Handbook

DEFECTS, DETERIORATION, AND DURABILITY 9.15

In 1988, the European Union established a goal of increasing public health through bet-
ter building practices. This EU directive motivated the British Standards Institute (BSI) to
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draft Durability Requirements for Products, presenting categories of design life for various
construction systems. Some results of the BSI study are included in Tables 9.1, 9.2, and 9.4
in this chapter.
Similarly, ASTM International has published several diverse standards in recent years
emphasizing the durability of building materials and products, including the following
examples:

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ASTM E2136: Standard Guide for Specifying and Evaluating Performance of Single
Family Attached and Detached Dwellings—Durability
ASTM E2094: 21 Standard Practice for Evaluating the Service Life of Chromogenic
Glazings
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ASTM E774: Standard Specification for the Classification of the Durability of Sealed
Insulating Glass Units
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ASTM F793: Standard Classification of Wallcovering by Durability Characteristics
The above list, which is not exhaustive, includes standards that deal primarily with dura-
bility. In addition, there are countless other standards that classify durability among other
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properties for individual materials; for example, ASTM C406, Standard Specification for
Roofing Slate, states the following:
Expected service life of the various grades, depending on geographic location and environ-
mental exposure, is as follows:
Grade S1 over 75 [years]
Grade S2 40 to 75 [years]
Grade S3 20 to 40 [years]

Manufacturer’s Technical Literature. Unfortunately, many building products continue
to lack clear standards for durability. Information provided by manufacturers is a blend of
marketing and science, often with no clear distinction between the two. Many manufactur-
ers do not directly address product design life in their literature. Special attention should be
paid to the language in the manufacturer’s literature to ensure that the expectations of the
owner can be met.
Sometimes the only indicator of design life is the guarantee period provided by the man-
ufacturer; however, guarantees usually limit the liability of the manufacturer in the case of
a premature failure of the component. Some owners may mistakenly assume that a guaran-
tee is a maintenance agreement or insurance policy; in fact, most guarantees severely
restrict the legal remedies available to the owner and do not cover incidental or conse-
quential damages, loss of profits, or inconvenience.
Manufacturer’s guarantee periods alone do not always provide reliable information
regarding product durability. They are established by manufacturers based on several fac-
tors, including the length of time a product has been on the market (longer guarantee peri-
ods with proven success), increased durability from product improvements, the guarantee
periods set by competitors, and the product’s performance under accelerated wear and
weathering tests.
Liability is often difficult to isolate when products fail, since proper product selection
by the designer and installation by the contractor are beyond the control of the manufac-
turer. This sharing of liability can reduce the accountability of the manufacturer, and the
written guarantees reflect these limits.