Planned Replacement or Major Renovation - Effective Building Maintenance: Protection of Capital Assets - page 41

Chapter 2
Planned Replacement or
Major Renovation
Theconceptofentropyisthatnaturetendsfromordertodisorderin
isolatedsystems—therefore,componentfailureisinevitable.
BUILDING COMPONENT LIFE
Every building is assembled from a great many individual com-
ponents—materials, systems, sub-systems, devices, equipment, etc. But,
every one of these building components will ultimately fail and must be
replaced or renovated when it does. Historically, the life-cycle of building
components has been represented by the “bathtub curve” of Figure 2-1.
However, the bathtub curve does not define the point at which
“normal aging” failures finally require that the component be replaced or
renovated.
Maximum “performance life” of a building component is the time
over which the component serves its anticipated function over the range
from 100% (when installed or initially placed in service) to 0% (when
it fails and the only option is to replace it). However, once the level of
performance falls below some minimum (just how many roof leaks are
acceptable?) and the cost of continuing to maintain a failing component
threatens to exceed the cost of replacement, then the component has
reached the end of its “design service life” (often referred to as its “eco-
nomic life”).
Figure 2-2, an enhancement of the “bathtub curve,” ignores “infant
mortality” failures associated with new construction and shows a more
definitive relationship between component performance and time. Over
any component's performance life, function degrades slowly, even with
adequate maintenance, until a “tipping point” is reached where function
begins to degrade at an accelerating rate until failure occurs.
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