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Environmental loads
and construction degradation
More often than not, construction deterioration is due to environmental loading and failure of the environmental separations (such as the building envelope) with the result of reduced durability. These environmental loads are at least partially overlooked, misunderstood or under-estimated in contemporary projects. This is one area where a prudent owner or developer should make a small additional investment and get a second opinion. Some of these environmental loads include (but are not limited to): moisture, temperature, radiation such as sound and light, hail, seism, floods, mud slides, avalanches, air movement/pressure (including not only wind and hurricane / tornado, but also currents in cavity walls), chemicals (both acids and alkalis), deformations, various vibrations.
Generaly speaking, there is a continuous cycle working on buildings. For pavements and for concrete or masonry structures this vicious circle is: weather - (differential) movement - cracking, then again weather...
Deterioration mechanisms include:
Durability is dealt with poorly in the US Building Codes (UBC, BOCA, Southern...). Canada is doing slightly better in Part 5 of the 1995 NBC. By the way, the NBC 1995 contains a rather elegant model for deformations in construction elements in the Commentary on Part 4: Effects of Deformations in Building Components.
Durability may be determined based on investigation of actual field performance, accelerated testing or compliance with predetermined guidelines. This investigative work should be done by an independent third party, preferably a consultant specializing in field assesments and testing, rather than the prime design consultants who have rarely the expertise for such activities and may be also limited by their own involvement and interest in certain outcames of the project.
Actual service life depends, besides design and actual construction process, on the materials used and the environment to which they are exposed. Proper design should take into consideration these factors, the particular function of the building component, its interaction with the structure as a whole and with the environment, as well as the implications of premature failure, the accessability for maintenance, repair or replacement, and the cost of such work. Whenever it is known or expected that maintenance, repair or replacement is likely to be required for certain elements before the project is subject to major rehabilitation, restoration or retrofit, special consideration should be given to providing an accessible path to such elements. To illustrate: Meany/masonry anchors to come soon
Where the use of a building or space, or the services for a building or space are changed significantly, an assessment of the impact of the changes on the environmental separators should be conducted to preclude premature failures that could create hazardous conditions. Example to come: PCC in Fremont
Just remember, in the construction game things are seldom whatever they seem to be... And yes, there is much more to go wrong on the long run than meets the eye!
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